Bottom bracket removable cup loosened while riding
I came to a sudden, grinding halt while riding my '08 Schwinn Madison fixed gear this afternoon.
I was shocked when I found the source of the problem: the removable bottom bracket cup backed out so far that it contacted with the crank, the rotation of which loosened it more, causing the entire BB assembly to go into compression and sieze. The drive side crank was pulled inward so hard that the chain wheel contacted the chain stay.
I was expecting the threads on the BB shell to be fouled and the frame to be more or less trashed. Miraculously, the threads look fine (on the BB shell, at least). The removable cup didn't fare well, but I'm going to replace the bottom bracket.
After working on bikes for years, I wasn't aware that this could even happen. What caused this? Was the bottom bracket simply not installed in accordance with torque specifications? The BB was a SRAM PowerSpline.