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Thread: Knife Edges for Crank Balancing

  1. #21
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    [continued from previous post because it was 35 words too long]

    --------------------
    Sidebar: The difference in weight of the bronze in an original 1" ID bushing and the current 13/16" reducing bushing in the small end:

    Density of steel = 7.75-8.05 gram/cm3
    Density of bronze = 8.7 grams/cm3
    Width of connecting rod = 0.87"
    Width of current reducing bush = 1.065" (tapered)
    OD of bush = 1.1875"
    ID of original bush = 1.000"
    ID of current bush = 0.8125"
    From this, the excess weight of the small end over that with the stock bush = 7.4 g
    ---------------------

  2. #22

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    Quote Originally Posted by T. Cotten View Post
    Folks,

    Without getting into the quagmire of factor and rpm yet,
    I found that it is most practical to determine an existing factor of an assembly when the 'edges' are suspended high enough to accept installed rods, and perhaps a piston.
    (It saves a lot of math!)



    .....Cotten

    Yes. Exactly. The same is true if you are using bearings rather than edges, of course.

    The traditional way to balance early Indian twins is to do it with both rods, one piston, both pins, and all of the rings suspended from the crankpin.




    Kevin


    .

  3. #23
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    Quote Originally Posted by TechNoir View Post
    Hi Cotten, thanks for posting the picture of your rig.

    You have confirmed what I had intended to do which was make my rig high enough to hang a rod and piston under it. Tommo had mentioned something similar previously so thats what I am going with.

    From the axle to the end of the rod on my 20F is about 12 inches and I would obviously need a bit more to allow for a piston. I have a 1950's Matchless single that will need attention in the foreseeable future but that crank/rod assembly is a couple of inches less than the F. I am guessing (without checking the engine specs) that a JD would be a bit more than the J Harleys? I would also assume that a Big X or an Indian would be similar dimensions to a J or JD and that all of those would be more than most British singles? So, if you don't mind me asking, what height would you go for from the top of your base to the top of the knives if you were to do it again?

    John
    Good question John!

    Taking a tape measure to a Chief crank for a model, it looks like the single-piston/rods assembly that Kevin suggests, at ninety degrees balanced position would need at least ten inches for comfort. (A full travel beneath the edges isn't necessary, just workable clearance at 'level'.)

    I err'd on the side of caution, and built mine far taller than I can now explain the reasoning, at 15.5".
    But that's better than too short.

    ....Cotten
    PS: I think bearings could work fine, Kevin!
    Or even just between centers if your lathe is big enough.
    Last edited by T. Cotten; 12-18-2017 at 02:36 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  4. #24

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    You'd need 1/2 the stroke plus the rod center to center length plus the compression height of the piston plus a little more for good measure.




    Kevin


    .

  5. #25
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    Quote Originally Posted by Shaky Jake View Post
    ...The traditional way to balance early Indian twins is to do it with both rods, one piston, both pins, and all of the rings suspended from the crankpin....
    I shouldn't trust my memory, Kevin,

    Wish I could find my copy, but I think the later Military Chief manual uses just one piston, one pin, and one set of rings hanging on the rods, which back-calculates around 64%.
    Can you back-calculate the percentage produced by the earlier method? It would seem quite a bit higher!

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

  6. #26
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    Quote Originally Posted by T. Cotten View Post
    I shouldn't trust my memory, Kevin,
    ....Cotten
    When I first dipped my toe into the subject of balancng I posted this thread

    http://www.antiquemotorcycle.org/bbo...in!&highlight=

    Tommo was kind enough to reply and post some extracts from the Q&A book which are there. I am not sure if this is the text that you are referring to but it does talk about balancing using various combinations of pistons, pins and rings.

    John

  7. #27
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    The Q&A illustration of the flywheels on 'rails' still intrigues me, Folks!

    Note that the center of the crankpin is not level with the center of the mainshaft, suggesting the countermass is still heavy, yet the holes are drilled symmetrically level to the mainshaft.

    (When checking an assembly on edges, I gently hold the wheels to where the crank and mains are level, and then observe which way the crank moves when released.)

    The page 177 illustration makes me wonder if wood might deaden the action of the wheels on the edges.
    Ideally, a balanced assembly could rock.

    At any rate, methods that eliminated a scale for weighing hardware were needed for "field repairs".
    The enigma of the Indian Military manual is that it went into balancing at all!

    ....Cotten
    Last edited by T. Cotten; 12-19-2017 at 09:55 AM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  8. #28

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    Quote Originally Posted by T. Cotten View Post
    I shouldn't trust my memory, Kevin,

    Wish I could find my copy, but I think the later Military Chief manual uses just one piston, one pin, and one set of rings hanging on the rods, which back-calculates around 64%.
    Can you back-calculate the percentage produced by the earlier method? It would seem quite a bit higher!

    ....Cotten
    I think you're right Tom. Your memory is better than mine. If I recall correctly, the PowerPlus back calculated to 58% when done that way.

    I feel like it is a waste of time to put too much effort into being accurate when balancing these old engines. They're rugged and slow. The old way is as good as any way.





    Kevin


    .

  9. #29

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    Quote Originally Posted by T. Cotten View Post
    The Q&A illustration of the flywheels on 'rails' still intrigues me, Folks!

    Note that the center of the crankpin is not level with the center of the mainshaft, suggesting the countermass is still heavy, yet the holes are drilled symmetrically level to the mainshaft.

    ....

    ....Cotten
    Cotton, I've been thinking on this, and I'm not sure if I agree with your conclusion. Or perhaps the scotch whiskey is clouding my mind, and I don't understand what you're saying. Note that the document itself says "when properly balanced, the wheels will remain stationary in any position on the parallels."

    Here is a link to a video that illustrates that:

    https://youtu.be/iNY-wvHfZ9g



    Food for thought.




    Kevin


    .

  10. #30
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    Quote Originally Posted by Shaky Jake View Post

    Food for thought.
    Jake, thanks for asking that question, I had pondered the same thing. The youtube video that I mentioned at the start of the thread is here

    https://www.youtube.com/watch?v=HuyYAEIXvqI

    And shows the same thing at about 3 mins and 40 seconds.

    John

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