If they are really stubborn, and double nuts aren't working too well, try this:
I apply Kroil penetrating fluid for at least overnight.
Get some aluminum jaws for your bench vise. The kind that have some v-slots machined into the aluminum faces.
Clamp one stud at a time as hard as you want in those aluminum jaws, turning a bit at a time , reclamping as needed. Obviously, working the first stud, you only get a few degrees of rotation in the vise.
After removal of all the studs, chase the threads on the studs and in the cylinder with a thread restorer, NOT a tap and die. I find all of the threads get slightly stretched. Check to be sure they will all hand thread all the way in again. I have the studs plated with the rest of the fasteners and reassemble with plenty of anti-sieze.
Take advantage of the bare cylinder by cleaning up the head surface on a surface plate along with the head itself.
Barry
