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troubleshooting KH onza hub/cranks?

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  • troubleshooting KH onza hub/cranks?

    My new KH muni developed a little lateral play in the wheel. I assumed it would only need the old loctite treatment to resolve the issue. When I took it to my LBS, they told me that there is a rubber bushing between the bearing and the axle and that the bushing was responsible for the looseness. My uni is about a month old and I've only been off road twice. Did I really trash the bushing that quickly?

    Another question they brought up at the LBS: the mechanic observed that the hub and crank design "sideloads" the bearings. He noticed, as I have, that when the bearing caps are really tightened to the frame, the wheel doesn't spin very freely. I'm hoping he and I are missing something here. I've read in the past that there is a stepwise process to putting the crank arms on and tightening the bearing caps. Is it possible we're tightening things in the wrong order and ending up with a tight wheel and "sideloaded" bearings?

    Any ideas are appreciated.
    ****************************
    Chop wood and carry water.

  • #2
    The hub does have a plastic (I think?) spacer between the bearing and the crank, but I don't think this is directly responsible for any play in the wheel. You will probably find it is just because the cranks aren't tightened down enough. I have an earlier version of the Onza hub, and it needs the cranks tightening or reinstalling every couple of months to get rid of a slight "slop" feeling and creaking when putting force through the cranks. It may well have not been fully tightened when it was new.

    It doesn't really matter in which order you install the frame and cranks, as they load the bearings in different directions. I generally put the frame on first, so you can get a better hand-hold when you come to tighten the cranks and pedals.

    When you tighten the cranks it will compress the bushing and the inner sleeve of the bearing; this should be as tight as you can get it to prevent any play and creaking. I use some grease on the splines to get the crank to slide on as tight as possible.

    You need to be very careful when tightening the bolts to attach the frame. As you have noticed, overtightening can crush the bearings and result in a wheel that doesn't spin very well. The best way to do these is slowly, testing whether you can twist the frame relative to the wheel. Too loose and the frame will turn slightly, which will feel very odd when riding; too tight and the bearings will bind and not spin freely.

    The way the bearings are clamped always seems like a weak point in the design to me. My 29er has shims around the bearings which make it easier for the frame to twist over the wheel; it is a very fine line indeed between a frame that moves and binding bearings.

    Phil

    Of course, not actually owning a KH muni this could all be utter rubbish. I'm sure someone more knowledgeable will be along to correct me if so...
    "Cattle Prods solve most of life's little problems."

    Comment


    • #3
      Re: troubleshooting KH onza hub/cranks?

      Originally posted by onewheeljoe
      My new KH muni developed a little lateral play in the wheel. I assumed it would only need the old loctite treatment to resolve the issue. When I took it to my LBS, they told me that there is a rubber bushing between the bearing and the axle and that the bushing was responsible for the looseness. My uni is about a month old and I've only been off road twice. Did I really trash the bushing that quickly?
      I am not sure from your explanation where the problem can be. Locktite should not be needed in any aspect of the new design. The only known area of problems has been in a few bearing shims that have not been press fit (they are steel by the way). If this is seen to be the problem then contact your retailer and they should be able to send you replacements.

      Another question they brought up at the LBS: the mechanic observed that the hub and crank design "sideloads" the bearings.

      Simple answer, no.
      The centre of the bearing is under compression (as is correct in any bearing system and should be a high load in this case) the outer race is free to run on the same centres as the frame which is 100mm and suffers side load when the frame is twisted or bent.

      He noticed, as I have, that when the bearing caps are really tightened to the frame, the wheel doesn't spin very freely.

      You have over tightened the bearings - check the instructions supplied. You should tighten them only slightly over hand tight, you will have crushed the bearing making them oval and stopping them from rotating. You may even have damaged them permenantly.

      Sorry I can not be more clear on the initial queery, but I hope this helps.

      Roger
      ++++++++++++++++++
      Roger Davies
      Unicycle.com in the UK
      The UK's Unicycle Source
      www.unicycle.co.uk
      +++++++++++++++++++

      Comment


      • #4
        I hope that what my mechanic is calling "bushings" you are calling "shims."

        The problem I had was that I could feel a general looseness in the bearing area when riding. When I grabbed the wheel by hand I was able to pull it sideways in the frame. This problem kind of mimicked a problem I resolved on an older cycle with the locktite solution.

        I guess this time it must be the "bushing" or "shim"?

        I HAVE overtightened the bearing clamp before but the mechanic said the bearings looked and performed perfectly so I must not have done any serious damage. I've been riding with the bearing clamp tightened only to the point where the wheel spins freely.
        ****************************
        Chop wood and carry water.

        Comment


        • #5
          Before assuming that this is the problem you should check it out. It is not hard.

          You need to remove the wheel. (6mm alan key)

          Remove the crank (8mm allan key - you should be using one at least 6" long to get enough torque on it)

          Have a look at:
          http://www.unicycle.uk.com/images/hubexplanation.tif

          This will give you some idea of what is there.

          When you have the assembly disassembled to the bearings and shim you should see if the bearing is a tight fit on the shim. If it is not then this may be the problem. If not then you will need to start looking elsewhere, but from this point you should be able to see where the problem is.

          If the problem is the shim, as a temporary measure you should be able to take up the slack under that shim with a slither of baking foil. Wrap the foil on the shaft then slip the shim over the top then push the bearing over the top. This is a standard fudge and one I have not tried in this situation but I cannot see why it will not work.

          When re-assembling remember that the 8mm bolt should be very tight, while the 6mm ones are only just over hand tight.

          Hope this helps.

          Roger
          ++++++++++++++++++
          Roger Davies
          Unicycle.com in the UK
          The UK's Unicycle Source
          www.unicycle.co.uk
          +++++++++++++++++++

          Comment


          • #6
            This "shim" you speak of... Is this the piece of metal that goes between the bearing and the axle? Wraps around said axle, with a split in the shim at one point, and then the bearing holders go around the shim? I've been getting some play in it, and it annoys me with the THUNKing sound
            Last edited by evil-nick; 2005-07-22, 02:31 PM.

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