All-direction turning solution - cnc lathe insert types

Profilometers can usually provide a range of surface parameters, including Rz (which is roughly 6X the Ra value in most conversion tables). Of course, many shops don’t own a basic hand held profilometer, let alone know how to use one. And those that do may only use their profilometer to check surface finishes if there’s a problem. The rest of the time, it stays in the box

With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter.

Let’s refocus on the status of PCD tools in the automotive industry at the beginning of the 1980s. Using PCD tools for the external and internal turning of materials such as copper, electrographite carbon and, of course, aluminium was fairly well known. The same milling heads previously fitted with carbide inserts were now available for the starting production of aluminium engines and upcoming milling tasks. Soldered PCD milling heads were at that time not yet a solution for aluminium machining.

Cutting tool material consisting of natural or synthetic diamond crystals bonded together under high pressure at elevated temperatures. PCD is available as a tip brazed to a carbide insert carrier. Used for machining nonferrous alloys and nonmetallic materials at high cutting speeds.

'Poly–poly–or what?' fourth part – a trade show initiates a brilliant idea, Part 4   (Published 12/6/2018)

As gasket technology has evolved, surface finish requirements at the OEM level have eased a bit. Most Asian car makers today specify a surface finish of 20 Ra or less, while most domestic vehicle manufacturers say 30 Ra or less is required.

The keyword “Tradeshow FAMETA 80 in Essen” gives me an opportunity to point out another event, quasi a world premiere. At that time, PCD monoblock milling cutters, straight-edged as well as profiled cutting edges, were already in use in the furniture industry, particularly in the kitchen cabinet industry.

Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush.

When Ford introduced the 4.6L modular V8, they specified a factory surface finish is 8 to 12 microinches Ra. By comparison, many Japanese auto makers such as Honda and Mazda were specifying surface finishes in the 8 to 20 Ra range back in the early 1990s for their engines. The MLS gaskets they were using at that time had two to five layers of heat treated steel, each covered with a relatively thin (.001 in.) coating of nitrile rubber or Viton.

“Grinding requires a certain amount of pressure to cut metal,” says Usher. “Dry milling does not. It just shaves across the surface. If you’re wet grinding a large diesel block, the pressure and cutting action of the stones can change as the grinding head rides over the surface. The metal between the cylinder bores creates more resistance and cuts differently than the areas around the cylinder bores. This can leave a lot of waviness across the surface of the block – as much as .002?. You won’t get that with dry milling. It will cut the block flat with no high spots.”

The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head.

McKnight said the type of process or equipment used to surface a head or block doesn’t matter as long as it leaves a good finish. “You can dry mill or wet grind or sand and get good results when the resurfacing is done right.”

This also indicates the contemporary mentality at a time when pros and cons of numerically controlled machines and robots were intensely debated for serial industrial production.

Crystal manufactured from boron nitride under high pressure and temperature. Used to cut hard-to-machine ferrous and nickel-base materials up to 70 HRC. Second hardest material after diamond. See superabrasive tools.

Lach-Spezial is the sister company of the family-managed Lach Diamant Jakob Lach GmbH & Co. KG., founded in 1922. It developed from a diamond grinding shop for natural diamonds with approximately 600 employees, and already in the mid 1930s, it had targeted the metal industry with a special program. Initially, it included industrial diamonds for dressing conventional grinding wheels in the automobile, ball bearings and rolling bearings industries, but in the early 1960s the programme was extended, and e.g. natural turning diamonds were offered for turning copper commutators for the electrical industry (Bosch, Siemens, AEG). The following production of resin- and metal-bond diamond and Borazon/CBN grinding wheels completed this program.

Meyer said his milling equipment can deliver any surface finish that’s required to seal a gasket. “But I think there’s been a conspiracy among the vehicle manufacturers as to the smoothness that’s really necessary. They’ve been telling everybody that you have to have a mirror-like finish otherwise the gasket won’t seal.

Cutting tool material consisting of polycrystalline cubic boron nitride with a metallic or ceramic binder. PCBN is available either as a tip brazed to a carbide insert carrier or as a solid insert. Primarily used for cutting hardened ferrous alloys.

This Late Model Engines build is centered around Concept Performance’s new LTR block, which is the first aftermarket as-cast aluminum Gen V LT block.

