Head gasket
(→Replacing blown head gaskets) |
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Don't use Scotch-Brite pads. | Don't use Scotch-Brite pads. | ||
| − | Don't use wire brushes -- the wires | + | 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 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. | ||
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| + | Common products include [http://www.barsproducts.com/1100.htm Bar's Leaks head gasket repair], [http://www.rxauto.com/ Thermagasket]and GOSS Chem-i-Weld. 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. | ||
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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. | ||
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| + | ===Head gasket re-torquing=== | ||
| + | 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 regardless of 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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| + | The purpose of re-torquing the cylinder heads 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. | ||
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| + | The seating of the gaskets and threads results in a commensurate relaxation of the head bolts when the engine cools. Re-torquing the head bolts/studs 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. | ||
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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.<BR> | ||
| + | The process for re-torquing is as follows:<BR> | ||
| + | Start the engine & run with no load until operating temperature is reached.<BR> | ||
| + | Shut down the engine & let cool completely (overnight).<BR> | ||
| + | Retracing the original torque pattern, one fastener at a time, loosen slightly to overcome the friction set of the bolt or nut, then re-torque to specified torque setting. | ||
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| + | 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. | ||
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| + | ===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. Some engines require NEW Torque-to-yield head bolts and these bolts should come with sealant already applied. | ||
| + | *Follow specific torque settings and bolt-tightening sequence perfectly. Re-torque as specified. | ||
| + | *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 underside 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. | ||
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| + | ===Re-using head gaskets=== | ||
| + | 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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| + | When re-using gaskets they can be coated with the head gasket sealants listed above in "Head gasket sealants"; traditional copper gaskets can also be sealed with aluminum spray paint available from [http://www.vhtpaint.com/products VHT]. ''(confirm this product name and description)''. | ||
==Suppliers and manufacturers of head gaskets== | ==Suppliers and manufacturers of head gaskets== | ||
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