Engine Toro Timecutter ZTR 16-44 came with new house, died after 6th use on 2.5 acre yard

Hello! This is my first post, just joined the forum. I inherited a Toro Timecutter ZTR 16-44, not sure what year, but it's used. Has the Briggs and Stratton model 331977 engine that I was told got a rebuild about a year prior to me taking ownership. Last night I was mowing normally, had been running about an hour, I stopped to clean off some berries that had fallen on me from getting too close to a bush, and the engine just died. Tried to start it and heard a loud bang, then nothing. Turning the key mades a loud click at the starter. Checked the oil and a bunch of smoke came out of the oil pan. Has anyone experienced this? Any suggestions on how to proceed? I'm assuming the worst, sadly.

Edit: just read and saw video about the flywheel key that breaks to prevent damage to the engine. I'll check that out after work.

Thanks!

Brian

:welcome:
Sounds like it might be terminal.
If there is a sticker on the engine from whoever repaired it, don't go back there.
Smoke from the dip stick tube usually signifies a blown head gasket, cracked block or hole in the piston.
So start by removing the spark plugs and see if you can turn the engine over by hand
DO not sit there cranking the engine because all you are going to do is further damage the engine.

If you can not turn the engine over then remove the rocker cover and check that the pushrods are still connected to the rockers.