When Fritz wanted to remove the pistons from his stubble-field CB450 - they were rusted in pretty seriously, the rings had disintegrated and expanded into oxide, jamming into the cylinders and more-or-less becoming one with the liners - we used my hydraulic press. Because the crank would rotate, the cylinders would move up and down by some portion of the stroke, running up and down the studs extending from the cases. We braced the bottom of the cylinders with steel between the barrels and cases, and a length of wood (which blew up a couple of times, and a chunk of which nearly inserted itself into Fritz) shifted the stuck piston. It wouln't have worked if the pistons had been at TDC or BDC, or if it had been a 4, but it worked ok. No amount of beating would have done it, not until the pistons had been reduced to shards and the tension released.
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