I have had great success cleaning steel and iron parts using EVAPORUST. The web site is
www.theruststore.com. I heard that Harbor Freight has it in some stores
The military uses it to disolve the rust off tank engines. It does not touch anything except rust. It uses a chealation process to replace the oxygen in iron-oxide with sulfer. The resulting iron-sulfide is a black powder that can be washed off with water. It is ph neutral and can be disposed of down the drain.
I used evaporust to disolve the rust in a set of bearings from a RRV McCoy 29. The bearings were completely frozen and after a 24 hour soak the would turn and I could clean them out. The engine runs great now. I had a crankshaft the was a big lump of rust after being recovered from a flood of 20 years ago. A soak and scrubbing with a brush cleaned it right up.
I have not had to free up a rusted piston/cylinder, all mine were varnished together. I used dishwashing soap and an ultrasonic cleaner to solve that problem.
DO NOT put non-ferrous parts in evaporust. While it does not seem to hurt it, it get a real stained look. Also, evaporust removes blueing since that is a form of rust.
Try it on your stuff. Use a plastic food container with enough solution to totally immerse the part. Let it sit for several hours and then remove the parts and brush them off under a running stream of water. If rust remains, repeat the process.
What really works is using evaporust in a heated ultrasonic cleaner. It even cleans up screw threads.
Hope this helps. sorry for the length
Lee