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G15-CS Fork Basics

Discussion in 'Other Norton Motorcycles' started by AgentX, Jul 11, 2018.

  1. AgentX

    AgentX

    Joined:
    Jul 2, 2015
    Good morning all-

    Apologies for a rather open-ended question, but I am hoping to gather knowledge I haven't been able to from manuals, the vast quantity of old paperwork and magazines I inherited, and the Internet.

    Previous (original) owner of my 1965 G15-CS (not yet on the road, but very close) told me a priority would be getting the "top-out issue" solved, and provided me a number of links and resources for the traditional roadholder fixes. I've yet to be inside the fork but planned on doing so once I got it running.

    Based on original input, I had been looking at the JS Motorsport kits, but looking at the fork schematics and the manual, the G15-CS fork is noted as having both compression and rebound damping, which it seems the standard Roadholders don't...?

    Can anyone with experience help me out?

    1) are the G15-CS forks prone to the same damper issues for which the standard Roadholders are noted? If not, any idea what could be causing the problems noted by the original owner?

    2) If so, can they be fixed through the same methods? (Relocation of damping ports and/or spacers, it seems?) Is this handled in the same manner as the standard Roadholder? Would any of the commercially-available fixes be appropriate, or will I need to do it all from scratch?

    Thanks for an insight and experience you're willing to share.

    -Mike
     
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  2. mdt-son

    mdt-son

    Joined:
    Jan 19, 2012
    The early G15-N and G15-M models (aka. Atlas Scrambler) featured special dampers and external springs derived from AMC's own "Teledraulic" forks, providing the "Roadholder" with two-way damping.
    This version should be compatible with JS Motorsport upper bushes offered for Commando forks. Dampers are still available from Norvil Motorcycles and possibly others. Re. springs, maybe Russell Motors still has them. I hold a set and may provide dimensions if you want to have a pair of springs taylor made. I can't remember if the conversion included buffer springs - please check the '63/'64 parts book. Buffer springs would help to minimize the "bottoming out" impact.

    Sometime in 1965/66 a further rationalization of the G15 range took place at AMC, and the "hybrid forks" were dropped on production models, maybe realizing that few of the G/N15CS bikes would be raced and rebound damping was considered sufficient for a street scrambler.

    For a quick check of your forks, just raise the gaiters to verify weather external springs are fitted or not.

    "Topping out" occurs when the suspension extends fully and cannot mechanically extend any more, producing a metallic clunk. This is a common feature to all Roadholder forks. The effect can be reduced by improving rebound damping and careful adjusting the oil level. Follow Jim's advice on how to achieve best rebound daming, and get rid of corroded damper rods.

    For improvement of compression and rebound damping, please read Jim's web page (J.S. Motorsport) and this link:
    https://www.nortonownersclub.org/support/technical-support-common/roadholder-forks

    Modern damper performance of the late G15 forks may be acieved by using the Cosentino Engineering fork kit (i.e., cartridge dampers) and appropriate damper rods.

    -Knut
     
  3. AgentX

    AgentX

    Joined:
    Jul 2, 2015
    Knut, thanks very much for the info. I'd contacted JS Motorsport but Jim was unable to say if his kits would fit the G15-CS fork.

    The previous owner fitted the roadgoing tubular fork shrouds (said the rubber boots would never last him more than a year and was tired of replacing) so I haven't been able to lift up a rubber boot to check them. I guess getting a shroud taken off just became a priority... Once I know if it's a hybrid fork or a standard roadholder I guess it'll guide my moves from there.
     

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