Sram Force GXP BB Play

Discuss light weight issues concerning road bikes & parts.
jlok
Posts: 1058
Joined: Tue Jun 30, 2015 3:30 am

by jlok

I always think that the DS wavy washer is to gently push the DS dust cover against the bearing. Radial bearing doesn't like too much side load, correct?
Litespeed T1sl Disc / BMC TM02 < Giant Propel Advanced SL Disc 1 < Propel Adv < TCR Adv SL Disc < KTM Revelator Sky < CAAD 12 Disc < Domane S Disc < Alize < CAAD 10

TobinHatesYou
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by TobinHatesYou

jlok wrote:
Thu Jun 28, 2018 9:40 am
I always think that the DS wavy washer is to gently push the DS dust cover against the bearing. Radial bearing doesn't like too much side load, correct?

It's basically to discourage the bearings or pressed-in cups from being dislodged due to BB shell flex and other forces acting on the NDS bearing. It preloads the entire assembly sandwiched between the cranks.

by Weenie


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kkibbler
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by kkibbler

What kind of play? Lateral play? Radial?

Some photos would help a lot here.

Also...sure you are tightening the crank bolt and not the self-extracting cover by mistake?

foreigngreg
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Joined: Wed Jun 27, 2018 7:42 pm
Location: Bern Switzerland

by foreigngreg

@ kkibler:

Defo not tightening the cover, I would not have got anything close to 54Nm on that one I think ;-)

Play detected:
- Radial play at the drive side bearing.
- Very slight axial play detectable

I think this makes sense as the nds bearing is clamped on the inner ring by the nds crank arm (with the crank bolt). The inner ring of the ds bearing on the other hand just sits on the axle, no axial guidance. This means there is no preload: therefore play is inevitable.

I therefore just ordered a new crank bolt (could not find it in stock locally) and a wavvy spring washer, (FSA sell one with a 24mm id). My thiking is the following: I am getting play as it is not preloaded, if I want to eliminate play: preload the drive side bearing with a spring washer (just like on FSA cranks, and some Sram models), otherwise play is going to be unavoidable.

I do not understand why sram sell these without a spring washer, for me, this is a design flaw. Either that or if play is to be expected they should say so in their instructions...

Ill keep you updated on results once I get my parts (1 week or so).

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kkibbler
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by kkibbler

No, I’m fairly confident you have other things going wrong there. Short of factory defect, GXP on BSA is probably the most foolproof install among all the standards. Again, some photos would really help.

TobinHatesYou
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by TobinHatesYou

If you can detect radial play on the DS then that is very bizarre. Either the tolerances between spindle and inner race are bad, the bearing itself has radial play, the bearing is loose inside the external cup, etc.

Axial play would again be from the NDS side.

You say that axial play would be inevitable, but it would be immeasurably different than the axial play you'd experience with other BBs. The axial loads aren't that significant.

foreigngreg
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Joined: Wed Jun 27, 2018 7:42 pm
Location: Bern Switzerland

by foreigngreg

Yeah, the axial play is very minor, more radial play can be felt.

A visit to my LBS , got a new bolt for the crank, cant find any issues in how I mounted the crank. We found a bike in the shop with the same setup (BSA/GXP Rival), upon inspection, it also had a tiny bit radial of play. The guys from the shop say it happens on GXP, if really too much they reccomend to mount a shim on the drive-side spindle...

I measured the spindle and inner bearing races, both came close to +15um/-15um for the bearing and spindle, so play is not coming from the inner race. I think play is therefore coming from the bearings, as the ds bearing is free in the axial direction, therefore no preload. Bearings without preload have play, this is inevitable.

Interesting thing to point out; we often use bearing setups like on the GXP system in the industry, for applications with low axial loads: Bearing clamped on one side, and opposite bearing free on the shaft. The only difference is we always use preload (from the outside of the free bearing), as without it play is inevitable, furthermore, berings without preload get shock loaded if there is any sort of varying load.

