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Hi All,

I have a customer that wants me to change the type of bottom brackets from a 10 years old Burley Rumba tandem. They are currently press fitted bearing using a square taper axle and they want to upgrade their cranksets.

I had the frame in the shop for about 1/2 hour and here's what I think I can do.

The rear BB shell is 83 mm wide, so I'll remove 5mm off both sides and braze a 73mm bb shell inside.

For the front BB shell (the excentric) I would trim around 10mm off both sides and take a standard excentric bb shell machined to the smaller ID of the Burley. I will probably loose a little in adjustment but with a half link I think we would be able to do something good. Or should I just take the front BB off with a hole saw and put a phil wood BB shell?

If you have performed or know someone who had performed such a modification let me know if I'm on the right path.


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