Quote:
Originally Posted by Licensed to kill
It's my understanding that this "tension" is achieved by a specific amount of bolt/stud stretch and that the torque spec is the torque required to achieve a specific amount of stretch. This is also, to my understanding, why critical bolts/studs ( heads on high compression/high performance applications) should never be reused. They should only be "stretched" once.
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My Cummins diesel requires the head bolts be torqued to 60 ft. lbs., then marked and turned an additional 120 degrees to get to the proper stretch. They do not require replacing the bolt each time it is stretched.
My Ford 7.3 diesel just gives a torque number and requires that the bolts be replaced each time they are torqued.
It is my assumption that the Cummins bolts are more resilient (like a spring) and the Ford bolts stretch to provide the correct tension, but do not return to original length. I have heard of connecting rod bolts that are not torqued, but measured before installation and tightened until they reach a specific length. They have a certain maximum length at which point they are replaced. The number of times they have been tightened is unimportant.
My point is, it's not like buying a baseball cap, one size does not fit all.