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Thread: balancing a jd

  1. #1
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    Default balancing a jd

    1927 74" panhead low compression pistons. timing is set at 35 degrees btdc. Using s&s's formula I have tried 60,55,and 50 percent. At 60 the bars were trying to come off, now at 50 it is a lot better but still not right. I've done several pans and shovels with good results but this jd has got me stumped. Anybody familiar with these? Do I need a different formula or what?

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    Can you post up your formula....

    Like to see what numbers you have for front and rear reciprocation weights of the rods ..??

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    front top is 205.55 rear is 196.98. bottoms,, front350.73 and the rear 274.66. remember on a jd the rear rod is the male. my total recip at 50% is788.35 and rotating is 1165.89 . this makes for 977.12 on each wheel. I might have found a lot of the problem. I've been bumping the timing up from 35 to about 45 and it has helped a lot. At 45 mph it is just fine and going through the gears feels a LOT better

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    Information on these motors is hard to come by. One fellow who is a well known balancing whiz told me that the higher the rpm a motor turns the lower % factor should be used. But everything I can find says the earlier pans knucks and shovels were done at 50% and the later models were 60%. The higher the speed that was normal to drive the higher the %age. I've done a few pans and shovels at 52 and have been very pleased with the outcome.

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    Click image for larger version. 

Name:	Capture JDB.JPG 
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ID:	85996

    Does this look bout what you have ... ??
    Question, did you weigh each piston to see if they was close to the same weight .. ??

    Got the numbers for the crank pin etc...?
    And pistons etc...?
    Last edited by Dragstews; 07-27-2018 at 5:43 PM.

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    Pistons complete were,,,,,,,,,,,front587.15 and rear588 crank pin,nuts, keepers and screws were540.5. On your chart you show 60% mine was 50 I was using s&s's balance formula ,,,balance weight complete was1954.24 or 977.12 each wheel

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    Lets see what I come up with ....

    Hang on .....

    Click image for larger version. 

Name:	Capture JDB2.JPG 
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ID:	85999

    Now let's plug in the diff. balancing factor ...
    What was the % you used...??
    Last edited by Dragstews; 07-27-2018 at 6:30 PM.

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    50

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    Click image for larger version. 

Name:	Capture JDB3.JPG 
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ID:	86000

    You could have helped smooth out the motor by matching the recip. weights on both rod/piston combos...
    Just bout a 10 grams diff.
    Also for a rigid mounted motor, think I would have stayed with the 60% factor....



    Rubber mount like the lower balance % numbers, moves the sweet spot where they like it.....
    Last edited by Dragstews; 07-27-2018 at 7:22 PM.

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    yep same thing I got

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