The Lycoming studs have a slightly larger thread on the
head end and are an interference fit. They must be double-nutted and
driven all the way. If your studs are backing out they're likely the
wrong studs or the cylinders have been overhauled too many times.
We run six Lycs and have no trouble with studs coming out.
Of course, these are all factory overhauls and Lycoming won't reuse
cylinders.
The proper nuts are plated with somethng better than the
usual stuff and do not easily corrode. You might have plain AN coarse-
thread nuts instead of the Lycoming nuts.

Dan