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Worn PW3 cam

Discussion in 'Norton Commando Motorcycles (Classic)' started by Fullauto, Apr 20, 2018.

  1. Madnorton

    Madnorton

    Joined:
    Jun 9, 2008
    Knowing DNC and who else he makes cams for, this sounds like a batch issue - the PW3 has been around a long time. With the current steel supply in overdrive and long delays in delivery, there is an awful lot of remelt being used at the moment of dubiuos quality. There must be some owners out there doing big mileages, what do they have fitted.
     
  2. jseng1

    jseng1

    Joined:
    Nov 26, 2009
    Part of the problem could be the Comstock conical springs. They have more pressure over the nose compared to other springs set up for street. More pressure = more wear. Figures below are for recommended installation height (each is different).

    Comstock conical 240 lbs at .4" valve lift.
    recommended install 1.4" (seat pressure 103)

    Stock Norton dual springs 224 lbs at .4" valve lift.
    recommended install 1.250" (seat pressure 85)

    RD racing springs 218 lbs at .4" valve lift.
    recommended install 1.350" (seat pressure 97)

    JS conical beehive 225 lbs at .4" valve lift.
    recommended install 1.450" (seat pressure 93)

    oldmikew asked about EN40B steel.
    I have used Newman cams made of EN40B steel with special Plasma nitriding (more expensive) and no problems.
     
    Last edited: Apr 22, 2018
  3. oldmikew

    oldmikew

    Joined:
    Jul 25, 2015
    Thanks for posting on Newman cams... that is reassuring. Spring pressure may well contribute to cam wear and I wonder if revs are kept down to say 7,500 whether there is any need for such high pressures to prevent valve float but then that presumably would also depend on the cam profile.
     
    Last edited: Apr 22, 2018
  4. Fullauto

    Fullauto VIP MEMBER

    Joined:
    Apr 13, 2009
    DNC is code for?
     
  5. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    David Newman Cams
     
  6. Snotzo

    Snotzo

    Joined:
    Mar 12, 2013
    JS

    The nose pressures you quote are only found in a stationary engine.
    The moment the engine runs, the nose pressures are reduced, and the higher the engine revs, the greated the reduction.
    A correctly ground PW3 profile has no dynamic issues when used with Comstock's conical springs, but the choice and quality of the camshaft material is another matter entirely.
     
  7. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Snotzo
    Is that really true?
    Intuitively I would have guessed peak pressures would go up on a running engine compared to stationary.
    Statically you are only dealing with the spring constant times deflection (plus gravity if you're picky)
    Dynamically you still have the spring constant (+ gravity) plus inertial forces associated with accelerating the mass of the valve train.
    This logic would, of course, see a lower pressure during valve closure (hence valve "float") - but higher peak pressures (during valve opening).
    This, of course, ignores situations of valve springs reaching harmonic frequencies - not predictable or welcome!

    Has your statement been proven empirically? Not trying to be rude - just inquisitive.
    Cheers
    Rob
     
    Last edited: Apr 23, 2018
  8. SteveA

    SteveA VIP MEMBER

    Joined:
    Dec 20, 2011
    I call mine a premature fail.......it ran one race season of 26 races in 2015, I pretty much think it was OK until the last race day, as I wasn't needing to adjust valve clearances.

    Supplied by Norman White in 2014. I asked Norman at the time I found the failure ( 2 years ago) and he said he had not had reported problems of lobe wear.

    It could have been associated with revving occasionally to 8K? with a momentary 8.5K! on the last race day

    I worried about shortage of oil, but can't be specific on whether there was or wasn't, but I did what I could to improve oil supply to the pump.

    And I fitted a Webcam! This cam runs very strong, but the motor does not rev as much as it did. I think on lap times it is probably about even with the PW3. I need to dyno it.

    However, I think the PW3 profile suited me and my motor/exhaust a little more, so if there was a hard welded one available that ran flat followers I might refit one for the profile, and adopt a lower rev limit.