When multi-layer steel (MLS) head gaskets became commonplace a number of years ago, there was a lot of concern that aftermarket surfacing procedures might not be able to reproduce the mirror-like finish that the vehicle manufacturers said was absolutely necessary to seal MLS head gaskets. The challenge was to duplicate the factory finish using out-dated equipment and methods that may or may not produce the desired results. Related Articles - Travel a New Road to AAPEX this Season - Randy Breaux, Group President, GPC North America, Talks to AMN Drivetime - Holley’s Latest LS Engine Giveaway Aftermarket equipment suppliers rose to the occasion and introduced a new generation of high speed precision milling machines that could meet or exceed the factory surface finish requirements for original equipment MLS head gaskets. Wet grinding was out and dry milling was in as the new way to surface cylinder blocks and heads. Wet grinding was capable of producing high quality surface finishes when done properly. But according to Anthony Usher of Rottler Manufacturing, it was a “very messy” process compared to dry milling. “Grinding requires a certain amount of pressure to cut metal,” says Usher. “Dry milling does not. It just shaves across the surface. If you’re wet grinding a large diesel block, the pressure and cutting action of the stones can change as the grinding head rides over the surface. The metal between the cylinder bores creates more resistance and cuts differently than the areas around the cylinder bores. This can leave a lot of waviness across the surface of the block – as much as .002?. You won’t get that with dry milling. It will cut the block flat with no high spots.” Usher says most shops in the U.S. have converted over to dry milling, but wet grinding is still common overseas. “Some shops have converted their old grinding machines for dry milling, but the results are not the same as what you get with equipment that is designed especially for dry milling. The spindle bearings in old grinding machines are not rigid enough to provide the proper support for precision dry milling.” Skip Anderson of DCM-Tech agreed that dry milling is the only way to surface today’s engines. “Most of the equipment we sell is for industrial applications, so we are using the same industrial technology in our automotive surfacing equipment. We use a ball screw feed mechanism rather than hydraulics because it is quieter, smoother and more consistent. You won’t get feed rate changes with temperature as you can with a hydraulic feed system. We also use industrial precision bearings for the spindles and balance the rotors so our customers can achieve surface finishes that meet their specification. If a customer wants a surface finish as smooth as 5 to 9 Ra (Roughness Average), our equipment can do it.” Usher and Anderson both said the best surface finishes are achieved by using the correct inserts for the application: PCD (polycrystalline diamond) for milling Aluminum, and CBN (cubic boron nitride) for cast iron. PCD works well on aluminum because aluminum won’t stick to the insert like it can to a CBN insert. In addition, special PCD and CBN inserts with specific edge profiles may be required for milling hard metals such as blocks made of compacted graphite iron (CGI), diesel heads with precombustion chamber cups or spray welded diesel heads. “The corner of the insert must be prepared properly to cut smoothly,” said Usher. “We have found that a thin layer of CBN or PCD bonded to carbide provides a good combination of surface finish, tool life and cost. We have six or seven different CBN inserts designed for different kinds of milling applications.” Other equipment suppliers have a somewhat different take on the selection of inserts. Tim Whitley of T&S Machines & Tools said he recommends using CBN for everything. “It delivers great results and works just as well on aluminum as it does on cast iron. The key is the edge preparation on the insert.” Using the same insert for milling both aluminum and cast iron saves time because you don’t have to switch inserts when going from one metal to the other. It also works well on bimetal aluminum blocks with iron sleeves. Whitley said Ford sent him some 4.6L heads to see if he could match the factory finish. When he checked the heads, he found the factory finish was 12 Ra. When he finished the heads on his equipment, he said the finish was 8 Ra. “We can deliver any finish specification the OEMs or gasket suppliers require. The rigidity of our machines makes such smooth finishes possible. You can stop and start the machine halfway through a job and not leave a mark on the finish.” Matt Meyer of RMC Engine Rebuilding Equipment said he also favors using CBN inserts for most milling applications. “We use a specific edge prep on our inserts so they can cut both aluminum and cast iron. We also have special CBN inserts for cutting blocks with hard sleeves and diesel heads that have been spray welded or have precombustion chamber cups. You don’t want aluminum binding to the insert, especially when you are cutting a bimetal surface. It can drag metal across the surface and leave marks. An aluminum oxide coating on an insert is not a good idea because it can bind with aluminum chips and cut unevenly.” Meyer said his milling equipment can deliver any surface finish that’s required to seal a gasket. “But I think there’s been a conspiracy among the vehicle manufacturers as to the smoothness that’s really necessary. They’ve been telling everybody that you have to have a mirror-like finish otherwise the gasket won’t seal. That may have been true with the early generation original equipment MLS gaskets, but it’s no longer true with most aftermarket MLS gaskets. The coatings they are now using can handle a more traditional surface finish.” When Ford introduced the 4.6L modular V8, they specified a factory surface finish is 8 to 12 microinches Ra. By comparison, many Japanese auto makers such as Honda and Mazda were specifying surface finishes in the 8 to 20 Ra range back in the early 1990s for their engines. The MLS gaskets they were using at that time had two to five layers of heat treated steel, each covered with a relatively thin (.001 in.) coating of nitrile rubber or Viton. Consequently, the gaskets required a very smooth surface finish. By comparison, traditional solid or perforated steel core head gaskets with composition facings or graphite gaskets typically required a finish in the 54 to 113 Ra (60 to 125 RMS) range. As gasket technology has evolved, surface finish requirements at the OEM level have eased a bit. Most Asian car makers today specify a surface finish of 20 Ra or less, while most domestic vehicle manufacturers say 30 Ra or less is required. What Gasket Suppliers Say Bill McKnight of Mahle/Victor-Reinz Gaskets said the surface finish requirements for modern MLS gaskets are not are critical as they once were. “You had some manufacturers saying we had to produce a 8 to 10 Ra finish to seal the head gasket. But the coatings on today’s aftermarket MLS gaskets can handle anything in the 40 to 70 Ra range with no problems.” McKnight said the type of process or equipment used to surface a head or block doesn’t matter as long as it leaves a good finish. “You can dry mill or wet grind or sand and get good results when the resurfacing is done right.” Jim Daigle of Fel-Pro/Federal Mogul also said today’s aftermarket MLS head gaskets don’t require the super smooth finishes originally specified by the vehicle manufacturers. “Our blue coated MLS gaskets can typically handle surface finishes from 70 to 80 Ra, while our black coating is typically designed for surface finishes of 30 Ra or less. We put our surface finish recommendations right on our packaging because it can vary from one application to another. “Smoother is better for many applications, but is not absolutely necessary. If you’re building a NASCAR motor that’s running 280 to 300 degrees F, a surface finish of 30 Ra or less is better and recommended. Even though some of our Performance MLS gasket coatings can accommodate above 30 Ra we really encourage a 30 Ra target (or less) for any Performance MLS application. But for a typical street or strip application, we’ll use a gasket coating that is more conformable to handle a more traditional surface finish.” One point Daigle emphasized with respect to surface finish is the need to de-emphasize Ra numbers and focus more on Rz. Roughness Average (Ra) can actually have a wide variance across a given surface profile. Rz, which is the average difference between the peak height and valley depth, is actually a much more accurate representation of true surface topography. He said that most Asian vehicle manufacturers don’t even talk about Ra anymore, referring instead to Rz values for surface finish. Profilometers can usually provide a range of surface parameters, including Rz (which is roughly 6X the Ra value in most conversion tables). Of course, many shops don’t own a basic hand held profilometer, let alone know how to use one. And those that do may only use their profilometer to check surface finishes if there’s a problem. The rest of the time, it stays in the box A profilometer is a precision instrument that typically costs $800 to $1800 for a basic hand held unit, or as much as $100,000 for a sophisticated lab model. The hand held units drag a diamond tipped stylus across the metal to measure the microscopic peaks and valleys on the surface. It then displays the various values and calculates an Ra number for the surface finish. One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment. According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows: • Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket). • Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz). • The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

• Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets.

Removal of undesirable materials from “loaded” grinding wheels using a single- or multi-point diamond or other tool. The process also exposes unused, sharp abrasive points. See loading; truing.

In the 1970s, development and use of PCD tools were, with few exceptions, limited to the production of so-called “indexable inserts.” This term is quite wrong, since PCD was simply soldered onto one side of these inserts. After the discovery of spark erosion (1978) for the systematic removal of polycrystalline electroconductive particles such as polycrystalline synthetic diamonds (PCD and boron nitrides PCBN), this should change. Since 1980, progressive developments in electrical discharge grinding (EDG) and wire EDM turned the “niche tool” PCD into a global player.

Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings.

Process similar to ram electrical-discharge machining except a small-diameter copper or brass wire is used as a traveling electrode. Usually used in conjunction with a CNC and only works when a part is to be cut completely through. A common analogy is wire electrical-discharge machining is like an ultraprecise, electrical, contour-sawing operation.

Whether you’re scouring junkyards, ordering cores, investigating factory options, looking at aftermarket cast iron or aluminum blocks, or spending big bucks on billet LS blocks, you’ve probably noticed it’s been harder to find exactly what you want for the foundation of your LS build than it historically has.

Last year, the idea was simple: Find a junker, fix it up with the best from the automotive aftermarket, and drive it to Las Vegas for AAPEX 2022. This year, it’s anything but simple. Related Articles – Race Oils – Facts About Engine Bearings – Does Connecting Rod Length Matter? The automotive aftermarket is at

A profilometer is a precision instrument that typically costs $800 to $1800 for a basic hand held unit, or as much as $100,000 for a sophisticated lab model. The hand held units drag a diamond tipped stylus across the metal to measure the microscopic peaks and valleys on the surface. It then displays the various values and calculates an Ra number for the surface finish. One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment. According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows: • Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket). • Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz). • The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

The answer could be explicitly clear: The automotive industry was not ready yet to fully use the advantages of PCD tools in serial production. It was easier for woodworkers. During my preparation for LIGNA 1979, I could already assert, that at that time the machine development in the wood industry already fulfilled the requirements for the use of cost-saving, long-lasting PCD diamond tools.

Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

Aftermarket equipment suppliers rose to the occasion and introduced a new generation of high speed precision milling machines that could meet or exceed the factory surface finish requirements for original equipment MLS head gaskets. Wet grinding was out and dry milling was in as the new way to surface cylinder blocks and heads.

An example: multiple-axis routers on which it was already easy to measure the advantages of PCD endmills/profile mills compared to carbide. Of course, the same applied to the immediate success of diamond tool combinations on so-called double-end profile machines.

