so I am installing the alloy head, threads chased clean ,new UK made headbolts and an accurate torque wrench....Second go around a 20 ft lbs when the bolt goes soft....Threads torn off, expensive scrap..UNF 3/8-24 Heli coils, grade 8 bolts,replace all 9 bolts, back in business...
Actually all the various bolt and studs that have same thread as US fasteners have been replaced..