are you sure it's the bb? could be pedals. try another set of pedals. or try overhauling the pedals. i always overhaul new-to-me pedals, but every once in a while you may run into a rusted pedal axle that crumbles on you. adjusting pedals as a final step in their overhaul may take patience -- it's a bit of trial and error like adjusting a bb or headset.