Originally Posted by
WhyFi
Little bolt or biggin'? Little bolts usually just pinch the crankarm on to the spindle, essentially the same as stem to a steerer. Big bolts usually thread in to the spindle. Either way, being under-tightened was likely the problem.
It was a big bolt. He said that he had been feeling some play while riding but every time he would stop there wouldn’t be any play in it. Looks like the play lead to the bolt thread stripping off. The threads in the spindle looked okay from what I could see. This is my uneducated guess.