Pieces of steel in cylinder??
Yep that will do 'er in.
It's called Malleability, reshaping bearing inserts at room temperature by hammering on them.
That crank had no where else to go being being the pistons were bottomed out against the valve seat pieces at TDC, so the soft crank bearing inserts took the brunt of the rotating force. Enough so the piston could go past TDC and come around again for another wack, with crank taking the same beating on every rotation. Bearings not only had the pressure on them, but the rotational force under pressure too. On and on until the owner finally turned off the key.
Dynamite, Bing, Bang, Ka-Boom
Down and Out . . .