Loose crank question

I searched the threads for my particular problem, but I couldn’t find anything relevant enough, so I’m starting a new one.

I have a mountainuni set-up with brand new SINZ cranks installed onto my Impact Exceed hub (2 years of use or so). During the last two muni rides my right crank (the side on which the rotor and brake are installed) comes loose every mile or two. During the rides, I stop to re-tighten to the point that the cranks touch the spacers again, and I continue with the ride. Then about a mile later, I start hearing a horrible squeaking noise with nearly every rotation.

So tonight I took apart the cranks and inspected them.They appear fine. But when I looked inside the hub, I noticed some of the threading looked a bit strange. I thought it was just lubricant, so I thread the crank bolt into the hub, and there was a bit of resistance at times (meaning, it took a little bit more effort to tighten the bolt), but once I got through that resistance, the bolt screwed in easily. When I took the bolt out, a TINY TINY sliver of metal from the hub threading came out. The bolt now goes in and out perfectly without any resistance.

Also, I noticed that my crank bolts are of different lengths, the shorter of which was on the affected side. So I just switched over the long crank bolt onto the brake side, and the short crank bolt onto the unaffected side. I’m thinking that the short crank bolt was the reason the crank was coming loose. Does that seem plausible?

Now regarding my hub, do you think it’s ruined because a tiny bit of metal from the threading came out? If I keep riding on it, will that tiny bit of metal make a difference, given the fact that the bolt threads through it just fine now? Do you have any ideas about why my hub threading was messed up in the first place?



i did a bit of googling on the parts you mention but i can’t get specifics. Sinz cranks seem to be available with both the isis and the square tapered crank holes. Can you post some pictures? I have had some problems with cranks and i noticed that it is important to clean and re-lubricate the interface before installing new stuff. You could try cleaning with a dry toothbrush if the thread is internal and has some dirt inside. I seems that if the parts which are supposed to slide in place along a tapered (inclined) surface get stuck prematurely they will start to rotate when you apply pressure on the pedal. If this happens it will pry itself loose.

I have the isis version. I can’t post pictures right now, but I might be able to later today. Maybe I’ll take some later.

I think I’ll try to go for a ride this evening and see if pedals causes it to loosen up again. Thanks!

Just my opinion, but it may be possible that your spacers are too wide. If the cranks hit the spacers before you are able to get the bolts up to full torque, they will always come loose. (Are you installing the cranks with a torque wrench? Not absolutely required, but it usually gets them tighter than most people achieve with a regular hex wrench.)
It’s been my (limited) experience that different cranks get tight at different places along the axle. Sinz cranks may be a little wider (particularly with the brake disc attached), and may get to their “tight spot” a little farther up the axle.
Just a thought. Good luck!
(I don’t think a tiny metal sliver will hurt the bolt/axle interface too much.)

Are the bolts and hub threads dry? Do they have loctite? Or are they greased?

There’s also some difference in tightening your cranks to the spacer and tightening your cranks. Make sure they are as tight as they will regardless of where the spacer is. If that doesn’t work, I’d try smaller spacer and as a last resort: loctite.

Thanks! The affected side actually has a less wide crank spacer than the other side (I think 6mm vs. 8mm?) I can’t use any wider or narrower because the rotor will then hit the frame. I’ve tried tightening with a longer wrench, but ultimately it still comes loose. This is why I think it might have been because of the short crank bolt.

I tend to over-grease everything , if anything. I don’t think any of it is dry.

Seems odd. Does the hub have a disc brake rotor mount? Is it asymmetrical for some other reason? Supposing the bolts came with the hub, following the ISIS spec, why would they be different? Could the short one actually be broken?

Never a good thing, but if it’s really “TINY TINY” as you say then it should be OK. It could be a little piece of swarf from manufacturing that didn’t get cleaned out, or maybe one time the bolt was started cross-threaded but stopped before doing any more damage than that. On the other hand, it could be the tip of the iceberg.

Inspect very well, test fit very carefully, assume the worst and then try to prove yourself wrong–that’s how I’d go at it. Good luck!

This is a long shot…

Unlike the the pedals, both the crank bolts should be tightened clockwise. If you try tightening the left side crank bolt in an anticlockwise direction then the thread will shear and the bolt will loosen.

Hope this helps

Uh, wouldn’t the bolt come out?

Here’s what I suggest. Take the spacer off altogether, and put the crank/brake disc onto the axle, just to see how far it goes before it gets tight. If the disc hits the frame before the crank is fully seated and tight, then I don’t think this combo will work in your application. There is a 1 degree angle on both the axle and the crank that need to tighten against each other in order to be fully tight. Tightening the crank against the spacer is not the right approach. Some cranks just don’t work with some hubs. (I had this happen on the first set of cranks I tried with my Schlumpf hub. They were simply too narrow, and the bolt bottomed out before the crank “cinched up” against the spline angle, and the cranks were always loose.)

@ Killian. If you force the bolt in the wrong direction it may attempt to re-thread itself giving it some grip so that it doesn’t come out completely, at least not immediately.

The loose piece of metal suggests to me that the thread is damaged.:frowning:

From what I understand with isis hubs and cranks the splines should be greased but the bolt should never have grease on it. Only loctite should be applied to the bolt and hub threads. Perhaps your bolt is loosing up because of the grease or a combo of the grease and spacer size.

I put anti sieze on my bolts and have never really had an issue. Maybe I’m not supposed to, but I do :stuck_out_tongue:

I’ve read both ways actually… My thinking is you grease a bolt that you want to be able to loosen fairly easy.
You put loctite on a bolt you don’t want to loosen. (fairly easy) :smiley:

Which way would you turn the bolt if you simply want to remove it without shearing the thread? :roll_eyes:

wouldn’t the bolt come out?

I’ve heared from some riders that the SINZ cranks are made of weaker material than the KH cranks and thus tend to loosen. For me it sounds as if with your setup (disc brake –> spacer width) you are not able to tighten the crank far enough on the axle. I suppose you do a test with a narrower spacer (and no disc). If the problem still appears it may be caused by sth else, if not, than you might have to figure out how to get your disc brake working with the narrower spacer (modification of crank/ disc bolts/ disc diameter/ frame).

As far as I know, I’ve always tightened both crank bolts to the right. Right tighty. I have no clue why there is a thread issue in the hub.

I think you’re on to something here, bc yesterday I took the uni out for a short ride on pavement and dirt, hopped around, went up some hills, and sure enough the right crank started to squeek. I checked the bolt and it was loose again, even with a longer crank bolt. So this weekend I will install some different cranks, and try out different spacer combinations and see if this all continues. If the different cranks keep loosening even with more narrow spacers, the issue should be the hub. If the problem stops with different cranks and/or different spacers, it should be the SINZ cranks. I don’t understand why it would be the spacers though, because I already have the most narrow spacer I’ve ever used on any of my unicycles to accommodate the mountainuni set-up. Since the bolt length wasn’t the issue, my next guess is yours, that the cranks and hub aren’t compatible.

Quite frankly, I miss the days of not having a brake. I like the mountainuni set-up and the fact that my legs are slightly less tired after a muni ride, but I miss the simplicity of not having to maintain a brake, and I also feel like I have more control with my saddle when I don’t have a brake. If I can’t figure out what’s going on, I may just forgo the disc brake for awhile.

Somewhere along the line of acquiring multiple parts, used and new, I received a hub with two different sized crank bolts. It’s never been a problem until now. :-/

I’ll use caution with the hub. My hope is that it is still fully functional, and the cranks are the problem.