Aluminium milling was still left to PCD cartridge mills, fitted with PCD inserts. Regarding the world premiere: At FAMETA 80 in Essen,  Lach Diamant presented the first PCD monoblock milling cutter for aluminium – featuring an elaborate profile – and demonstrated milling at high feed rates in creep speed.

Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish.

According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows:

Matt Meyer of RMC Engine Rebuilding Equipment said he also favors using CBN inserts for most milling applications. “We use a specific edge prep on our inserts so they can cut both aluminum and cast iron. We also have special CBN inserts for cutting blocks with hard sleeves and diesel heads that have been spray welded or have precombustion chamber cups. You don’t want aluminum binding to the insert, especially when you are cutting a bimetal surface. It can drag metal across the surface and leave marks. An aluminum oxide coating on an insert is not a good idea because it can bind with aluminum chips and cut unevenly.”

Horst Lach is not only CEO of LACH DIAMANT Germany, but also of LACH DIAMOND INC., Grand Rapids, MI 49512, Tel. (616) 698-0101.

With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

Part 1 – A good project car brings people together. Driving the rare Lincoln Blackwood into Ohio Technical College (OTC) turned heads. And once Babcox Media’s Joe Keene, an ASE-certified technician, and the technicians-in-training at OTC got to pop the hood and slide under it on a creeper to get their hands in it, its

Please accompany me now to the beginnings of forming and rotating PCD tools with an all-encompassing focus on the automotive world. So far, we touched on the here and now. Back to the year 1980. One of the questions at the time was: Is it possible to transfer the looming success of PCD tools in the industrial series production of wood and plastic to the metal and composite industry?

He said that most Asian vehicle manufacturers don’t even talk about Ra anymore, referring instead to Rz values for surface finish.

As pioneer in machining, development and application of polycrystalline diamond and CBN machining tools, Lach Diamant achieved worldwide reputation after superabrasive manufacturer General Electric offered PCD cutting material for the first time in 1973 (see also part 1 of this article series “Poly – poly – or what?”).

One point Daigle emphasized with respect to surface finish is the need to de-emphasize Ra numbers and focus more on Rz. Roughness Average (Ra) can actually have a wide variance across a given surface profile. Rz, which is the average difference between the peak height and valley depth, is actually a much more accurate representation of true surface topography.

For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication

Materials composed of different elements, with one element normally embedded in another, held together by a compatible binder.

Poly – Poly - or what? Part 7: Stumbling blocks on the way into the automotive world …, Part 7 (Published 4/15/2019)

A look at the (still existing) Lach production and order book, beginning with the first entry in 1979, tells us the following: The first so-called dreboform PCD profile turning tools/threaded steel/endmills et al. were successfully used for machining nonferrous and composite materials at customers such as Rowenta in Offenbach, Grundig in Georgensmünd, Messerschmitt Bölkow Blohm GmbH in Donauwörth, Waldrich in Coburg, FAG in Schweinfurt, Behr in Wendlingen, Bosch in Stuttgart, Fokker in the Netherlands and Vielmetter in Berlin.

This year’s Road to AAPEX is a tale of two roads: One metaphorical, paved with questions that face the automotive aftermarket like the impact of EV adoption and sustainability efforts; and one quite literal, that was paved at the start of the 20th century and conceptualized the first transcontinental highway. The Lincoln Highway, which begins

Usher says most shops in the U.S. have converted over to dry milling, but wet grinding is still common overseas. “Some shops have converted their old grinding machines for dry milling, but the results are not the same as what you get with equipment that is designed especially for dry milling. The spindle bearings in old grinding machines are not rigid enough to provide the proper support for precision dry milling.” Skip Anderson of DCM-Tech agreed that dry milling is the only way to surface today’s engines. “Most of the equipment we sell is for industrial applications, so we are using the same industrial technology in our automotive surfacing equipment. We use a ball screw feed mechanism rather than hydraulics because it is quieter, smoother and more consistent. You won’t get feed rate changes with temperature as you can with a hydraulic feed system. We also use industrial precision bearings for the spindles and balance the rotors so our customers can achieve surface finishes that meet their specification. If a customer wants a surface finish as smooth as 5 to 9 Ra (Roughness Average), our equipment can do it.” Usher and Anderson both said the best surface finishes are achieved by using the correct inserts for the application: PCD (polycrystalline diamond) for milling Aluminum, and CBN (cubic boron nitride) for cast iron. PCD works well on aluminum because aluminum won’t stick to the insert like it can to a CBN insert. In addition, special PCD and CBN inserts with specific edge profiles may be required for milling hard metals such as blocks made of compacted graphite iron (CGI), diesel heads with precombustion chamber cups or spray welded diesel heads. “The corner of the insert must be prepared properly to cut smoothly,” said Usher. “We have found that a thin layer of CBN or PCD bonded to carbide provides a good combination of surface finish, tool life and cost. We have six or seven different CBN inserts designed for different kinds of milling applications.” Other equipment suppliers have a somewhat different take on the selection of inserts. Tim Whitley of T&S Machines & Tools said he recommends using CBN for everything. “It delivers great results and works just as well on aluminum as it does on cast iron. The key is the edge preparation on the insert.” Using the same insert for milling both aluminum and cast iron saves time because you don’t have to switch inserts when going from one metal to the other. It also works well on bimetal aluminum blocks with iron sleeves. Whitley said Ford sent him some 4.6L heads to see if he could match the factory finish. When he checked the heads, he found the factory finish was 12 Ra. When he finished the heads on his equipment, he said the finish was 8 Ra. “We can deliver any finish specification the OEMs or gasket suppliers require. The rigidity of our machines makes such smooth finishes possible. You can stop and start the machine halfway through a job and not leave a mark on the finish.” Matt Meyer of RMC Engine Rebuilding Equipment said he also favors using CBN inserts for most milling applications. “We use a specific edge prep on our inserts so they can cut both aluminum and cast iron. We also have special CBN inserts for cutting blocks with hard sleeves and diesel heads that have been spray welded or have precombustion chamber cups. You don’t want aluminum binding to the insert, especially when you are cutting a bimetal surface. It can drag metal across the surface and leave marks. An aluminum oxide coating on an insert is not a good idea because it can bind with aluminum chips and cut unevenly.” Meyer said his milling equipment can deliver any surface finish that’s required to seal a gasket. “But I think there’s been a conspiracy among the vehicle manufacturers as to the smoothness that’s really necessary. They’ve been telling everybody that you have to have a mirror-like finish otherwise the gasket won’t seal. That may have been true with the early generation original equipment MLS gaskets, but it’s no longer true with most aftermarket MLS gaskets. The coatings they are now using can handle a more traditional surface finish.” When Ford introduced the 4.6L modular V8, they specified a factory surface finish is 8 to 12 microinches Ra. By comparison, many Japanese auto makers such as Honda and Mazda were specifying surface finishes in the 8 to 20 Ra range back in the early 1990s for their engines. The MLS gaskets they were using at that time had two to five layers of heat treated steel, each covered with a relatively thin (.001 in.) coating of nitrile rubber or Viton. Consequently, the gaskets required a very smooth surface finish. By comparison, traditional solid or perforated steel core head gaskets with composition facings or graphite gaskets typically required a finish in the 54 to 113 Ra (60 to 125 RMS) range. As gasket technology has evolved, surface finish requirements at the OEM level have eased a bit. Most Asian car makers today specify a surface finish of 20 Ra or less, while most domestic vehicle manufacturers say 30 Ra or less is required. What Gasket Suppliers Say Bill McKnight of Mahle/Victor-Reinz Gaskets said the surface finish requirements for modern MLS gaskets are not are critical as they once were. “You had some manufacturers saying we had to produce a 8 to 10 Ra finish to seal the head gasket. But the coatings on today’s aftermarket MLS gaskets can handle anything in the 40 to 70 Ra range with no problems.” McKnight said the type of process or equipment used to surface a head or block doesn’t matter as long as it leaves a good finish. “You can dry mill or wet grind or sand and get good results when the resurfacing is done right.” Jim Daigle of Fel-Pro/Federal Mogul also said today’s aftermarket MLS head gaskets don’t require the super smooth finishes originally specified by the vehicle manufacturers. “Our blue coated MLS gaskets can typically handle surface finishes from 70 to 80 Ra, while our black coating is typically designed for surface finishes of 30 Ra or less. We put our surface finish recommendations right on our packaging because it can vary from one application to another. “Smoother is better for many applications, but is not absolutely necessary. If you’re building a NASCAR motor that’s running 280 to 300 degrees F, a surface finish of 30 Ra or less is better and recommended. Even though some of our Performance MLS gasket coatings can accommodate above 30 Ra we really encourage a 30 Ra target (or less) for any Performance MLS application. But for a typical street or strip application, we’ll use a gasket coating that is more conformable to handle a more traditional surface finish.” One point Daigle emphasized with respect to surface finish is the need to de-emphasize Ra numbers and focus more on Rz. Roughness Average (Ra) can actually have a wide variance across a given surface profile. Rz, which is the average difference between the peak height and valley depth, is actually a much more accurate representation of true surface topography. He said that most Asian vehicle manufacturers don’t even talk about Ra anymore, referring instead to Rz values for surface finish. Profilometers can usually provide a range of surface parameters, including Rz (which is roughly 6X the Ra value in most conversion tables). Of course, many shops don’t own a basic hand held profilometer, let alone know how to use one. And those that do may only use their profilometer to check surface finishes if there’s a problem. The rest of the time, it stays in the box A profilometer is a precision instrument that typically costs $800 to $1800 for a basic hand held unit, or as much as $100,000 for a sophisticated lab model. The hand held units drag a diamond tipped stylus across the metal to measure the microscopic peaks and valleys on the surface. It then displays the various values and calculates an Ra number for the surface finish. One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment. According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows: • Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket). • Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz). • The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

