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Old 2013-08-31, 11:21 AM   #1
one4all
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Something went wrong today with my QX 36" crank - help is needed

Hi All,

I had a ~20 KM ride today with my 36er when at approx. half way I started to feel as if the pedal or the wheel axis knocking softly at specific point of the crank turn.
When I stopped to check it I was amazed to see that the right side crank peeled off some of the paint of the wheel bearing closure area and that basically some offset occurred in the distance between the crank and the chassis (fork).

I immediately took apart the fork closure around the bearing of the right side and tried to figure out what happened.
I couldn't find anything that would explain it and still the crank is sitting way to close to the fork after I put everything back together again.

I did notice that the crank screw had something like 0.00001... to be tightened with the Allen key, but it practically had nothing to do with it and no movement of the crank had been influenced by that before or after I tightened it.

I'm afraid it's something bigger going on here - maybe even related to the HUB itself.

Had anyone ran into such issue ever before?

Thanks a lot for the help



Last edited by one4all; 2013-08-31 at 11:21 AM.
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Old 2013-08-31, 11:39 AM   #2
davejh
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at minimum your crank has catastrophically failed and needs binning.

does the unicycle have spacers between the cranks and the bearings?

trying to ride on an already damaged crank may trash the splines on the hub needing a full replacement. hopefully the hub is still in good condition
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Old 2013-08-31, 12:06 PM   #3
one4all
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Quote:
Originally Posted by davejh View Post
at minimum your crank has catastrophically failed and needs binning.

does the unicycle have spacers between the cranks and the bearings?

trying to ride on an already damaged crank may trash the splines on the hub needing a full replacement. hopefully the hub is still in good condition

Well the crank seems perfectly ok.

However, if I had wanted to better descibe the situation then my guess would be that somehow the bearing moved along the wheel axis and got too close to the crank's connection point.
Then in the middle, between the crank and the bearing comes the fork which is attached around the bearing and that's why it is sitting too close to the crank.
But that's of course only my assumption.
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Old 2013-08-31, 12:53 PM   #4
davejh
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ok that makes sense, i thought crank moved in, you think bearing moved out...

The attached image shows why neither action should happen. The crank and bearing should be separated by a 6mm spacer on an isis unicycle (that doesnt use moments or have a schlumpf hub). The primary purpose of that is to stop the crank riding up the splines and deforming leaving a wobbly crank.

If the spacer isnt present the problem might be solved by fitting it. or i may be barking up the wrong tree again and if the spacer is present im afraid im out of ideas.
Attached Images
 

Last edited by davejh; 2013-08-31 at 12:54 PM.
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Old 2013-08-31, 12:59 PM   #5
jtrops
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Check to see if the spacing between the bearings is 100mm's (c-c). If the frame spacing is off it can cause this sort of problem. The bearings may have been holding the fork blades together, and when they finally started to move you noticed the problem. If that's what happened it was probably like that from the factory, and they should replace the frame.

Of course it does sound like you probably don't have spacers which would prevent the bearings from creeping even on a suspect frame. Spacers should have been included with the hub, but may not have been. There are plenty of posts where the need for them has been argued one way or the other.

If the frame is off it should be replaced. That kind of problem will lead to premature bearing wear even with the right spacers.
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Old 2013-08-31, 01:10 PM   #6
muni tasmania
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even if spacers are absent, correctly spaced providing the hub suits the frame the frame should be fine and come back to shape fine. Paint off looks more cosmetic than structural.

I have a KH36 i had arrive with a 4mm spacer on one side behind a crank arm and a 6mm spacer the other....

Take your wheel out and see what doesnt look right. Hopefully it will be staring at you whats happening exactly

Hope it works out ok and an easy fix for you. Be sure to share your finding!!!
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Old 2013-08-31, 01:27 PM   #7
one4all
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I guess you all are right, it does seem that the spacer got evaporated, because I have never ever took out the crank.
What's also been seen is a small offset distance of the bearing from the HUB on the other side which I guess it is because of the absent spacer.

Here are the pictures, for your observation.

The good side:




The faulty side:




Thanks a lot for your help!

Last edited by one4all; 2013-08-31 at 01:27 PM.
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Old 2013-08-31, 03:15 PM   #8
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Does anyone know where I can find such spacer (other then QU-AX's factory)?

Thanks
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Old 2013-08-31, 03:24 PM   #9
Shmolagin
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Quote:
Originally Posted by one4all View Post
Does anyone know where I can find such spacer (other then QU-AX's factory)?

Thanks
Good 'ol UDC. Just search for spacer and it should come up.
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Old 2013-08-31, 04:05 PM   #10
tholub
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So, what actually happened was that your bearings slid along the axle, so the frame started rubbing the crank (rather than the crank moving and starting to rub the frame). You'll need to reinstall the bearing in the proper location; I'd probably try to put it there before installing the crank, which you could do by putting an old piece of seatpost over the end of the axle and hammering. If it's particularly loose I might recommend green Loctite sleeve retainer.

You can likely get a spacer at a local bike shop, it's probably the same diameter that they use for headsets.
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Old 2013-08-31, 05:15 PM   #11
one4all
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Quote:
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Good 'ol UDC. Just search for spacer and it should come up.
Thanks, I'll check it out.
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Old 2013-08-31, 05:16 PM   #12
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Quote:
Originally Posted by tholub View Post
So, what actually happened was that your bearings slid along the axle, so the frame started rubbing the crank (rather than the crank moving and starting to rub the frame). You'll need to reinstall the bearing in the proper location; I'd probably try to put it there before installing the crank, which you could do by putting an old piece of seatpost over the end of the axle and hammering. If it's particularly loose I might recommend green Loctite sleeve retainer.

You can likely get a spacer at a local bike shop, it's probably the same diameter that they use for headsets.
Thanks for the tips!

I think I would want to do a paint job to fix the scratches - got any ideas who deals with it; car paint shops maybe?
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Old 2013-08-31, 07:18 PM   #13
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Thanks for the tips!

I think I would want to do a paint job to fix the scratches - got any ideas who deals with it; car paint shops maybe?
Yeah, although to make it look decent you'd probably have to strip the whole thing and re-powdercoat, which would be non-trivially expensive.
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Old 2013-08-31, 07:19 PM   #14
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Originally Posted by one4all View Post
Thanks for the tips!

I think I would want to do a paint job to fix the scratches - got any ideas who deals with it; car paint shops maybe?
Yeah, although to make it look decent you'd probably have to strip the whole thing and re-powdercoat, which would be non-trivially expensive. Although it looks like it's just on the bearing holder, which would be a small piece you might be able to get them to throw in with something else they're powdercoating.
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Old 2013-08-31, 07:45 PM   #15
one4all
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Quote:
Originally Posted by tholub View Post
Yeah, although to make it look decent you'd probably have to strip the whole thing and re-powdercoat, which would be non-trivially expensive. Although it looks like it's just on the bearing holder, which would be a small piece you might be able to get them to throw in with something else they're powdercoating.
I've read somewhere that nail polish would do the trick and it comes in various colors so it should be easy to find the right one.
Did anyone have experience with such nail polish to fix paint chips?
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