    I don't want another chilled iron one.
     
    Last edited: Apr 23, 2018
  9. oldmikew

    oldmikew

    Joined:
    Jul 25, 2015
    Dunstall used to offer a so called pressure feed kit for use with his racing cams- they had a very narrow nose. It bled oil through the original Atlas early commando crankcase breather and presumably exited through the breather holes halfway along the cam.. This would at least ensure there was oil getting splashed about whether it penetrates to where it is needed ,or just cavitates on the bottom of the camshaft tunnel is another matter.

    I suspect thenotion is ex Jim Boughen , and he built a number of engines -not just for Dunstall but also for Gus Khun , so maybe some one somewhere
    has one and could point to the approximate size of the restrictor jet
     
    Last edited: Apr 23, 2018
  10. bill

    bill

    Joined:
    Jun 1, 2003
    I am NOT buying your assessment of this. 10 -15 lbs added spring pressure should have NO effect on wear IF it was a properly made ie material and hardened camshaft along with a using the proper oil and break in.

     
  11. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Actually, the added pressure over the nose helps improve the cam life. Cams fail from loss of valve train control and pressure over the nose helps maintain control.
    Of course lubrication has an impact.
    Chilled iron cams have a spotty track record and any cam with high ramp rates is going to push things to the limit as far as durability. Jim
     
  12. bill

    bill

    Joined:
    Jun 1, 2003
    like i said i was not buying his thinking. in the automotive world 240 on the nose is not that high on flat tappet cam. a friend has a big inch drag motor with a roller cam and it is scary numbers. 1.080 lift 1,400 lbs open pressure on a 2.620 intake valve. and yes these numbers are correct
     
  13. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    No doubt, but a lot of that pressure is used to hold the valve closed against 100 psi of blower pressure....
     
  14. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    So for Fullauto with his low Rev requirement, highly enforced speeding rules and single carb, a standard lift cam and standard springs would make sense in every way. More grunt and less stress.
    I think Webcam has a standard profile, or very close to it.

    Glen
     
    Fast Eddie likes this.
  15. bill

    bill

    Joined:
    Jun 1, 2003
    no blower just 2 monster 4 barrel carbs. the engine was built to run carbs but with that much lift on relatively short duration cam it would need a stout spring. it also uses 1/2 dia. pushrods
     
  16. Snotzo

    Snotzo

    Joined:
    Mar 12, 2013
    rob ss
    the poundages quoted by js were at peak lift, whereas you are talking about pressures at other lift positions.

    The worst situation for camshafts and followers is at very low engine speeds, usually only a few hundred rpm. Here the oil entrainment is chronically bad, in the region of 0.04 microns thick, while Hertz stress is very high, typically 950 Mpa. At 8000 rpm the oil entrainment is drastically improved by better than a factor of 10, while the Hertz stress is almost halved.

    At high rpm the inertia of the valve, retainer, collets and a portion of the upper spring coils, rocker inertia, pushrod and cam follower, leaves very little spring pressure available to bear on the surface of the cam.
     
  17. Fullauto

    Fullauto VIP MEMBER

    Joined:
    Apr 13, 2009
    Wrong. The power characteristics of the PW3 cam are far better than the standard cam in my application from idle on up. I'll persevere with the PW3, just make sure that the new one is suitable.
     
  18. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Yes, and when spring pressure overcomes the inertia of the opening valve -just after peak lift - this is when the valve comes back down to hard contact with the cam. That hard contact just after peak lift is what causes the little wear line down the center of your lifter. Jim
     
  19. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    You are going against everything the experts say ( don't include myself in that group, but I can read)
    Nonetheless, its your money...and engine grindings.

    Glen
     
  20. Fullauto

    Fullauto VIP MEMBER

    Joined:
    Apr 13, 2009
    I presume you are talking to me? Which experts am I going against? Which theories? Be a bit more specific.
     
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