Guys, I need help 🙁
Installing a replacement GXP bottom bracket on my gravel bike. It's a Planet X full monty with a 68mm shell and Sram apex crankset. BB is a new skylene, which is one of those HTII/ GXP compatible jobs. I have the shim to make the BB fit GXP installed from the inside of the non-drive side cup (checked 94 times as this is apparently a common mistake).
Done plenty of googling and apparently I don't need any spacers, but with everything torqued up, I've still got play in the crank. I initially put a spacer onto the drive side, thinking I was mistaken and ran it for a week, however the crank started to feel tight. Removing the spacer and it spins freely again, but still has play when tightened up.
One thing of worry, is I've seen people refer to a wavy spacer - can anyone confirm if I should have one on an Apex crankset? I'm wondering if I've lost that...
Is there anything else obvious I'm missing here?
I'm tempted to just try buying a genuine GXP one at this point, but not sure if it'll solve the problem....
Please help!
One thing of worry, is I’ve seen people refer to a wavy spacer – can anyone confirm if I should have one on an Apex crankset? I’m wondering if I’ve lost that…
This suggests you only need the wavy washer if it's PressFit GXP (p22).
How much play? I always feel like you have to torque SRAM cranks to infinity and beyond to get rid of all the play
tons, but looking at that link above, I'm missing the dust cover on the non drive side.... I'm hoping that could be it
I’ve always fitted the wavy washer to GXP as it’s the only way to compensate for axial float, plus it help load the outer bearing seals/keep the muck out. The problem with most HT2 BBs is the non-drive bearing isn’t designed to take any axial load (unlike GXP) and therefore if overloaded will fail rapidly. If the BB shell width is slightly over and the crank fully tightened then you’re asking the bearings to compensate - the extra NDS top hat spacer isn’t helping in this case. I would go back to the SRAM tech docs and check the BB shell width requirements.
I spent ages on this with my Tempest and Sram Red cranks when the sram BB died (which took less than a year). From what I remember, GXP works by locking the axle to one of the bearings (nds I think) and the other is axially free - so only one of the bearings sees axial load and the other is purely radial. The problem with HT2 type BBs is that they rely on a bit of axial compression as they are angular contact bearings (hence the preload tool you get with Shimano cranks). You can't really use this type of BB with GXP cranks and acheive the right preload.
I went for a Gusset GXP BB and it's been quite good for about 4000km so far.
Sorry I can't recall if the wavy washer was needed or not, but for a small outlay I'd probably just get a GXP specific BB. Gusset were very helpful when I called them up.
with a 68mm shell
apparently I don’t need any spacers
I could quite happily be wrong but I always thought HT/GXP (and compatible) BBs and chainsets were for a 73mm BB shell width so you're missing 5mm of spacers for your 68mm shell?
I could quite happily be wrong but I always thought HT/GXP (and compatible) BBs and chainsets were for a 73mm BB shell width so you’re missing 5mm of spacers for your 68mm shell?
Road chainsets are designed for a 68mm shell so no spacers required.
I use a wavy washer on my gxp cranks to keep the seal in place, it started wandering without it in place.
About 3 mins
Right, follow up in case anyone finds this with the same problem. I ordered a genuine Sram GXP BB and that came with the missing star shaped dust cover. As soon as that was added back between the non-drive side crank and BB cup, all the slop was gone. Hurrah!
Big thanks to everyone that helped out, particularly @frogstomp for the link that led to the lightbulb moment.
Cheers
From memory, it's the drive side of SRAM gxp bottom brackets that a loaded during use and the non drive side that floats about. It was always the non drive side bearing that failed though, don't know why 🤔
Makes sense now that people are using wavy compression washers to take up any slack from wear of the bearings and manufacturing imperfections. Wasn't aware of this option when I ran gxp bottom brackets.
I didn't need to run a wavy washer when I first installed my GXP cranks but when I switched them to another bike (same cranks and BB) the non drive side seal started wandering so I stuck a wavy washer in and it's been fine since
Nope, drive side was the floater. Hambini does a pretty good breakdown of how it works, and why it's flawed (with far more bad language than they allow here) on youtube, or as Sram GXP: an engineering guide on Hambini.com
That would actually better explain that most the wear was always on the non drive side bearing 🙃