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. chopperoli Forum Member

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    Hi Romain,
    Did you ever get this engine built? Did you know that GTI Engineering stopped using the 90.5mm crank for conversions back in the day because it was "found to be a source of vibrations"...
     
  2. romaingirardlamamy

    romaingirardlamamy Forum Member

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    Hi choperolli
    It s still in the process
    Collecting bits little by little
    And was stuck waiting for the valves kit group buy to happen
    And it s finally happening

    No I didn't know that
    But I know that drake used it for their race engine and was happy with it
    And that crank was the closest (stroke wise)
    To the kit car specs
    I am planning on having it balance anyway then superpolished
    Will certainly post something on group buy for the superpolishing

    And I am having a fluidamper like I said for peace of mind
     
  3. HPR

    HPR Administrator Admin

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    once there was an article in MTZ ( motortechnische zeitung) about 1800 Gti
    On the cranckdamper: there is no need , but we mounted it, as it makes the engine a bit more silent....
     
    Last edited: Jan 23, 2011
  4. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Do you know which one? I may be able to find it.
     
  5. HPR

    HPR Administrator Admin

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    Must be around 1982 ?
    I must have it here somewhere....but were
     
  6. A.N. Other Banned after significant club disruption Dec 5th 2

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  7. challice Forum Member

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    Lightweight crank pulleys = Bad

    I've had a set of lightweight pulleys fitted to my engine for around 2yrs/7k miles, pictured below...

    [​IMG]

    I've recently been reading up on these on here and other forums, Badger5 posted up with an engine that had destroyed itself an it had a lighweight pulley fitted.

    I no that there is no evidence that 100% proves that these type of pulleys cause problems but i have just removed all mine an refitted the standard crank pulley along with std power steering pulley and alt pulley, i have done this to stay in the safe zone if you understand that, removing the risk of destroying my bottom end.

    I also have a helix SMF fitted so i had an amount of gearbox "chatter"

    On starting the Golf up tonight to check the pulleys/belt are ok i noticed somthing very good in my eyes...

    The gearbox chatter has been reduced by around 75%, its still there but very minimal, also along with this the engine idle is much smoother...

    This is very good in my eyes an i strongly recommend to anyone who has these fitted to remove them, goin off my findings.

    Im simple terms the bottom end is like a see saw, the flywheel one end crank in the middle an lightweight pulley at the other, the bottom end is going to be bias to one end due to the weight differance across the crank.

    Now i have the standard weight on the pulley end of the crank its evened itself out which is proved by the gearbox "chatter" being massively reduced.

    I understand the theory of the lightweight pulleys in reducing the weight the engine has to "spin up" thus giving a slightly faster rev/throttle response but you have to ask yourself at what cost?

    I'm happy with the choice i made to remove these :thumbup:
     
    Last edited: Nov 19, 2011
  8. A.N. Other Banned after significant club disruption Dec 5th 2

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    Good info and adds weight to the previous discussion earlier in this thread where said picture from Badger5 resides, concerning a Neuspeed pulley in that instance:

    The main pulley of concern is the bottom crank one - 3 pulleys in your pic, the other two are immaterial to the issues here.

    Your engine presumably is a 20vt?
     
  9. drunkenalan Paid Member Paid Member

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    not 20v but, i was amazed when i put the lighten OE GTI one back on my car after running the steel driver one for 6 months, i wont fit a solid / lightweight one again
     
  10. challice Forum Member

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    Yeap mines 20vt...
     
  11. A.N. Other Banned after significant club disruption Dec 5th 2

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    Now merged / tidied
     
  12. Matt82

    Matt82 Forum Addict

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    My 1.8t has had smf since Feb this year and gained almost zero gear chatter, could barely hear it.


    I did the cambelt etc the other week, suddenly a massive gain in gear chatter, so much so even the gf commented. The pulley is still original, its on straight and true, and can only go on one way. Ideas?
     
  13. A.N. Other Banned after significant club disruption Dec 5th 2

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    Anyone fancy taking a chance? !

