They can't. He's a teen and has little/no experience. Probably was told that was what happened by another person who didn't know what they were talking about.

Some folks learn by asking questions. Could use more young folks interested in these old machines. I'm 40 and I feel like the young guy most of the time! Gotta have someone to sell them to someday :biggrin2:

Nothing wrong with sharing a little knowledge.

Which is what I did. Told him it can't happen, and the guy that said so was wrong. Bearing can spin, block can crack, crank can gauld.... but the bearing can't "explode". Unless by explode he means "failed".

Is it somehow possible that the bearing seized and somehow there was enough crank momentum that it shattered a chunk of block? I would think it would just spin the bearing in the block first though.

Main crank bearing failure has to be a fairly rare occurrence in a lawnmower engine. seems like 90% of the time rods go first.

Not likely. Even if it did, it was a block failure, not the bearing. Yes, the rod usually goes first. It's the one on a crank journal swinging around. When that bearing loses oil, or gets loose, it has all the force on it. Mains just support a rotational load.