Crank pulley vibration dampers & harmonics. Update: Lightweight crank pulleys = Bad

Discussion in 'Engines' started by A.N. Other, Jan 18, 2010.

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  1. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Creating Pfredstarke
    Yes after time the rubber cracks up/breaks due the dissipation of heat energy.
     
  2. alexisblades99 Forum Member

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    i remember my old dt250 having rubber pads inside the rear sprocket. same idea as a dmf?

    they'd go hard with age/temp/use and need swapping for fresh ones, so it seems sensible that the rubber in a damper pulley would change its properties with age. the one that came with my engine i threw in the bin as it was all perished looking.
     
  3. RobT

    RobT Forum Junkie

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    nope - thats a cush-drive - fitted to many road bikes to reduce the shockloadings on the chain and gearbox and increase lifespan

    not used on race bikes that are regularly rebuilt
     
  4. alexisblades99 Forum Member

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    so what is a dual mass flywheel if it's not a cush drive?
     
  5. RobT

    RobT Forum Junkie

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    a cush-drive is a straightforward shock-loading damper

    a dual mass flywheel is a harmonic damper by the sounds of things
     
  6. Ess Three Forum Member

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    I was under the impression that a DMF acted at least partly like a cush-drive, taking the shock loading out of the clutch and smoothing things out. Does it not?
     
  7. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Creating Pfredstarke
    The harmonic damper cancels 3rd order forces from torsional vibration that can lead to fatigue or failure. Torsoinal vibration is a maximum away from PTO or flywheel end.
    The DMF filters high frequency forces of torsional vibration ( not the lower frequencies that are responsible for drive torque) to drive train giving a pleasant feel to operator/driver.
     
  8. VR6T

    VR6T Forum Member

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    Toyotec, having a blond moment! what is "NVH" short for?
     
  9. MUSHY 16V

    MUSHY 16V Moderator Staff Member Moderator

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    Noise vibration and harshness
     
  10. VR6T

    VR6T Forum Member

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    OK makes sense now...

    Cheers
     
  11. danster Forum Addict

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    The dual mass flywheels do have a cush drive effect. If you check a clutch friction disc out of a DM setup it generally has no springs as the flywheel absorbs the torsional force when the clutch pedal is released. Conventional solid flywheels applications generally have a sprung inner section to the clutch friction disc that does a similar job.
    Saves excessive shock loads to the transmission and crank too.
     
  12. A.N. Other Banned after significant club disruption Dec 5th 2

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    Akin to a clutch plate centre spring?
     
  13. alexisblades99 Forum Member

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    that was the way i understood DMFs, fitted because of the higher torsional acceleration from modern turbodiesels (and a lesser extent turbopetrols) making it necessary, or at least desirable, in order to extend drivetrain service life and reduce bad vibes.

    if the greatest torsional vibration of the crankshaft is at the pulley end, the ideal solution would be another dual mass flywheel fitted there? which is basically what these expensive damper pulleys are a scaled down version of, no?
     
  14. badger5

    badger5 Club GTI Sponsor and Supporter Trader

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    fluid damper is nothing like a dual mass flywheel
     
  15. alexisblades99 Forum Member

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    so how does it reduce the amplitude of torsional vibration? does it vibrate out of phase with the crankshaft vibrations and cancel them out?
     
  16. s1m0n Forum Member

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    It changes the harmonic of the rotational parts

    No, the common theme is harmonic resonance
     
    Last edited: Jan 31, 2010
  17. A.N. Other Banned after significant club disruption Dec 5th 2

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    Is harmonic resonance in any way exacerbated by higher revs?
     
  18. s1m0n Forum Member

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    Maybe ;)

    Let's put it this way, your at 3555rpm and 1.2634 bar boost and at this revs/boost there is a "new" "aggressive" harmonic in your crank caused by your change of flywheel and/or crank pully...

    By 3556 rpm the harmonic is decreasing but this lap your at 3555 rpm for .032 seconds longer than "normal" and the crank explodes...

    Unlikely? Of course!

    Much more likely to be while your reving you new toy over 8k again and again BUT without the ability to measure it your better erring on the side of caution (like Bill).

    ABF (i.e. RobT) is completely different engine but still subject to the same physical laws (ditto VR6) but (in my limited experience) the NA KR/9A/ABF seems not to "mind" running a billet pulley combined with a light flywheel

    Of course that's not to say that the "built" engine failures that have been publicised on the forum (GVK etc) have not been down to harmonics, of course, without extensive testing you can't really say.
     
    Last edited: Jan 31, 2010
  19. A.N. Other Banned after significant club disruption Dec 5th 2

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    Interesting read. But if the time period was extended further, that comes back to what I'd posted earlier:

    But this would suggest the opposite.

    Harmonics. Still trying to get my head around the notion these aren't sophisticated vibrations, but I need to go back and read a couple of the links in this thread properly.
     
  20. A.N. Other Banned after significant club disruption Dec 5th 2

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    Now that's interesting. So what you're really saying is harmonics building (from your experieces of those engines) don't get too destructive.

    They're all 4 cyl N/A motors... [:s]
     

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