Can anyone give me any ideas as to why my drive side Crank arm keeps working itself loose, to the point if I didn’t have a chain guide on it would fall off

2 of the last 4 rides its worked itself totally loose from 50nm

I have checked and checked everything and it all fits fine, it’s all nice and tight by feel and no play once it’s tightened up

The threads look fine on it and it tightens up to a solid stop once at around 40-50nm

Cant understand what else is going on

Any ideas

Use a drop of loctite 234 on the bolt

You mean on the threads, it’s a self extracting type jobby, never had this before and it’s only just started doing it Ivd had them 5 months so it’s a bit odd all of a sudden

I can never get mine off! Irrespective of what I torque them to or what I grease them with they seem to be self tightening.

I used to have some Sixc cranks (very similar design) that were ace in comparison.

Is the preload adjuster wound out on the NDS before fitting onto the DS splines? And are you sure you’re putting 50nm through them? Worth checking the ds splines for any sign of damage.

I’d hesitate to put loctite on the splines – it’s hard enough to get the buggers undone as it is.

^ this.
They are normally very hard to get off, not falling off by themselves.

Is the bolt in good condition?

Yep like you guys that’s what makes it odder, I used to have a right bastard time getting them off when i first had them to the point I felt like I was gonna snap something

Now they tighten up to 50nm (torque wrench) and then I check make sure its as tight as can get and then I can now easily undo them, still have to put force through but they do come undone way easier than I remember which is odd

The threads look perfect to me and it all lines up fine

Preload it’s wound out all the way out then I tighten up the Crank to 50nm then do wind the preload in till it just about touches and takes out the play

Again all as normal as I’ve ever done without this happening

The threads look absolutely fine to me and there’s nothing odd or odd noises when they are correctly first installed again

Hmmmm

And as above I’d have thought as pedalling it would tighten it up if anything not loosen them!?

Bump incase anyone else has had this problem

If its been ridden loose the splines can be deformed and it will keep coming loose.

Bugger!

How would they have worked loose in the first place tho?

Sounds likely something like that has happened to them then

Is it likely be a warranty issue or not?

Not dub but my current bike used to work the crank arm loose continuously which is the raceface type with self extracting bolts. Turns out I hadn’t really put enough torque on them and I hadn’t put any threadlock on which seems to have fixed the problem. They need to be tighter than you think – are you using a torque wrench?

Yep using a torque wrench

And then double double cranking it up after with just a long 8mm hex

Something isn’t quite right as never had to loctite it before the are renowned for being a absolute bugger to get off even below the recommended torque

I’ve never really spent enough (or had enough) time to have a proper look at how they work.

Does the spline have a slight taper on it from memory? I’d be checking the ds crank arm for cracks on the splines which would open up when torqued.

I lag mine with grease during assembly, if you do the same I’d try assembling it dry and try it for a ride to see if it made any difference.

The only other thing I can think of without having it in front of me is if the cap is bottoming out in the axle thread and coming up to torque before the ds arm is properly seated on to the axle leaving it free enough to work loose.

not sure on the spline being tapered, I haven’t got it to hand either as its been cleaned and put back together

i’ve not added any grease this time (I usually do the same as you and grease everything on it) so will see if it makes a difference or not

the crank comes to a firm stop (like normal) when torqueing it up, so nothing obvious like its spinning for ages and ages before (like the threads are gone somehow)

its pretty **** though if its only lasting 2 rides before it completely falls off

I have no idea whether this is a warranty thing or not but ive never had it before on any other crank 🙁

Had this before with a set of cranks dude. Sram warrantied them for me no problem. Let me know If you want them sending back and ill happily sort them for you.

Yo Pete that’s mega kind of you dude, was it on a dub version?

They started to come loose after 14 miles the other night after tightening them right before the ride so they are defo ****

Means buying something else to keep me riding in the mean time which is pretty frustrating

But nice one for offer mate hopefully lbs will sort me but if not ill be in touch