Fitting a GXP SRAM Chainset

BlueNGT
BlueNGT Posts: 119
edited March 2018 in Workshop
I am fitting SRAM eTap and when the GXP Chainset is fitted the spindle is partly visible with a gap of about 5mm, or more, between the BB Cup outter edge and the left arm.

The bottom bracket is English Threaded

I currently have a Shimano Dura Ace BB fitted and understood this would be fine.

Are the bearing cups wider on a GXP bottom bracket than on a Shimano bottom bracket?

I cannot see why the SRAM Chainset does not tighten all the way to the cups. The spindle is the same length as the Shimano cranks (in fact the Shimano spindle is a few mm longer).

Any help very welcome!!!!

Comments

  • sandyballs
    sandyballs Posts: 577
    I’ve fitted many SRAM cranks press fit and English thread only ever using SRAM BBs with no issues, always torqued up perfectly so at a guess Shimano BB is your problem.
  • timothyw
    timothyw Posts: 2,482
    Yeah, it's not fine.

    Look at the picture of this bottom bracket - http://www.chainreactioncycles.com/sram ... -prod27856

    As you can see, the non drive side has a star type fitting. In GXP this is where the bottom bracket clamps onto.

    You have two choices;

    - Buy and fit a gxp bottom bracket. Eg this one http://www.chainreactioncycles.com/sram ... -prod55194
    - Buy an adapter to use your existing bottom bracket with the GXP fitting - eg this one - http://www.chainreactioncycles.com/hope ... -prod26899

    To be clear, I offer no guarantee that the Hope converter will work with anything other than a hope bottom bracket (ie your shimano one...)

    I'd just get a new BB personally, save the shimano one for another bike or sell it on (perhaps with your existing chainset?)
  • BlueNGT
    BlueNGT Posts: 119
    I see, the non-drive side has the outline of the splines within the cup!!

    I contacted C-Bear who also said the cups on the GXP are wider than the Shimano BB.
  • sungod
    sungod Posts: 17,338
    plus the gxp spindle is 24mm diameter on the drive side and 22mm on the non-drive side!

    just get a gxp bb
    my bike - faster than god's and twice as shiny
  • ryan_w-2
    ryan_w-2 Posts: 1,162
    What sungod said.

    NDS is 22mm diameter spindle on a GXP, your Shimano BB will be 24mm both sides.

    You need a GXP specific BB.
    Specialized Allez Sprint Disc --- Specialized S-Works SL7

    IG: RhinosWorkshop
  • paulbnix
    paulbnix Posts: 632
    Basically the gpx crank fits into a HT2 BB but that’s all it does.
    It’s not held properly and will slide from side to side.
    As above the options are a SRAM gpx BB or you can use a Hope HT2 BB with a gpx / truvativ adapter.
  • radhartgeorge
    radhartgeorge Posts: 37
    Hi folks,

    So I have a a related issue... I’m attempting to fit a SRAM exogram crankset into a Hope BB with GXP adapter. This is my first time straying from Shimano.

    The adapter was successfully fitted (with notch). The BB screwed into the cleaned and greased B.B. shell beautifully. The axle connected to the drive side crank arm (with chainrings) glides into the BB and the non-drive side crank slots onto the teeth just as it should do. All good so far. However when I start to tighten the non drive side crank to the drive side crank everything becomes unacceptably stiff.

    In terms of spacers on the B.B. I have followed the Hope instructions for 68mm shells - 2 spacers on the drive side and 1 spacer on the non-drive side.

    Anyone else have this issue?!

    Thanks
  • timothyw
    timothyw Posts: 2,482
    Most likely explanation is that you have more spacers than you need, one way or another.

    The GXP system clamps the axle onto the non drive side, preventing the axle from sliding from side to side at that one point.

    Shimano clamp across both the drive and non drive side cups - preloading the bearings a small amount, and preventing side to side movement - the shimano system basically works in the same way as threadless stems, with the plastic bolt working like the top cap in providing preload, which is then secured with the two allen bolts which hold the non drive crank in that position, without applying any more force to the bearings.

    If you have too many spacers then it might be that you tightening the bolt is pulling the drive side of the cranks into the bearing there, before it is clamping on the non drive side - causing the system to seize up.

    You can verify this is the case by removing the bottom bracket, and threading the cranks only into the non drive side - you should be able to tighten up the bolt to a good level of torque without it affecting the smoothness of rotation (and as you tighten up you should find that side to side play is near eliminated).

