When a vehicle is towed to your shop with a “cranks but will not start” complaint, you hope that it will remain in a no-start situation after it arrives so that you can quickly diagnose and repair the problem.
Sometimes circumstances just erase all doubts: the engine drips oil from the stump of a connecting rod hanging out are covered with recently-molten aluminum: a sample of oil from the crankcase twinkles with tiny shards of journal and bearing metal, grit rubbing sharply between your fingers.