My opion from a distance not enough free play and over rotation of the lifter shaft is what pulled the head off. Did you do any adjustment or just the dealer? Also what does the steels look like besides the warpage you refered to? Do they have any burn marks on them? And what brand and grade of oil were you running ? Over rotation will make the slot on the lifter shaft lift the small diameter of the lifter piece and put ina bing tearing the head off or 2ith evem more bind snap the lifter shaft.