The bolts bottoming out was a mistake on my part. I'm quite aware of the results of bottoming a bolt out. The old rule of thumb of thread engagement being equal to dia. of bolt. Equals bare minimum. You should not establish a standard for thread engagement. Just far too many variables. Such as in steel, alloys, heat treat etc. In aluminum and bronze, you deal with cast and billet and different alloys. How many engine builders have you seen strip threads out of a head. When using stock bolts to hold rocker shafts down? Just one example. Maximum thread engagement is very critical in engine buildiing. And I screwed up by going too extreme.