Thanks for your help.
The engine is a single cylinder MTD. Not sure about the model number.
The funny thing is, I can only turn the crankshaft 360 degrees, even though this should be 4 stroke engine. I believe the end of the turn, either right or left, is TDC as the piston comes all the way...
I ran over a piece of uneven lawn and my riding mower (17 HP) stopped. I was able to restart it and mow for about 5 more minutes.
But, then the mower died and wouldn't start. It was misfiring and popping.
Then, I took off the OHV plate and noticed that the intake push rod and rocker arm was...