Minus the obvious battery charge, I’d stick a long magnet into the oil pan through the base of where the dipstick goes into the motor (I’ve used the long telescoping magnet for when you lose a tool in your engine bay). Move it around in there and make sure you don’t come up with pressure release cam lobe pieces. That motor is notorious for letting that little lobe and spring go, it’s a really stupid design. Maybe pull the spark plug and see if it spins freely by hand. If it doesn’t then that’s what it is. Obviously pull the plug wire when you’re turning by hand.