I recently took apart my rear derailleur as it was on a 10 year old bike and really old and stiff.
So I thought I would unscrew both jockey wheels and clean them, they had a silver bit either side, but then when I tightened them back up in the derailleur two things happened.
I completely tightened the bolts on the jockey wheels and derailleur and then the jockey wheels wouldn't turn freely.
Or I didn't completely tighten the bolts on both jockey wheels, and they would turn, so the chain would move.
I ended up going with the second option, Until after a few days of riding the derailleur jockey wheel screw came loose while riding and I lost the silver part on the inside of the jockey wheel. After not being able to replace the silver part on the wheel I bought a new derailleur .
Can derailleur be taken apart and cleaned if really stiff and dirty?
HOW DO YOU PUT THEM BACK TOGETHER AGAIN PROPERLY SO THEY DON'T FALL APART
Some mechanics say don't take them apart. But I say... super stiff and its an allen key bolt designed to be undone. Otherwise why don't they rivet it together?
Others say you can, but use Lock-Tite. I shouldn't need that I don't think or I will end up in scenario (1) again, jockey wheels not moving inside derailleur and chain getting caught.