Head gasket
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Blown head gaskets can generally be detected by various techniques. | Blown head gaskets can generally be detected by various techniques. | ||
| − | ==Different types of head gaskets== | + | ==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. | 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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''(needs more info on various types of head gaskets)'' | ''(needs more info on various types of head gaskets)'' | ||
| − | ===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 leak coolant. They're 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. They are re-usable, although they have to be re-annealed. They seal combustion well, but they are prone to leak coolant. They're less forgiving to imperfections in the head and deck surfaces. | ||
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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. | ||
| − | ==Aluminum cylinder heads== | + | ===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. | 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. | ||
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. | 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. | ||
| − | ==Symptoms of a blown head gasket== | + | =="Blown" head gaskets== |
| + | ===Reasons why head gaskets fail=== | ||
| + | *Overheating, possibly from a blown hose, water pump, or thermostat. | ||
| + | *Engine pre-ignition or detonation. | ||
| + | *Improperly torqued cylinder head. | ||
| + | *Faulty cylinder head bolts. | ||
| + | *Some blocks are more prone to head gasket failure, because the bolt positioning applies uneven pressure. | ||
| + | *Stretched cylinder head bolts. | ||
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| + | ===Symptoms of a blown head gasket=== | ||
Some of the symptoms below may also indicate a cracked cylinder head. | Some of the symptoms below may also indicate a cracked cylinder head. | ||
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*Car misfires or runs rough at low speeds, due to antifreeze in the combustion chamber. '''(confirm)''' | *Car misfires or runs rough at low speeds, due to antifreeze in the combustion chamber. '''(confirm)''' | ||
*A test kit indicates combustion by-products in the coolant. | *A test kit indicates combustion by-products in the coolant. | ||
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| + | ===Compression testing and leakdown 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 you can, do a leakdown 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. | ||
==Replacing blown head gaskets== | ==Replacing blown head gaskets== | ||
| − | === | + | ===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. | |
| − | + | It can also take out the whole bottom end of your engine: broken or bent pistons and rods, cracked block, etc. | |
| − | + | ===Removing an old head gasket=== | |
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| − | ===Removing | + | |
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. 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]. | ||
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Don't use wire brushes -- the wires can break off, get into the oil pump, and lock it up. (What about 3M "hair brush" pads? What are those? Safe to use?). | Don't use wire brushes -- the wires can break off, get into the oil pump, and lock it up. (What about 3M "hair brush" pads? What are those? Safe to use?). | ||
| + | ===How to choose a head gasket=== | ||
| + | Will depend on desired quench, and engine performance characteristics. | ||
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| + | Small compression ratio adjustments are possible by altering gasket thickness. | ||
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| + | ''(need to expand on this section)'' | ||
===Head gasket sealants=== | ===Head gasket sealants=== | ||
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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. Pour a quart of it into your engine. ''(confirm)'' | 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. Pour a quart of it into your engine. ''(confirm)'' | ||
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===Head gasket re-torquing=== | ===Head gasket re-torquing=== | ||
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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=== | ||
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*Pre-fit the head gasket. | *Pre-fit the head gasket. | ||
*Don't use sealant unless the manufacturer explicitly specifies it. | *Don't use sealant unless the manufacturer explicitly specifies it. | ||
| − | *Follow specific torque settings and bolt-tightening sequence perfectly. | + | *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)'' . Use a little bit of oil on the underhead of the bolt, to aid getting the proper torque reading. | *Oil the tips of the cylinder head bolts with light oil. ''(confirm this, and expand)'' . Use a little bit of oil on the underhead of the bolt, to aid getting the proper torque reading. | ||
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