More head gasket questions....

[Bill R.]

retorque them after the initial torque. Retorqing is not needed and can cause damage. The whole point of torque to yield is that the bolts are torqued until they reach the elastic point where they are stretching. If you retorque later then they odds are you'll break a bolt since they have already been stretched.
Normally on a non torque to yield bolt the aluminum head and block expand as the engine warms up. They expand much faster than the steel bolts do so as the engine warms up the gasket is squeezed harder, then when the engine cools off it shrinks back down and the gasket gets looser, this compression and release over and over tends to lead to the head gasket failing an leaking eventually, this is how the m30 is without torque to yield bolts. With torque to yield like you have, you tighten the bolts down to the point where they start to stretch and become somewhat elastic. With this type of bolt the clamping force of say 90lbs cold when the engine heats up the bolts stretch more and the clamping force stays the same 90lbs, this keeps an even pressure on the head gasket all the time and prolongs the life of the head gasket. So when you initially torqued these to that point the bolts are now at the ideal point for this to happen as designed.

Well, unless someone thinks differently, I'll leave it as is.

Thanks,

Dave M

[Dave M]

retorque them after the initial torque. Retorqing is not needed and can cause damage. The whole point of torque to yield is that the bolts are torqued until they reach the elastic point where they are stretching. If you retorque later then they odds are you'll break a bolt since they have already been stretched.
Normally on a non torque to yield bolt the aluminum head and block expand as the engine warms up. They expand much faster than the steel bolts do so as the engine warms up the gasket is squeezed harder, then when the engine cools off it shrinks back down and the gasket gets looser, this compression and release over and over tends to lead to the head gasket failing an leaking eventually, this is how the m30 is without torque to yield bolts. With torque to yield like you have, you tighten the bolts down to the point where they start to stretch and become somewhat elastic. With this type of bolt the clamping force of say 90lbs cold when the engine heats up the bolts stretch more and the clamping force stays the same 90lbs, this keeps an even pressure on the head gasket all the time and prolongs the life of the head gasket. So when you initially torqued these to that point the bolts are now at the ideal point for this to happen as designed.

Phew, thanks for smart people. Now I can sleep well.

Dave m

[rob101]

anyone ever head of the porsche 2.7L 911 engine's head studs, they break or pop out of the block eventually....