Mccubbins

Hi folks, I've recently taken on a sportstar frame, late 70's early 80's at a guess, which seems to have an annoyingly unique BB. no thread with locking tabs. the bb itself has a lockring on the non-drive side only and it's a cotter pin design.

the bb I have is still useable so things aren't desperate as yet, but I'm spending alot of time on this bike and I'd like to fit a sealed square taper to give me a wider and lighter selection of cranks. anyone out there had the same problem? Is there a solution?

Mccubbins

I just measured the shell, 38mm ID. if that helps any?

JohnDThompson 

38mm ID? That's going to be tough. I suspect that it needs some sort of proprietary Malvern bottom bracket. Are you in Australia? Perhaps you can scare up an old one someplace.

I'm not sure if a modern threadless cartridge BB would work with a 38mm ID, but perhaps a shop would let you try it.

Otherwise, you may need to braze a threaded sleeve inside the current shell, or pull the entire shell and replace it with a more standard one. Neither of these options is likely to be cheap, so unless you can do the work yourself you may need to consider another frame.

dscheidt

You sure it's 38 mm nad not 40? 40mm is the size most Thompson style bottom brackets are. If you can find one, of course.

Mccubbins

yeah definately 38. The frame just isn't worth that much trouble (hi-tensile, pressed head lug and dropouts) so I'll just put up wit the massively heavy BB and crankset I have. put some money into a future build.

thanks for your help guys!