dsmyers

Hi all,
I recently purchased a Truvativ GXP-based tandem crankset off of ebay, and I'm having an odd problem with one of the two bottom brackets. Both the captain's and stoker's crankset will install properly in one of the BBs, but neither will install in the other. The problem that occurs is that the "pipe" of the crankarm will not pass through the bottom bracket--the opening seems to be a millimeter or so too small, although both BBs look superficially similar. Is it possible that the BB is defective? Are there two generations of GXP BBs or something? I'm not at all familiar with the system.

Thanks,
Daniel

pmt

The GXP bottom bracket has a shim installed on the left (non drive) side. Normally, a GXP-compatible crankset is slightly smaller on that side, and so fits correctly.

Are you sure the cranks are actually GXP-compatible? Labeled as such? What brand and model?

If not, if they are like Shimano Hollowtech II (uniform diameter axle), then you just press out the shim from the left side, and you're all set.

HillRider

I wonder if you got two standard single-style cranks. The captain's crank obviously installs "backwards", i.e. with the chainring to the left, and if the spindle isn't set up properly it won't fit through the cups in reverse orientation.

pmt

Oh, that's a good point. Perhaps the spacer has to be pressed out of the left side, and put into the right side. Then it should be ok, if that's indeed the problem.

HillRider

One other point. A true captains's crank will have left-hand pedal threads on the chainring side. If the crank you get has right-hand pedal threads on the chainring side, you have the wrong type of crank.