Editing Head gasket
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− | , and can be detected with certain techniques. Left unfixed, a blown head gasket could cause severe engine damage. Many symptoms of a bad head gasket are not apparent until the problem is very bad, including the ones listed later in this article. | + | {{youcanedit}} |
+ | ==Overview== | ||
+ | The '''cylinder head gasket''' provides the critical seal between the engine block and the [[cylinder head]]. They seal the combustion in the [[combustion chamber]]s and keep [[coolant]] contained to the cooling ports in the heads and block. | ||
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+ | 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. Many symptoms of a bad head gasket are not apparent until the problem is very bad, including the ones listed later in this article. | ||
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. | 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. | ||
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===O-ring sealing=== | ===O-ring sealing=== | ||
− | + | To accomplish combustion sealing with standard copper head gaskets, grooves are machined into the block or the head outside of the combustion sealing area to a width that will retain a stainless wire by friction resistance, the depth of the groove is determined by subtracting the desired protrusion (height) of the installed O-ring from the wire diameter. Stainless steel wire (most often .041" diameter) is then seated into the groove by tapping with a soft faced hammer or other tool such as plastic or wood (hard faced hammers can cause dents which create combustion leakage paths). It is advisable to begin and end the O-ring nearest a bolt location to take full sealing advantage of increased loading near the bolt upon the joint in the O-ring. | |
− | To accomplish combustion sealing with standard copper head gaskets, grooves are machined into the block or the head outside of the combustion sealing area to a width that will retain a stainless wire by friction resistance, the depth of the groove is determined by subtracting the desired protrusion (height) of the installed O-ring from the wire diameter. Stainless steel wire (most often .041" diameter) is then seated into the groove by tapping with a soft faced hammer or other tool such as plastic or wood (hard faced hammers can cause dents which create combustion leakage paths). It is advisable to begin and end the O-ring nearest a bolt location to take full sealing advantage of increased loading near the bolt upon the joint in the O-ring. | + | |
Although copper is a relatively soft material, there is a limit to which it can be displaced by an O-ring. Generally speaking, this limit is about 25% of the gasket thickness. For instance, with a 0.032" thick gasket, you would want to limit the height of the O-ring to about 0.008" above the head or deck surface. For an 0.043" thick head gasket which is the most common thickness, set the o-ring protrusion at 0.010", for an 0.050" thick gasket about 0.012", for an 0.062" thick gasket about 0.015" and so forth. If the groove is cut into the head for the wire, a "receiver groove" can be machined into the block. If the groove is cut into the block deck for the wire, then a receiver groove can be 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. However most street/strip applications do not require receiver grooves, receiver grooves are only required on the most extreme racing applications. | Although copper is a relatively soft material, there is a limit to which it can be displaced by an O-ring. Generally speaking, this limit is about 25% of the gasket thickness. For instance, with a 0.032" thick gasket, you would want to limit the height of the O-ring to about 0.008" above the head or deck surface. For an 0.043" thick head gasket which is the most common thickness, set the o-ring protrusion at 0.010", for an 0.050" thick gasket about 0.012", for an 0.062" thick gasket about 0.015" and so forth. If the groove is cut into the head for the wire, a "receiver groove" can be machined into the block. If the groove is cut into the block deck for the wire, then a receiver groove can be 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. However most street/strip applications do not require receiver grooves, receiver grooves are only required on the most extreme racing applications. | ||
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=====Modern copper head gaskets===== | =====Modern copper head gaskets===== | ||
