How tight should my swing arm feel?

Discussion in 'General' started by motokid837, Jun 12, 2018.

  1. motokid837

    motokid837 New Member

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    On most other dirtbikes/motorcycles I've worked on, the swing arm becomes completely flaccid and falls down if you take the rear suspension linkages off. But on the 70, it actually take a good amount of force to move the swing arm around once it's tightened down. Is this normal? I'm assuming because any modern bike uses bearings and this bike is just simply bushings. I removed all the rust and re-greased the pivot bolt and its still pretty tights.

    Does the rubber bushing simply stretch and compress to allow for swing arm movement? Or is there actually a spinning action that is supposed to happen like a bearing? Thanks is advance!

    Also, do bushings need maintenance? Obviously they can be replaced, but can you spray penetrating oil to lubricate the spaces between the metal and rubber?
     
    #1 motokid837, Jun 12, 2018
    Last edited: Jun 12, 2018
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  3. kirrbby

    kirrbby Well-Known Member

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    I believe the rubber just flexes...no spinning involved. (Maybe some minimal spinning actually). Wait until you have the shocks installed before you torque the swingarm bolt, so it's in the correct position when you lock it down.
     
  4. motokid837

    motokid837 New Member

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    Thanks man!
     
  5. racerx

    racerx Administrator
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    Yep, it's more like an automotive leaf spring eye bushing. The rubber takes the shear, no actual surface-to-surface friction involved. If you look closely at the rear suspension setup, you'll find that the total rotational movement, at the pivot, is less than 20 degrees. 10 degrees, plus/minus, isn't very much...thus it's easy to spec a polymer (in this case, rubber) with a high enough modulus (stretchiness) to survive...indefinitely. In principle, it's kinda crude, imho, but there's no arguing with success and this definitely works well.

    FYI, most aftermarket swingarms use rubber pivot bushings. The few exceptions, that use needle bearings, are high-dollar, Japanese products...G`Craft.
     
  6. motokid837

    motokid837 New Member

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    Cool, thanks for the info, and yes it is very crude, to simply rely on the properties of the material to provide a rather large function of the rear suspension, but its lasted for the last 40 years so I'm not gonna be too concerned about it now!
     
  7. racerx

    racerx Administrator
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    Cars have been using this same technology...for leaf spring mounts...and....drum roll please ...control arm pivots. FYI this is still being used in 2018.
     

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