[HawgRyder]

Old...very old trick was to use just Coke.
Fill cylinder...let sit either for a few hours...or overnight for really stuck pistons...and then hammer down on the piston with the handle of a hammer.
This was common for inline 6's and 8's.
Coke will erode steel...so use is subjective...how much vs how long....experience is king.
It works...but on V8's and flat 4's and 6's you would have to rotate the engine into a piston/vertical position.
It's extreme...but in the long run...if you are considering it...it probably means you're going to toss the cylinders anyway.
Bob