Bottom Bracket for M2000 (70x122, BC 1.37x24T)

[Andy Huang]

I acquired my third Cannondale, an M2000 with a Manitou fork, as a frameset and need to build it up. As always, Cannondale's innovativeness means a lot of scrambling. Right now I'm stuck on finding a bottom bracket. It's a 70mm shell and a test fitting of a Shimano 68x122 UN55 with a triple Sugino shows the right alignment of rings and gears and sufficient left crank clearance. But I can't figure out where I'll find a 70 x 122 BC 1.37 24TPI bottom bracket! It seems that the 70x122 is mostly an Italian size (36mm x 24TPI). Does anybody have a recommendation for a source to search?

First Cannondale is an M200 currently as a daily rider.
Second is a SystemSix race bike, built up DuraAce from a frameset
The M2000 will be a fast and comfortable all road bike - dropped bars, compass tires

 

[black lightning 1987]

Sure that you have a 70 mm shell? I've never seen a Cannondale that had a 70 mm shell. If it is in fact 70 mm and has English threading, have a bike shop face the shell down to 68 mm. You could also run a Phil Wood or similar type bottom bracket. It (like some other brands) has no ledges on the cups. The outside faces of the cups can be recessed into the shell as long as the spindle is long enough to keep the crank from contacting anything. You can also shift the whole BB sideways to adjust chainline.

 

[Andy Huang]

Thanks for the response!

Yes, I put a caliper to the shell and it was 70mm. In addition, when I installed the 68mm BB (clearly English with LH thread on the right), with both retainers snugged tight (no gap to the shell), I could see a gap between the inner race and the left cup.

Facing 1mm off both sides is a thought, it would make future maintenance easier. It would put the spindle 1mm to the left, a minor change to the chainline and more crank clearance on the left.

I'm not considering spending a lot on this project so the Phil Wood is out. But perhaps I'll take the shoulder off the plastic left cup so that I can sink it 2mm inside the shell.

Still, I wonder what Cannondale used originally.

 

[black lightning 1987]

The only explanation I can offer is that the BB shell didn't get faced to the right width during the production process. You haven't provided the year of the bike but I'm guessing that it's 1992-3. Shimano BB-UN70 was the BB that was specified for the XT equipped bikes at the time. The UN70 was replaced by the UN71 around 1994 along with the UN51, which was the contemporary LX bottom bracket. Both the 71 and 51 have a left hand cup that lacks a shoulder, so either should work fine in a wider shell as long as the right hand cup placement gives you a good chainline. I have much later NOS UN26 122.5 BBs on hand but I'm pretty sure that they are made for E type front derailleurs and would require a spacer under the drive side cup if used with a clamp-on front derailleur. Dirt cheap though.

 

[Andy Huang]

Good call on the year - the seller didn't identify the year but looking through the catalogs shows a match to the 92 M2000s.

FWIW, the serial number is 51801933828, but most important is your clue that the UN71 and UN51 don't have a flange on the left cup to take up the extra room from a 68 cartridge. That means that I can stop looking for a 70x122 BC cartridge and modify a 68 to work. Shouldn't be hard - either find a cup from a 71/51, or trim off the shoulder from the one I have.

Thanks for the knowledge/experience!