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TECH GUIDE 1 1-5 Gaskets/Decks 4/15/09 10:51 AM Page 2 2009 APRIL Pg 1 Head & Block Decks & Gaskets Pg 6 Cylinder Bores & Piston Rings Pg 12 Valves & Valve Seats Pg 16 Cam Bores, Bearings & Camshafts Circle 101 or more information 1-5 Gaskets/Decks 4/15/09 10:51 AM Page 1 ince the days of sealing Smooth Operation or chatter when it makes an interrupt- engines with asbestos, cork, How smooth is smooth enough? You ed cut. S rope and paper are, for the used to be able to tell by dragging For example, a converted grinder most part, ancient history, your fingernail across the surface of a may be able to mill heads and blocks. new-age materials and designs have cylinder head or engine block. And But the spindles and table drives in elevated the critical role gaskets and besides, it didn’t really matter because many of these older machines cannot seals play in the longevity of an the composite head gasket would fill hold close enough tolerances to engine. Finding the optimum sealing any gaps that your equipment or tech- achieve a really smooth, flat finish. material and design remain a chal- nique left behind. One equipment manufacturer said lenge many gasket manufacturers face But with MLS gaskets the require- grinding and milling machines that as engines are asked to do more. ments have changed. To seal properly, are more than five years old are prob- Gaskets that combine high per- a head gasket requires a surface finish ably incapable of producing consistent formance polymers with metal or that is within a recommended range. results and should be replaced. fiber substrates are being used in more This range varies depending on the Most of the surfacing equipment and more engine applications. type of gasket.Too rough (or in some that’s being sold to shops today has Furthermore, engines that are sealed cases too smooth) and the gasket may been redesigned for high speed using these higher quality gaskets are not seal properly and leak or fail. milling with CBN and PCD. The lasting longer, performing better and According to surfacing experts, the machines have been beefed up with with less maintenance or chance of recommended surface finish for a tra- more powerful motors, heavier cast- the dreaded warranty comeback ditional composite-style soft-face ings, electrically driven ball screw claim. head gasket in an engine with cast tables, and tighter assembly tolerances. There are many considerations iron heads and block is 60-120 Some can hold machining tolerances engine builders must take into microinches Ra (roughness average). to .0001˝! account when selecting the best gas- The recommended finish for the same Doing the job right may be more kets for an application. With engines head gasket with an aluminum head challenging than ever, but doing the having higher performance require- on a cast iron block is typically 20-50 job wrong may cost you even more. ments, stricter emission regulations, microinches Ra. and tighter design tolerances along For engines with MLS gaskets, the Head Gasket Evolution with production cost considerations OEM surface finish recommendations The cylinder head gasket is arguably and quality standards that are increas- are even smoother, perhaps 20-30 or the most important seal in the engine. ing, the last thing any engine builder even 7-15 Ra. Since the very first internal combus- wants to worry about is a gasket or Accurately measuring the surface tion engines were produced, gasket seal failure. finish can be done using a profilome- designers have specified many materi- It doesn’t matter if you’re building ter, an electronic instrument that drags als to meet this difficult sealing chal- a Pro Stock or stock production a diamond-tipped stylus across the lenge. engine: the risks are simply too great surface to calculate its profile charac- to use a subpar gasket or seal. teristics. The profilometer then shows Three Types of Head Gaskets It’s more complicated to seal today’s various values for the surface includ- Composite – this technology is engines because, depending on the ing roughness average (Ra), average used mostly on older stock engine application, modern engines are peak height (Rpk), average valley applications and in some performance expected to last well over 150,000 depth (Rvk) and even waviness. applications. Typically these types of miles without fail. Performance These critical surface finishes gaskets are made from graphite and engines are pumping out more power require high quality resurfacing equip- can be more prone to blowouts than than ever. So keeping these engines ment to achieve low Ra numbers. MLS gaskets. In the aftermarket, com- sealed can be a tall order and creates a Extremely smooth finishes require posite gaskets are still required for hefty job for engine gaskets and seals high quality resurfacing equipment to many older applications and are also to handle. achieve