− | There are several manufacturers of copper head gaskets. Copper gaskets come in many thicknesses, and in most cases are reusable. | + | There are several manufacturers of copper head gaskets. Among them is . Copper gaskets come in many thicknesses, and in most cases are reusable. [http://www.scegaskets.com/page/sitemap.html SCE Gaskets] makes the Titan ICS (Integral Combustion Seal) copper head gaskets with coolant and oil passage seals bonded to the sealing surfaces of the head gaskets. These built-in seals eliminate the need for additional sealants. These head gaskets are installed dry and there are two versions available: one for engines with machined O-ring combustion seals and one for those without O-rings. The copper head gasket offered by SCE for engines without machined O-rings includes both coolant seals and and the Integral Combustion Seal which eliminates the need to have O-ring grooves machined into the block or heads. These head gaskets allow engine builders to exploit the benefits of of copper, such as the wide range of thicknesses, superior strength, superior combustion sealing, conformability to deck surfaces and superior heat conductivity, with none of the prior disadvantages of 'old fashioned' copper head gaskets. |
− | [[File:Sce titan cu hg.jpg|thumb|300px|left|SCE ICS copper head gasket with silicone sealing beads]] <br style="clear:both"/> | + | [[File:Sce titan cu hg.jpg|thumb|300px|left|SCE ICS copper head gasket with silicone sealing beads and combustion ring]] <br style="clear:both"/> |
====Steel shim head gaskets==== | ====Steel shim head gaskets==== | ||
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====MLS head gaskets==== | ====MLS head gaskets==== | ||
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Sealant use may be required when retrofitting MLS (multi-layer steel) head gaskets to engines which were not originally produced with MLS head gaskets, or when using MLS head gaskets on engines that have not been properly prepared. For proper coolant, oil, and combustion sealing, MLS head gaskets require surface finishes of 30 RA (Roughness Average) or finer, this is because the elastomeric coating on the sealing surfaces of MLS head gaskets is approximately .001" thick which is too thin to seal leak paths in the peaks and valleys of rougher (RA30+) finishes. | Sealant use may be required when retrofitting MLS (multi-layer steel) head gaskets to engines which were not originally produced with MLS head gaskets, or when using MLS head gaskets on engines that have not been properly prepared. For proper coolant, oil, and combustion sealing, MLS head gaskets require surface finishes of 30 RA (Roughness Average) or finer, this is because the elastomeric coating on the sealing surfaces of MLS head gaskets is approximately .001" thick which is too thin to seal leak paths in the peaks and valleys of rougher (RA30+) finishes. | ||
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====Graphite head gasket==== | ====Graphite head gasket==== | ||
− | Graphite head gaskets | + | Graphite head gaskets excel when used on aluminum heads with an iron block (they work equally well with iron heads on an iron block). Graphite is excellent in handling high temperatures and is anisotropic (draws heat away from hot spots). It also seals very well too. Some drawbacks to using graphite is that it cannot withstand exposure to oil over a over a long period of time, can be crushed and extruded, and it also leaves a coating on the block and heads that is harder to remove than traditional head gaskets. |
− | + | <!--Pls. see the discussion page for this article. Cobalt327 15:10, 3 May 2012 (MDT) --> | |
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===Aluminum cylinder heads=== | ===Aluminum cylinder heads=== | ||
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=="Blown" head gaskets== | =="Blown" head gaskets== | ||
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===Reasons why head gaskets fail=== | ===Reasons why head gaskets fail=== | ||
*Too much outward pressure that overcomes the clamping force of the head to the block | *Too much outward pressure that overcomes the clamping force of the head to the block | ||
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==How to choose a head gasket== | ==How to choose a head gasket== | ||
− | ===Quench | + | ===Quench=== |
− | The head gasket thickness | + | The head gasket thickness will depend on desired quench, and desired compression ratio. Piston to valve clearance must be verified. |
− | 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 this doesn't cause the | + | 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 this doesn't cause the [[quench]] (or "squish") dimension (piston crown to under side of cylinder head with the piston at TDC) to be out of spec. Generally speaking, this figure is 0.035" to 0.045" for engines built with steel rods. 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. Flat-top pistons having no valve reliefs will work best, such as the ones offered by Keith Black. The "D"-shaped dished pistons offered by them and other manufacturers having the flat area opposite the dish also work well (better than a round dish) when a dish is needed for compression ratio adjustment. |
