Guys I took a 642 apart to clean it. I reassembled it, and now the cylinder carries up but the hammer does not go back! This revolver has the lock on it, does this affect the revolver thusly???? BTW no key ! Boo!!!!!

Missing DA sear or sear spring would be a guess. Did you remove the sear from the hammer?

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Ret. LE, FA Instr, S&W Armorer

Nope. It worked prior to disassembly.. took the side plate off and no hammer cocking... relatively new revolver, I did notice the hammer was MIM, though.

Take the side plate off again. First take a couple pictures, one uncocked, another cocked. Then spray it with carb cleaner. if it still don't work post the pictures and amybe we can help you out.

When I lock my J-frame, I can't thumb the hammer back for SA, and can't pull the trigger through DA.

Doesn't read like the lock is your problem.

Check for a broken hammer stud. Fairly common when people dry fire the gun without the side plate on.