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Mark III Isos

Discussion in 'Norton Commando Motorcycles (Classic)' started by MichaelB, Dec 4, 2019 at 4:40 PM.

  1. MichaelB

    MichaelB VIP MEMBER

    Joined:
    Jan 14, 2004
    What's the logic behind Norton putting the adjustables on opposite sides.
    With the front on the right, it pushes to the left, with the rear on the left, it pushes to the right, further angling the rear tire. I don't get it.

    Since the drivetrain is offset to the left, makes more sense to me to set the adjustables on the left, to push it right. Once set up, adjust spokes accordingly, if necessary.
    What am I missing?

    Seems to me A more correct method would be to center the rear wheel with the front and shim accordingly. But that's shims..
     
  2. jimbo

    jimbo VIP MEMBER

    Joined:
    Sep 25, 2004
    In my view, the rubbers stuck inside of the tubes will give one way or another, that's the only thing centering the isos, so the placement of the adjusters is only for accessibly
     
  3. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    I always figured they said put them both on the left when they built the bike.

    But one guy was looking from front of the bike and the other was standing behind the bike.

    IE-It makes no sense to me either.
     
    MichaelB likes this.
  4. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004


    Tightening (or slackening) the Mk3 vernier adjustment reduces (or increases) the overall width of the complete Iso. assembly, it's not pushing or pulling against an immovable object.
    When the vernier Iso. through-bolt or stud is retightened (as it must be slackened to adjust the Iso.) it's the frame tubes each side of the Iso. assembly that are pulled inwards to Edit: compensate for the reduction in Iso assembly width but it's only a few thousandths of an inch which, in frame terms is practically nothing.



    The 850 Mk3 front Iso. threaded adjuster has to go on the right-hand side, regardless, as it's wider than the pre-vernier Iso. abutment. The Mk3 front Iso. tube is machined down to accommodate the additional width on that side, therefore, clearly must have been designed that way* and is what's stated in the Mk3 manual so obviously wasn't a production line mistake.

    The pre-Mk3 front Iso. conversion kit adjuster, however, could go on the left as the conversion kit threaded adjuster is the same width as the previous abutment. Same goes for the Hemmings conversion adjuster.

    Edit:
    *One possible reason why the front adjuster was placed at the right-hand end was so the same 06-4665 adjuster collar could be used for both front and rear Isos.
    Due to the front Iso tube/engine/cradle offset it would not have been possible to fit the 06-4665 adjuster at the left-hand end.
     
    Last edited: Dec 5, 2019 at 4:44 AM
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  5. MichaelB

    MichaelB VIP MEMBER

    Joined:
    Jan 14, 2004

    I asked for logic and that sounds logical.
    Back of my brain is whispering the original engineer probably had in mind both from the left.
    With manufacturing cost compromises, the same adjuster was used as stated moved it to the right in the front.
    The rear wheel can be corrected in the swing arm to align with the front, then the chain is out etc. etc.
    We're talking thousandths of an inch on a road bike.
    Does it really matter?

    Not sure, Just one of the Norton Weirdnesses that has bugged me.
     
  6. cash

    cash

    Joined:
    Nov 10, 2006
    I fitted my adjusters on the same side years ago and everything lines up spot on. Sadly I cannot for the life of me remember if or how I had to modify anything.
     
  7. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    I agree, it really makes no difference. As stated the frame does flex the same on both sides when the iso is tightened.

    But, If I were to have designed it, they would have an adjuster on both sides.... and the frame would not have to flex as the iso is adjusted. Then cradle alignment would be obtainable with just a simple adjustment.

    On second though, I would have done away with the adjustments and the washers all together like I have done on my bike. The isolastics mounts are located with easy to adjust tie rods.
     
    Last edited: Dec 5, 2019 at 8:57 AM
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  8. cash

    cash

    Joined:
    Nov 10, 2006
    I think I just swapped the rear adjusters over.

    This old age sucks I'll tell you.
     
  9. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Is there any reason that 4 identical adjusters won't work on the otherwise standard MK3 front and rear isos?

    Glen
     
  10. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    With that nice lathe I'm sure they could be made to work.
     
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  11. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    With the front and rear adjusters on opposite sides there is a very slight potential for misalignment if the clearances at each end of the Iso. are not roughly equal but so small as to be unimportant.

    If, for argument's sake, it is assumed the cradle/swingarm assembly is in alignment when both Isos. are, for instance, set to 0.010" clearance with an equal (0.005") clearance at each end then the maximum potential for cradle misalignment at each Iso. is 0.005" but in opposite directions.
    The distance between the rear Iso. and rear wheel spindle/axle is not much greater than that between the front Iso. and the rear Iso. so the potential for misalignment or offset at the rear wheel from opposing adjusters or unequal clearance is negligible in my opinion.
     
  12. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    It would require one wide and one narrow adjuster at the front (unless the front Iso. mount was modified in some way) as there isn't sufficient space at the LH end to fit a wide or an identical adjuster. Edit: (I suppose it would be possible to fit four identical 'short' adjusters and an additional three spacers?)

    The reason the wide adjuster could be fitted at the RH end was that the section of mount tube projecting from the bracket plate at the RH end was longer than the left so could be machined down.
     
    Last edited: Dec 5, 2019 at 10:34 AM
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  13. MichaelB

    MichaelB VIP MEMBER

    Joined:
    Jan 14, 2004
    I'm currently working on a 72 Combat that has had the Mark III Isos installed.
    I put it all back like the factory cause, well, that's the way the factory did it and it's been bugging me ever since.
    Since the front won't flip, thinking of flipping the rear, like Cash did, or thinks he did.
    Drive train is in.
    Question, how hard is it to pull the rear ISO's, with the drive train in. Can the rear stud and head steady be pulled and rotate the assembly up to clear the Iso.
    Battery tray assenbly is not currently installed.
     
  14. cash

    cash

    Joined:
    Nov 10, 2006
    Okay I check it tonight.
     
  15. cash

    cash

    Joined:
    Nov 10, 2006
    Yes that's what I did. I don't recall any difficulties getting the adjusters out, the iso rubbers can be changed in place but it can be a bit of a fight.

    I hope you appreciate this, I got attacked by three hungry Labradors and it bloody cold outside.
     
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  16. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    My 76 MK 111 has both vernier adjusters on the same side . The bike was a ground up restoration by a very knowledgeable builder who had the frame powder coated before the isos went back in. So I think there was no mistake but I was surprised after I bought it. But all seems well. They were dry and needed lube then vibrations smoothed out after.
     
  17. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    It was either a mistake or done deliberately as the rear adjuster would normally go on the left-hand side as stated in the Mk3 manual and drawn on the parts diagram.

    https://andover-norton.co.uk/en/shop-drawing/136/engine-mountings-spring-head-steady-
     
  18. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    Both front and rear adjusters are (now) on the same side, Right side. When I bought the bike for big coin it had vibration issues. It had spent most of it's life being trailered back and forth to shows and never driven , so I peeled back the gaiters , lubed and adjusted the isos. and was surprised to see the swap-over. A bad vibration issue was over with some lube and adjustment. 8 X show(s) winner , "Best in Show". But never driven ! Until moi.
     

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