Head gasket
(→Head gasket basics) |
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Various different types of head gaskets exist today, for different applications. Care must be taken in removal of the old gasket, selection of a new gasket and proper installation of the new gasket. | Various different types of head gaskets exist today, for different applications. Care must be taken in removal of the old gasket, selection of a new gasket and proper installation of the new gasket. | ||
| − | + | ==Head gasket basics== | |
| + | ===Different types of head gaskets=== | ||
| + | Copper and brass were originally used as head gaskets, followed by asbestos gaskets in the 1950's, and composite metal and impregnated fiber or graphite composites in the 1980's. In the 1990's the Multi-Layer-Steel gasket (MLS) came into widespread use. Most new engines today are designed with MLS gaskets. | ||
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| + | In MLS gaskets, multiple thin layers of cold-rolled steel are coated with a very thin layer of elastomeric material. The elastomer "micro-seals" the surface imperfections in the metal, and resists gases, oils, coolants, and high combustion temperatures. | ||
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| + | ''(needs more info on various types of head gaskets)'' | ||
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| + | ====Copper head gaskets==== | ||
| + | Copper head gaskets are typically less forgiving. They're commonly used in high-performance applications where extreme cylinder pressures will be encountered, such as very high static compression ratios on naturally-aspirated motors or where superchargers or turbochargers are used. They are re-usable, although they have to be re-annealed. They seal combustion well, but they are prone to leaking coolant and are less forgiving to imperfections in the head and deck surfaces. | ||
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| + | To take full advantage of copper head gaskets, you have grooves machined into the block or the head. Stainless steel wire is then imbedded into the groove so that it sticks up slightly above the block deck or head surface. Although copper is a relatively soft material, there is a limit to which it can be compressed by an o-ring. Generally speaking, this limit is about 10% of the gasket thickness. For instance, with a 0.030" thick gasket, you would want to limit the height of the o-ring to about 0.003" above the head or deck surface. For a 0.060" thick gasket, about 0.006" and so forth. If the groove is cut into the head for the wire, then a "receiver groove" is machined into the block. If the groove is cut into the block deck for the wire, then a receiver groove is machined into the head surface. When the head is bolted to the block, the wire pushes some of the copper up into the receiver groove and makes a very effective seal. ''(confirm and expand)''. You'll also need a good sealer around the water passages. If copper head gaskets are used with an o-ring, they are NOT reuseable. | ||
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| + | UPDATE: | ||
| + | Gasket Works now makes a stainless steel o-ring that is only 0.004" thick and eliminates the need to groove the block or head. | ||
| + | http://www.headgasket.com/images/olympic%20rings.jpg | ||
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| + | However, copper head gaskets have superior thermal conductivity, thought to stabilize head and block temperature, and provide elasticity and strength. | ||
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| + | ===Aluminum cylinder heads=== | ||
| + | Though aluminum is lighter than cast iron, it expands faster. This quicker cycle of expansion and contraction stresses head gaskets. To handle this, a non-stick coating is often applied to the gasket, like Teflon or molybdenum. | ||
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| + | With iron heads, a product can be applied for the opposite effect. Silicone, Viton, or other fluoroelastomer sealants are applied to '''increase''' the pressure between the iron heads and the iron block. | ||
=="Blown" head gaskets== | =="Blown" head gaskets== | ||
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