Originally Posted by
dedhed
While helpful, the exact make and model # of the existing crankset is more helpful, particularly if they plan to just replace the BB and keep the existing crankset
+1. If the cranks are wobbling then the issue is a loose crank bolt, maybe both. If the wobble has been allowed to go on to long, it's possible the square hole in the crank has been rounded and no amount of tightening will fix it. So check that. If it is rounded, it needs to be replace. If you do replace the bb, as noted above, spindle will need to be the same length as the existing one (and depending on the age of the bike the spindle could be symmetric or asymmetric, so check that), and if you have to replace the crankset, a new bb would have to be purchased to work with the new crankset.