This afternoon's ride was supposed to be a nice 4 hours blast, but it wasn't!!

Non drive side crank arm worked itself loose 4 times. In the last 3-4 years the bike hasn't given me a single problem and now it wants to spit off the crank arm.

I put it back and tighten the bolts and within half an hour its working itself loose again. Fortunately I was on gentle climbs and sat in the saddle each time it came off.

What causes it? Old age? Is it time to buy new cranks? New BB? What exactly is the problem?
A bit of Loctite on the bolts? Which Loctite???

what type?

Shimano HT2.

Pinch bolts not tight enough. What condition are the splines in now?

Pinch bolts were, when retightened, nice and tight! It didn't crunch through the splines, just slid off! Splines look fine.

Where's the end-cap?

Somewhere in the forest! It fell off during a descent… But that isn't going to stop the crank from falling off, is it?

yes.

You need a new mechanic.

How?

Is there a piece of stone/grit in the split which the crank bolts tighten up (thus stopping the bolts being able to be tightened sufficiently) ? Can't think of any other reason why the crank would come off.

If the pinch bolts were tight the end cap couldn't have fallen off, surely, as the NDS crank clamps the end cap when the pinch bolts are tightened.

The end cap is held on place when the pinch bolts are tightened, which means the axle is clamped in place by the pinch bolts and prevented from moving out-over by the end-cap. The end-cap should not have been able to come off if the pinch bolts were properly tightened.

EDIT pardon me Naranjada, we were typing at the same time.

It's not just a cap, its the preloader. Pushes the arm on to the spline and preloads the bb. Without it it's not being pushed together. I know, you think the pinch bolts would hold it on but they wont with out the end cap especially if they have come loose a couple of times.
Here you go.
http://www.chainreactioncycles.com/Models.aspx?ModelID=5095

If the splines are greased and slippy (in a normal situation) and you doing high torque then the end cap not being there I would think it could slip off esp if the cranks are old – I'd buy a new end cap – try that and if they still slip off then maybe the splines are worn?

Buy a new end cap (£2), strip, clean, reassemble and it'll be as good as it was.

I thought that too. There's a bit of dried mud but nothing that looks like it's preventing the bolts from pinching. That doesn't explain why it fell off the first time when the end cap was in place and there's been no movement for the last couple of years.
I assumed something had worn out, I guess not.

If consensus is that the bolts are not holding, I can get them tight and they seemto work themselves loose, then a spot of threadlock will do the job.

EDIT: I'll have a look for and end cap and see what happens, thanks.

The end cap fell off the last time because the pinch bolts weren't tight enough or it fell apart. There is no other explanation.

As others have said. Something seems to be preventing the lock studs pulling the crank together hard enough to grip on. Threadlock them in. If you take the arm off and tighten the bolts can you see the gap closing up? Maybe the bolts are bottoming out too soon? The tight lock bolts should serve to lock the pre-load cap in as well as holding the crank on. As the cap also butts on a seat on the crank and screws in to the spindle it should hold the arm on to a deg even if the pinch bolts slacken off.

Really good clean of everything, check threads, splines and get a new preload cap.

try that and if they still slip off then maybe the splines are worn?

The splines wouldn't appear to be worn, in that there is no play in the crank, but they are old so a possibility. Worn splines would cause the crank to slip under stress and not necessarily slip off, wouldn't they?

Blonde moment!!! 😆

New end cap on Monday.

Splines may be damaged, even if it's not obvious

Look here numpty. You do up the end cap first. Then the pinch bolts. The pinch bolts don't hold the end cap on and the end cap doesn't keep the pinch bolts tight. They just work together. Buy a new one and try it. Jeeze.

The pinch bolts don't hold the end cap on…

Yes they do. The end-cap should not be removable when the pinch bolts are tight.

Look here numpty.

No need for that capullo! 😀

Error realised and corrected. 😀

If you can't offer help with grace don't bother…

g-force mebby, did you do any fast right hand corners or berms ?

goog – Member

g-force mebby, did you do any fast right hand corners or berms ?

Good point, I do find that mountains tend to move under the force of my cornering… 😆

Three_Fish
You can remove the cap when the bolts are done up. Try it!

don simon – Member

If you can't offer help with grace don't bother…
Ahem!

TheSwede – Member

It's not just a cap, its the preloader. Pushes the arm on to the spline and preloads the bb. Without it it's not being pushed together. I know, you think the pinch bolts would hold it on but they wont with out the end cap especially if they have come loose a couple of times.
Here you go.
http://www.chainreactioncycles.com/Models.aspx?ModelID=5095

It was the numpty comment I was referring to.

Chill.

I was being polite. 😉

😆 😆 😆 😆 😆 😆 😆 😆 😆 😆 😆 🙄

Don't wear out the lol smilie you selfish bastard. That's 15 on your own post. We have to share him.

You can remove the cap when the bolts are done up. Try it!

Yeh you can but I wouldn't leave it off 🙂 Another smiley used – oops 😯

You can remove the cap when the bolts are done up. Try it!

I have three XT, one SLX, one Hone and one Saint HTII cranksets. Not one of them can have the end-cap removed when the pinch bolts are tightened. The LH crank is recessed to clamp the end-cap when the pinch bolts are tightened.

TheSwede – Member

Don't wear out the lol smilie you selfish bastard. That's 15 on your own post. We have to share him.

Whay are you giving me a bad time? What did I do to deserve being called a numpty (or w**ker, or f***wit, or k**bend,) ?

Whay are you giving me a bad time

This is singletrack not MBUK!

What did I do to deserve being called a numpty

What causes it? Old age? Is it time to buy new cranks? New BB? What exactly is the problem?

Its you I'm afraid. 😉

You're fu**ing strange. 😉

Can't argue with that one

You can remove the cap when the bolts are done up. Try it!

Yup he's right you cant take the cap off when the bolts are tight – I just tried it on and XT and Ultegra crank – never tried before – oops. Anyway that means there is something major up with your setup Don. Follow this if it helps when you get a new crank cap? Its HTII although a road setup but is exactly the same method!

http://www.cyclistno1.co.uk/features/maintenance/shimano-ultegra-hollowtech-ii-crank-service.htm

Cheers foxyrider, as I said above it'll be a new cap on Monday. I guess something must have been loose to begin with to make the crank fall off first time. When it was put back on, with end cap, I can only assume it wasn't tightened enough as trailside repair was done with one of these.

Now, should I get in touch with the shop that sold it to me and get some money back as they clearly not fit for purpose? 😉

LOL @ Don