Editing Head gasket

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.

==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.

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.

==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.

With iron heads, a product can be applied for the opposite effect. Silicone, Viton, or other fuoroelastomer sealants are applied to '''increase''' the pressure between the iron heads and the iron block.

==Symptoms of a blown head gasket==
Some of the symptoms below may also indicate a cracked cylinder head.

*Foaming or bubbling coolant. Indicates head gasket has failed between a cylinder and a passage in the water jacket.
*Rapid pressure buildup in cooling system, before engine is warm. Or, cooling system appears to be malfunctioning.
*Radiator frequently gets low on water (it could be being discharged through the tailpipe).
*White smoke in exhaust, or sweet smelling exhaust.
*"Milkshake" oil, caused by coolant in oil.
*Oil in coolant, causing foaming in coolant.
*Oil or coolant leaking from cylinder head.
*Low cylinder pressure.
*Milky-gray ring around the oil cap. It's a coolant deposit.
*Drops of coolant coming out of the tail pipe.
*When the heater is turned on, it smells like coolant. ''(confirm)''
*Spark plugs with coolant deposits. ''(confirm this, and add info if possible)''
*Sound of air rushing or whistling coming from cylinder head. You can also listen with a stethoscope.
*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)'''

==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)''

==Head gasket test kits==
Chemical test kits that test the coolant system for combustion by products. A blown gasket can thus be indicated by a color change in the test solution.

==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.

==Head gasket sealants and sprays==
Most modern head gaskets are installed dry, without any sealant. Follow the manufacturer's instructions.

Product recommendation: [http://www.dynatexinc.com/catalog.asp Dynatex Hi-Tack Gasket Spray].


==How to choose a head gasket==
Will depend on desired quench, and engine performance characteristics ''(expand on this)''.

Small compression ratio adjustments are possible by altering gasket thickness.

==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.

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?).

==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.

Re-torqueing should be done when the engine is completely cool.

==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.

==Compression 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.

==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.
*Prep the surface. Mating surfaces should be smooth, clean, and dry. Can be cleaned with brake cleaner, or denatured alcohol ''(confirm)''.
*Chase the bolt and stud holes. Clean with compressed air.
*Pre-fit the head gasket.
*Don't use sealant unless the manufacturer explicitly specifies it.
*Follow specific torque settings and bolt-tightening sequence perfectly.
*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)''
*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.
*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" with your gasket. Various gaskets are made to differently meter the coolant and direct its flow.

==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.

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)''.

==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.

To take full advantage of copper head gaskets, you have wire o-rings machined into the block or the head. 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.

==Suppliers and manufacturers of head gaskets==
*[http://www.bestgasket.com/ Best Gasket]
*[http://www.federal-mogul.com/en/AftermarketSolutions/NorthAmerica/SealingSolutions/Brands/Fel-Pro/ Fel-Pro gaskets]
*Mopar Performance Gaskets
*[http://flatoutgaskets.com Flatout Gaskets]
*[http://www.milodon.com/copper-gaskets/copper-head-gaskets.asp Milodon copper head gaskets]
*[http://www.mrgasket.com/ Mr. Gasket]
*[http://www.rolmfg.com/ ROL Gaskets]
*[http://www.scegaskets.com/ SCE Gaskets]
*[http://www.victorreinz.com/products.html Victor Reinz gaskets]

==References==
*[http://en.wikipedia.org/wiki/Head_gasket Head gasket] -- Wikipedia
*[http://www.allpar.com/eek/headgasket.html Replacing Chrysler, Dodge, or Plymouth head gaskets] -- Allpar.com
*[http://www.partstrain.com/ShopByDepartment/Head_Gasket Head Gasket] -- Partstrain.com
*[http://www.dupontelastomers.com/Applications/Automotive/head.asp Head Gaskets] -- DuPontElastomers.com
*[http://www.mobiloil.com/USA-English/MotorOil/Car_Care/DIY/Head_Gasket_Basics.aspx Head Gasket Basics] -- MobilOil.com
*[http://www.econofix.com/head.html Cylinder Head and Head Gasket Repairs] -- Econofix.com
*[http://wiki.answers.com/Q/FAQ/522 Head Gaskets and Valve Covers Q&A] -- Wiki.Answers.com