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Is my frame bent?

Discussion in 'Norton Commando Motorcycles (Classic)' started by Dutch, Nov 11, 2018.

  1. Dutch

    Dutch

    Joined:
    Sep 21, 2015
    My seat frame has me wondering if it has been tweaked.
    I am using the level as a straight edge to show the curve that when I look at other pictures of frames - does not look this way. I would not be surprised if it was - these things happen - learning to wheelie is hard! At least it can be easily fixed if need be.
    Thanks! [​IMG]
     
  2. Dutch

    Dutch

    Joined:
    Sep 21, 2015
    Another
    [​IMG]
     
  3. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    Mine is bent there in the other direction....drooping down likely due to heavy-set pillions ;-)

    Have not yet corrected mine, but some recommended heating with propane or acetylene at bend point until it can be bent back where it came from. Others discouraged use of heat and to bend it cold. Might be wise to put a block of wood/metal infront of the bend point to leverage against and then use a long pry bar.
     
  4. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    It certainly looks bent. You can check it pretty easily against the frame dimensions given in the factory service manual.

    750.JPG

    850.JPG

    Ken
     
  5. Dutch

    Dutch

    Joined:
    Sep 21, 2015
    Thank you for those drawings Ken.
     
  6. 1973x75

    1973x75

    Joined:
    Nov 15, 2015
    Mine was also bent, but down, like Tornado’s. It was far enough to kink the fender. I strapped the bike to the lift, took the wheel and fender off, and used a hydraulc jack to ease it back up. I was able to work the kink out of the fender, but I forgot how. Big channel lock pliers and a rag to prevent scratches comes to mind.
     
  7. KiwiNeill

    KiwiNeill

    Joined:
    Jul 25, 2011
    Dutch
    The drawing shows a similar kink if you can imagine a straightedge in the same position.
    I would say it,s pretty good and better than the usual tired droop mentioned.
     
  8. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    I note the rake for the 850 frame is 28 degrees, and for the 750 frame is 27 degrees. Do you have the corresponding information on the yoke offsets ?
     
  9. toppy

    toppy

    Joined:
    Dec 2, 2012
    Put your spirit level on the bottom frame tubes and level the frame front to back and the frame loop should also be level as in drawing shows. Not the most accurate way with just a spirit level but should give you a rough idea.
     
  10. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    I thought that at first, but then I noticed that Dutch's frame has a 'kink' (looks like it dips down then up) BEHIND the shock top mounts, whereas the drawing showing the 'kink' being before the shock mounts.

    It looks to me as though it was drooping, and has been 'corrected' by someone.

    But nothing critical is effected by this, so, as long as the seat and mudguard sit well, I wouldn't think there's anything to worry about.
     
  11. Dutch

    Dutch

    Joined:
    Sep 21, 2015
    Here it is when the bike was together.
    My guess is that it's bent.

    [​IMG]
     
  12. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    Yup it's bent , most are after 45 years of fun. No biggie . just bend it back cold , not hot.
     
  13. Ron L

    Ron L VIP MEMBER

    Joined:
    Feb 27, 2004
    And it appears the seat base is bent as well. Probably due to the same force that bent the loop!
     
  14. MikeM

    MikeM

    Joined:
    Jun 1, 2011
    Mine was bent in the other direction. I was told heavy passengers. Happened before I got it.
     
  15. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    This is data from the notes I made a while back while doing some frame mods on my Commando. These are not factory numbers, but measurements I made on 750 and 850 yokes that I have. I think they are pretty close, but might not match up exactly with factory drawings for the yokes. If anyone can provide original drawings for the yokes, that would be a better source of data.

    750 frame rake is 27 degrees.

    850 frame rake is 28 degrees.

    750 fork yoke offset is 2.750" (70.125 mm).

    850 fork yokes are bored at 2 degree angle.

    Upper offset is 2.780", and lower offset is 2.722".

    Ken