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Really got myself confused with this one...
Trying to fit a cheap Truvativ crankset that I purchased second hand, but cant seem to get it to fit.
The problem seems to be that the non drive side bearing is to small for the shaft of the drive side crank to fit through.
Is this a problem with the non drive side bearing, or am I doing something wrong.
See photo bellow, the non drive side is the one at the bottom.
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Cant find any instructions on the sram website newer than 2004/5
This seems to be the right sort of thing, but dosnt say anything different to do.
Help!
On GXP bbs the drive side bearing is ever so slightly larger than the non drive side.. for absolutely no reason whatsoever. They just wanted to be different.
It looks like there's some kind of spacer in the bottom bearing. I've not had that much experience with GXP stuff so that may be normal.
Probably a silly question, but it is a Truvativ GXP chainset that you're fitting,isn't it?They aren't compatible with other makes as the smaller bearing gets clamped between a step on the axle and the left crank, allowing the other end to float on the axle, and removing the need for an exact BB shell width.
As before, you need a truvativ gxp crank to go with this BB.
On GXP bbs the drive side bearing is ever so slightly larger than the non drive side.. for absolutely no reason whatsoever. They just wanted to be different.
partly true: there is a corresponding 'step' on the spindle so that when you tighten up the crank bolt on the non drive side you just fasten it really tightly on to the non drive side bearing alone, rather than preloading both the bearings like you do with that little cap
thingy on shimano ones.
I would have thought that this was an attempt at avoiding ham fisted over-the-top side to side preload on the bearings (and an early death!) however truvativ gxp bottom brackets are nevertheless not renowned for their logevity, and there have been many stories on here of non drive side crank arms coming loose and then knackering th splines. So not an altogether successful design!
That said, I do have a set of gxp's that have enduro bearings in them now and have always been on nice and tight. I check the crank bolt every so often but it has never loosened in the 2 years I've had it.
[EDIT: oh, coatsey said it. In about a third as many words as me!]
Yes the crankset is GXP, so your saying that the BB is wrong?
Thanks for the responses guys!
Im very perplexed, yes the crankset is GXP.
Is there suppose to be a gap on the drive side between the crank arm and the bb then?
I dunno but when i saw the weight of the truvativ bottom bracket I almost fainted, no wonder my bike is so heavy.
the non drive side cup is supposed to be smaller.
The crank spindle passes through the drive side and butts up against the non-drive bb cup. You then fit the non-drive crank arm and torque to around 50Nm.
The idea here is that the cranks are secured from lateral play by 'pinching' both sides of just one BB cup. This as someone has already mentioned stops people over tightening shimano type cranksets. Also Truvativ claim that as there is absolutely no preload on the drive side bb it increased bearing life significantly.
The setup just looks a bit odd compared to shimano/raceface etc as there is a gap between the inner chainring and BB cup when its all fitted.
The gap shown in the following photo is normal?
If so means that cant use a chain device as the gap compleatly throws the spacing out.
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yes the gap is normal. It shouldnt effect fitting a chain device either. you can get the installation instructions from the sram website, as long as you fit the correct spacers it should be fine.
[i]Is there suppose to be a gap on the drive side between the crank arm and the bb then?[/i]
Bit of thread resurrection and, given the photos have gone, anyone help with the query above as I'm having the same problem with an oldish (2007) GXP chainset.
There seems to be a 5mm gap between the inner surface of the drive side crank and the external BB...is this normal? Looks like the BB should butt up against the side of the crank like the non-drive side.
Yes, supposed to be a gap there, the non drive bearing is clamped between the crank and the step on the axle,the drive side of the axle floats in it's bearing, so you can't over-preload the bearings.
Cheers coatsey...thats re-assuring as it just looks a bit odd.