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primary chain hydraulic tensioner assembly doesnt make sense

Discussion in 'Norton Commando Motorcycles (Classic)' started by p400, May 16, 2019.

  1. p400

    p400 VIP MEMBER

    Joined:
    Jul 14, 2014
    I have received AN new tensioner parts and included were drawings of the assembly.
    When assembled as shown the tensioner rubber feet go coil bound and do not reach full contraction.

    When I disassembled, the plastic pistons were reverse of this and their small end was inside the spring with the piston against the end of the tube.

    WTF ?

    20190516_PrimaryChainTension2.jpg



    View attachment 10142
     
    Last edited: May 16, 2019
  2. MexicoMike

    MexicoMike

    Joined:
    Jan 31, 2010
    Any assembly I have seen like that would have the small diameter portion of the Nylon piece inserted into the spring. Otherwise, there is no reason to have a shoulder on it, it would just be a straight "rod" of nylon of proper diameter to fit in the housing (the diameter of the shouldered portion of that piece). Looking at the pic of the tensioner, I'd say the drawing is incorrect and that the tensioner cannot function as per the drawing. But hey, there are plenty of decidedly "odd" things about Norton construction... ;)
     
  3. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    The AN drawing/images show the nylon plug (B) oriented correctly.
     
    Last edited: May 16, 2019
  4. MexicoMike

    MexicoMike

    Joined:
    Jan 31, 2010
    Yep...decidedly odd! ;) Maybe AN got super deal on some discarded shouldered nylon pieces that would work since the shoulder serves no purpose in that assembly per the drawing. In fact, it create the possibility of abnormal wear on the tip of the nylon that bears against the plunger since it can "wobble" in the bore. Is that an original tensioner or a "modern" replica?
     
    Nater_Potater likes this.
  5. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004

    Agreed, it does look odd.

    Maybe reversing the plug was a factory mod. to increase spring preload?
     
  6. gtiller

    gtiller VIP MEMBER

    Joined:
    Nov 5, 2012
    @MexicoMike it was shouldered this way from the factory.

    ...not an Andover innovation, they have merely stuck to the original design.

    If the waisted section sits inside the spring
    1) it is not the under enough compression to tension the primary chain properly
    2) it acts as a stop, restricting the amount of movement of the plunger

    People (including Norton pros) have been reassembling this component incorrectly for many years.
     
    jimbo likes this.
  7. MexicoMike

    MexicoMike

    Joined:
    Jan 31, 2010
    Interesting stuff! :)
     
    gtiller likes this.
  8. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
  9. jimbo

    jimbo VIP MEMBER

    Joined:
    Sep 25, 2004
    Yep I just assembled mine wrong , with the button away from the spring. I looked at several used plungers and they have the the button towards the spring. But for now I am not going to it apart. I am wondering if they can be installed the "right" way, button towards the spring

    DSC09694 wrong.jpg
     
  10. jimbo

    jimbo VIP MEMBER

    Joined:
    Sep 25, 2004
    I am wondering if the steel plunger plate can be wiggled out from under the starter gear to get the plungers out without taking the stator and assembly off?

    DSC09860.JPG
     
  11. p400

    p400 VIP MEMBER

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    Jul 14, 2014
    It does not seem to make mechanical sense, but the drawing does show this config.
    The shoes when fitted, with this config, are hard down coil bound.
    Doesn't make sense.
    when the nylon pistons are fitted about, the" wrong "way, the system makes sense.
     
  12. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    Do you mean with the tensioner assembly fitted and the plungers tensioning the chain?

    It's certainly how the nylon plugs are fitted to my Mk3's tensioner plungers (see previous discussion).
     
  13. Esmerela

    Esmerela VIP MEMBER

    Joined:
    Jan 9, 2017
    Hi

    I experienced the tension coil bound issue when fitting a Chain man Duplex conversion and new AN plunger/slipper assemblies to my friends 77 MK3. I got over the issue by trimming 3mm off each of the old "Plastic pistons", saving the new full length plastic pistons for another day. Its not like we are never going in there again;).

    I should add when fitting exactly the same chain and AN tensioner parts to my 75 MK3 I never encountered the problemo_O
     
  14. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    Maybe fit the nylon plugs the 'wrong' way until the chain has 'stretched'?
     
  15. p400

    p400 VIP MEMBER

    Joined:
    Jul 14, 2014
    i cant believe this issue is not well known. You fit new plungers/rubber feet into existing tensioner body with the plastic as shown in picture and
    1. the plungers can not be fully pushed in to the body as the spring and plastic are so long they coil bind and leave 1/4" plunger shaft visible.
    2. when you fit this unretractable plunger/body into the primary chain, it pushes the primary chain off normal top track............allowing the top run of primary chain to "saw" immediately into the top plunger, while the plunger remains coil bound.

    This configuration doesn't make sense.
     
  16. jimbo

    jimbo VIP MEMBER

    Joined:
    Sep 25, 2004
    this photo shows the primary assembled with the plungers having the plastic button away from the spring and some of the plastic spacer inside the spring, the "wrong" way. The chain run on top is straight and the bottom has the extra and has a little bow which is correct . I don't think I could have put it together with more of the plungers sticking out. like p400 said.Anyways the weak little spring tension can only do so much. Probably just to hold the plungers in place when not running and the oil running out of them. Its all about the hydraulic action. With that being said I do have some primary chain slap, when taking off, maybe I did not get them filled well enough and they have some air in them. Its a messy job trying install them, they want to extend out and oil leaks everywhere

    DSC09860.JPG
     
  17. gtiller

    gtiller VIP MEMBER

    Joined:
    Nov 5, 2012
    @p400 it is well known, and has been discussed on here (and other forums/groups) in the past.

    We can only give you recommendations based on the factory drawings and how Norton employees at the Norton factory assembled the unit.

    Of course, if you decide to assemble it differently, and it works well for you, that’s great - happy days


    Remember to fill your primary with 200ml of engine oil, not ATF-F as we do with pre-MK3s
    The thinner ATF-F is too thin for the tensioner to work properly.
     
  18. dynodave

    dynodave

    Joined:
    May 28, 2003
    I'll take a look inside the primary of my 5 mile MKIII for how the real norton factory built them originally. But it won't be right away. I'm trying to build 2 engines to be running for the rally
     
  19. jimbo

    jimbo VIP MEMBER

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    Sep 25, 2004
    Funny I just had all this apart and cant remember what I dido_O, but heres some photos of the plastic piece in two different configurations. One seems to have the button part inside the spring.

    DSC09694.JPG DSC09695.JPG
     
    p400 likes this.
  20. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    Due to the previous discussion I know the nylon plugs in my Mk3's plungers are fitted as shown on the AN drawing.

    Both upper and lower plungers touch the tensioner body without becoming coil-bound so something must have changed.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
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