SRAM GXP Tightening help

mitchgixer6

Hi all,

So I fitted my new SRAM S950 crankset a few weeks back and everything is running fine, no play etc. I have been wondering about my method in which I fitted it though.

First off I don't have a torque wrench, and don't have easy access to one. Torque advised on the bolt for fitting is 43-46 Nm. I have a slight idea about torques, and on a bike 43Nm seems about as tight as most bolts.

I have been questioning my fitment though as something weird happened whilst fitting. The bolt got to a point where it was tight, but not tight enough according to my calibrated elbow! At that point it loosened off a bit (still whilst tightening) and then got tighter again! I presumed this was normal having never fitted a SRAM chainset before.

The reason I started thinking about it was I read a lot of threads on fitment before doing it, and a lot of replies mentioned that they had to remove and refit a number of times due to there still being play in the cranks. This didn't happen with me, I though I had just lucked out and got it right first time, but the more I think about it the more I think maybe the correct torque was at that point before it loosened off, and if it's overtightened I don't want to be damaging the bearings etc.

So, can anyone offer me any advice from previous experience? Might be able to hold of a wrench, but it's a long shot.

sungod

as long as you've screwed the gxp cups in all the way, the torque on the centre bolt shouldn't affect bearing load, it's holding the two sides of the crankset together so needs a bit of oomph

the parts are a tight fit, otherwise there'd be play, so especially the first time you fit them you can get the tight/loose/tight as everything snugs up

mitchgixer6

Thanks mate.

Just had the arm off again to have a look. Nothing obviously wrong. Re-greased and fitted again, and this time it didn't do the tight/loose/tight thing, so reckon you've got it spot on there. Seems to be whored up pretty tight, so don't reckon it's about to fall off! Still can't get my head round how it doesn't side load the bearings (ala Hollowtech) though??

topdude

Still can't get my head round how it doesn't side load the bearings (ala Hollowtech) though??

With Shimano hollowtech the preload bolt squeezes the two BB bearings together, therefore the torque applied is critical.
With Sram GXP the axle has a shoulder which contacts the inside face of the L/H bearing, so tightening the bolt is only squeezing the bearings inner race not applying any sideways load.