For real bad ones, I set the engine up so the head surface is level and pour some wd-40 on top of the pistons. Cover it up with a rag and let it sit for a couple of weeks or months. If I have to pound them out it usually scores the walls bad enough that .030" overbore won't clean it up. I hate resleeving. I take a die grinder and grind the top of the bore (just enough to smooth the edge) so the piston rings will slide out. I them take my die grinder and a wire brush and clean out the top of the cylinder bore (this is a rusty block) as much as I can. Don't pound on the rod, but pound the piston up and then down with a bouard and hammer wiping the bore clean after you move it one direction, repeat until loose. If the piston doesn't come loose in a couple of hits, I set it up and put more wd-40 in the cylinder and let it sit some more. When I bring an old truck home and don't plan on working on it for a while, I take the air cleaner and oil fill cap off and fill the motor as full as I can with deisel fuel before I park it. Then when I go to get it I can drain the fluid (whats left because most of it leaks out) and the motor has loosened up some already.
