I recently helped a friend who was working on a kid's bike that was frequently throwing its chain. The chain ring appeared to have been bent as it was wobbling significantly. A closer look revealed that the chain ring was not seated well against the one-piece crank. Upon disassembly we found that the washer behind the nut that held the ring to the crank was significantly messed up. The hole was mis-punched and the whole thing was bent, no doubt during manufacture. The chain ring was flat so a replacement washer worked perfectly.
The assembler on the factory floor surely had a choice to reject this obviously faulty piece but chose not to. This quick lazy decision resulted in a child's joy being frustrated by a less-than-ridable bike. Karma will prevail, no doubt.
