How many of you gas engine buffs got a hold of one of those real gas engine jewels that has been left out in the weather for thirty or forty years and everything is frozen up? You get it all apart and get down to the piston and can't get it out of the cylinder. Well, there is a way.
First, make sure the valves are well seated and you have a good head gasket. Then make an adapter for spark plug hole or make a plate for igniter hole with a zerk fitting in it. Then go to your local auto parts store and get a bucket of grease. Hand pack the cylinder up to the cylinder head. Install head and tighten. Install your adapter. Get yourself a good grease gun, preferably one with cartridge load. Or, if you have access to an air operated grease gun, that is better yet.
You're in business! Start pumping grease in the zerk. Now, it's going to be very slow. I pushed a piston out of a Fairbanks-Morse with 6 inch bore and put a dial indicator on the connecting rod and the piston moved only 0.005 to 0.006 thousandths each pump of the grease gun.
A friend of mine, Robert Siebert, pushed a piston that a hydraulic press wouldn't move, out of a Witte. All the press would do was bend the connecting rod. To give you an idea of how much pressure can be put on a piston with grease, a grease gun will put out 10,000 PSI x the square inch of diameter.
So, good luck, old engine buffs in distress!