Originally Posted by
jmpsmash
F
Upon taking off the crank arms and inspecting, i found out that the threads on the drive side of the bottom bracket shell was stripped. so much that i can just slide the BB (which visually still have all the threads intact) all the way in so the lip is flushed against the shell.
what i found strange and mysterious is how could this have happen. the only confirmation i know is the bb became loose and fell out.
This isn't all that rare. If threaded BB cups are loose, they can move up and down slightly with every pedal stroke. The process wears threads away by friction. Usually the process is stopped soon enough that the damage is minimal, as the owner notices the play, or hears the creaking with every stroke.
This is simply an extreme case, and your friend was probably riding it loose for a long while.