pstock

I am having a bit of if trouble with my LH crank arm coming loose.
I think this is the Hollowtech Correction: SRAM GXP system - outboard cups, splined BB axle - except that one inner bolt threads into the axle pulling the crank arm tight. The outer piece threads into the crank arm hole itself, like an old style dust cap.

But with that outer piece just snug my crank arm keeps loosening off.

So i am wondering if the outer cap is not just for show but needs to be cinched down very tight too, to maybe prevent the inner bolt from backing off...

choddo

I don’t think that’s hollowtech II. Seems to work more like GXP. I think that end cap has to be tightened very tight, like 30-40Nm with an 8mm but I’d be looking for official guidance.

pstock

You are correct. GXP.
and the manual seems to call for a #8 tightened to 48-54 N-m
(though this instruction sheet doesn't really show two NDS bolts. I might have the wrong instruction sheet.)

Iride01 

Whatever that crank is, it looks like that is supposed to be a self extracting crank. The thing you are calling a cover is what you stick a hex key through to get to the crank arm bolt. When you unscrew the crank arm bolt it applies force against that "cover" and pushes the crank arm off the spindle.

I'm wondering if your spindle is too short for that BB shell or do you have spacers under the external cups that shouldn't be there for your particular BB shell and it's not letting you get the crank arm all the way on the spindle.

Is this crankset and BB original to the bike or added later?

choddo

Think there’s only one bolt, integrated into the arm, with 10mm and 8mm interfaces. It should screw into an interior thread on the spindle, pulling the arm tight against the BB.

On mine, it has two torques printed on the arm, much higher for 8mm, like you have a choice between them, which honestly I don’t understand and just always use 8 as the 10 is pretty shallow.

Normally there’s a wave washer under the nds crank arm (maybe it’s on the drive side actually, think I slid it onto the spindle) and iirc a washer that prevents the bearing outer race being contacted.

Kontact

You guys don't know what you are talking about.

The 8mm is the crank bolt. The 10mm is the extractor cap.

If the bike uses external bearings, the drive side should have no spacers or washers.

There are directions available.

mpetry912 

thanks for that, I had not seen this one either. Makes sense A different twist on the "self extracting" idea.

/markp

79pmooney

@Kontact, question. Is this like the old square taper where the cranks tend to "rock" and loosen the snug fit against the bolt when the bike is ridden? (With the square taper cranks, each time you re-tighten to the proper initial torque, you push the crank a little further in onto the taper. Eventually, you can push the crank in so far it cracks; the cracks starting at the corners of the taper square.

So, any danger of doing damage by being "too careful" and repeatably tightening the bolt to spec?

Kontact

No, that doesn't seem to be a thing with splined spindles.

I don't know what is wrong with the OPs cranks, but given that people seem to have little understanding of how GXP works, he could be tightening the 10mm cap, or have a bunch of spacers on the drive side that are interfering with getting the crank tight.

GXP has as stepped spindle. The spindle goes through the right bearing and just floats. The step butts up against the inside of the left bearing and the left crankarm butts up against the outside of the left bearing. The crank bolt just pinches the left bearing between the spindle step and the crank arm.

There should be a splined bearing cover on the left between bearing and crank. There should be nothing on the right - the right bearing has a built in cover. If you put spacers on the right you might be compressing them as you tighten the fixing bolt rather than pinching the left bearing.



The above is how it works with threaded external cups. With various internal bearing systems that press into the frame, the attachment is all the same but a spacer and wave spring is used on the right side to keep the left bearing from drifting to the left out of the frame.

choddo

Entirely possible
hmm, I need to look at mine again. Didn’t touch the 10mm last time. Wonder if that’s a problem. Ridden a lot on it and never noticed an issue.
Mine’s internal pressfit bearings so that makes sense.


No it was me who said that, not him.

oldbobcat

Hand-tight should be sufficient to keep the extractor nut from rattling loose. Always make sure it's tight and clean before trying to remove the crank. I like to make sure the threads and interface with the crank bolt are thoroughly greased.

FBinNY 

I prefer something beyond hand tight to keep it from walking back when pulling the crank.

Likewise, be sure to grease as noted for the same reason.

oldbobcat

I was actually thinking about one good yank with the Allen wrench.

Kontact

It has a torque rating.

oldbobcat

Thanks. I'll look it up on my way out.

Kontact

Might be printed on the cap itself.

oldbobcat

Not SRAM 2x10.

tFUnK

The outer cover enables the self extraction, but it also helps keep the crank bolt (the bolt that threads onto the spindle) in place. The outer cover doesn't need to be super tight but it definitely should be tighter than finger tight. Torque it down a bit with the crank arm off the spindle (this ensures there's no room for the crank bolt itself to "walk" its way loose during normal use (which is what I suspect might be happening), and then torque down the crank bolt to spec onto the spindle.

choddo

I just took a look at mine (which is a Quarq power crank but I suspect they are the same spec) and it says 12-15Nm for the 10mmcap, now that I understand what it is.
That’s pretty damn tight.

pstock

I am back. (sorry, I seem to have have had Notifications turned on for this thread)
indeed it is 8mm for the bolt that affixes the crank arm to the BB spindle and a 10mm that tightens the outer "cap"

however, with the 8mm inner bolt tightened up VERY tight the 10mm outer "cap" (which I assume is meant to hold the inner bolt in place) does not engage with the inner bolt face. so it is not doing anything. it appears to bottom out on its threads before engaging with the inner bolt face
and so the crank arm keeps coming loose

it must need a washer in there to fill the void. tomorrow I will disassemble another bike using the same system and see what I am missing.

I could not find any documentation that exactly matched this setup.

Crankycrank

No, as mentioned already that is a self-extractor setup where when the spindle bolt is unscrewed it presses against the cap to act as a crank puller. DO NOT put a washer in there to take up the space. If your crank keeps coming loose, then you're not tightening the spindle bolt enough or there is damage to the crank/spindle interface. Also, don't use gorilla strength unscrewing the bolt against the cap to remove the crank arms. If the cap starts to show any signs of flexing or distorting, remove the cap and use a proper crank extractor tool.

Kontact

Please read all the stuff I wrote for your in your thread.

Did you check that there aren't any washers on the driveside between the crank and the bearing?

Take the crankarm off and look at the splines and their mates on the spindle. If the crank arm splines are damaged the arm can pivot back and forth on spindle and back the bolt out.

choddo

I did check mine after this discussion. And while it has different bearings, there’s nothing between the cap and the crank bolt. Kontact’s suggestion that there might be a washer, possibly the wave washer I have installed on mine, on the drive side seems the most likely explanation for the anomaly.

I don’t think a normal extractor tool can work on this can it? It would push against the inner bolt which is part of the crank arm you’re trying to remove.

Kontact

If you wanted to use some sort of extractor, you'd remove both the extractor cap and the bolt, just like on a traditional crank.

pstock

I will work through everything today.
thank you