My friend just bought a new bike from Performance Bike. It's a Zum GT, whatever that is. It's a campus type commuter hybrid type thingy. I dunno, lol. It has an 8 speed cassette in the rear and a single chainring in the front. I've adjusted the rear derailer for him and it shifts around just fine.
The problem is that when in the big cog in the back, the chain will try (and sometimes succeed) to jump off of the chainring to the inside and land on the BB housing. It looks to me like it's simply a matter of the chain not being flexible enough. But since there's nothing I can adjust in the front, and I can't seem to stop it from jumping off, I'm at a loss for what to do.
I've taken a few pictures to help (sorry for the resolution, it's just my old phone).
Any ideas from the wise mechanics?