Most of us antique engine collectors have encountered difficulty in removing a stuck piston, and the only easy way I have found is to watch someone else. However, the following might be of some help. Because of the wide range of removal methods, it seems best to separate them into two categories: head-type engines and headless engines.
1) Remove the head and get the cylinder in a vertical position.
2) Cover top of piston with a penetrating oil (Kroil, WD-40, Liquid Wrench, or equivalent). Place a cover over the top of cylinder to prevent evaporation.
3) Let engine soak and be patient. (I frequently wait three or four months.)
4) Check occasionally to see if any additional solvent is needed.
5) Remove flywheels, governor, and any loose parts.
6) Cut a piece of steel pipe 1/8 inch inch less outside diameter than bore of engine. (Use schedule 80 pipe on not less than schedule 40.) If pipe size is not available, weld a 3/4 inch plate on one end of the pipe with the diameter of the plate being 1/8 inch less than the bore. Weld the plate to the pipe.
Several people have recommended using a wood block of oak, hickory, or ash. My problem has been getting a square cut on the end and then the block splitting on a tough stuck piston. I went through three blocks on a six horse John Deere before going to steel. (I also tried rocking the flywheels on a loose rod cap with no results unless the piston is only barely stuck.)
7) Take the entire engine block to an open area and remove any remaining solvent.
8) Build a charcoal fire in the water hopper in a three horse engine or larger and heat for two hours. Sometimes a fan is necessary to get adequate air to the charcoal for combustion.
9) Put on safety glasses, get a ten pound sledge, and go to work. (Keep the pipe end snug against the piston before each hit.)
10) If available, some people recommend putting dry ice in the piston or using a carbon dioxide fire extinguisher but I have not used either of the above.
11) Hang in there. I have removed 42 pistons in this manner and broke one. (I used too small diameter pipe.)
1) Remove ignitor or spark plug and get the cylinder in a vertical position.
2) Cover the top of piston with solvent. (See step 2 from "head-type" instructions)
3) Same as steps 3, 4 and 5 from "head-type" instructions.
4) Make a huge slide hammer. I generally weld a piece of 1/2 inch by 1-1/2 inch by 6 foot bar to the connecting rod. (Sometimes a little improvising and shims are necessary to attach the rod to the bar.) For the hammer use a 6 inch diameter piece of round stock with a 2 inch hole and 8 inches long, making a rather heavy slide. Slide this over the bar stock and weld a strong cross piece perpendicular to the bar stock near the free end. In addition, it proves extremely helpful if you weld a piece of 1/2 inch pipe across the slide hammer to act as a handle.
5) Put on safety glasses, clear everyone out, especially in the direction of the slide hammer travel, and give it heck.
6) Carefully remove the weld from connecting rod and bar of hammer. If not careful, you will damage the rod.
Good luck and keep everybody clear when hammering.