    If the non drive side seizes up just by you tightening up the cranks, then that would imply that you've fitted the adaptor wrong - it might be worth seeking clarification from hope in that case.
  • ryan_w-2
    ryan_w-2 Posts: 1,162
    Too many spacers, 100%.

    Take ALL the spacers out. Tighten the crank bolt and see how much play you have.

    Remove cranks, add relative spacer (1 or 2mm less than required), then use preload adjuster to take up small amount of slack.
    Specialized Allez Sprint Disc --- Specialized S-Works SL7

    IG: RhinosWorkshop
  • paulbnix
    paulbnix Posts: 632
    Ryan_W wrote:
    ...then use preload adjuster to take up small amount of slack.

    Sorry but there is no preload adjuster on a gpx crankset. You don’t need one.
  • radhartgeorge
    radhartgeorge Posts: 37
    Thanks for the ideas guys.

    I tried taking one spacer out from the drive side (so now there was one 2.5mm spacer each side) and although things improved slightly - i could tighten up the axle bolt on the non-drive side more before the stiffness started- it was far from resolved.

    I thought that the issue would go if I removed yet another spacer from the Hope BB but after I did this the Hope BB would not tighten fully into the BB shell as the central tube of the BB was in the way. As a result there was a small gap- approximately the size of the spacer (2.5mm or so) where the spacer was!

    Stood there staring at it for 10 mins wondering if I’m being stupid - By the feel of it, I need to remove a spacer but clearly can’t be putting up with gaps!

    Any more ideas?
  • radhartgeorge
    radhartgeorge Posts: 37
    @TimothyW - I’ve now re-read your post and have twigged what your saying. Will try that tomorrow.
  • ryan_w-2
    ryan_w-2 Posts: 1,162
    Firstly, take ALL the spacers out and see if it spins freely.

    You need to narrow down what’s causing it.
    Specialized Allez Sprint Disc --- Specialized S-Works SL7

    IG: RhinosWorkshop
  • paulbnix
    paulbnix Posts: 632
    radhartgeorge wrote:
    I thought that the issue would go if I removed yet another spacer from the Hope BB but after I did this the Hope BB would not tighten fully into the BB shell as the central tube of the BB was in the way. As a result there was a small gap- approximately the size of the spacer (2.5mm or so) where the spacer was!

    Any more ideas?

    That was not the case when I fitted my hope bb. I could fit both sides with no spacers and the tube between them. I think you have the wrong length of aluminium tube.
  • radhartgeorge
    radhartgeorge Posts: 37
    @paulbnix Your comment was the inspiration that resolved this problem!! Thank you. I just called Hope and explained the situation. When I told them that I had installed the BB as per the instructions with 2 x 2.5mm spacers one side and 1 2.5mm spacer on the non-drive side they stopped me and told me that I have the MTB version! The road version has a shorter aluminium tube and comes with 2 x 1mm spacers!

    I checked my order with Evans Cycles (forgive me - my hand was forced through the Ride-to-Work scheme) and they sent me the wrong one! Fortunately Hope are exchanging the centre tube and spacers directly.

    Problem solved - many thanks for all your help.
  • timothyw
    timothyw Posts: 2,482
    Mmm, when I heard about the overlong tube I thought that sounded rather odd for a road setup! Glad it's sorted.
  • paulbnix
    paulbnix Posts: 632
    That’s good. It was your description of fitting a spacer between the bb shell and the frame that gave the clue :D
  • radhartgeorge
    radhartgeorge Posts: 37
    With a heavy heart I am coming back to this thread!

    Got the replacement parts from Hope who exchanged the tube for a shorter one and swapped the 3 x 2.5mm spacers for 2 x 1mm spacers.

    When I tried installing it, while it was MUCH closer than the previous attempt and while there was no concerning resistance as I had previously when the whole chainset was tightened up there remained a gap of approx. 1mm and correspondingly there was some horizontal play - if i held the spider and pushed/pulled in and out the whole chainset could be rattled (for lack of a better word). Clearly not what I was hoping for when I opted for a 'good' BB over the standard SRAM version.

    I called Hope and they insist that I just need to tighten the non-drive side more until the slack is taken up but I think I am already at the recommended torque setting of 13-15 Nm. Unfortunately I don't have an 8mm bit for my torque wrench (one is now on order) but using my long handled hex alan key I tightened it more than I felt comfortable doing and the gap remained. Once the bit arrives I can confirm this part but don't want to strip the thread on my brand new chainset!

