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1972 Commando front disc offset in caliper - correct?

Discussion in 'Norton Commando Motorcycles (Classic)' started by PJL, Apr 12, 2009.

  1. PJL

    PJL

    Joined:
    Mar 26, 2008
  2. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    The disc should be more or less dead central in the caliper slot, it certainly shouldn't be scraping the caliper, so something appears to be wrong?
     
  3. BillT

    BillT

    Joined:
    Jan 27, 2008
    Did somebody cut down the caliper? Caliper should bolt directly to the fork tube, and be centered on the disc.
     
  4. JimC

    JimC

    Joined:
    Oct 12, 2007
    Is the wheel properly laced?
     
  5. dave M

    dave M

    Joined:
    Oct 19, 2005
    The relationship of the hub to the forks and thus the caliper is determined by the combined spacer/dust cover that fits into the hub on the right side. The axle is tightened with the nut which pulls the whole assembly to the right against this spacer and is then tightened on the pinch bolt on the left fork slider at the bottom. It would therefore seem that the only option for moving the hub right or left in the forks would be to either skim some material off the spacer, or to add some shims - I have just measured a spacer in my workshop and found it to be 19.3 mm long. However you must be aware that any movement left or right will affect the centralisation of the wheel rim within the fork sliders, this can be adjusted by offsetting the rim one way or another, but this is quite a time consuming job requiring a bit of knowledge and experience with wheelbuilding. My suggestion is that you check that the wheel rim is indeed accurately equidistant from the fork sliders (1 or 2 mm either way may give you the clearance you need to simply shim the whole assembly) and if this is the case you could make a spacer ring to move the disc out by the appropriate amount necessary. You could also mill some material off either the caliper mounts on the fork slider, or the caliper itself, however it seems to me that this would be a poor second to getting everything lined up with the standard components as far as possible.
     
  6. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    The relationship between the hub/disc and fork/caliper certainly does seem to be wrong somewhere?
    Either the hub isn't spaced correctly, or something has been modified or the disc is wrong?

    Knowing what the precise measurement is between the face of the disc and the fork leg could answer a few questions?
     
  7. PJL

    PJL

    Joined:
    Mar 26, 2008
    Next time I get chance to get into the garage I'll check the dimensions of the spacer (thanks Dave M). The rim is equidistant in the forks (within a mm). However, the previous owner did have new rims fitted so something could have changed at that point.

    Either I should put a spacer behind the disc to move it outwards, and/or put a spacer between the caliper and the fork mounts to move it inward, both of which I'm not keen to do as it could increase strain on the mounts. As Dave M suggests I should prefer to stay with the standard setup as far as possible. The alternative is to cut the wheel spacer down 1-2 mm to move the hub to the right.

    What gap should there be between disc and fork leg?

    However, if I move the hub to the right then the rim will need to be moved left relative to the hub to maintain its position in the forks. I assume slackening off the right side spokes and tightening the left will shift the rim. As long as this is done in (very) small increments with checking and rechecking tension (pinging) this should work. I've done this before on an A65, many years ago, which helped correct a left steering tendency.

    Many thanks, Phil.
     
  8. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004

    Not an easy thing to measure, but I found a couple of washers that would both slide in together snugly between the disc and the slider, and they measured up at 2.6mm.
     
  9. PJL

    PJL

    Joined:
    Mar 26, 2008
    Thanks L.A.B.

    I've just checked, mine is 3.5 mm. That starts to explain things. Even a mm would stop the disc scraping on the caliper when it expands with the heat.

    Phil.
     
  10. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    OK, in that case it would seem to indicate a problem with the hub/disc offset somewhere?
     
  11. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    The 850 MkIII front hub assembly is different to the earlier disc hubs. Possibly there are some mismatched parts in your hub assembly? The dust cover/spacers are certainly different between the two hubs.
     
  12. PJL

    PJL

    Joined:
    Mar 26, 2008
    I do believe we've found the problem. Dave M suggests the spacer should be 19.3 mm, mine is 20.7 mm. This combined with the estimate of the difference in the disc to fork leg gap from L.A.B. gives a weight of evidence that the hub is in the wrong position, possibly due to mismatched parts.

    1.4 mm should be about right to centre the disc in the caliper (certainly enough to stop it catching).
     
  13. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    I've just measured my apparently correct MkIII wheel disc side spacer, it is 19.3mm!

    I don't have a pre-MkIII spacer to compare it with, but the part numbers are certainly different, MkIII is [Edit****** see next message] pre MkIII is 062448.
     
  14. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    CORRECTION

    Apparently the MkIII front wheel spacer part numbers are incorrectly listed on the Andover Norton MkIII parts list page!
    http://www.nortonmotors.de/ANIL/Norton% ... &Plate=022

    Also in the MkIII parts book, that has both spacer numbers listed as: "Disc Side" :roll:

    So the 06-2448 "right hand" spacer, but left hand (disc side) on a MkIII model would appear to be the same part for both MkIII and pre-MkIII wheels, only the non-disc side spacers are different.
     
  15. PJL

    PJL

    Joined:
    Mar 26, 2008
    I must say a big thank you to the contributors to the Forum. Very rapid advice, including measurements that one cannot find in manuals or elsewhere on the web to help us diagnose the problem.

    I've now shortened the wheel spacer to 19.3 mm and the disc is close to central in the caliper. I've moved the rim over so it is central in the forks - it only took 4-5 flats, less on the right than the left due to the steeper angle and offset. The spokes are all tuned to about the same note (higher on the right than left, as they are shorter) and it continues to run true (within a mm). And yes, I did check that no spokes were projecting inside the tyre.

    Now to find a mountain to ride over - perhaps next weekend.

    Many thanks! Phil.
     

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