Bolt torque discussion

krazykuda said
The clamp load is more than the load seen by the fastener... If the load on the bolt exceeds the clamp load on the fastener, then you will get failure/breaking of the bolt...

The bolt acts kind of like a spring, the clamp load is what keeps it together...

I saw a video by one of the major head gasket manufacturers and they were saying they had made a custom
Machine that monitors how much a cylinder head lifted off the block as the piston went through its cycles. Yes thats right lifted.
Although the head appears to be stationary during engine operation, the head actually lifts
A very small amount unloading the head gasket. If this unloading is excessive, the gasket will fail. The elasticity of the bolts allows this to happen
The sbm with its 4 bolts only per cylinder was particularly prone to this at high compression ratios.
The reason the Mls style head gaskets were a big help to the troublesome sbm is the spring steel can move with the head but still retain a seal and spring steel is noted for its ability to retain its shape.
So a certain amount of bolt stretch during operation is considered normal.