Cranks dont have bearings do they ? and if yopu take you BB out and clean every thing like the freewheel (assuming youre running FFW ) etc then that may help otherwise your BB threads may be screwed other than that you may have rounded the taper of (again assuming its Square taper) other than that all i can think of it the threads on the cranks have been stripped ? Adam Edit: shit i said "other than that alot didnt i" lol