I'm trying to take the crank off an old bike and put it on a newer bike. The problem is, I can't seem to get it off no matter what I do. One side is off, but the side with the crain rings is the one stuck. I have a crank puller, but the threads are damamged/stripped inside the crank arm. It will not thread on enough to bite. I've tried lightly tapping the back side of the crank to get it off. I've tried using WD40 to loosen it up, but no luck. Any suggestions?