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  • A small space where the axle is visible

    I'm very sorry if this problem has been addressed before, but after wading through the forums I haven't found quite the same thing.

    Yesterday I received my new 20" Nimbus trials from UDC. However, after a few minutes of very minor fooling around, I noticed something. There is a small space (maybe 1 or 2 millimetres) between the left crank arm and the bearing spacer, and through the space I can see the axle. When I ride the unicycle, it feels perfectly fine; there are no wobbles or creaks or anything of that nature.

    I just got this unicycle. Did UDC not put the crank on all the way? Should I remove the crank bolt, cover the crank with a piece of wood, and try to hammer it on further? I've actually tried doing that, but I was admittedly shy with the hammer. I didn't want to damage anything.

    Once again, I'm sorry if this type of question is wearing your patience thin.

  • #2
    I have the same thing on my nimbus. What kind of cranks do you have? I've only had that problem with KH moments. I've ridden pretty hard on mine like that and they're fine. As long as you make sure they're tight you won't have any problems.
    Last edited by crazyjoe; 2009-06-03, 05:58 AM.

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    • #3
      Originally posted by Caterpillar with a hookah View Post
      I'm very sorry if this problem has been addressed before, but after wading through the forums I haven't found quite the same thing.

      Yesterday I received my new 20" Nimbus trials from UDC. However, after a few minutes of very minor fooling around, I noticed something. There is a small space (maybe 1 or 2 millimetres) between the left crank arm and the bearing spacer, and through the space I can see the axle. When I ride the unicycle, it feels perfectly fine; there are no wobbles or creaks or anything of that nature.

      I just got this unicycle. Did UDC not put the crank on all the way? Should I remove the crank bolt, cover the crank with a piece of wood, and try to hammer it on further? I've actually tried doing that, but I was admittedly shy with the hammer. I didn't want to damage anything.

      Once again, I'm sorry if this type of question is wearing your patience thin.
      I don't understand why UDC puts a spacer on there; a space seems to me like a violation of ISIS standards. If there is a spacer, there should be space between it and the crank--if the crank is jammed up against a spacer, it's not installed properly.

      Comment


      • #4
        I believe the spacer is purely to stop the berrings drifting along the axle if they are loose fitting. It is not for the crank to come up against. Both ISIS and square taper hubs/cranks are tapered so as long as they are fitted corectly, drifted on far enough and the crank bolt is tight then it doesnt matter if there is a gap. Like tholub said, its better to see a small gap then to have no gap atall.
        Last edited by sp4rky-m4rky; 2009-06-03, 08:00 AM.
        Marcus Collings
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        • #5
          Originally posted by sp4rky-m4rky View Post
          I believe the spacer is purely to stop the berrings drifting along the axle if they are loose fitting. It is not for the crank to come up against. Both ISIS and square taper hubs/cranks are tapered so as long as they are fitted corectly, drifted on far enough and the crank bolt is tight then it doesnt matter if there is a gap. Like tholub said, its better to see a small gap then to have no gap atall.
          After changing my cranks from k1's to moments (it's temporary ;-) ), I realised the spacer does more than that. If you don't have the right spacer (of course k1 have different spacers to kh) - then your frame wobbles like hell.

          That could be cause my hub is a bit **** and the bearings come off by just pulling on them abit.

          Tighten the crank bolt as far as you can with a longish allen key, and then have a look again. The space shouldn't be a problem, but if you turn the key far enough - it'll dissapear ;-)

          Brendan
          I'm a soldja.

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          • #6
            The spacer is very important, it keeps the bearing from sliding on the axle. I was not running a spacer on my Isis equipped muni and the bearing slipped so far that the crank hit the frame

            The problem is that for each crank there is a different spacer specification:

            Nimbus/KH Isis + KH Moments = 6mm
            Nimbus/KH Isis + QuAx = 4mm
            Nimbus/KH Isis + K1 = 2-4mm

            Now the KH Ti hub, in my opinion, is a tab bit smaller at the splines, so it did better with a 2mm spacer when I ran the K1, but when I mounted Moments I tried a 4mm and there was too much spacer between the bearing and cranks, so I went back to a 6mm.

            Something to keep in mind is that there is also a spacer between the bearing and hub, so be sure your bearing and hub spacer is tight as well, esp if you're not running a spacer between the bearing and crank.

