I built a bike, second hand GX Crank kept coming loose. I put it down to the crack being nackered and bought a new replacement.

Has been fine for approx 350 miles and today I had to tighten it back up.

What am I doing wrong? It was torqued up properly when I put it together.

Cheers

Definitely tight enough? I had this issue (different SRAM crank though) and I just hadn’t tightened it up enough. You sure it is torqued enough?

If this has happened to the previous owner as well it’s possible the splines are damaged so it will keep doing this regardless of the torque.

Definitely tight enough? I had this issue (different SRAM crank though) and I just hadn’t tightened it up enough. You sure it is torqued enough?

Unless I looked the torque up wrong twice then it’s definitely tight enough. I didn’t have a torque wrench yesterday so just did it pretty tight, not f tight, which felt about right. And at the end of about 30k it was still tight. Will check it again when I get the bike back someone borrowing it.

If this has happened to the previous owner as well it’s possible the splines are damaged so it will keep doing this regardless of the torque.

That’s what I suspected, but new cranks are still doing the same. Which suggests it wasn’t a problem with the original cranks.

I’m wondering if there’s an issue with the bottom bracket width, it’s an Uberbike one that I think I put together properly.

SRAM cranks need tightening firmly so they bottom-out on the splines – there is no adjustment. Bottom bracket wouldn’t make any difference unless crank is bottoming out against cups – but it would be difficult to turn. You’d struggle to get that needed level of tightness needed with a regular Allen key or multitool.

Thanks. There’s no sign of the bearings getting crushed and it all turns freely etc. I guess the Allen key I borrowed yesterday was about 20cm so a reasonable size.

I won’t have the bike back for a few weeks unfortunately, I hope it doesn’t come loose and damage the splines in the mean time.

Does anyone know the torque for when I do get it back? To make sure I’m looking up the right one.

I think you have fallen prey to the ‘stupid **** design’ issue with GX cranks…..

They are not preload as a poster above correctly said. Unfortunately, they rely on a little sleeve thing that sits between the axle and the inner race of the bb bearing. You might not even notice it. In my experience, what happens is that the axle gets a bit cacky and the sleeve bit wears away. It then comes apart from the plate bit that acts as a bearing seal. When this happens, the axle can wiggle in the bearing.

A fix I have bodged is to have a rubber washing machine seal or two between the sleeve/seal thing and the crank arm. That way the sleeve/seal cannot wander out.

On later models SRAM specced a wavy washer to do this ‘bulking out’ and any engineer that specifies a wavy washer is essentially admitting there is a design flaw somewhere…….

My cranks did this and after a lot of messing about I noticed that the splines were knackered. New cranks solved the issue.

I had this problem and changed to
XT, no problems now.

My brief experience of SRAM cranks appears to be that you can have them in one of two states. Almost entirely seized – mine needed a long bar over the allen key to get off, or perpetually loosening off.

If they do come loose on a ride you are basically stuffed, unless you want to carry a monster allen key around to tighten them back up.

Mine are getting swapped for Shimano as soon as possible.

Does this apply to the DUB models too which have the same pre-tensioner thingy as RaceFace use on their Cinch cranks to take up the lateral play?

Not had any problem with mine yet but I’ve got the super heavy Eagle NX DUB Boost.

Incidentally the DUB BSA BB uses the same tool as the Cinch BB to remove it which is handy 🙂