The theory of not torquing studs in a head goes like this:
If you torque the stud in the block it bottoms and the pressure of
engagement is on the back side of the threads, especially towards the bottom
of the hole assuming that all the threads are uniform. When you stretch the
stud with head clamping tension it pulls the threads the opposite way,
especially towards the top of the block. You can easily see that for some
tension value there will be threads that are engaged on the backside
(towards the top) and threads engaged on the frontside (at the bottom), and
some hovering in the middle with no engagement at all. This actually makes
it more likely that you'll pull threads from the top of the block, or crack
the metal around the threads.
You never have this problem with bolts, though you do have the problem of
not getting full engagement if the bolt is not exactly the right length, and
the higher likelihood of shearing during torqueing since the bolt is being
turned as it's pulled (a stud is only being pulled).
There simply isn't a good reason to torque studs into a block.
|