            UDC sells spacers.
            I dream of hamsters and elderberries

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            • #7
              Regardless of whether it "violates" any specifications, in practice the spacers seem to work perfectly well with ISIS. The only contact I've had with ISIS is on unicycles (all my bikes are square taper apart from a weird Truvative proprietory splined thing), but both my ISIS unicycle setups came with spacers, so I didn't question it, and have had no problems. They're both Nimbus hubs, one with QuAx light cranks and one with Moments. It takes a fair torque to do the bolt up until the crank hits the spacer (I haven't measured it, but nowhere near as much as I normally use on a square taper crank) and I've never had one come loose, so it seems to be working well. Whatever the official ISIS spec says, I don't reckon ISIS cranks need to be forced onto the axle as tightly as sq-taper.

              Wasn't there somebody who did some actual research into what happens when square taper cranks deform under riding torque, and they reckoned they actually tend to move ONTO the axle momentarily, allowing the bolt to slacken? I'm sure I've seen links to that article somewhere, but I can't find it now. If that's the case, then the spacer would seem a good idea after all.

              Anyway, in reply to the OP's question, in my experience of ISIS cranks (not huge, as I mentioned) the cranks are always tightened up enough to hit the spacers - never needed a hammer, just used a normal 8mm allen key in the crank bolt (greased splines first). I'm not a big dropper though, but I do ride miles and miles of very rough rocky xc.

              Rob
              Last edited by rob.northcott; 2009-06-03, 03:54 PM.
              "Hedgehogs - why can't they just share the hedge?" (Dan Antopolski)

              "I would absolutely recommend a 29er to anyone who didn't prefer a larger or small wheel." (Mikefule)

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              • #8
                Originally posted by crazyjoe View Post
                I have the same thing on my nimbus. What kind of cranks do you have? I've only had that problem with KH moments. I've ridden pretty hard on mine like that and they're fine. As long as you make sure they're tight you won't have any problems.
                Yes, I have the moments as well.

                Originally posted by tholub View Post
                I don't understand why UDC puts a spacer on there; a space seems to me like a violation of ISIS standards. If there is a spacer, there should be space between it and the crank--if the crank is jammed up against a spacer, it's not installed properly.
                Originally posted by sp4rky-m4rky View Post
                I believe the spacer is purely to stop the berrings drifting along the axle if they are loose fitting. It is not for the crank to come up against. Both ISIS and square taper hubs/cranks are tapered so as long as they are fitted corectly, drifted on far enough and the crank bolt is tight then it doesnt matter if there is a gap. Like tholub said, its better to see a small gap then to have no gap atall.
                Ah, I see. Now I feel stupid, as I knew I probably would when I made this thread. I assumed that the left crank should look like the right one, which doesn't seem to have a space between the crank and the spacer. So then, what (if anything) should be done about the right crank? Thank you very much for your help so far.

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                • #9
                  Originally posted by Nurse Ben View Post
                  The spacer is very important, it keeps the bearing from sliding on the axle. I was not running a spacer on my Isis equipped muni and the bearing slipped so far that the crank hit the frame
                  That shouldn't happen, and it represents a problem for which a spacer is a bad fix. The bearing should be press-fit onto the axle, and it should stay where it's put; if you need a spacer to keep it from moving, your axles or your bearings are not properly machined.

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                  • #10
                    You shouldn't need one, but it can't hurt at all. My frames wobble, using kh hubs. The one 07 hub I got close to two years back had the bearing fall right off when I got it, you can slide them on and off with no force at all. Spacers should 'fix' that.

                    I'd say try tightening it with an allen key to get it as tight as the right, if it will not budge I'd say ride it as is.

                    A wobbling bearing will damage your axle though. The axle on my hub is kind of screwed up, the hub is all beat up and kind of rusted. I'd fix it, but it's an 07kh and the flanges look like they are about to pop off any day.

                    The new hubs seem better, my 08 worked fine. I'm picking up an 09 soon.
                    Last edited by wickedbob; 2009-06-03, 05:03 PM.

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                    • #11
                      Now I see the real problem. The problem is that I'm an idiot who is way too paranoid about breaking his new unicycle. Please, everyone, disregard this thread. Let my embarrassment die along with it.

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                      • #12
                        Caterpillar you should tighten the crank bolts on your new uni after every ride. the crank will gradually settle in until it hits the spacer, then it should be OK. Also it is ok to be paranoid about your most prized possesion. it shows you care about it.

