Head gasket
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==Head gasket basics== | ==Head gasket basics== | ||
===Different types of head gaskets=== | ===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. | + | 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 elastomeric material. The elastomer "micro-seals" the surface imperfections in the metal, and resists gases, oils, coolants, and high combustion temperatures. | 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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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. | 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. | ||
| − | To take full advantage of copper head gaskets, you have grooves machined into the block or the head. Stainless steel wire is then | + | To take full advantage of copper head gaskets, you have grooves machined into the block or the head. Stainless steel wire is then embedded 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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However, copper head gaskets have superior thermal conductivity, thought to stabilize head and block temperature, and provide elasticity and strength. | However, copper head gaskets have superior thermal conductivity, thought to stabilize head and block temperature, and provide elasticity and strength. | ||
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| + | STEEL (Shim)Gaskets | ||
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| + | Steel shim gaskets come in a variety of thicknesses as the name implies and range from .010 up to .080. Originally, the gaskets were of flat steel sheeting and went on to have an embossed surface. The embossing was strategically placed on the gasket surface around cylinder holes, water inlets, and outer surfaces. The embossing provided extra metal to fill in voids over the sealing surface when torqued into place. Shim gaskets could raise or lower compression in an engine without machining. They were the front runners of the now used fiber and non-ferrous metal gaskets. The term, "blowing a gasket" was common for top racers because they were using a very thin 10 or 20 thousandths shim gasket to raise compression, because of its thinness, the gasket would blow between two inner cylinders. They could stay in the race only as long as the gasket didn't disintegrate and expose the coolant passages to the combustion chamber. Engine builders of the day were often seen applying a couple coats of aluminum paint to both sides of a set of head gaskets to make them stick in place and seal the mating surfaces. The aluminum particles in the paint would fill in the voids in surfaces of the sand cast heads and block. | ||
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===Aluminum cylinder heads=== | ===Aluminum cylinder heads=== | ||
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*A test kit indicates combustion by-products in the coolant. ''(expand)'' | *A test kit indicates combustion by-products in the coolant. ''(expand)'' | ||
| − | ===Compression testing and | + | ===Compression testing and leak down testing=== |
*If a compression test shows two cylinders with equal but low compression, then that may indicate a blown head gasket, with a leak between those two cylinders. | *If a compression test shows two cylinders with equal but low compression, then that may indicate a blown head gasket, with a leak between those two cylinders. | ||
| − | *If you can, do a | + | *If you can, do a leak down test. |
*If you can, pressure test the coolant system. If you pressurize the system, and you lose pressure, you may have a blown head gasket. | *If you can, pressure test the coolant system. If you pressurize the system, and you lose pressure, you may have a blown head gasket. | ||
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===Head gasket sealants=== | ===Head gasket sealants=== | ||
| − | Most modern head gaskets are installed dry, without any sealant, the reason for this is because of expansion and contraction, especially in Aluminum head/ cast iron block combinations, any heat expansion/ contraction would break the seal, with cast/ cast applications, | + | Most modern head gaskets are installed dry, without any sealant, the reason for this is because of expansion and contraction, especially in Aluminum head/cast iron block combinations, any heat expansion/contraction would break the seal, with cast/ cast applications, sealant creates a better seal for a short period of time. Follow the manufacturer's instructions. |
Products: | Products: | ||
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Common products include [http://www.barsproducts.com/1100.htm Bar's Leaks head gasket repair] and [http://www.rxauto.com/ Thermagasket]. Also, sodium silicate (known also as "water glass") can be used, and it's an ingredient in some commercial head gasket repair additives. It can be found at a pharmacy. It is incompatible with antifreeze, thus the system must be emptied before the water glass can be used. Then the system is flushed and the antifreeze replaced. | Common products include [http://www.barsproducts.com/1100.htm Bar's Leaks head gasket repair] and [http://www.rxauto.com/ Thermagasket]. Also, sodium silicate (known also as "water glass") can be used, and it's an ingredient in some commercial head gasket repair additives. It can be found at a pharmacy. It is incompatible with antifreeze, thus the system must be emptied before the water glass can be used. Then the system is flushed and the antifreeze replaced. | ||
| − | ===Head gasket re- | + | ===Head gasket re-torquing=== |
| − | Although most head gaskets purchased today will be the "no re-torque" type of gasket, a few head gaskets will typically need to be re-torqued after a number of heating/cooling cycles. Copper head gaskets need more frequent re- | + | Although most head gaskets purchased today will be the "no re-torque" type of gasket, a few head gaskets will typically need to be re-torqued after a number of heating/cooling cycles. Copper head gaskets need more frequent re-torquing. Even head gaskets that say: "No re-torquing necessary" may need to be occasionally re-torqued. |
| − | Re- | + | Re-torquing should be done when the engine is completely cool. |
===When replacing a blown head gasket=== | ===When replacing a blown head gasket=== | ||
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*Follow specific torque settings and bolt-tightening sequence perfectly. Re-torque as specificied. | *Follow specific torque settings and bolt-tightening sequence perfectly. Re-torque as specificied. | ||
*Replace both at the same time, even if only one has blown. | *Replace both at the same time, even if only one has blown. | ||
| − | *Oil the tips of the cylinder head bolts with light oil. ''(confirm this, and expand)''. Also, you can use a little bit of oil on the | + | *Oil the tips of the cylinder head bolts with light oil. ''(confirm this, and expand)''. Also, you can use a little bit of oil on the underside of the bolt, to aid getting the proper torque reading. |
*Sometimes a sealant will need to be used on the head bolts, as they may intersect the water jackets, and be exposed to engine coolant. Use a non-hardening sealer ''(confirm and expand)''. | *Sometimes a sealant will need to be used on the head bolts, as they may intersect the water jackets, and be exposed to engine coolant. Use a non-hardening sealer ''(confirm and expand)''. | ||
*Change the oil and oil filter too -- they're likely contaminated with coolant. | *Change the oil and oil filter too -- they're likely contaminated with coolant. | ||
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==Suppliers and manufacturers of head gaskets== | ==Suppliers and manufacturers of head gaskets== | ||
*[http://www.bestgasket.com/ Best Gasket] | *[http://www.bestgasket.com/ Best Gasket] | ||
| − | * | + | *Cosmetics |
*[http://www.federal-mogul.com/en/AftermarketSolutions/NorthAmerica/SealingSolutions/Brands/Fel-Pro/ Fel-Pro gaskets] | *[http://www.federal-mogul.com/en/AftermarketSolutions/NorthAmerica/SealingSolutions/Brands/Fel-Pro/ Fel-Pro gaskets] | ||
*[http://flatoutgaskets.com Flatout Gaskets] | *[http://flatoutgaskets.com Flatout Gaskets] | ||
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