Ran across this article in the last issue of Farm Show magazine. It was about getting a 302 piston unstuck. Thought it might be of interest to those of you that have run into an engine that isn't being cooperative in disassembly. They're talking about a Farmall Super M tractor with a Ford 302 engine transplant. He's way off on his estimate of shrinkage. Given the coefficient of expansion for aluminum, the maximum amount for a nominal 4" diameter would be ~ 0.027 for ▲119º (78 to -44) . That's if the piston were completely isolated and brought to that temp; which in this case is not. I'm guessing it would be around 0.010; maybe as little as 0.005 However, that's probably enough to free the piston and rings from the cylinder wall. It may be something to consider if penetrating oils don't work.
Wouldn't the cylinder walls also shrink from the cold? They expand when they get hot. Also, anyone trying this should be aware of the hazards to their face,skin and eyes when using ultra cold liquids/gases. Beyond that, it sounds like it worked. I once had a motorcycle fork that was rusted solid. Threw it in a cleaning tank of kerosene. Kept throwing it back in there for a couple months. It eventually came apart........but it was junk anyway. If anyone has an old engine that won't turn over, pour the kerosene (or diesel fuel) in the spark plug holes and let it sit under the workbench till you get to it.
True, the cylinder wall would shrink too, but not nearly as much, because cast iron has a much lower coefficient of expansion; about 1/3 to 1/4 that of aluminum. And the isolation issue not to be ignored. Good advice regarding the hazards.
I would guess the problem would be a rusted piston ring stuck to the cylinder wall more so than a piston stuck to the wall. ...
I was there last summer. Most of the top ring stayed in place while the top of the piston broke off, wanted just the rod anyways.
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