I have an old Toro 14,44hxl mower. I thought my battery was flat because mower all of a sudden wouldn't turn over, Its had heavy use of late with Humid wet weather.. After charging a charged battery it sti wouldn't turn over, I took out plug and voila cranks beautifully. Put plug back in and wont budge again. Have now taken head off to reveal a slice out of piston (see pic) No bit of piston to be seen in or around head.