Started my Yardman this morning , ran great then stopped. Gas is good, battery is good. When I try to start it, it kicks over and there is a clunk. Same when I move it by hand. Checked oil was Down a bit but not much, manual mentions an oil switch, may need to be reset. Know a bit about engines but not enough to disassemble.

Loose flywheel, possibly a bad connecting rod or cracked piston.