When I took this engine apart, the head bolts were really really tight. Friend Ernie said "get new headbolts" but considering the dilemma about headbolt thread sealing and retightening headbolts ( you can't retighten a bolt retained with a thread locking compound) I decided the best thing would be to use studs instead. I could not find 1/2" x 4" studs at what I thought was a reasonable price so I bought 4" long 1/2" grade 5 bolts and made a set of proper studs in my lathe. The center of my studs is reduced in diameter to the minor diameter of the 1/2" national coarse end 0.410". It looks much smaller than the nominal 1/2" shank but it actually is stronger as all of the stress is otherwise concentrated on the first thread or two of the coarse threaded end. (That is where an unmodified bolt normally breaks at the end of its fatigue life.) "Waisted" bolts and studs not only hold better, they also last longer than straight sided fasteners. Carried to the extreme, this concept gives us to the single use bolt. I would not suggest making single use studs as too much labor is involved. $12 per stud does not seem so much after spending a day making studs.