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. | |
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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. | + | [[File:O-ringdrawing.jpg|thumb|right|450px|O-ring diagram]] |
| + | 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. <br style="clear:both"/> | ||
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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====MLS head gaskets==== | ====MLS head gaskets==== | ||
| + | [[File:Mls felpro hg.jpg|thumb|400px|Felpro MLS head gasket showing the layers]] | ||
| + | Be sure to consult the manufacturer's recommendations concerning surface preparation, sealers, and application. | ||
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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. | ||
| − | Cometic has a 'Phuzion' head gasket that "combines MLS tech with a gas-filled, aerospace-alloy O-ring for ultimate head sealing" without special block mods. | + | Cometic has a 'Phuzion' head gasket that "combines MLS tech with a gas-filled, aerospace-alloy O-ring for ultimate head sealing" without special block mods. <br style="clear:both"/> |
====Graphite head gasket==== | ====Graphite head gasket==== | ||
| − | Graphite head gaskets can be 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 | + | Graphite head gaskets can be 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 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. |
An article that mentions graphite gasket technology is '''[http://www.enginebuildermag.com/Article/2585/gasket_technology_the_science_of_sealing.aspx here]'''. | An article that mentions graphite gasket technology is '''[http://www.enginebuildermag.com/Article/2585/gasket_technology_the_science_of_sealing.aspx here]'''. | ||
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=="Blown" head gaskets== | =="Blown" head gaskets== | ||
| + | {| | ||
| + | |[[File:Morris Marina Blown head gasket.jpg|360px]] | ||
| + | |[[File:Boosted pontiac 400 engine+blown head gasket.jpg|350px]] | ||
| + | |[[File:Blown into cooling.jpg|350px]] | ||
| + | |} | ||
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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 vs. head gasket thickness=== |
| − | The head gasket thickness | + | The head gasket thickness depends on the desired quench measurement 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 [[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 | + | 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 no less than 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\. |
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| + | The turbulence caused by the piston coming in close proximity of the underside of the cylinder head will "squish" the unburned mixture out of the area and jet it towards the spark plug, thus fully mixing the mixture. This action contributes to a more complete combustion, more power, less emissions and suppresses detonation. | ||
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| + | [[File:Round dish sbc piston.jpg|thumb|left|340px|This stock type SBC piston is the least desirable design as far as quench action is concerned]][[File:KB P-N 135 SBC 383 PISTON.jpg|thumb|330px|The D-cup design is much better for quench action if a dish is required]] | ||
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| + | The best piston design 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 band around the perimeter of the piston to accomplish squish. Flat top pistons having minimal valve reliefs will work best. The D-cup pistons offered by various manufacturers also work well (better than a round dish) when a dish is needed. <br style="clear:both"/> | ||
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== | |
| − | + | Follow the sequence for the engine being worked on. If no sequence can be found, start from the inner fasteners and work outward. | |
| − | + | Use at least three steps, i.e. if the torque is 65 ft/lb, torque the first step to 20 ft/lb, second step to 40 ft/lb and the last step to 65 ft/lb. | |
| − | + | [[File:80632permatex.jpg|right]] | |
| + | If using OEM fasteners, most times the recommendation is for the clean threads to be lubricated with motor oil before torquing. Threaded holes can be cleaned with a thread chaser. Do not use a tap for this, it can enlarge the hole and/or thin the threads by removing metal, increasing the chance of pulling the threads. | ||
| − | One re-torque is all that is necessary (unless the manufacturers instructions indicate otherwise) | + | Fasteners that enter the cooling jackets have to be sealed. Various sealants can be used depending on personal preference. Some sealers are: |
| + | *Hylomar | ||
| + | *Permatex #2 | ||
| + | *Permatex High Temp Thread Sealant | ||
| + | *Permatex High Performance Thread Sealant 56521 | ||
| + | *Permatex 80632 with teflon | ||
| + | *[http://www.summitracing.com/parts/ARP-100-9904/ ARP thread sealer] | ||
| + | *Locktite thread sealant | ||
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| + | Follow the factory torque specs unless aftermarket fasteners are used. In that case, follow the fastener manufacturer's directions for what type of lube to use and what torque to use- this will often differ from the factory specs. | ||
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| + | {{Note1}} Do not use RTV or any type of sealant or adhesive that hardens or sets up. The sealant needs to be pliant, not hardened or brittle. | ||
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| + | ===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. The idea behind this is 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. | ||
| + | *One re-torque is all that is necessary (unless the manufacturers instructions indicate otherwise) | ||
| + | *If your engine uses torque-to-yield head bolts (TTY), do not re-torque | ||
| + | *If there's any doubt, ask the manufacturer for a recommendation | ||
