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Thread: Flywheel Balance Factor for VL Motor

  1. #1

    Default Flywheel Balance Factor for VL Motor

    Can anybody (or Steve) tell me what the factory flywheel balance factor should be for a stock VL motor. I know about 50-60% factors for later motors, but I have read several places the stock VL motor has a flywheel balance factor in the 40%'s. If so, why so much difference and what is the factor. Thanks!!

  2. #2
    Join Date
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    I don't see why a 60% factor wouldn't work very good on a VL. It's been proven to be good for late motors. The reciprocating motion isn't any different between early and late motors. Maybe back in the 30's the factory didn't know any better. I'd also like to hear what other people have to say about this.

  3. #3
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    If you do a search for "harley balance factors" there was a good discussion on this site back in 05. Its worth the read.

  4. #4
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    I've been using a 46% balance factor on my last dozen VL motor builds and they seem fine. This came from my flywheel balancing guy about 15 years ago who said he found it in a notebook. He said the more modern Harley motors were balanced 58-60% as they were meant to blat around town at low revs. Most of the old books seem to imply 50% balance facors as they talk about halving weights when calculating for balance. It can't be that critical, as Shop Dope 112 of 17 December 1934 says it is not altogether necessary to rebalance flywheels when changing from iron pistons to the new T-slot aluminium pistons, as long as both pistons are changed. Those big VL flywheels must be very forgiving.

  5. #5

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    How do VL flywheels compare to UL flywheels in regard to mass?

  6. #6
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    Very comparable, the physical dimensions are almost identical.
    Robbie Knight Amca #2736

  7. #7
    Join Date
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    Harleytoprock!

    The reason for the lower factor for Vs is the different mounting within the frame.

    Kozy!

    Factor is totally independent of total mass.
    Heavy wheels and light wheels can have the same factor.

    The real shame Folks,..

    ..is that nobody takes the time to back-calculate unmolested motors before they molest them. Thus choice of factor is nearly always based upon hearsay or blind conjuring.

    Fortunately, V-twins are enormously forgiving!

    ....Cotten
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  8. #8

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    I am building a fixture with parrell sharp edge bars (similar to what Cotton shows at Virtual Indian site) to static time the assembled flywheels. Current balance holes at heavy end of flywheel are drilled from interior of flywheel. If I have to drill additional holes, can they be drilled from exterior of flywheels as long as they do not line up with current holes on interior sides. My flywheels currently have two drilled holes on one flywheel and one drilled hole on the other flywheel. If factor is below 50% (say 46%) would not the weighted end of the flywheels be lighter than the measured recipricating + rotating assembly. I do not have OEM pistons and will be using after market pistons. To static the assembled flywheel assembly on my parrell bar fixture, whould not I have to temporarily add weights to the heavier counter weighted area of the flywheels. I am over my head, but I am going to learn how to do this. Thanks!!

  9. #9
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    Apr 2003
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    You should balance the wheels seperately.

  10. #10
    Join Date
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    Buster!

    I'm not clear on your question, but first,..
    "knife edges" aren't really 'sharp', but ground to a narrow flat on top.
    If I were to do it again, I would just use ground round stock instead of ground planer blades.

    The flywheels won't know if you drill all the way through to another hole.

    And most factory-mated wheels are already "equalized" satisfactorily. Balancing them separately is often an exercise in feeling good. You hope they are moving as one mass anyway!

    When on edges, you will be stacking weight upon the rods (or conjuring a bobweight) to simulate the reciprocating mass, until it comes to balance. Then you can calculate the existing factor, and stew about changing it.

    There is only one total reciprocating mass in the motor balancing formula, and only one counterbalance mass. The percentage of the total reciprocating mass that brings it to balance is your factor.

    So you need to know your total. Weighing the piston assemblies is easy.
    The rod tops only take a little more attention.
    This can be achieved, even while assembled, as shown in the attachment.

    ....Cotten
    Attached Images Attached Images
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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