ORIGINAL: Gray Beard
If it's really rusted then the CP and anti freeze will work most of the time. Depending on the engine sometimes pulling the prop and tossing the engine is a better choice.
It sounded like just hardened Caster Oil so heat should break it loose.
Good advice, thanks. I freed up a badly rusted Enya .19 I bought at an auction and used a propane torch and some gentle persuasion with a peice of hardwood dowel and a hammer to break the bond between the cast iron piston and steel cylinder. I was lucky, no new parts and it cleaned up fine.
Bill