Just my idea...
The crankshaft could be broken due metal fatigue stress vibrations...
Ones the crankshaft separated in two, the shaft has pushed / slammed the piston against the cilinder head.
Doing this, it could has bended the connecting rod and breaking the crankshaft bearing bolts.
I have sailed on a tug boat, where the crankshaft had been broken and after woods welded back together!!
Needless to say that engine was a pain in...(You know where)
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Ford Anglia '62, Mercedes 200 '86, Transit ambulance/camper '88, Mercedes CE300 '89, caravan Puck '75
My ambulance conversion