Usher and Anderson both said the best surface finishes are achieved by using the correct inserts for the application: PCD (polycrystalline diamond) for milling Aluminum, and CBN (cubic boron nitride) for cast iron. PCD works well on aluminum because aluminum won’t stick to the insert like it can to a CBN insert. In addition, special PCD and CBN inserts with specific edge profiles may be required for milling hard metals such as blocks made of compacted graphite iron (CGI), diesel heads with precombustion chamber cups or spray welded diesel heads. “The corner of the insert must be prepared properly to cut smoothly,” said Usher. “We have found that a thin layer of CBN or PCD bonded to carbide provides a good combination of surface finish, tool life and cost. We have six or seven different CBN inserts designed for different kinds of milling applications.” Other equipment suppliers have a somewhat different take on the selection of inserts. Tim Whitley of T&S Machines & Tools said he recommends using CBN for everything. “It delivers great results and works just as well on aluminum as it does on cast iron. The key is the edge preparation on the insert.” Using the same insert for milling both aluminum and cast iron saves time because you don’t have to switch inserts when going from one metal to the other. It also works well on bimetal aluminum blocks with iron sleeves. Whitley said Ford sent him some 4.6L heads to see if he could match the factory finish. When he checked the heads, he found the factory finish was 12 Ra. When he finished the heads on his equipment, he said the finish was 8 Ra. “We can deliver any finish specification the OEMs or gasket suppliers require. The rigidity of our machines makes such smooth finishes possible. You can stop and start the machine halfway through a job and not leave a mark on the finish.” Matt Meyer of RMC Engine Rebuilding Equipment said he also favors using CBN inserts for most milling applications. “We use a specific edge prep on our inserts so they can cut both aluminum and cast iron. We also have special CBN inserts for cutting blocks with hard sleeves and diesel heads that have been spray welded or have precombustion chamber cups. You don’t want aluminum binding to the insert, especially when you are cutting a bimetal surface. It can drag metal across the surface and leave marks. An aluminum oxide coating on an insert is not a good idea because it can bind with aluminum chips and cut unevenly.” Meyer said his milling equipment can deliver any surface finish that’s required to seal a gasket. “But I think there’s been a conspiracy among the vehicle manufacturers as to the smoothness that’s really necessary. They’ve been telling everybody that you have to have a mirror-like finish otherwise the gasket won’t seal. That may have been true with the early generation original equipment MLS gaskets, but it’s no longer true with most aftermarket MLS gaskets. The coatings they are now using can handle a more traditional surface finish.” When Ford introduced the 4.6L modular V8, they specified a factory surface finish is 8 to 12 microinches Ra. By comparison, many Japanese auto makers such as Honda and Mazda were specifying surface finishes in the 8 to 20 Ra range back in the early 1990s for their engines. The MLS gaskets they were using at that time had two to five layers of heat treated steel, each covered with a relatively thin (.001 in.) coating of nitrile rubber or Viton. Consequently, the gaskets required a very smooth surface finish. By comparison, traditional solid or perforated steel core head gaskets with composition facings or graphite gaskets typically required a finish in the 54 to 113 Ra (60 to 125 RMS) range. As gasket technology has evolved, surface finish requirements at the OEM level have eased a bit. Most Asian car makers today specify a surface finish of 20 Ra or less, while most domestic vehicle manufacturers say 30 Ra or less is required. What Gasket Suppliers Say Bill McKnight of Mahle/Victor-Reinz Gaskets said the surface finish requirements for modern MLS gaskets are not are critical as they once were. “You had some manufacturers saying we had to produce a 8 to 10 Ra finish to seal the head gasket. But the coatings on today’s aftermarket MLS gaskets can handle anything in the 40 to 70 Ra range with no problems.” McKnight said the type of process or equipment used to surface a head or block doesn’t matter as long as it leaves a good finish. “You can dry mill or wet grind or sand and get good results when the resurfacing is done right.” Jim Daigle of Fel-Pro/Federal Mogul also said today’s aftermarket MLS head gaskets don’t require the super smooth finishes originally specified by the vehicle manufacturers. “Our blue coated MLS gaskets can typically handle surface finishes from 70 to 80 Ra, while our black coating is typically designed for surface finishes of 30 Ra or less. We put our surface finish recommendations right on our packaging because it can vary from one application to another. “Smoother is better for many applications, but is not absolutely necessary. If you’re building a NASCAR motor that’s running 280 to 300 degrees F, a surface finish of 30 Ra or less is better and recommended. Even though some of our Performance MLS gasket coatings can accommodate above 30 Ra we really encourage a 30 Ra target (or less) for any Performance MLS application. But for a typical street or strip application, we’ll use a gasket coating that is more conformable to handle a more traditional surface finish.” One point Daigle emphasized with respect to surface finish is the need to de-emphasize Ra numbers and focus more on Rz. Roughness Average (Ra) can actually have a wide variance across a given surface profile. Rz, which is the average difference between the peak height and valley depth, is actually a much more accurate representation of true surface topography. He said that most Asian vehicle manufacturers don’t even talk about Ra anymore, referring instead to Rz values for surface finish. Profilometers can usually provide a range of surface parameters, including Rz (which is roughly 6X the Ra value in most conversion tables). Of course, many shops don’t own a basic hand held profilometer, let alone know how to use one. And those that do may only use their profilometer to check surface finishes if there’s a problem. The rest of the time, it stays in the box A profilometer is a precision instrument that typically costs $800 to $1800 for a basic hand held unit, or as much as $100,000 for a sophisticated lab model. The hand held units drag a diamond tipped stylus across the metal to measure the microscopic peaks and valleys on the surface. It then displays the various values and calculates an Ra number for the surface finish. One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment. According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows: • Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket). • Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz). • The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