                        Now I am about to come across as a prick so I would like to apologise in advance.

                        Originally posted by tholub View Post
                        I don't understand why UDC puts a spacer on there; a space seems to me like a violation of ISIS standards. If there is a spacer, there should be space between it and the crank--if the crank is jammed up against a spacer, it's not installed properly.
                        This statement is wrong. The ISIS specs call for a "crank stop" as part of the interface. In fact this is the datum for the whole system. ISIS is not like the square taper interface at all. it is more of a parallell spline drive but with a slight taper to remove the movement between the splines. Technically without the crank stop (spacer) it is not ISIS at all, which leads to problems like most schlumpf hub owners seem to be having (loose cranks, Cranks creeping and hitting frames,etc)

                        If you are interested in the ISIS drive please check here:

                        ISIS Drive

                        The entire spec is avaliable to download from the "documentation" section of the website. There is most of the reasoning to do with the crank stop in that section

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                        • #13
                          Originally posted by Big H View Post
                          Now I am about to come across as a prick so I would like to apologise in advance.
                          It's not you who looks like a prick mate.

                          This statement is wrong. The ISIS specs call for a "crank stop" as part of the interface. In fact this is the datum for the whole system. ISIS is not like the square taper interface at all. it is more of a parallell spline drive but with a slight taper to remove the movement between the splines. Technically without the crank stop (spacer) it is not ISIS at all, which leads to problems like most schlumpf hub owners seem to be having (loose cranks, Cranks creeping and hitting frames,etc)
                          Thanks for that - I'd not read the official ISIS spec before, and it confirms most of what I suspected from my limited exposure to ISIS (and extensive exposure to sq-taper). I assumed the spacers were there to provide a stop for the crank because the taper seems much shallower than on a sq-taper axle - it seems like it would be far too easy to wind the crank way too far onto the splines otherwise. Good to see that's what they're supposed to be for (and obviously have a nice side-effect of stopping the bearings creeping on the axle), otherwise it'd be a bit silly for all ISIS unicycle hubs to be sold with these spacers.

                          Rob
                          "Hedgehogs - why can't they just share the hedge?" (Dan Antopolski)

                          "I would absolutely recommend a 29er to anyone who didn't prefer a larger or small wheel." (Mikefule)

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                          • #14
                            Originally posted by rob.northcott View Post


                            Thanks for that - I'd not read the official ISIS spec before, and it confirms most of what I suspected from my limited exposure to ISIS (and extensive exposure to sq-taper). I assumed the spacers were there to provide a stop for the crank because the taper seems much shallower than on a sq-taper axle - it seems like it would be far too easy to wind the crank way too far onto the splines otherwise. Good to see that's what they're supposed to be for (and obviously have a nice side-effect of stopping the bearings creeping on the axle), otherwise it'd be a bit silly for all ISIS unicycle hubs to be sold with these spacers.
                            You are spot on Rob. The square taper is 2 degrees (per side) and ISIS is 1 degree. Square taper also has a much larger surface area to try to compress, but on the ISIS spline only the the bottom of the ten flutes are actually tapered, the rest is parallell. This makes it much easier to deform and hence loosen up.

                            The crank stop also increases the strength of the interface by effectively increasing the diameter of the axle and supporting the crank, reducing the chance of bending the axle. Add the ability to clamp your bearings (requiring less interference on the inner race) which clamps your frame into position (holding the whole system together = stiffer frames) I personally think that ISIS is nearly perfect for unicycles!

                            Also, you should never need to hammer on either type of interface, althought it may take a few rides to settle sometimes. I see no reason to be shy with the allen key though, I am renowned for stripping and breaking bolts at work, but i have never had any problem with crank bolts (sq taper or ISIS)
                            Last edited by Big H; 2009-06-04, 11:46 AM.

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                            • #15
                              Spacers

                              You are not supposed to tighten the bearing holders very tight onto the bearings. Kris himself warns about this. therefore with time the bearings will move.

                              When I bought my KH24 I got the non standard 165mm cranks. I guess that when they replaced the 150's they forgot to put the spacers back on. I rode fine for a year and then in a MUni ride the bearing fell right out of the holder. I put it back in and finished the ride. Later I wrote to the seller and they sent me spacers and new cranks to rectify this problem.

                              Unicorn
                              Keep your eyes on the stars and your feet on the pedals, and you will accomplish great feats!

                              The Unicycling Commune

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