Pieces of steel in cylinder??

George Jets said
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 . . .

Ya know.... that makes sense if the crank kept running and running and running. I realize that the only bearing failures I've seen are oil starvation, and the only piston impacts were violent enough to stop the engine dead in its tracks or bend the rod. If the seat shattrered at the first blow, then those smaller impacts might indeed just heat the lower main bearing and the #3 rod bearing and slowly melt the materials out. Makin' more sense....