One factor unique to tandem BB choices is the need to have both cranks' LH rings end up pretty much the same distance from the frame (in other wards be in line with each other). So when changing out the rear Bb not only does the usual RH side need to be paid attention to but also the LH side. If the OE BB was asymmetrical then have fun finding the correct current cartridge one, for a reasonable price, that matches up. Of course there's always Phil BBs that can be had in asymmetrical and custom off sets. This also would solve any loosening up issues, what with their retaining rings being Locktighted in place. Andy