    In any case, having been prevented from cycling for 2 weeks now, I've now ordered the standard SRAM Team BB to identify if it's the BB or the chainset that is at fault.

    Anyone else have this issue?
  • ryan_w-2
    ryan_w-2 Posts: 1,162
    Strange.

    So it’s free spinning now but with some lateral play?

    You could try a cheap fix of a wavey washer?
    Specialized Allez Sprint Disc --- Specialized S-Works SL7

    IG: RhinosWorkshop
  • radhartgeorge
    radhartgeorge Posts: 37
    'Spinning freely' is unfortunately a subjective term. I had rather quixotically imagined that once installed my expensive Hope BB that I might be able to gently spin the crank arms (with no chain attached) and they continue spinning for 30 seconds or so - I would then be comfortable knowing that I'm losing very few watts due to the various interference fits that make up a BB. Unfortunately this is already far from reality - it revolves perhaps 5 times and comes to a stop. Is something wrong or are my expectations unattainable?!
  • timothyw
    timothyw Posts: 2,482
    Chainset freely spinning for 30 seconds or so?

    Yeah, I mean, i've never dropped £100 on a bottom bracket, but that sounds like a pretty unattainable goal.

    Chainsets are pretty inherently unbalanced when you think about it - one side the load sticks out one way, the other side it's the other way....

    I think a few complete revolutions, and not making any horrible noises when you are actually riding the thing, that's what I aim for.
  • paulbnix
    paulbnix Posts: 632
    I don't know where you got the 13-15 nm torque from but I've seen 34-41 quoted.

    Basically all you are doing is clamping the nds crank and the step on the axle around the gpx adapter you fitted to the Hope BB.

    To be honest I wouldn't bother with a torque wrench - just tighten it until it stops moving. It does take a lot of force but you are tightening a reasonably sized bolt into a load of metal - you are not going to break it.

    I seem to remember mine moved after I first fitted it so I used a bigger handle on the allen key.
  • sungod
    sungod Posts: 17,338
    unless the bb has no seals and is only lightly lubricated, 5-6 revs is the most i'd expect, so no issue with that, if there's fresh grease to be squished out it can be fewer, anything under 3 and i'd wonder why

    depends on the crankset's moment of inertia and how much oomph you use to get it spinning, but the numbers above are reasonable i think

    afaik correct torque on the gxp crank bolt is c. 50Nm, if it's only tightened to 13-15 it probably isn't clamping on the bearing
    my bike - faster than god's and twice as shiny
  • svetty
    svetty Posts: 1,904
    The 'spinning cranks' is more a reflection of the seals on the bearings than the bearings themselves. 5 complete revolutions is more than I would generally expect TBH. Once you've given the bolt a bit more welly and cinched down the NDS you might find this drops - I usually see 2 revs on a newly fitted crank with fresh Hope bearings. This increases over time as the BB wears and the seals get less draggy. Either way it's a fraction of a watt and nothing to worry about.
    FFS! Harden up and grow a pair :D
  • joey54321
    joey54321 Posts: 1,297
    30s sounds incredibly unattainable. I'd say you should be counting in revolutions rather than seconds.
  • ryan_w-2
    ryan_w-2 Posts: 1,162
    My £350 CeramicSpeed coated BB spins maybe 5-7 seconds.

    You’ve been watching too many YouTube videos.
    Specialized Allez Sprint Disc --- Specialized S-Works SL7

    IG: RhinosWorkshop
  • timothyw
    timothyw Posts: 2,482
    Ryan_W wrote:
    My £350 CeramicSpeed coated BB spins maybe 5-7 seconds.

    You’ve been watching too many YouTube videos.
    Coated in what? Gold and Diamonds? :P
  • whyamihere
    whyamihere Posts: 7,715
    There's 2 torque specs printed on the cap of a GXP crank... One of them is 12-15 Nm, which is the fitting of the cap into the crank arm - This keeps the bolt captive, and allows removal of the crank arm. The other is 48-54 Nm on all the ones I have within easy reach, which is for tightening the crank arm onto the spindle.
  • radhartgeorge
    radhartgeorge Posts: 37
    @whyamihere You are right - I was reading the wrong torque settings. I've now tightened it up to 50Nm and everything is snug.

    @Svetty you are also right- the revolutions have dropped to 2-3 now that things are tight.

    Thanks everyone for your help - when things aren't going to plan the garage at midnight at sub-zero temperatures is a fairly unpleasant place but the helpful comments, ideas and experience from this forum really helped.

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