Head gasket
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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, and prevent coolant and engine oil from leaking into the cylinders. | 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. | ||
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| + | Blown head gaskets can generally be detected by various techniques. | ||
==Different types of head gaskets== | ==Different types of head gaskets== | ||
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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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| + | ''(needs more info on various types of head gaskets)'' | ||
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| + | ===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. | ||
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| + | To take full advantage of copper head gaskets, you have wire o-rings machined into the block or the head ''(confirm and expand)''. You'll also need a good sealer around the water passages. | ||
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| + | 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 | + | 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== | ==Symptoms of a blown head gasket== | ||
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*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 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. | ||
| − | == | + | ==Replacing blown head gaskets== |
| − | + | ===How to choose a head gasket=== | |
| + | Will depend on desired quench, and engine performance characteristics. | ||
| − | + | Small compression ratio adjustments are possible by altering gasket thickness. | |
| − | + | ''(need to expand on this section)'' | |
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| − | == | + | ===Removing a 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]. | |
| − | + | Don't use Scotch-Brite pads. | |
| − | ==Head gasket sealants== | + | 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?). |
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| + | ===Head gasket sealants=== | ||
Most modern head gaskets are installed dry, without any sealant ''(confirm and expand)''. Follow the manufacturer's instructions. | Most modern head gaskets are installed dry, without any sealant ''(confirm and expand)''. Follow the manufacturer's instructions. | ||
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*[http://permatex.com/products/automotive/automotive_gasketing/gasket_sealants.htm various Permatex gasket sealants] ''(expand on which ones are used)'' | *[http://permatex.com/products/automotive/automotive_gasketing/gasket_sealants.htm various Permatex gasket sealants] ''(expand on which ones are used)'' | ||
| − | == | + | ===Head gasket repair additives=== |
| − | + | Engine additives that claim to repair questionable head gaskets should only be considered a temporary fix, at best. Nevertheless, they may occasionally be used. | |
| − | + | 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)'' | |
| − | == | + | ==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. | |
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| − | ==Head gasket re-torquing== | + | ===Head gasket re-torquing=== |
Head gaskets will typically need to be re-torqued. Copper head gaskets need frequent re-torqueing. Even head gaskets that say: "No re-torqueing necessary" may need to be occasionally re-torqued. | Head gaskets will typically need to be re-torqued. Copper head gaskets need frequent re-torqueing. Even head gaskets that say: "No re-torqueing necessary" may need to be occasionally re-torqued. | ||
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*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. | ||
| − | ==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. Can be cleaned with brake cleaner, or denatured alcohol ''(confirm)''. | *Prep the surface. Mating surfaces should be smooth, clean, and dry. Can be cleaned with brake cleaner, or denatured alcohol ''(confirm)''. | ||
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*Don't be surprised if some of the water ports are "blocked off" with your gasket. Various gaskets are made to differently meter the coolant and direct its flow. | *Don't be surprised if some of the water ports are "blocked off" with your gasket. Various gaskets are made to differently meter the coolant and direct its flow. | ||
| − | ==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, are too great to risk. | 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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==Suppliers and manufacturers of head gaskets== | ==Suppliers and manufacturers of head gaskets== | ||
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