Originally Posted by
FBinNY
I haven't seen the bike, so can't speak with authority, but I suspect that you're on more on the long list of victims of running a single speed set up with a tight chain. Whenever I hear a single speed owner claim that he made sure that "the tension is sufficient" I'm willing to bet a few beers that it's excessive. Single speed chains cannot have tension, they must be slack at all times. Not very slack, but slack none the less. The rule of thumb is about 1/8-1/4" sag in the lower loop.
A tight chain is the surest, fastest way to bend the axle as the rigid chain pulls the sprocket forward.
Yeah, that's likely actually. I followed sheldon's recommendation to set it "tight as it can be without binding" but I might have gone a bit over the limit. Lesson learned.