ABATTBQ11 said:
Marvel mystery oil or another penetrating oil into the cylinder may loosen it, but you could have easily damaged the cylinder and/or block. In that case, you're SOL and a new mower might be the best option.
To try to work the piston had free, first drain the oil and fuel. Then remove the spark plug and spray the penetrating oil in the spark plug hole. Wait an hour, then do it again. Wait another hour, then try to work the mower blade back and forth to move the piston in the cylinder. Do that with the spark plug out. If you can get the piston head moving freely with the mower blade, put new oil in, gas it up, replace the plug, and try to start it. If you can't get the piston moving, you're basically SOL.
I agree. This actually works, although my penetrating oil of choice is Kroil (
don't spoil it, Kroil it).
Also depending upon the position of the piston and the head configuration, you might be able to insert a wooden dowel into the spark plug hole and strike it with a hammer to jar it loose.
Be extra careful if you try turning the blades. I knew a guy who damn near cut his thumb off when he lost his grip and slipped. It never did heal back right, despite a ER visit when it happened.
Some of those old motors are pretty damn resilient. We once bent a crank by running the mower over a piece of channel iron, and knowing the motor was probably toast, just beat it back into place the best we could and got some more life out of it. No, it didn't last forever, and vibrated fairly badly, but it lived a while longer.