Thread: Slipping fork tubes

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  1. #1

    Slipping fork tubes

    I've got a problem which throws up several questions.
    I've fitted some aluminium yokes to my Guzzi with the standard 34mm fork tubes.But the Marzochi yokes are designed to grip 36mm tubes.I made some sleeves from steel tube to adapt the yokes to hold smaller diameter tubes. The sleeves are slit vertically to match the slit in the yoke and to allow for the pinch during tightening.Lock-tightened them to the yokes.3000 miles later the left hand tube slips about 7mm.The pinch bolts in the yokes are m10 stainless cap heads,is there a torque setting for steel into ally ? I am concerned about stripping the thread.Would replacing the steel sleeves for ally help them grip better ? The previous owner did just that and I 'heli coiled' it. I've considered using lock tight to in effect glue the tubes in,but this would cause problems if and when I need to drop the front end out.It has also been suggested to roughen up the internal surface of the sleeves to provide a key for increased grip.But anything along those lines would scratch the tubes during removal and replacement.

  2. #2
    Senior Member mhbsmark's Avatar
    Join Date
    Mar 2014
    Enfield, North London
    The obvious solutions would be to either swap the forks for the correct size or change the yokes, but I suspect you're looking for a cheaper fix?
    If there is enough material around the pinch bolt threads you could drill them out and use use a bigger bolt but with a finer pitch, say 11 x 1 or 12 x 0.75.
    With a finer thread you would get more friction on the threads and they should stay tight. Not sure about torque settings but this company should be able to help
    If you don't learn from your mistakes then they are just mistakes

  3. #3
    Thanks for replying.They are the correct forks.The yokes came with a load of other parts when I purchased the doner bike.I decided to use them as the standard originals were ugly.
    As a solution to my problem I've decided to drop the forks out,a light rub with emery paper where they make contact with the yoke face,thorough clean and an application of bearing retainer.
    I have a few other ideas,but I'll see how plan 'A' works out.Watch this space.

  4. #4
    If you want to sleeve yokes down to fit forks the sleeves really need to be turned up on a lathe so you get a good fit on both the fork and the yoke,rolling up a piece of handy steel sheet will very rarely do the job.
    Roughing up the fork tube ? Would you score your brake disc surface to get more friction ? No, you are just cutting down the surface contact area.
    Bearing retainers and other such "glues" are exactly what it says on the tube.
    Bigger bolts so you can do them up tighter ? Nope, barking up the wrong tree.
    Take the forks and Yoke(s) to a friendly machine shop, explain what you want and you should be fine.
    Steel or Ali will be fine but I prefer ali for the anti corrosion aspect.
    The sleeve need to be a "top hat" shape with the wider diameter going under the yoke, this may seem odd but it stops them pushing through the yoke IF there is any movement under braking (that is when the biggest load is applied on them).
    Hope that helps you out.