“Smoother is better for many applications, but is not absolutely necessary. If you’re building a NASCAR motor that’s running 280 to 300 degrees F, a surface finish of 30 Ra or less is better and recommended. Even though some of our Performance MLS gasket coatings can accommodate above 30 Ra we really encourage a 30 Ra target (or less) for any Performance MLS application. But for a typical street or strip application, we’ll use a gasket coating that is more conformable to handle a more traditional surface finish.” One point Daigle emphasized with respect to surface finish is the need to de-emphasize Ra numbers and focus more on Rz. Roughness Average (Ra) can actually have a wide variance across a given surface profile. Rz, which is the average difference between the peak height and valley depth, is actually a much more accurate representation of true surface topography. He said that most Asian vehicle manufacturers don’t even talk about Ra anymore, referring instead to Rz values for surface finish. Profilometers can usually provide a range of surface parameters, including Rz (which is roughly 6X the Ra value in most conversion tables). Of course, many shops don’t own a basic hand held profilometer, let alone know how to use one. And those that do may only use their profilometer to check surface finishes if there’s a problem. The rest of the time, it stays in the box A profilometer is a precision instrument that typically costs $800 to $1800 for a basic hand held unit, or as much as $100,000 for a sophisticated lab model. The hand held units drag a diamond tipped stylus across the metal to measure the microscopic peaks and valleys on the surface. It then displays the various values and calculates an Ra number for the surface finish. One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment. According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows: • Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket). • Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz). • The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush.

Cutting tool material consisting of natural or synthetic diamond crystals bonded together under high pressure at elevated temperatures. PCD is available as a tip brazed to a carbide insert carrier. Used for machining nonferrous alloys and nonmetallic materials at high cutting speeds.

Actually, this presentation already established the basis for the introduction of soldered monoblock PCD milling cutters in the automotive industry, but, unfortunately, the time was – even in retrospect – not quite right for this yet.

LS swaps are popular for many reasons, but there are a lot of variations and details to sort through – more of them than you may expect – and many of them are associated with the intake manifold.

• Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz).

Jim Daigle of Fel-Pro/Federal Mogul also said today’s aftermarket MLS head gaskets don’t require the super smooth finishes originally specified by the vehicle manufacturers. “Our blue coated MLS gaskets can typically handle surface finishes from 70 to 80 Ra, while our black coating is typically designed for surface finishes of 30 Ra or less. We put our surface finish recommendations right on our packaging because it can vary from one application to another.

With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have).

Using the same insert for milling both aluminum and cast iron saves time because you don’t have to switch inserts when going from one metal to the other. It also works well on bimetal aluminum blocks with iron sleeves.

Process that vaporizes conductive materials by controlled application of pulsed electrical current that flows between a workpiece and electrode (tool) in a dielectric fluid. Permits machining shapes to tight accuracies without the internal stresses conventional machining often generates. Useful in diemaking.

From the many press releases covering this issue in 1980, I quote an excerpt from the trade journal “Produktion” in March 1980: “In excellent shape with long tool times: Nothing is more precise than diamonds. Synthetic diamond cutting edges for machining nonferrous and plastic materials are unstoppable. New grinding procedures (this refers to Lach DiamantI’s so-called spark erosion method) made it possible to produce blades from sintered diamonds in any desired shape and form. Ground into shape, they are perfect for turning and milling aluminium, brass, copper and various carbon and plastic composites. The blade can be shaped in any manner, concave or convex, similar to a saw or threaded profile, with all conceivable options up to a maximum insertion width of 13 mm” (at the time the available maximum for PCD) – today 70 mm to a maximum width of 100 mm.

That may have been true with the early generation original equipment MLS gaskets, but it’s no longer true with most aftermarket MLS gaskets. The coatings they are now using can handle a more traditional surface finish.” When Ford introduced the 4.6L modular V8, they specified a factory surface finish is 8 to 12 microinches Ra. By comparison, many Japanese auto makers such as Honda and Mazda were specifying surface finishes in the 8 to 20 Ra range back in the early 1990s for their engines. The MLS gaskets they were using at that time had two to five layers of heat treated steel, each covered with a relatively thin (.001 in.) coating of nitrile rubber or Viton. Consequently, the gaskets required a very smooth surface finish. By comparison, traditional solid or perforated steel core head gaskets with composition facings or graphite gaskets typically required a finish in the 54 to 113 Ra (60 to 125 RMS) range. As gasket technology has evolved, surface finish requirements at the OEM level have eased a bit. Most Asian car makers today specify a surface finish of 20 Ra or less, while most domestic vehicle manufacturers say 30 Ra or less is required. What Gasket Suppliers Say Bill McKnight of Mahle/Victor-Reinz Gaskets said the surface finish requirements for modern MLS gaskets are not are critical as they once were. “You had some manufacturers saying we had to produce a 8 to 10 Ra finish to seal the head gasket. But the coatings on today’s aftermarket MLS gaskets can handle anything in the 40 to 70 Ra range with no problems.” McKnight said the type of process or equipment used to surface a head or block doesn’t matter as long as it leaves a good finish. “You can dry mill or wet grind or sand and get good results when the resurfacing is done right.” Jim Daigle of Fel-Pro/Federal Mogul also said today’s aftermarket MLS head gaskets don’t require the super smooth finishes originally specified by the vehicle manufacturers. “Our blue coated MLS gaskets can typically handle surface finishes from 70 to 80 Ra, while our black coating is typically designed for surface finishes of 30 Ra or less. We put our surface finish recommendations right on our packaging because it can vary from one application to another. “Smoother is better for many applications, but is not absolutely necessary. If you’re building a NASCAR motor that’s running 280 to 300 degrees F, a surface finish of 30 Ra or less is better and recommended. Even though some of our Performance MLS gasket coatings can accommodate above 30 Ra we really encourage a 30 Ra target (or less) for any Performance MLS application. But for a typical street or strip application, we’ll use a gasket coating that is more conformable to handle a more traditional surface finish.” One point Daigle emphasized with respect to surface finish is the need to de-emphasize Ra numbers and focus more on Rz. Roughness Average (Ra) can actually have a wide variance across a given surface profile. Rz, which is the average difference between the peak height and valley depth, is actually a much more accurate representation of true surface topography. He said that most Asian vehicle manufacturers don’t even talk about Ra anymore, referring instead to Rz values for surface finish. Profilometers can usually provide a range of surface parameters, including Rz (which is roughly 6X the Ra value in most conversion tables). Of course, many shops don’t own a basic hand held profilometer, let alone know how to use one. And those that do may only use their profilometer to check surface finishes if there’s a problem. The rest of the time, it stays in the box A profilometer is a precision instrument that typically costs $800 to $1800 for a basic hand held unit, or as much as $100,000 for a sophisticated lab model. The hand held units drag a diamond tipped stylus across the metal to measure the microscopic peaks and valleys on the surface. It then displays the various values and calculates an Ra number for the surface finish. One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment. According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows: • Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket). • Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz). • The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

Now you will ask yourself what happened at FAMETA 80 during the premiere presentation of monoblock PCD milling cutters for aluminium machining? You will be surprised to hear about the following developments, which also lead to an international patent. You can read more about this topic in the next article of “Poly – poly – or what?”