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− | The best piston | + | |
This is a very important area 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. | This is a very important area 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. | ||
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Any "leak stopper" or head gasket "repair additive" should be avoided. Use of such products leads to further engine damage, such as seized or leaking water pumps, clogged water or oil passages, or clogged radiators and thermostats. If you use these products, be aware of possible problems caused by them. | Any "leak stopper" or head gasket "repair additive" should be avoided. Use of such products leads to further engine damage, such as seized or leaking water pumps, clogged water or oil passages, or clogged radiators and thermostats. If you use these products, be aware of possible problems caused by them. | ||
− | ==Head gasket torquing== | + | ===Head gasket re-torquing=== |
− | + | The purpose of re-torquing the cylinder head fasteners is to restore the proper stretch to the head bolts after the first heat cycle. Physics dictates that the engine assembly will expand as the engine temperature increases, this expansion will increase the compressive load on the head gaskets causing a seating effect (sometimes referred to as creep relaxation) in composite head gaskets. | |
− | + | The seating of the gaskets and threads results in a commensurate relaxation of the fasteners when the engine cools. Re-torquing the fasteners restores the proper stretch to the fasteners which will insure proper cold sealing of the gaskets as well as proper combustion sealing under full load. | |
− | + | Stock replacement head gaskets do not generally need re-torquing. Steel shim head gaskets should be retorqued. Racing engine head gaskets should be re-torqued according to the manufacturer's instructions and the type of gasket being used. If your engine calls for torque-to-yield head bolts (TTY), do not re-torque. | |
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− | + | One re-torque is all that is necessary (unless the manufacturers instructions indicate otherwise), subsequent re-torquing can cause plastic deformation (stretch) of the head fasteners and damage to the head gaskets. | |
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====The process for re-torquing is as follows:==== | ====The process for re-torquing is as follows:==== | ||
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*Retracing the original torque pattern one fastener at a time, slightly loosen the bolt or nut (to overcome the friction set), then re-torque to the specified torque setting | *Retracing the original torque pattern one fastener at a time, slightly loosen the bolt or nut (to overcome the friction set), then re-torque to the specified torque setting | ||
− | + | It is suggested by some to retorque cast iron heads/blocks while still warm (not hot). This should NOT be done with aluminum blocks or heads. | |
===When replacing a blown head gasket=== | ===When replacing a blown 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. | *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. | ||
*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. 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 | + | *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 | + | Some head gaskets are re-usable several times and others should never be re-used. Steel shim head gaskets are designed for one use only. Composite or graphite head gaskets are most often not re-usable because of [[rust]] damage to the steel core, disintegration of the surface material or damage or loss of the sealant material. MLS gaskets are most often not re-usable because the elastomeric coating is scubbed off of the combustion and coolant seals by abrasion from temperature induced expansion and contraction. Traditional copper head gaskets are re-usable, Titan and ICS Titan copper head gaskets from SCE are also re-usable. 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. |
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==How to differentiate the top and bottom of a head gasket== | ==How to differentiate the top and bottom of a head gasket== | ||
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==SBC head gasket applications== | ==SBC head gasket applications== | ||
− | Many SBC head gaskets are going to have a 4.090 | + | Many SBC head gaskets are going to have at least a 4.090" gasket bore diameter, so are usable on a 0.060" over 4" block. |
