Here's a method I used to remove the stuck piston from my Model M 6 HP International engine. The stuck piston was about 4" down from the top. After getting the head off, which was cracked and both valves were rusted solid, and the crankshaft out of the block, I stood the International engine up on its bottom end so the stuck piston was looking skyward.
I tried using a block of hard wood and a 10 lb. "sweat maul" to move the stuck piston with no success. For two weeks I used just about everything in the line of liquids on that piston with no success so I decided to try something else.
Going through my iron pile I found four round slugs 1" thick and just 4" in diameter that would just slide down the cylinder and onto the top of the stuck piston. (Soaking is still going on.) On top of the slug I welded a hook so I could retrieve it if this new system didn't work out. Next I cut a piece of 4" well casing 7" long and placed this on top of the slug, on top of the piston.
Then I drilled two holes in a scrap of 1" flat iron with the holes matching two opposite head bolts. (Now don't jump to conclusions. I didn't use the head bolt nuts to push the piston out with.) All the bolts were used to act as a guide and to keep things together.
I then used my 10 lb. sweat maul, striking that 1" plate on top with no more force than the weight of the maul. About five times a day for a week I would let that maul strike its mark. On the eighth day I could see daylight under the head bolt nuts. "Eureka! She's on the move!" I did not rush it. More chain saw gas/tranny fluid was poured onto the piston. By day 10 the piston was out. Even the connecting rod was freed from the pounding. You see, here in Montana we don't rush things, just take our time and use a bigger hammer. Four of the five rings were stuck. I soaked the piston in diesel oil and would tap lightly on the rings with a brass hammer. No luck. They were rusted onto that piston. Finally I took the piston and went to work on those rings. A small screwdriver and my little brass-head hammer was all I needed. By prying up the ring a little, then tapping it back down I got all the rings off. I broke one ring as I tried to push my luck.
The picture shows the piston, on the right, and the 1" slugs, casing, more slugs, spacers to take up the slack as the piston was driven down the cylinder, and then finally, the top bar with the washers and nuts, which held all this hi-tech tooling together.
This might not work for everyone but it does make a great story. I have this on video to prove it works.
Contact John M. Edgerton at 603 Loon Lake Road Bigfork, Montana 5991