Managing Director and CEO of LACH DIAMANT, Jakob Lach GmbH & Co. KG,  Donaustr.17, 63452 Hanau, Germany. After 55+ professional years in the world of diamonds - Horst Lach, born on April 3rd, 1940, is known as one of the pioneers of the diamond tool industry. His outstanding and brilliant ideas were simply remarkable, and he initiated a complete new way of thinking in the tool industry. Tool life should no longer be measured in hours, but in weeks and months. In 1960, Horst Lach joined his father's diamond cutting facility, founded in 1922.

“The corner of the insert must be prepared properly to cut smoothly,” said Usher. “We have found that a thin layer of CBN or PCD bonded to carbide provides a good combination of surface finish, tool life and cost. We have six or seven different CBN inserts designed for different kinds of milling applications.”

Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush.

From a historical perspective, this question was initially posed to Lach-Spezial-Werkzeuge GmbH, which was worldwide the first manufacturer of diamond tools for machining all wood and plastic materials (Feb. 1979 – see part 5 of this article series “Poly – poly – or what?”).

Only one driving force is the appropiate explanation for the rapid acceptance of diamond tools in the furniture industry: the stakeholders. At the time, all necessary decisions during the introduction of polycrystalline tools were shaped by medium-sized enterprises: All manufacturers of PCD tools – without exception family-managed companies – and equally the buyers, therefore the decision makers. Incidentally, I experienced identical developments not only in Germany, in Europe and in the United States, but also worldwide. The “big players” often came much later – manufacturers as well as buyers.

Part 1 – A good project car brings people together. Driving the rare Lincoln Blackwood into Ohio Technical College (OTC) turned heads. And once Babcox Media’s Joe Keene, an ASE-certified technician, and the technicians-in-training at OTC got to pop the hood and slide under it on a creeper to get their hands in it, its service needs raised eyebrows.

Other press reports of this year allow the conclusion that expectations regarding the future use of PCD tools in the automotive industry had increased enormously. A quote from “Fachberichte für Metallbearbeitung” Nov./Dec. issue in 1980: “Tripling today’s production capacities (as announced by Lach Diamant at FAMETA 80 in Essen and Stuttgart) promises security to consumers in a now economically viable machining technology – and ultimately, this is attributed to Lach Diamant as a counter-initiative to the Japanese challenge.”

One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment.

Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

In a nutshell, polycrystalline cutting tools became a continuing success story, for tool manufacturers and for users – from stationary turning tools and cutting inserts to rotating milling cutters, drills, step drills, reamers, saws, dressing rolls and other tools.

Many industries have profited from this in the most literal sense of the word during the last decades – first and foremost the automobile industry by implementing the principle of “energy savings through light-weight designs.” This success would have been unimaginable without PCD tools. Other pioneer accomplishments include the aircraft industry, machining of propellers in the wind-turbine industry and in general the wood and plastic (composite) industry, even spanning to achievements in electro engineering and in medical technology. The list could easily be continued. Whoever thinks that we are at the end of this development is mistaken. For example, laser technology will one day be so advanced that it will take its place as an efficient, precise manufacturing alternative, next to spark erosion and grinding.

'Poly – Poly – or what?' Part 8: How the 'issue with the comma' became a success, Part 8 (Published 6/25/2019)

Skip Anderson of DCM-Tech agreed that dry milling is the only way to surface today’s engines. “Most of the equipment we sell is for industrial applications, so we are using the same industrial technology in our automotive surfacing equipment. We use a ball screw feed mechanism rather than hydraulics because it is quieter, smoother and more consistent. You won’t get feed rate changes with temperature as you can with a hydraulic feed system. We also use industrial precision bearings for the spindles and balance the rotors so our customers can achieve surface finishes that meet their specification. If a customer wants a surface finish as smooth as 5 to 9 Ra (Roughness Average), our equipment can do it.”

• Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket).

Lead times are no longer months upon months as they were in the middle of 2020 and throughout 2021, but the situation is still of some concern, and it’s forced engine builders to get creative at times.

Machine designed to use a serrated-tooth blade to cut metal or other material. Comes in a wide variety of styles but takes one of four basic forms: hacksaw (a simple, rugged machine that uses a reciprocating motion to part metal or other material); cold or circular saw (powers a circular blade that cuts structural materials); bandsaw (runs an endless band; the two basic types are cutoff and contour band machines, which cut intricate contours and shapes); and abrasive cutoff saw (similar in appearance to the cold saw, but uses an abrasive disc that rotates at high speeds rather than a blade with serrated teeth).

Originally, we were talking about names like GE Superabrasives or DeBeers. Today, PCD buyers must get used to the fact that the respective companies and departments have changed owners and names up to four times. Other, additional products intermittently offered on the market, such as mono diamonds and CVD (chemical vapor deposition), do not make any difference in this regard. The latest DeBeers/ Element Six product – so-called “Labour-made” jewel diamonds on CVD basis – are by the way currently the hype on the jeweller market. Such diamonds (brilliants) should be offered to consumers at a 70% “cheaper” price, and via a separate distribution channel than to natural diamonds. DeBeers/Element Six is building a large production facility in Pennsylvania for these “Labour-made” gem diamonds. Sales in the U.S. have already started, branding it “Lightbox Jewelry.”

Consequently, the gaskets required a very smooth surface finish. By comparison, traditional solid or perforated steel core head gaskets with composition facings or graphite gaskets typically required a finish in the 54 to 113 Ra (60 to 125 RMS) range.

To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?).

Bill McKnight of Mahle/Victor-Reinz Gaskets said the surface finish requirements for modern MLS gaskets are not are critical as they once were. “You had some manufacturers saying we had to produce a 8 to 10 Ra finish to seal the head gasket. But the coatings on today’s aftermarket MLS gaskets can handle anything in the 40 to 70 Ra range with no problems.” McKnight said the type of process or equipment used to surface a head or block doesn’t matter as long as it leaves a good finish. “You can dry mill or wet grind or sand and get good results when the resurfacing is done right.” Jim Daigle of Fel-Pro/Federal Mogul also said today’s aftermarket MLS head gaskets don’t require the super smooth finishes originally specified by the vehicle manufacturers. “Our blue coated MLS gaskets can typically handle surface finishes from 70 to 80 Ra, while our black coating is typically designed for surface finishes of 30 Ra or less. We put our surface finish recommendations right on our packaging because it can vary from one application to another. “Smoother is better for many applications, but is not absolutely necessary. If you’re building a NASCAR motor that’s running 280 to 300 degrees F, a surface finish of 30 Ra or less is better and recommended. Even though some of our Performance MLS gasket coatings can accommodate above 30 Ra we really encourage a 30 Ra target (or less) for any Performance MLS application. But for a typical street or strip application, we’ll use a gasket coating that is more conformable to handle a more traditional surface finish.” One point Daigle emphasized with respect to surface finish is the need to de-emphasize Ra numbers and focus more on Rz. Roughness Average (Ra) can actually have a wide variance across a given surface profile. Rz, which is the average difference between the peak height and valley depth, is actually a much more accurate representation of true surface topography. He said that most Asian vehicle manufacturers don’t even talk about Ra anymore, referring instead to Rz values for surface finish. Profilometers can usually provide a range of surface parameters, including Rz (which is roughly 6X the Ra value in most conversion tables). Of course, many shops don’t own a basic hand held profilometer, let alone know how to use one. And those that do may only use their profilometer to check surface finishes if there’s a problem. The rest of the time, it stays in the box A profilometer is a precision instrument that typically costs $800 to $1800 for a basic hand held unit, or as much as $100,000 for a sophisticated lab model. The hand held units drag a diamond tipped stylus across the metal to measure the microscopic peaks and valleys on the surface. It then displays the various values and calculates an Ra number for the surface finish. One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment. According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows: • Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket). • Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz). • The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

