Re: Chain jumps off what to do?????
Just a guess. See if your tensioner is tilted in such a way as to actually derail the chain. I had leaned my tensioner away from the chain stay a bit to prevent the chain from rubbing it. I figured it out by looking down on the chain, perpendicular to the ground.
“You're only young once, but you can be immature as long as you like" -Unknown