Thanks for the help TVP.
The bolt material is very well controlled.
The bolts yeild in test conditions at the calculated torque it is only when it is assembled onto the cylinder head that we see the problem.
I am interested to hear that friction plays such a significant role, is it...
I am having a problem with M12 bolts not yeilding at their specified torque. I understand that friction can have a large effect on torque. Can anyone help me understand bolt behavior?