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BB spacing question with BB mounted guide.

nowlan

Monkey
Jul 30, 2008
496
2
I am trying to install a new external BB on my Tracer. Its 73mm and I am using a BB mounted MRP lopes guide. For some reason I can not get my Truvative stylo Cranks to sit perfectly flush to the drive side of the BB. I can get it to sit flush with a spacer on the non drive side, but when I torque it down the cranks wont budge. I know its a spacing issue, and I know the BB i have is meant for 73mm.

Any ideas? Also, would running my cranks on the drive side about 3mm non flush with the drive side BB be bad? I am assuming it would. Just curious.
 

Dogboy

Turbo Monkey
Apr 12, 2004
3,135
273
Chapel Hill, NC
If I remember correctly the GXP BB uses 2 spacers (1 per side) on a 68mm BB shell and no spacers on a 73mm shell. That would mean using a BB mount chainguide will not work on a 73mm shell with that BB. Hope this helps - and I am remembering it right.
 

nowlan

Monkey
Jul 30, 2008
496
2
Ya I think your right man, it doesn't seem to be working out no matter what spacing configuration I use.
 

Racebike

Monkey
Jul 28, 2008
463
4
Sweden
Just a FYI, Truvativ cranks often have a gap between the bottom bracket and the RH crank even when tightened up.

If the BB is spaced so the RH arm presses against the RH seal/bearing the cranks will not turn well, or at all.

So, if you have the chain guide installed and still see a small gap between the RH crank and the RH seal, no problem.
 

nowlan

Monkey
Jul 30, 2008
496
2
The gap is aprox 3mm. I was thinking this would created more force on the bearings.
I am going to put the old BB on tomorrow and see if there is a noticeable gap. The 2 BB's are slightly different but both SRAM. Either way thanks for the info.
 

nowlan

Monkey
Jul 30, 2008
496
2
What it ended up being, was that the inner side of my crank arm was sitting flush to the BB outer race when fully compressed, and not against the inner bearing like it should. A few smaller spacers against the crank arm itself did the trick.