Just 3,356 Lincoln Blackwoods exist in the world. For comparison, the Ford F-150—the Blackwood’s inspiration—has spawned more than 40 million since its launch in 1948. Guess which one is harder to track down parts for? Babcox Media’s Joe Keene, an ASE-certified technician, has tracked down his fair share of elusive parts, but fixing up a

After the discovery of spark erosion for forming polycrystalline cutting materials, it should now become possible to offer more and more customized solutions for the use of PCD tools (see part 1-3 of this article series “Poly – poly – or what?”). Why was this not implemented – or better – why could this not yet be implemented during the early 1980s? Analogous to the successful introduction of diamond tools in the furniture industry?

Loosely, any milling tool. Horizontal cutters take the form of plain milling cutters, plain spiral-tooth cutters, helical cutters, side-milling cutters, staggered-tooth side-milling cutters, facemilling cutters, angular cutters, double-angle cutters, convex and concave form-milling cutters, straddle-sprocket cutters, spur-gear cutters, corner-rounding cutters and slitting saws. Vertical cutters use shank-mounted cutting tools, including endmills, T-slot cutters, Woodruff keyseat cutters and dovetail cutters; these may also be used on horizontal mills. See milling.

CTE is happy to be publishing a series of articles by Horst Lach. To date we have published the following :

For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders.

Wet grinding was capable of producing high quality surface finishes when done properly. But according to Anthony Usher of Rottler Manufacturing, it was a “very messy” process compared to dry milling.

When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones.

Regarding further developments of the supply of polycrystalline synthetic diamonds (PCD) by the “biggest” suppliers for the tool manufacturing industry, I must express my scepticism whether we can “soon” expect significant improvements in one or the other components for advanced production and use.

Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother.

As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

• The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.

Another showstopper was at the time the developmental stage of numerical controls; there were initial approaches from perforated discs to punched tapes for scanning specified machine data. But compared to today, these were small beginnings to successfully execute only a few electromotoric axial movements. The real takeoff into the future of freely programmable controls can be pinpointed between the years of 1984-1990; starting with the design of toy computers and going as far as the complete replacement of perforation strips for tooling machines.

High-temperature (1,000° C or higher), atmosphere-controlled process in which a chemical reaction is induced for the purpose of depositing a coating 2µm to 12µm thick on a tool’s surface. See coated tools; PVD, physical vapor deposition.

The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing.

If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter.

Other equipment suppliers have a somewhat different take on the selection of inserts. Tim Whitley of T&S Machines & Tools said he recommends using CBN for everything. “It delivers great results and works just as well on aluminum as it does on cast iron. The key is the edge preparation on the insert.”

It looks like an ordinary inline 4-cylinder flathead engine. Essentially it is, but it has quite a cult following here in the UK.

