My chain keeps coming off the lower jockey wheel and running through the cage beside it rather than on it.
I noticed this a while ago and replaced the jockey wheel, which was very worn, and assume that it would fix it. But it became clear the other day that it is still happening.
So I changed the hanger. And it is still happening. Within a couple of minutes of me putting the chain back on the jockey wheel it will have slipped off, especially if I shift a couple of times.
It's not clear why it is happening. Nothing looks massively out of alignment but it must be or it wouldn't keep happening. The only other thing that I can think of is that the cage must have got bent. I don't know how as I don't recall any incident, but I can't think what else it could be.
Any tips on how to straighten a cage? Can I just yank it, or does the mech need to come to pieces? Does it need a new cage?
Or anything else that could be causing it?