[Help] Crank arm falling off

[Reme Le Hane]

Hey guys,

 

So this weekend past during the Oak Valley relay, my crank arm (Shimano XT) slipped off twice, was slipping off again but I kept it in check, but it seems simply tightening the bolts is not enough.

 

What is my next step, is there a DIY solution to this, or is this more of a mechanics fix?

 

Thanks

[NotSoBigBen]

Hey guys,

 

So this weekend past during the Oak Valley relay, my crank arm slipped off twice, was slipping off again but I kept it in check, but it seems simply tightening the bolts is not enough.

 

What is my next step, is there a DIY solution to this, or is this more of a mechanics fix?

 

Thanks

 

Would be helpful to say what crank (make/model) it is as there are a few different tightening options?

[Long Wheel Base]

Pictures please. Or like NSBB says, a more detailed description.

[Reme Le Hane]

Would be helpful to say what crank (make/model) it is as there are a few different tightening options?

 

Valid point, it is the Shimano XT

[Long Wheel Base]

Valid point, it is the Shimano XT

Is it the model that has 2 screws on the side of the left arm and then the cap screw in the middle going into the shaft(Which one piece with the drive side)?

[Reme Le Hane]

Is it the model that has 2 screws on the side of the left arm and then the cap screw in the middle going into the shaft(Which one piece with the drive side)?

 

I can confirm the 2 bolts on the side, but I know nothing about a cap screw, updated OP with a pic, its from the other side, but best I have access too from work so hope its of use.

[Martin PJ]

Have the same problem on my son's bike. It is SLX crank. I bought a cap screw from eBay, which is better than the one that comes with the crank, the original is plastic and is not designed to tighten much. The metal eBay part can be tightened with a big Allen key. I thought about using threadlock on the cap screw and also on the shaft where the left crank attaches. It that fails, I reckon I need to buy a new crank.

[JJDT]

This is the cap screw that Long Wheel Base referred to.

 

http://s700.photobucket.com/user/erikkellison/media/June%2021st%202010/Shimano-SLX-M660-175mm-Triple-Cr-1.jpg.html

 

http://i700.photobucket.com/albums/ww6/erikkellison/June%2021st%202010/Shimano-SLX-M660-175mm-Triple-Cr-1.jpg

[Jewbacca]

You lost your cap screw.

 

It is a black screw that pre loads the crank arm to the correct tension on the BB.

 

Procedure to installing XT cranks:

 

1. Insert drive side crank arm spindle through BB.

 

2. Make sure pinch bolts are loose.

 

3. Slide Non drive side crank arm onto spindle.

 

4. Use the correct tool or a butter knife to tension the black pre load cap.

 

5. Tension the 2 pinch bolts.

[cfcjim]

 

It'll tell you all about it.

 

Hopefully you'll notice what's different.

[Reme Le Hane]

This is the cap screw that Long Wheel Base referred to.

 

http://s700.photobucket.com/user/erikkellison/media/June%2021st%202010/Shimano-SLX-M660-175mm-Triple-Cr-1.jpg.html

 

That was definitely not there, I slipped the arm on, tightened the 2 bolts on the side and that was that.

[Reme Le Hane]

It'll tell you all about it.

 

Hopefully you'll notice what's different.

 

I was just watching that one now, and there was no crank cap. Looks like LBS for me later.

[the nerd]

Have the same problem on my son's bike. It is SLX crank. I bought a cap screw from eBay, which is better than the one that comes with the crank, the original is plastic and is not designed to tighten much. The metal eBay part can be tightened with a big Allen key. I thought about using threadlock on the cap screw and also on the shaft where the left crank attaches. It that fails, I reckon I need to buy a new crank.

 

Its not supposed to be tightened with an Allen Key... its only there for preload tension!

[Amberdrake]

The Crank Cap screw is not there to hold the crank in place.

DO NOT over tighten, it will strip and be useless (likely why its missing).

 

The crank cap screw is for preloading as mentioned before, then you clip in the little black safety clip between the bolts before tightening crank arm in place. 

 

Reason your arm falls off is likely due to play as preloading has not happened.

[Tomik]

The bolts are what tighten the crank arm onto the crank, not the big plastic tensioner. If teh two bolts don't work, then the splines might be stripped (which could've been caused by loose screws in the first place).

 

Or, by not tensioning the plastic "screw" properly, you mat have introduced some play into the crank which forced the arm off (and possibly damaged the splines too).

 

Best case, you need a plastic tensioner. Worst case, a new crank.

[Long Wheel Base]

I am pretty sure you won't have the tool to tighten the cap screw so probably best to get your LBS to do the whole job for you. 

Next problem for you will be, Does cool heat have stock of that item?

Like mentioned before that screw doesn't tighten the crank to the shaft, So you actually don't make it very tight as you could damage the BB but it all helps with keeping the crank on. In theory the crank shouldn't come off if those other 2 screws are tight enough.