All this to say: I think the play in the GXP system on BSA, as it is designed is normal. This is not ideal, and also will lead to poor bearing life. So for myself: I will mount a spring waved washer on the ds of the spindle (MW120) to get controlled preload, for now I have just slipped an o-ring on which seems to have eliminated play, so that can also work.

Intrerestingly, I just saw that Praxis also make a GXP compatible BB; their instructions indicate to mount with a spring waved washer on the ds spindle, so they also reccomend preload.

Anyways, sorry for the long-winded answer, for my part I am pretty dissapointed with the Sram GXP system as it is proposed for BSA, the reccomended setup is flawed at best and instructions are poor.

TobinHatesYou
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by TobinHatesYou

The Praxis M24 BSA BB probably doesn't use circlips to retain the bearings, so the wave washer is necessary.

I still find it odd that you're dogging GXP. It's honestly one of the best BB and spindle design combos in the industry.

foreigngreg
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Location: Bern Switzerland

by foreigngreg

GXP uses circlips? Mine did not have any, nor did the instructions specify any.

Actually, the press fit GXP uses a spring waved washer, so its really the BSA GXP that I do not understand.

TobinHatesYou
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by TobinHatesYou

foreigngreg wrote:
Fri Jun 29, 2018 8:33 am
GXP uses circlips? Mine did not have any, nor did the instructions specify any.

Actually, the press fit GXP uses a spring waved washer, so its really the BSA GXP that I do not understand.

Yes, with pressed in bearings, you use the wave washer. I have a Trek with BB90...I have a wave washer installed. With the SRAM branded GXP BSA BBs, the bearings are behind retaining clips and a wave washer is not necessary. It doesn't look like the Praxis M24 BSA BB uses retainer clips in the same fashion.

foreigngreg
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Joined: Wed Jun 27, 2018 7:42 pm
Location: Bern Switzerland

by foreigngreg

Huh, mine has a plastic spacer on the drive side, and a washer on the nds which fits on the spline and presses on the bearing race, exactly like shown here:
https://www.sram.com/sites/default/file ... nksets.pdf

The praxis I was talking about is this one:
https://praxiscycles.com/wp-content/upl ... A_Inst.pdf

Advertised to be GXP compatible, and uses a wavvy spring washer on the nds.

We must not be talking about the same versions, or is there something I missed?

TobinHatesYou
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by TobinHatesYou

Yes, they do not show the circlip in the exploded diagram of the BSA GXP BB. They don't even show the bearing. It's not really meant to be a serviceable part.

And no, the wave washer goes on the DS in the case of the Praxis BB. There is nothing to preload on the NDS. I feel like we are talking in circles now.

foreigngreg
Posts: 11
Joined: Wed Jun 27, 2018 7:42 pm
Location: Bern Switzerland

by foreigngreg

That was a type-o, I meant ds for the wave washer, otherwise you just crush it.

Ok for the circlip, I did not dismantle the BB cups (no reason to), so thats probably why I ded not see it.

Anyways: Install a wave washer on the ds of the GXP BSA setup, and voila, no more play! Works for me, then maybe some people don't mind the play, in any case installing the wave washer on the ds most likely improves bearing life.

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Juanmoretime
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by Juanmoretime

I’ve been riding GXP cranks for years. In the past the crank, not the bottom bracket, came with a wave washer and I have a wave washer on all my bikes. Some have a GXP BSA bottom brackets and one has a Wheels Manufacturer GXP adapter for BB30 using the wave washer. All spin freely with no play in them.
RESIDENT GRUMPY OLD MAN.

by Weenie


alcatraz
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Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Are you sure your left side bb bearing is gxp? It should have a very wide inner bearing race, be 22mm id and have a funny starlike looking dust cover.

I'd try to take the cup out (it's threaded right?) and try to clamp it in the crank. It should get clamped snugly when you use the right assembly.

If you have some weird kind of 22mm id bearing that isn't wide enough then you might need to add an appropriately sized 22mm steel washer to have it clamp the inner race. Pay attention to the play on the drive side when choosing the placement of the washer (outside/inside or both).

For DS radial play you must have a moving cup, cracked cup or busted bearing. Make sure to inspect it thoroughly and that it's torqued properly.

/a

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