Whitley said Ford sent him some 4.6L heads to see if he could match the factory finish. When he checked the heads, he found the factory finish was 12 Ra. When he finished the heads on his equipment, he said the finish was 8 Ra. “We can deliver any finish specification the OEMs or gasket suppliers require. The rigidity of our machines makes such smooth finishes possible. You can stop and start the machine halfway through a job and not leave a mark on the finish.” Matt Meyer of RMC Engine Rebuilding Equipment said he also favors using CBN inserts for most milling applications. “We use a specific edge prep on our inserts so they can cut both aluminum and cast iron. We also have special CBN inserts for cutting blocks with hard sleeves and diesel heads that have been spray welded or have precombustion chamber cups. You don’t want aluminum binding to the insert, especially when you are cutting a bimetal surface. It can drag metal across the surface and leave marks. An aluminum oxide coating on an insert is not a good idea because it can bind with aluminum chips and cut unevenly.” Meyer said his milling equipment can deliver any surface finish that’s required to seal a gasket. “But I think there’s been a conspiracy among the vehicle manufacturers as to the smoothness that’s really necessary. They’ve been telling everybody that you have to have a mirror-like finish otherwise the gasket won’t seal. That may have been true with the early generation original equipment MLS gaskets, but it’s no longer true with most aftermarket MLS gaskets. The coatings they are now using can handle a more traditional surface finish.” When Ford introduced the 4.6L modular V8, they specified a factory surface finish is 8 to 12 microinches Ra. By comparison, many Japanese auto makers such as Honda and Mazda were specifying surface finishes in the 8 to 20 Ra range back in the early 1990s for their engines. The MLS gaskets they were using at that time had two to five layers of heat treated steel, each covered with a relatively thin (.001 in.) coating of nitrile rubber or Viton. Consequently, the gaskets required a very smooth surface finish. By comparison, traditional solid or perforated steel core head gaskets with composition facings or graphite gaskets typically required a finish in the 54 to 113 Ra (60 to 125 RMS) range. As gasket technology has evolved, surface finish requirements at the OEM level have eased a bit. Most Asian car makers today specify a surface finish of 20 Ra or less, while most domestic vehicle manufacturers say 30 Ra or less is required. What Gasket Suppliers Say Bill McKnight of Mahle/Victor-Reinz Gaskets said the surface finish requirements for modern MLS gaskets are not are critical as they once were. “You had some manufacturers saying we had to produce a 8 to 10 Ra finish to seal the head gasket. But the coatings on today’s aftermarket MLS gaskets can handle anything in the 40 to 70 Ra range with no problems.” McKnight said the type of process or equipment used to surface a head or block doesn’t matter as long as it leaves a good finish. “You can dry mill or wet grind or sand and get good results when the resurfacing is done right.” Jim Daigle of Fel-Pro/Federal Mogul also said today’s aftermarket MLS head gaskets don’t require the super smooth finishes originally specified by the vehicle manufacturers. “Our blue coated MLS gaskets can typically handle surface finishes from 70 to 80 Ra, while our black coating is typically designed for surface finishes of 30 Ra or less. We put our surface finish recommendations right on our packaging because it can vary from one application to another. “Smoother is better for many applications, but is not absolutely necessary. If you’re building a NASCAR motor that’s running 280 to 300 degrees F, a surface finish of 30 Ra or less is better and recommended. Even though some of our Performance MLS gasket coatings can accommodate above 30 Ra we really encourage a 30 Ra target (or less) for any Performance MLS application. But for a typical street or strip application, we’ll use a gasket coating that is more conformable to handle a more traditional surface finish.” One point Daigle emphasized with respect to surface finish is the need to de-emphasize Ra numbers and focus more on Rz. Roughness Average (Ra) can actually have a wide variance across a given surface profile. Rz, which is the average difference between the peak height and valley depth, is actually a much more accurate representation of true surface topography. He said that most Asian vehicle manufacturers don’t even talk about Ra anymore, referring instead to Rz values for surface finish. Profilometers can usually provide a range of surface parameters, including Rz (which is roughly 6X the Ra value in most conversion tables). Of course, many shops don’t own a basic hand held profilometer, let alone know how to use one. And those that do may only use their profilometer to check surface finishes if there’s a problem. The rest of the time, it stays in the box A profilometer is a precision instrument that typically costs $800 to $1800 for a basic hand held unit, or as much as $100,000 for a sophisticated lab model. The hand held units drag a diamond tipped stylus across the metal to measure the microscopic peaks and valleys on the surface. It then displays the various values and calculates an Ra number for the surface finish. One dimension simple hand held profilometers cannot measure is waviness. It takes megabuck lab equipment to do that. But waviness is another critical dimension that can affect head gasket sealing, too. Waviness problems can be caused by vibrations and a lack of rigidity in milling equipment. According to Fel-Pro, the recommended surface finishes for various engine and gasket applications are as follows: • Cast iron and aluminum engines assembled with Permatorque MLS head gaskets should have a surface finish of no more than 80 Ra (480 Rz) or less (as compared to 30 Ra or 180 Rz for a typical original equipment MLS head gasket). • Cast iron or aluminum cylinder heads and blocks assembled with conventional steel/fiber composite head gaskets or expanded graphite head gaskets should have a surface finish no smoother than 40 Ra (240 Rz) and no rougher than 100 Ra (600 Rz). Rougher surfaces limit gasket conformance, while smoother surfaces increase the tendency for gaskets to flow, reducing the gaskets blow out resistance. The optimum recommended surface finish for these applications is 60 to 80 Ra (360 to 480 Rz). • The maximum amount of out-of-flat should not exceed .001? within three inches in any direction. For four-cylinder and V8 engines, the maximum allowable out-of-flat specification for the cylinder head and block deck surfaces is .004? lengthwise and .002? sideways. For V6 and three-cylinder engines, .003? lengthwise and .002? sideways. For in-line five- and six-cylinder engines, .006? lengthwise and .002? sideways. • Waviness (which requires special “skidless” lab equipment to measure, should not exceed a waviness height (Wt) of .0008? with conventional composite or graphite head gaskets, and no more than .0004? with MLS head gaskets. Surfacing Tips The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head. To achieve the best possible finish, use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001?). If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter. With CBN or PCD inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter. With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens. Cylinder Bore Finishes The surface finish in the cylinder bores is just as important for proper ring sealing as the surface finish is on the block and heads for proper head gasket sealing. Regardless of what type of rings or cylinder liners are used in a block, rings usually seat best and last the longest when the cylinder bores are given a plateau finish. A plateau finish essentially duplicates a “broken-in” bore finish, so there is less scrubbing and wear on the rings when the engine is assembled. What’s more, if the surface is finished correctly it will provide plenty of flat, smooth bearing surface to support the rings while also retaining oil in the crosshatch valleys to lubricate the rings. The only exception to this is in motors where there is a lot of bore distortion. If the bores go out of round when the head bolts are torqued down, the rings may not seat as well allowing increased blowby and oil consumption. Thinner rings that can conform to the bore will work better in these kind of applications, but it’s also a good idea to use torque plates when honing when honing the bores to simulate the distortion that occurs when the cylinder heads are installed. The other option is to go with a slightly rougher “peaked” finish to seat the rings. Most ring manufacturers recommend using a two- or three-step honing procedure to achieve a plateau finish. First, rough hone to within .003? of final bore size to leave enough undisturbed metal for finish honing. For plain cast iron or chrome rings in a stock, street performance or dirt track motor, hone with #220 grit silicon carbide stones (or #280 to #400 diamond stones) to within .0005? of final size. Then finish the bores with a few strokes using an abrasive nylon bristle plateau honing tool, cork stones or a flexible abrasive brush. For moly faced rings in a street performance, drag or circle track motor, hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly honing to final size with a #400 grit vitrified stone or #600 grit diamond stone (or higher), plateau honing tool, cork stones or a brush. For stock and street performance engines with moly rings, an average surface finish of 15 to 20 Ra is typically recommended. for higher classes of racing, you can go a little smoother provided you don’t glaze the cylinders. For moly or nitrided rings in a performance motor, hone with #320 or #400 vitrified stones, and finish with #600 stones, cork stones, a plateau honing tool or brush. If the cylinders are rough honed with diamond, they can be finish honed with a finer grit diamond, a fine grit vitrified abrasive or a plateau honing tool or brush. Because diamond is a harder material and wears more slowly than conventional abrasives, it cuts differently and may require more honing pressure. But many newer diamond stones now use a more friable bond that stays sharp and doesn’t load up, allowing the stones to cut smoother and leave a rounder, smoother bore finish. When using diamond honing stones instead of vitrified abrasives, you generally have to use a higher number grit to achieve the same Ra (roughness average) surface finish. For example, if you have been using #220 grit conventional stones to finish cylinders for plain cast iron or chrome rings, the equivalent diamond stones might be a #280 to #325 grit. If you have been using #280 grit conventional stones to hone for moly rings, the diamond equivalent might be #400 to #550 grit stones. The actual numbers will vary somewhat depending on the brand and grade of the stones. Bristle style soft hones (plateau honing tools) have mono-filament strands that are extrude molded with a fine abrasive material embedded in the strands. The filaments are mounted in different types of holders for use with portable or automatic honing equipment. Another type of brush uses molded abrasive balls that are mounted on flexible metal shafts so the balls can easily conform to the surface. Brushing helps sweep away torn and folded metal on the surface while removing many of the sharp peaks to make the surface smoother. As with any type of machine shop equipment, proper technique is required to do the job right with these tools, so be sure to get  the necessary instruction from your supplier. With the right plateau honing techniques, you should be able to get the surface down to an average roughness of 8 to 12 Ra or less, with RPK (relative peak height) numbers in the 5 to 15 range, and RVK (relative valley depth) numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can measure them (which a growing number of shops now have). When finishing a performance block with nickel silicon-carbide liners, the microscopic pores in the coasting do an excellent job of retaining oil for the rings. Consequently, the bore can be finished to a super smooth finish of 4 to 6 Ra or less to reduce friction even more. Such low numbers would be too smooth for grey cast iron and would likely starve the rings for proper lubrication Dennis Westhoff of Sunnen cautions that honing coated cylinders is not the same as honing conventional cast iron cylinders. “Engine manufacturers and racers are developing new thermal spray coatings for cylinder walls that contain a mix of ceramics and other materials,” said Westhoff. “We are working with these people to develop a database of honing procedures that can achieve the best surface finish. The porosity in many of these coatings retains oil quite well, so it is usually possible to go with a much smoother plateau finish in the bores.” Westhoff’s advice for engine builders who may be working with coated cylinders is to find out what type of coating is being used, then call the machine supplier to find out what combination of honing stones and honing procedures will produce the best finish. For contact information for suppliers of surfacing machines and abrasives, as well as gasket manufacturers, click on our online Buyers Guide tab.