IMO a contributing factor is the poor machining done by Crysler's production equipment. The blocks I've inspected and machined show the mounting surface for the main cap to be out of flat by .0015". This is one each cap surface, not the total condition. This would cause the main cap to contact the block only on the 'crests' of the surface reducing the compression strength by limited contact. It would also allow more motion in the cap than if there were full contact. Motion of the cap will be transferred to the main bulkhead through the cap bolts resulting in vibration that will eventually cause cracking and failure of the main bulkheads. My solution would be to machine the mounting surface and caps flat and use a girdle to eliminate or at least reduce cap motion.