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Old 02-19-2021, 10:32 AM   #3
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Join Date: Apr 2018
Location: Mebane NC
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Default Re: Stud boss height for stock heads

Originally Posted by Jack Shaft View Post
A stud or bolt is only as strong as its width, burying threads beyond its width does not add to its grip strength.
The technical way of saying this is that the strength of a steel-to-steel joint increases as the length of thread engagement increases, up to one nominal diameter (e.g., for a 7/16"-14 stud, 7/16" depth of tapping or about six full turns). Beyond that there is no appreciable increase in strength.

Although this is correct, there are reasons to favor inserting the stud to the maximum practical depth. First, the beginning and end of the threaded engagement is chamfered the top of the internal threads are chamfered in the block and the bottom of the external threads are chamfered on the stud so there's minimal thread engagement in that section of the joint. Second, it's safe to assume the block threads are degraded to some degree, so only a proportion of the threaded engagement is taking the load.

If the effective loss of engaged length from these two factors, plus the amount you're backing the stud out of the block, were to exceed 0.31", you'd be below the one-nominal-diameter threshold.

So I agree there's a margin for error in backing out the stud, but because we don't know how much the internal threads are degraded, I don't think we should be backing out the stud unless it's required to properly clamp a head that's taller than stock. My question is about how an individual should go about calculating whether this is required on their engine.
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