    [​IMG]

    [​IMG]

    Click
     
  14. LeftcoastTigger Paid Member Paid Member

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    Omitting crank dampeners

    No - - thank - - you

    Ignore engineering speculation and empirical evidence and consider the logic - - surely no manufacturer in such a competitive field is going to test for, develop, manufacture, and fit proprietary harmonic balancers - - plus carry yet another spare part, Worldwide - - unless justifiable[:|]
     
  15. Mike_H Forum Addict

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    Bought a 1.6 XFlow lump recently for the head. I noticed that there's no damper element in the crank pulley - just pressed and welded steel. I'll weigh it if I get a chance.

    [​IMG]
     
  16. mec82 Forum Member

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    This is something I come across at work and I'd say vibration dampers are essential if fitted as standard, engines produce huge instantaneous torques at the crank and this torsional vibration will fatigue parts and can even break cranks.

    a 4 cylinder diesel engine that makes 400Nm can have an instantaneous torque profile that goes up to perhaps 1500Nm and as low as -500Nm. 400Nm is the mean torque.

    torsional vibration at the crank has 2 components;

    1 - gas torque - this depends on combustion pressure and mechanical advantage of the crank
    2 - inertia torque - this depends on engine speed as its caused by the piston motion and reciprocating mass

    so the profile changes with speed and the inertia component can add to the gas torque or subtract from it at different speeds. the equations are pretty simple, I'll dig them out if anyone interested.

    cranks and other components are usually designed with a natural frequency way above the main frequencies of the vibration but there are higher order components that will overlap. If you get a resonance set up then things will break. the damper isn't really a damper, it just adds a mass/spring with some hysteresis into the system which takes some energy out at a problem frequency. Chris might be right that NA engines can rev quickly through the critical frequencies and have less issues.

    remember that the camshaft and other ancillaries might be driven off the crank and these will see the vibrations as well, belt stretch and tensioner movement can interact with it as well to damage or throw off the belt.

    this website has good info and some good graphs showing the vibration;

    http://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htm
     
    Last edited: Feb 20, 2012
  17. Mike_H Forum Addict

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    But they seem to be stopping - at least on some engines. Have improved machining and balancing removed some of the need? If so, does a lightened and balanced bottom end still need one?
     
  18. LeftcoastTigger Paid Member Paid Member

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    Deterministic chaos www.wikipedia.org/wiki/Chaos_theory

    Agreed - - but I suspect some bright folk aided by super computers have created software which guides the modification of formerly semi compatible components through changes in material, mass, rigidity, dampening etc etc - - and, just possibly, have tweaked the cost/benefit formulaes slightly while gambling the consumer, in a world where steady engine speeds are increasingly infrequent, will not have the opportunity to discover that destructive harmonic[xx(]

    Best practical example is the old trick of gently rubbing a moistened finger around the lip of a crystal wine glass while it's held by the base - - I've seen one shatter from that simple action alone[:^(]

    Place a teaspoon of water in the glass - - hold it by the stem rather than base - - smear some honey around the bowl - - any such change prevents vibrations from propagating and the wine glass is spared:thumbup:
     
  19. dUff

    dUff Administrator Admin

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    Humm i have a set of these on my 1.8T , perhaps its time to find a OEM crank pulley
     
  20. mec82 Forum Member

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    More so I'd say! The crank webs are there to balance the engine and to smooth out the torque pulses, along with the flywheel. if you lighten the crank and flywheel the torsional vibration gets bigger! the properties of the damper will need to be modified to work at the right frequency though.

    A damper costs money, OEMs wouldn;t fit them if they didn't have to.

    if its fitted then the OEM found a vibration problem in development. that might be simple NVH issue thats not relevant in a track car or it might be because they were stretching belts or snapping cranks!

    Remember that all the well built race engines that you see without dampers aren't built to last unlike a road engine. IMO the lightweight pulleys are pointless on a turbo motor anyway as the main transient issue there is boost lag.
     

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