====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). | + | {{!}}It is suggested by some to retorque cast iron heads/blocks while still warm (not hot). Whether or not to do this when using iron castings is up to the builder (''research this beforehand''). But 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 siamesed, 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 reusable several times over, while others should never be reused. Most head gaskets are designed for one use only. Composite or graphite head gaskets are most often not reusable because of rust damage to the steel core, disintegration/delamination/peeling of the surface material or damage to or loss of factory-applied sealant material. |
| + | *MLS gaskets are most often not reusable because the elastomeric coating is scrubbed off of the combustion and coolant seals by abrasion from temperature induced expansion and contraction. | ||
| + | *Copper head gaskets are often reusable. Examples are Titan and ICS Titan copper head gaskets from SCE. | ||
| + | *Even if a head gasket may be reusable, many 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. | ||
==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 | + | Many SBC head gaskets are going to have a 4.090"-4.100" 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 0.038"-0.041". |
===SBC head gaskets having less than 0.040" compressed thickness=== | ===SBC head gaskets having less than 0.040" compressed thickness=== | ||
| − | + | *GM p/n 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 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 p/n 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 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 p/n 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. |
| − | *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. | + | *Victor Reinz Nitroseal p/n 5746, has a compressed thickness is 0.025", 4.1” gasket bore diameter. NAPA carries Victor. |
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| − | 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=== | ||
| − | * | + | *FelPro's p/n Q1094 is a steel shim with a 4.1" gasket bore diameter and 0.015" compressed thickness. 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. |
| + | *SCE #511101 Specialty Component Engineering | ||
| + | **Bore: 4.100" | ||
| + | **Gasket Material: Graphite coated steel core laminate | ||
| + | **Compressed Thickness: 0.015" | ||
| + | **Compressed Volume: 3.245cc | ||
| + | **Lock Wire: No | ||
| + | **Coolant sealing '''not''' compatible with GM lightweight head castings used on 305-350 from 1987-95. | ||
*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. | ||
| + | *Jegs p/n 210044- embossed shim w/rubber coating. Bore 4.150", compressed thickness is 0.024". | ||
| − | + | ===400 SBC=== | |
| − | * | + | *[http://www.summitracing.com/parts/CGT-C5248-027/ 400 SBC 0.027” head gasket] |
| + | *Felpro p/n's #1004, #1034, #1044 | ||
| + | |||
| + | ===SBC by displacement=== | ||
| + | From [http://www.amotion.com/csb.html amotion.com] | ||
| + | |||
| + | *262 Solid steel core 3.850 McCord 7039M | ||
| + | *262 Embossed Steel 3.850 McCord 6908 | ||
| + | *267 Solid steel core 3.850 McCord 7039M | ||
| + | *267 Embossed Steel 3.850 McCord 6908 | ||
| + | *283 Graphite 4.090 McCord 7104G | ||
| + | *283 Performance Graphite 4.140 McCord 94-2025 | ||
| + | *283 Solid steel core 4.090 McCord 6631M | ||
| + | *283 Embossed Steel 4.100 McCord 6910 | ||
| + | *302 Graphite 4.090 McCord 7104G | ||
| + | *302 Performance Graphite 4.140 McCord 94-2025 | ||
| + | *302 Solid steel core 4.090 McCord 6631M | ||
| + | *302 Embossed Steel 4.100 McCord 6910 | ||
| + | *305 Solid steel core 3.850 McCord 7039M | ||
| + | *305 Embossed Steel 3.850 McCord 6908 | ||
| + | *307 Graphite 4.090 McCord 7104G | ||
| + | *307 Performance Graphite 4.140 McCord 94-2025 | ||
| + | *307 Solid steel core 4.090 McCord 6631M | ||
| + | *307 Embossed Steel 4.100 McCord 6910 | ||
| + | *327 Graphite 4.090 McCord 7104G | ||
| + | *327 Performance Graphite 4.140 McCord 94-2025 | ||
| + | *327 Solid steel core 4.090 McCord 6631M | ||
| + | *327 Embossed Steel 4.100 McCord 6910 | ||
| + | *350 Graphite 4.090 McCord 7104G | ||
| + | *350 Performance Graphite 4.140 McCord 94-2025 | ||
| + | *350 Solid steel core 4.090 McCord 6631M | ||
| + | *350 Embossed Steel 4.100 McCord 6910 | ||
| + | *400 Graphite 4.180 McCord 6837M | ||
==Suppliers and manufacturers of head gaskets== | ==Suppliers and manufacturers of head gaskets== | ||
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==References== | ==References== | ||
| + | ===Compression calculators=== | ||
| + | ====Static CR==== | ||
| + | *[http://www.wheelspin.net/calc/calc2.html Static compression ratio] | ||
| + | |||
| + | ====Dynamic CR==== | ||
| + | *[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | ||
| + | *[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator] | ||
| + | *[http://www.uempistons.com/calc.php?action=comp2 KB/Silvolite DCR calculator] | ||
| + | *[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | ||
| + | {{Note1}} Some dynamic compression rtatio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure. This works OK on older, slower ramped cam lobes, but the faster lobe profiles may need to have 25 degrees or more added to be accurate. | ||
| + | |||
| + | {{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated: | ||
| + | # Divide the intake duration by 2 | ||
| + | # Add the results to the lobe separation angle (LSA) | ||
| + | # Subtract any ground-in advance | ||
| + | # Subtract 180 | ||
| + | This result does not need to have any amount added to the IVC point, like the KB calculator calls for. | ||
| + | |||
===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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*[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 | ||
| + | ==Chevy R07 vs. LSx head gaskets== | ||
| + | [[File:LR07 top vs LSx.jpg]] | ||
| + | |||
| + | Chevy racing engine R07 top, LS1 type head gasket bottom. | ||
| + | <br><br> | ||
[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:Good articles]] | [[Category:Good articles]] | ||
| − | + | [[Category:Cylinder head]] | |
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