Head gasket
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====Copper head gaskets==== | ====Copper head gaskets==== | ||
| − | Copper head gaskets are | + | Copper head gaskets provide the strongest combustion seal which is why they are used in all nitromethane (Top Fuel) and methanol (Blown Alcohol) applications. 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. Copper head gaskets are re-usable, and they do not have to be re-annealed, however since they are made from a flat sheet of copper, they require relatively flat deck surfaces (no more than .002" across). Copper head gaskets are quite forgiving of machining imperfections from higher RA (Roughness Average) surfaces or small scratches in the head and deck surfaces since they are made of malleable (soft) copper which conforms readily to surface irregularities under the compressive clamp load of the tightened head bolts. |
| − | To | + | To accomplish combustion sealing with standard copper head gaskets, grooves machined into the block or the head outside of the combustion sealing area to a width that will retain a stainless wire by friction resistance (usually .039" to .040" wide), the depth of the groove is determined by subtracting the desired protrusion (height) from the wire diameter . Stainless steel wire (most often .041" diameter) is then embedded into the groove by tapping with a soft faced hammer (heard faced hammers can cause dents which create combustion leakage paths) so that it pro slightly above the block deck or head surface. It is advisable to begin and end the o-ring near a bolt location to take advantage of increased loading upon the joint in the o-ring. 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 25% of the gasket thickness. For instance, with a 0.032" thick gasket, you would want to limit the height of the o-ring to about 0.008" above the head or deck surface. For an .043" thick head gasket which is the most common thickness, set the o-ring protrusion at 0.010", for an 0.062" thick gasket, about 0.015" and so forth. If the groove is cut into the head for the wire, a "receiver groove" can be machined into the block. If the groove is cut into the block deck for the wire, then a receiver groove can be 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. However most street / strip applications do not require receiver grooves, receiver grooves are only required on the most extreme racing appliactions. You'll also need a good sealer around the water passages (K&W Copper Coat is easy to use and easy to find). Copper head gaskets can be re-used several times, simply use a solvent such as brake cleaner to remove any sealant and inspect the area of the gaskets around the combustion seal to insure that there is no 'carbon tracking' which will appear as a shadow on the head gaskets, this is evidence of combustion leaking. If combustion leakage has occured, the gasket(s) must be replaced. |
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| − | + | ----Modern Copper Head Gaskets---- | |
| + | SCE Gaskets makes copper head gaskets with coolant and oil passage seals bonded to the sealing surfaces of the head gaskets. These built in seals eliminate the need for additional sealants, these head gaskets are installed dry and there are two versions available, for engines with machined o-ring combustion seals or for those without o-rings. The copper head gasket offered by SCE for engines without machined o-rings includes both coolant seals and an Integral Combustion Seal which eliminates the need to have o-ring grooves machined into the block or heads. Development of these head gaskets allow users to exploit the benefits of of copper, wide range of thicknesses, superior strength, superior combustion sealing, conformability to deck surfaces and superior heat conductivity, with none of the prior disadvantages of 'old fashioned' copper head gaskets. | ||
| + | Gasket Works makes a stainless steel o-ring that is only 0.004" thick and eliminates the need to groove the block or head. See: http://www.headgasket.com/images/olympic%20rings.jpg . | ||
====Steel (shim) gaskets==== | ====Steel (shim) gaskets==== | ||
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