really low Ra numbers. It more forgiving of less than perfect Engine seals and gaskets are sup- doesn’t matter if you use carbide, surface finishes. posed to prevent the leakage of oil, cubic boron nitride (CBN) or poly- Copper - A solid sheet of copper coolant and air between mating sur- crystalline diamond (PCD) tool bits to typically requires machining for O- faces, internal passages and the outside resurface a head as long as you use the rings that place a piece of wire around of the engine. Seals and gaskets also correct feed rate and speed – and the the circumference of the cylinder to prevent the entry of dirt and air into equipment is rigid enough to hold the bite into the copper.When used with the engine. cutter steady so the tool bit doesn’t lift O-rings, copper gaskets are extremely www.enginebuildermag.com | PERFORMANCE PARTS & MACHINING TECH GUIDE 1 1-5 Gaskets/Decks 4/15/09 10:51 AM Page 2 durable. Copper gaskets are mostly and is unmatched by any other sealing als are taking the place of older, less used in performance applications system to this point.Today,it is rough- compatible and less durable materials. where there is a lot of cylinder pres- ly estimated that 80 percent of new The following list shows the types of sure. Recently some gasket companies engines are designed with MLS gas- materials used in automotive applica- have started producing copper gaskets kets as standard equipment and further tions and the characteristics of each with integral sealing wires permitting growth is projected. type. their retrofit into engines without the In the MLS gasket, multiple thin Viton – Viton is a registered trade- need to machine the engine block. layers of cold-rolled spring grade mark of DuPont Performance Copper and brass gaskets were stainless steel are coated with 7-25 Elastomers and is commonly called some of the earliest materials used but microns of elastomeric material. The Fluoroelastomer/ Viton (FPM). It is gave way to metal and asbestos com- resilient elastomer is essential to the best known for its ability to tolerate posite gaskets in the 1950s, superseded structure by providing micro-sealing high temperature environments in turn by composite metal and of metal surface imperfections while (400°F), which makes it well suited for impregnated fiber or graphite com- resisting aggressive combustion gases, automotive applications. posites by the 1980s. However, those oils and coolants at temperatures up to Viton can also easily withstand systems were largely overtaken by the 250°C or 480° F. aggressive fuels and chemicals and has development of the Multi-Layer Steel excellent mechanical properties as (MLS) gasket in Japan during the early Better Sealing well. This material is also resistant to 1990s. Through Chemistry abrasion and cuts. With a broad array Multiple Layer Steel (MLS) – Gasket manufacturers use all kinds of of applications in the automotive, this type of head gasket typically con- materials and designs to keep engine chemical processing and industrial sists of three layers of steel. Most mod- oil, coolant, vacuum and compression markets,Viton fits many performance ern engines today are produced with separated from each other. Through specifications. MLS gaskets. The contact layers are the use of computer aided design Neoprene Polychloroprene – usually coated with a rubber-like (CAD), finite element analysis (FEA) Neoprene polychloroprene was the first coating such as Viton that adheres to and polymer science, gasket engineers synthetic elastomer able to resist oil and the cylinder block and cylinder head can now more thoroughly understand is still a popular material in a number of respectively while the thicker center many facets of the joint they are try- automotive applications. Neoprene layer is bare, allowing for movement as ing to seal and are able to design a gas- remains a popular choice for many if it were like a spring. ket with materials that will withstand automotive applications that require a MLS gaskets remain the automo- the pressures of the environment. reasonably priced, mid-performance tive industry’s preferred method of Materials such as Teflon, Viton, polymer with a good all-around bal- sealing the cylinder head and block, Graphite and other specialized materi- ance of performance properties. Circle 102 for more information 2 PERFORMANCE PARTS & MACHINING TECH GUIDE | April 2009 Circle 103 for more information 1-5 Gaskets/Decks 4/15/09 10:51 AM Page 4 Nitrile (NBR) – NBR provides excellent resistance to mally from minus 100°C to plus 250°C (212° to 482° F). petroleum oils and gasoline as well as mineral and vegetable When compared to natural rubbers, silicone has better fire oils. However, NBR has poor resistance to the swelling resistant properties and is an excellent electrical insulator. action of oxygenated solvents such as acetone and ketones.
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