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Valve train...

Discussion in 'Norton Commando Motorcycles (Classic)' started by olympus, Jul 11, 2018.

  1. olympus


    Aug 5, 2017
    I read with interest all the posts on cam lobe wear/hardening issues etc.
    Just putting the top end back together. New valves, springs & collects following a very slight cut of the seats.
    I'm normally use to seeing a smaller amount of valve protruding from the top cap, but hey ho... Compressed the new springs & broke my trusty valve spring compressor... so bought a new one not thinking much about it
    Installed both the inlets & I'm amazed at the amount of pressure /compression being exerted... a tap test on the top of the valve to make sure the collets are seated isn't moving anything + the springs are almost coil bound
    Bottom caps & insulators are fitted, everything is seated correctly
    Somewhat worried I have stripped then both out & checked valve s, spring length inner & outer, and the collect
    Dry fitted everything on the bench using old & new and everything looks exactly the same.
    So a couple of questions
    Is what I'm seeing correct....have others noted this
    Is a significant amount of spring compression needed to fit the collects
    Should I be fitting two springs
    Have I missed something or done something wrong??

    Its no wonder cam wear is such an issue

    Thank you
  2. lcrken

    lcrken VIP MEMBER

    Mar 15, 2009
    Are you using stock parts or aftermarket?
    The valve tips do stick up significantly more than you usually see on some other bikes and most automobiles engines, typically something like .340" - .370" above the collets, depending on whether they are stock or aftermarket, and whether they have been had the tips re-ground.
    Are you able to measures the assembled spring length, and compare it to the specifications? Stock installed spring length is 1.259" (1.321" for Combat) for intakes and 1.284" for exhausts. Aftermarket springs can have different specs. If the springs are almost coil bound, something is certainly wrong.
    Not sure what you mean by "fitting two springs"? Stock is two springs, an inner and an outer.
    FWIW, my old British C-clamp type spring compressor bends a bit when installing Norton springs, but a more modern type meant for automobile engines doesn't.
    And it does take a pretty hefty hit with the hammer to move the valve when checking collet fit.

  3. olympus


    Aug 5, 2017
    Many Thanks Ken,
    Two springs, I do mean inner & outer
    I have measured spring free length & installed length both are spot on spec
    Don't have coil bound springs, but the clearance between the coils does seem small compared what I'm used to seeing... glad I don't have a high lift cam!!
    I'm glad you have had the same experiences of high compression needed to compress them & having to hit the valve hard to confirm collet seating.
    The valve length is also correct along with distance down the stem a collect seating
    Probably just being over cautious
  4. lcrken

    lcrken VIP MEMBER

    Mar 15, 2009
    Better to be cautious than otherwise, but it sounds like everything is normal. Probably still worthwhile to check for coil clearance with a valve at full lift, after the engine is assembled.


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