Head gasket
(→Different types of head gaskets) |
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| − | Cylinder head gaskets provide the critical seal between the engine block and the cylinder head. They seal all of the combustion chambers | + | Cylinder head gaskets provide the critical seal between the engine block and the cylinder head. They seal all of the combustion chambers and prevent coolant and engine oil from leaking into the cylinders. |
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. | ||
| − | 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 | + | 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== | ==Head gasket basics== | ||
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====Copper head gaskets==== | ====Copper head gaskets==== | ||
| − | Copper head gaskets are typically less forgiving. They're commonly used in high-performance applications. They are re-usable, although they have to be re-annealed. They seal combustion well, but they are prone to leaking coolant | + | Copper head gaskets are typically less forgiving. They're commonly used in high-performance applications. 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 | + | To take full advantage of copper head gaskets, you have grooves machined into the block or the head. Stainless steel wire is than imbedded into the groove so that it sticks up slightly above the block deck or head surface (approx. 0.010") 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. |
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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*Improperly torqued cylinder head. | *Improperly torqued cylinder head. | ||
*Faulty cylinder head bolts. | *Faulty cylinder head bolts. | ||
| − | *Some blocks are more prone to head gasket failure, because the bolt positioning applies uneven pressure. | + | *Some blocks are more prone to head gasket failure, because the bolt positioning applies uneven pressure or there are too few bolts surrounding the cylinder. |
*Stretched cylinder head bolts. | *Stretched cylinder head bolts. | ||
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*Spark plugs with coolant deposits. ''(confirm this, and expand)'' | *Spark plugs with coolant deposits. ''(confirm this, and expand)'' | ||
*Sound of air rushing or whistling coming from cylinder head. You can also listen with a stethoscope. | *Sound of air rushing or whistling coming from cylinder head. You can also listen with a stethoscope. | ||
| + | http://store.summitracing.com/partdetail.asp?autofilter=1&part=WMR%2DW80582&N=700+115&autoview=sku | ||
*Two adjacent cylinders with low but equal pressure. Indicates head gasket failure between the two cylinders. | *Two adjacent cylinders with low but equal pressure. Indicates head gasket failure between the two cylinders. | ||
*Car misfires or runs rough at low speeds, due to coolant in the combustion chamber. ''(confirm)'' | *Car misfires or runs rough at low speeds, due to coolant in the combustion chamber. ''(confirm)'' | ||
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==Replacing blown head gaskets== | ==Replacing blown head gaskets== | ||
===Damage caused by a blown head gasket=== | ===Damage caused by a blown head gasket=== | ||
| − | Time is of the essence when replacing a blown head gasket. If the car overheats, it can warp the cylinder head, especially if it's aluminum. If it warps too much, it will have to be discarded. | + | Time is of the essence when replacing a blown head gasket. If the car overheats, it can warp or crack the cylinder head, especially if it's aluminum or a thin-wall iron casting. If it warps too much, it will have to be discarded. |
It can also take out the whole bottom end of your engine: hydrolocking, broken or bent pistons and rods, cracked block, etc. | It can also take out the whole bottom end of your engine: hydrolocking, broken or bent pistons and rods, cracked block, etc. | ||
===Removing an old head gasket=== | ===Removing an old head gasket=== | ||
| − | Use a putty knife or gasket scraper. You can also use acetone thinner, ''(confirm)'' or [http://www.permatex.com/products/automotive/automotive_gasketing/gasket_removers/auto_Permatex_Gasket_Remover.htm Permatex gasket remover]. | + | Use a putty knife or gasket scraper, but be very careful that you do not gouge the material with the tool. Perhaps a better idea is to use a 3M rotary pad that is commercially available for this purpose. Use it in your electric drill to clean off the surfaces perfectly without damage. You can also use acetone thinner, ''(confirm)'' or [http://www.permatex.com/products/automotive/automotive_gasketing/gasket_removers/auto_Permatex_Gasket_Remover.htm Permatex gasket remover]. |
Don't use Scotch-Brite pads. | Don't use Scotch-Brite pads. | ||
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Will depend on desired quench, and engine performance characteristics. | Will depend on desired quench, and engine performance characteristics. | ||
| − | + | Although static compression ratio should be determined by the piston configuration and the volume of the combustion chamber, small compression ratio adjustments are possible by altering gasket thickness as long as they don't throw you out of spec on the squish dimension (piston crown to under side of cylinder head with the piston at TDC) | |
''(need to expand on this section)'' | ''(need to expand on this section)'' | ||
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===Head gasket re-torqueing=== | ===Head gasket re-torqueing=== | ||
| − | + | 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-torqueing. Even head gaskets that say: "No re-torqueing necessary" may need to be occasionally re-torqued. | |
Re-torqueing should be done when the engine is completely cool. | Re-torqueing should be done when the engine is completely cool. | ||
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===When replacing a blown head gasket=== | ===When replacing a blown head gasket=== | ||
*Check to make sure the heads and block are straight. If they're warped, you could easily end up with another blown head gasket. This can be done with a straight edge and a feeler gauge. This is also a good time to check for cracks. This is especially important if using a thin gasket. The thicker gaskets are made to compensate for low spots on the deck. | *Check to make sure the heads and block are straight. If they're warped, you could easily end up with another blown head gasket. This can be done with a straight edge and a feeler gauge. This is also a good time to check for cracks. This is especially important if using a thin gasket. The thicker gaskets are made to compensate for low spots on the deck. | ||
| − | *Prep the surface. Mating surfaces should be smooth, clean, and dry | + | *Prep the surface. Mating surfaces should be smooth, clean, and dry and can be cleaned with brake cleaner, or denatured alcohol if used in a well-ventilated area. ''(confirm)''. |
*Chase the bolt and stud holes. Clean with compressed air. | *Chase the bolt and stud holes. Clean with compressed air. | ||
*Pre-fit the head gasket. | *Pre-fit the head gasket. | ||
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*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. | ||
| − | *Don't be surprised if some of the water ports are "blocked off" on your gasket. Various gaskets are made to differently meter the coolant and direct its flow. Gaskets are also made differently for street and race applications. | + | *Don't be surprised if some of the water ports are "blocked off" on your gasket. Various gaskets are made to differently meter the coolant and direct its flow. Gaskets are also made differently for street and race applications. 400 small block Chevys are a special case. There are steam holes drilled in the block that release steam pockets which are formed in the block as a result of the cylinders being siamezed, with no water passage between the cylinders. You must use 400 gaskets on this motor that have the holes in the gasket which coincide with the holes in the block deck. If using heads other than 400 heads (which are also drilled with corresponding holes), you must drill steam holes into the deck of the heads to allow the steam to escape from the block and up into the heads to be dispersed. |
===Re-using head gaskets=== | ===Re-using head gaskets=== | ||
| − | Some head gaskets are re-usable, and some aren't. Copper head gaskets are re-usable, although they have to be re-annealed. Even if a head gasket is re-usable, many people prefer to use a new one. The labor involved in replacing a head gasket, and the potential for engine damage from a blown gasket | + | Some head gaskets are re-usable, and some aren't. Copper head gaskets are re-usable, although they have to be re-annealed. Even if a head gasket is re-usable, many people prefer to use a new one. The labor involved in replacing a head gasket, and the potential for engine damage from a blown gasket are too great to risk. |
When re-using gaskets, they can be coated with high-temp aluminum exhaust paint, available from [http://www.vhtpaint.com/products VHT]. ''(confirm this product name and description)''. | When re-using gaskets, they can be coated with high-temp aluminum exhaust paint, available from [http://www.vhtpaint.com/products VHT]. ''(confirm this product name and description)''. | ||
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