M
MisterTurbineTwister
Guest
Sometimes the head sees warpage, because it's aluminum, but that's only if the engine was neglected with a BHG and driven for a prolonged period of time.
Like Americanjebus said, the things that are attacked are primarily in the oiling system and some things in the cooling system.
Think about what is happening when a head gasket fails.
-The gasket loses it's shape and allows oil and antifreeze to pass through it.
-Fluids exchange into the combustion chamber, destroying combustion properties, which allows unburned fuel to pass through the rings down the cylinder walls.
-The antifreeze can make contact with the piston tops, causing distortion in extreme cases.
-The oil, antifreeze and air can return into the cooling and oil passages, including your turbo cooling and oil feed and return lines, heater core and radiator, which can block passages.
-In a turbocharged engine, the oil and antifreeze can destroy the bearing seal and allow the fluids to pass through to the compressor side of the turbo and into the intake side of the engine as well, fouling your air flow meter, air filter, intercooler, it's hoses and pipes as well as the intake manifold and valves with oil and antifreeze.
-Antifreeze and air can return into the pressure side of the oiling system, creating air and water pockets in the oil pump, which feeds into your rod and main bearings, camshafts, etc. This is due to the compression of the combustion chamber forcing the fluids and gasses into the oiling passages that route through the head gasket that is damaged or partially missing.
-The engines Vacuum (on down stroke) pulls the oil and antifreeze into the combustion chamber and out the exhaust as well, fouling cataletic converters, O2 sensors, etc.
If you suspect a blown head gasket, don't drive your car. Have the oil drained and check it for water and glycol content.
You should invest in a 14mm internal hex, 3/8 drive socket a 3-4 inch extension and a torque wrench. Buy a pair of valve cover o rings and retorque your head gasket to 68 ft lbs to further prevent it from failing on you. Follow the TSRM (Toyota Supra Repair Manual) online (found on this site) for the torque sequencing. When you retorque the bolts, losen the bolt being torqued 1/8-1/4 of a turn or until it barely breaks loose and NO FURTHER! This is to assure that you have the correct amount of torque readout on the wrench and you are not fighting any kind of forgein lockup in the threading. Follow up with the higher torque down specifications and tighten the bolt to the higher number of ft. lbs.
Make sure that you do this one bolt at a time and do NOT losen all of the bolts 1/4 turn before retorque. Only do one at a time in sequence.
There was another member of this forum that had run a plasticity test on a new factory bolt. I'm not sure who it was, but I know that someone here does. It was discovered that the bolt had the correct stretch and reached it's plastic level at 72ft lbs of torque and that Toyota's factory specs (52ft lbs?) are too low. I suggest 68ft lbs. because you ARE re-using your original bolts. I have heared of some people going to 71ft lbs. on reused bolts with no report of any problems, but 68 is still quite an improvement over stock.
Check into some other sections on this site to find more info on BHG as well. I would suggest reading some of the write up's on it in the FAQ section on this site.
Like Americanjebus said, the things that are attacked are primarily in the oiling system and some things in the cooling system.
Think about what is happening when a head gasket fails.
-The gasket loses it's shape and allows oil and antifreeze to pass through it.
-Fluids exchange into the combustion chamber, destroying combustion properties, which allows unburned fuel to pass through the rings down the cylinder walls.
-The antifreeze can make contact with the piston tops, causing distortion in extreme cases.
-The oil, antifreeze and air can return into the cooling and oil passages, including your turbo cooling and oil feed and return lines, heater core and radiator, which can block passages.
-In a turbocharged engine, the oil and antifreeze can destroy the bearing seal and allow the fluids to pass through to the compressor side of the turbo and into the intake side of the engine as well, fouling your air flow meter, air filter, intercooler, it's hoses and pipes as well as the intake manifold and valves with oil and antifreeze.
-Antifreeze and air can return into the pressure side of the oiling system, creating air and water pockets in the oil pump, which feeds into your rod and main bearings, camshafts, etc. This is due to the compression of the combustion chamber forcing the fluids and gasses into the oiling passages that route through the head gasket that is damaged or partially missing.
-The engines Vacuum (on down stroke) pulls the oil and antifreeze into the combustion chamber and out the exhaust as well, fouling cataletic converters, O2 sensors, etc.
If you suspect a blown head gasket, don't drive your car. Have the oil drained and check it for water and glycol content.
You should invest in a 14mm internal hex, 3/8 drive socket a 3-4 inch extension and a torque wrench. Buy a pair of valve cover o rings and retorque your head gasket to 68 ft lbs to further prevent it from failing on you. Follow the TSRM (Toyota Supra Repair Manual) online (found on this site) for the torque sequencing. When you retorque the bolts, losen the bolt being torqued 1/8-1/4 of a turn or until it barely breaks loose and NO FURTHER! This is to assure that you have the correct amount of torque readout on the wrench and you are not fighting any kind of forgein lockup in the threading. Follow up with the higher torque down specifications and tighten the bolt to the higher number of ft. lbs.
Make sure that you do this one bolt at a time and do NOT losen all of the bolts 1/4 turn before retorque. Only do one at a time in sequence.
There was another member of this forum that had run a plasticity test on a new factory bolt. I'm not sure who it was, but I know that someone here does. It was discovered that the bolt had the correct stretch and reached it's plastic level at 72ft lbs of torque and that Toyota's factory specs (52ft lbs?) are too low. I suggest 68ft lbs. because you ARE re-using your original bolts. I have heared of some people going to 71ft lbs. on reused bolts with no report of any problems, but 68 is still quite an improvement over stock.
Check into some other sections on this site to find more info on BHG as well. I would suggest reading some of the write up's on it in the FAQ section on this site.