Head gasket
(→Reasons why head gaskets fail) |
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[[Image:Head gasket ford 298-302.jpg|thumb|220px|Head gasket Ford 289 - 302 CID]] | [[Image:Head gasket ford 298-302.jpg|thumb|220px|Head gasket Ford 289 - 302 CID]] | ||
| − | '''Cylinder head gaskets''' provide the critical seal between the engine block and the [[cylinder head]]. They seal | + | '''Cylinder head gaskets''' provide the critical seal between the engine block and the [[cylinder head]]. They seal the combustion in the [[combustion chamber]]s and keep [[coolant]] contained to the cooling ports in the heads and block. |
Blown head gaskets can be caused by various engine problems, and can be detected with certain techniques. Left unfixed, a blown head gasket could cause severe engine damage. | Blown head gaskets can be caused by various engine problems, and can be detected with certain techniques. Left unfixed, a blown head gasket could cause severe engine damage. | ||
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Copper and brass were originally used as head gaskets, followed by asbestos/steel 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. | Copper and brass were originally used as head gaskets, followed by asbestos/steel 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. | ||
| − | In MLS gaskets, multiple thin layers of cold-rolled steel are coated with a very thin layer of | + | In MLS gaskets, multiple thin layers of cold-rolled steel are coated with a very thin layer of elastometric material. The elastomer "micro-seals" the surface imperfections in the metal, and resists gases, oils, coolants, and high combustion temperatures. |
====Copper head gaskets==== | ====Copper head gaskets==== | ||
| − | Copper head gaskets provide the strongest combustion seal which is why they are used in all | + | Copper head gaskets provide the strongest combustion seal which is why they are used in all nitro-methane (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" differential in any direction). 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 accomplish combustion sealing with standard copper head gaskets, grooves are 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) of the installed o-ring from the wire diameter. Stainless steel wire (most often .041" diameter) is then seated into the groove by tapping with a soft faced hammer or other interface tool such as plastic or wood (hard faced hammers can cause dents which create combustion leakage paths). It is advisable to begin and end the o-ring nearest a bolt location to take full sealing advantage of increased loading near the bolt upon the joint in the o-ring. Although copper is a relatively soft material, there is a limit to which it can be displaced 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 .050" thick gasket about .012", 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 applications. 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 occurred, the gasket(s) must be replaced. | To accomplish combustion sealing with standard copper head gaskets, grooves are 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) of the installed o-ring from the wire diameter. Stainless steel wire (most often .041" diameter) is then seated into the groove by tapping with a soft faced hammer or other interface tool such as plastic or wood (hard faced hammers can cause dents which create combustion leakage paths). It is advisable to begin and end the o-ring nearest a bolt location to take full sealing advantage of increased loading near the bolt upon the joint in the o-ring. Although copper is a relatively soft material, there is a limit to which it can be displaced 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 .050" thick gasket about .012", 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 applications. 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 occurred, the gasket(s) must be replaced. | ||
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