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.

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 and proper installation of the new gasket.

==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.

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.

''(needs more info on various types of head gaskets)''

====Copper head gaskets====
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 imbedded 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. 

However, copper head gaskets have superior thermal conductivity, thought to stabilize head and block temperature, and provide elasticity and strength.

===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 fluoroelastomer sealants are applied to '''increase''' the pressure between the iron heads and the iron block.

=="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 or there are too few bolts surrounding the cylinder. 
*Stretched cylinder head bolts.

===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 expand)''
*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.
*Car misfires or runs rough at low speeds, due to coolant in the combustion chamber. ''(confirm)''
*A test kit indicates combustion by-products in the coolant. ''(expand)''

===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==
===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 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.

===Removing an old head gasket===
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 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.

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). Generally speaking, this figure is 0.035" to 0.045". There will be some flex in the crankshaft, rods and pistons as they whip around at speed and this clearance will be diminished as a result, with the piston coming in close proximity of the underside of the cylinder head. This will "squish" the otherwise dead mixture out of the area and jet it towards the spark plug, thus fully mixing the mixture, contributing to more complete combustion and the elimination of detonation. The best piston to use for this is one which has a dead flat area where it will meet the cylinder head. Stock Chevy pistons, for instance, have only a thin ring around the perimeter of the piston to accomplish squish. Absolutely flat-top pistons will work best, such as the ones offered by Keith Black. Even the dished pistons offered by them have the flat area opposite the dish.  

This is probably one of the most important areas of engine building and should be considered carefully before ever buying any parts. You must know what the piston deck height (distance from the crown of the piston to the block deck surface with the piston at top dead center) is before continuing. I'll use a 350 Chevy for this explanation. If the piston deck height is, for instance, 0.025", then a gasket with a thickness of 0.015" (Fel-Pro FPP-1094) would put the squish at 0.040". If the piston deck height is, for instance, 0.012", then a gasket with a thickness of 0.028" (GM 10105117) would put the squish at 0.040". Mix and match the piston deck height with the gasket thickness in your particular application to achieve this ideal 0.035" to 0.045" squish.     

''(need to expand on this section)''

===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, sealent creates a better seal for a short period of time. Follow the manufacturer's instructions.

Products:
*[http://www.dynatexinc.com/catalog.asp Dynatex Hi-Tack Gasket Spray]
*[http://www.hylomar.com/market_served_automotive_oem_3.shtml Hylomar Universal Blue]
*[http://www.permatex.com/products/automotive/automotive_gasketing/gasket_sealants/auto_Permatex_Copper_Spray-A-Gasket_Hi-Temp_Adhesive_Sealant.htm Permatex Copper Spray-A-Gasket Hi-Temp Adhesive Sealant]
*[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. 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-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.

===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 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.
*Pre-fit the head gasket.
*Don't use sealant unless the manufacturer explicitly specifies it.
*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.
*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 underhead 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)''.
*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. 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===
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)''.


==Suppliers and manufacturers of head gaskets==
*[http://www.bestgasket.com/ Best Gasket]
*Cometics
*[http://www.federal-mogul.com/en/AftermarketSolutions/NorthAmerica/SealingSolutions/Brands/Fel-Pro/ Fel-Pro gaskets]
*[http://flatoutgaskets.com Flatout Gaskets]
*[http://www.milodon.com/copper-gaskets/copper-head-gaskets.asp Milodon copper head gaskets]
*Mopar Performance 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]

==Further reading==
*[http://www.rolmfg.com/media/pdf/gasket_training_manual/gasket_training.pdf Gasket training manual] -- ROL Gaskets

==References==
===Forum discussions===
*[http://hotrodders.com/forum/blown-head-gasket-4231.html Blown head gasket?], ''Hotrodders Bulletin Board'', October 28, 2002.
*[http://hotrodders.com/forum/head-gasket-installation-20256.html Head gasket installation], ''Hotrodders Bulletin Board'', July 27, 2003.
*[http://hotrodders.com/forum/removing-head-gasket-block-35708.html Removing head gasket from block], ''Hotrodders Bulletin Board'', March 9, 2004.
*[http://hotrodders.com/forum/reusing-un-run-head-gasket-37571.html Re-using an un-run head gasket], ''Hotrodders Bulletin Board'', April 12, 2004.
*[http://hotrodders.com/forum/oil-head-bolts-head-gasket-40119.html Oil on head bolts and head gasket], ''Hotrodders Bulletin Board'', May 25, 2004.
*[http://hotrodders.com/forum/about-copper-head-gaskets-45146.html Question about copper head gaskets], ''Hotrodders Bulletin Board'', August 7, 2004.
*[http://hotrodders.com/forum/what-head-gaskets-do-i-need-58756.html What head gaskets do I need?], ''Hotrodders Bulletin Board'', February 25, 2005.
*[http://hotrodders.com/forum/head-gaskets-provide-best-seal-81605.html Which head gaskets provide the best seal?], ''Hotrodders Bulletin Board'', February 13, 2006.
*[http://hotrodders.com/forum/bars-leak-head-gasket-repair-anyone-use-before-104370.html Bar's Leak head gasket repair -- anyone use this before?], ''Hotrodders Bulletin Board'', December 12, 2006.
*[http://hotrodders.com/forum/head-gasket-109943.html Head gasket], ''Hotrodders Bulletin Board'', February 25, 2007.
*[http://hotrodders.com/forum/blown-head-gasket-how-do-i-know-111090.html Blown head gasket...how do I know?], ''Hotrodders Bulletin Board'', March 11, 2007.
*[http://hotrodders.com/forum/chevy-head-gaskets-112365.html Chevy head gaskets], ''Hotrodders Bulletin Board'', March 26, 2007.
*[http://hotrodders.com/forum/leaky-head-gasket-112604.html Leaky head gasket], ''Hotrodders Bulletin Board'', March 28, 2007.
*[http://hotrodders.com/forum/thin-head-gasket-best-112543.html Which thin head gasket is best?], ''Hotrodders Bulletin Board'', March 28, 2007.
*[http://hotrodders.com/forum/head-gasket-question-118236.html Head gasket question], ''Hotrodders Bulletin Board'', June 15, 2007.
*[http://hotrodders.com/forum/head-gasket-question-120345.html Head gasket question], ''Hotrodders Bulletin Board'', July 17, 2007.

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