23. Is it possible to use 3/8" coarse-threaded bolts in place of studs for installing heads and manifolds?

The practice of using bolts instead of studs puts considerably more stress on the threads in the block.

The explanation centers around the fact that studs impose a straight-line pull on the threads in the block, as the nuts are torqued on the upper threads. By contrast, bolts "grind" into the threads in the block as the bolts are tightened and torqued. The threads in the block will seldom tolerate more than one or two "torquings" of bolts before failing.

There is also a problem with the effectiveness of the torquing process itself. Due to the steeper slope of the coarse threads on the bolts, a torque value of 35 foot-pounds will result in less downward force on the head than will the shallower slope of the 3/8" fine threads in the upper end of the studs. Happily, there seems to be enough safety margin in the torque value itself, so that problems related to under torquing seldom manifest. - Updated: November 6, 2003