− | There are a large selection of head gasket types and thicknesses for the SBC engine. Many composite head gaskets are right at 0.041" compressed thickness. Suffice to say ALL manufacturers of SBC head gaskets will have one or more that compress to 0. | + | There are a large selection of head gasket types and thicknesses for the SBC engine. Many composite head gaskets are right at 0.041" compressed thickness. Suffice to say ALL manufacturers of SBC head gaskets will have one or more that compress to 0.040"-0.041". |
===SBC head gaskets having less than 0.040" compressed thickness=== | ===SBC head gaskets having less than 0.040" compressed thickness=== | ||
− | *GM | + | *FelPro's FEL 1094 is a steel shim with a 4.1" gasket bore diameter and 0.015" compressed thickness, if you've got super flat surfaces on the deck and head, this is a great gasket. It does not tolerate the engine being overheated. |
− | *GM | + | *GM 3830711 is also a steel shim with a 4.1" gasket bore diameter, and is 0.026" thick. Good flat surfaces are required, same rules apply as the Fel Pro above. This is the GM production gasket for '''non''' 400 bore SBCs. Simple and low cost. |
− | *GM | + | *GM 10105117, this head gasket is a multi-layered stainless steel gasket with a 4.1" gasket bore diameter, is 0.028" thick, works with iron or aluminum heads, good for holding back high compression, and tolerates some surface irregularities in the deck and head surfaces. This is the “revised” gasket, see [http://www.thirdgen.org/techboard/tech-general-engine/269378-head-gasket-thickness-gm.html post #23]. |
− | + | *GM 14096405, it has stainless faces over a graphite core, 4.1" gasket bore diameter and 0.028" compressed thickness. This thing hangs tough on uneven surfaces and puts up with high compression ratios. Good for iron or aluminum, this makes a good race engine gasket as it's very tolerant of engines running very hot. It lets the block and head move around to adjust for their temperature differences without breaking its seal. | |
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+ | ==Other possibilities (nowhere near a complete list):== | ||
+ | ===Composite type=== | ||
+ | Victor Reinz Nitroseal p/n 5746, has a compressed thickness is 0.025", 4.1” gasket bore diameter. NAPA carries Victor. | ||
===Shim type=== | ===Shim type=== | ||
− | * | + | *Jegs p/n 210044- Embossed Shim w/ Rubber Coating. Bore 4.150", compressed thickness is 0.024". |
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*Mr. Gasket p/n 1130 0.018”- 0.020” compressed thickness, steel embossed w/coating. | *Mr. Gasket p/n 1130 0.018”- 0.020” compressed thickness, steel embossed w/coating. | ||
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− | + | There are several thinner coated shim type gaskets like: | |
− | * | + | *Fel-Pro Q1094- SBC 307 327 350 283 #1094. Used in some sportsman drag race and flat top oval track categories. Rubber coated steel shim, 4.100 in. gasket bore diameter, 0.015" compressed thickness. |
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==Suppliers and manufacturers of head gaskets== | ==Suppliers and manufacturers of head gaskets== | ||
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==References== | ==References== | ||
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===Forum discussions=== | ===Forum discussions=== | ||
*[http://hotrodders.com/forum/blown-head-gasket-4231.html Blown head gasket?], ''Hotrodders Bulletin Board'', October 28, 2002. | *[http://hotrodders.com/forum/blown-head-gasket-4231.html Blown head gasket?], ''Hotrodders Bulletin Board'', October 28, 2002. | ||
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===Articles=== | ===Articles=== | ||
*[http://www.scegaskets.com/techtips/benefitsof.html Benefits of Copper Head Gaskets] -- SCEGaskets.com | *[http://www.scegaskets.com/techtips/benefitsof.html Benefits of Copper Head Gaskets] -- SCEGaskets.com | ||
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*[http://www.econofix.com/head.html Cylinder Head and Head Gasket Repairs] -- Econofix.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://www.partstrain.com/ShopByDepartment/Head_Gasket Head Gasket] -- Partstrain.com | ||
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*[http://www.allpar.com/eek/headgasket.html Replacing Chrysler, Dodge, or Plymouth head gaskets] -- Allpar.com | *[http://www.allpar.com/eek/headgasket.html Replacing Chrysler, Dodge, or Plymouth head gaskets] -- Allpar.com | ||
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[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:Good articles]] | [[Category:Good articles]] | ||
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