Dynamic Balance

Discussion in 'Vincent' started by worntorn, Dec 14, 2017.

  1. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Sorry Glenn - my comment was directed a the Norton twin crankshaft - I should have been more specific.
    You comment holds true for singles' crankshafts as well - although I personally don't see much merit in dynamically balancing those as the mass of the flywheels is very narrow/central.
    The same logic could be true for Vincents?

    Rob
     
  2. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    I can't say for sure as I have only had the dynamic balancing done to this one Vincent crank and we also changed the bf dramatically.
    John Mcdougall, who rebuilt scores of Vincent engines, swore by the dynamic balance after trying it on one engine and getting an excellent result.

    Glen
     
  3. p400

    p400 VIP MEMBER

    Joined:
    Jul 14, 2014
    so, my reciprocal weight is
    2 piston assemblies - 930gm
    2 rod pin ends - 380
    total - 1310gms

    if my desired balance factor is 46%, then .46 x1310=603gms
    subtract the fixed pin ends 603-380=223gms
    then I would expect my Pit Posse rig hanging balance weight to be 223gms.

    It seems I measured 220gms.
    close enough?
     
  4. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    You bet!

    Glen
     
  5. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Finally some decent riding weather!
    Tried out the bike again to determine the sweet spot for rpm to see if a gearing change is needed.
    The standard Vincent is already very high geared at 3.5 to one overall for " relaxed touring" as Irving put it.
    This compares to a standard Commando with about 4.39 overall gearing when using a 21 tooth cs.
    In trying to quell the vibrations of this 1360 I had mounted a 22 cs sprocket and 42 tooth rear sprocket for an extremely high overall ratio of 3.04 to one.
    This works out to 2800 rpms at 70 mph, barely ticking over. It didn't help much with vibration, it was unbearable at anything over 50 mph!
    With the dynamic balance done it's a world better as mentioned earlier.
    Today I found the engine to be smooth at almost any rpm above an idle .If anything, things are smoother yet as the revs go up.

    Starting in top gear at about 2000 rpm, with the Dakota Digital speedo/tach switched to full screen, tach only, I tried cruising at ever increasing rpms . Things started out well and got very smooth at 3500 then stayed that way to 5000 rpm at which point the windage on my body was getting quite strong. So I held it at 5 k rpm for awhile , engine just purring along at about 1/3 throttle, mirrors clear.

    Went home and did the speed calcs.
    5000 rpm is 125 mph.
    No wonder the wind pressure was high!

    Private road, of course.

    Now very happy with this engine !

    Glen
     
  6. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Sounds brilliant Glen.

    Glad to see you have such big, long, private roads near you... like me!
     
  7. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    The scary/nice thing was that opening the throttle at 125 mph resulted in strong acceleration.
    I think the bike would easily pull to 6500 with the tall gearing.
    It would be good to have at least a 1/4 fairing like the Thruxton has in place for that . And maybe a racetrack rather than a private road!

    Glen
     
    Last edited: Apr 22, 2018 at 9:46 AM
  8. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Impressive. What max speed would that equate to do you think?
     
  9. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    If it will pull to 6500 that figures to 162 mph.
    One day I would like to see whether it will actually do this, but it will have to be on a track.

    Glen
     

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