R100 Big Tube swingarm questions

Discussion in 'Airheads' started by xavier296, Sep 16, 2011.

  1. xavier296

    xavier296 Alaska n'Back

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    I bought a good looking "big tube" swingarm, from the 81-84 model year, to install on my 79. You can immediately see why this would make a difference in handling on the rear. Max bmw microfiche makes it look like the pivot pins are a different length, does anyone know if I need the shorter pivots to run this swingarm?

    Or maybe I can put earlier style bearings and seals and use the original pins? I was expecting to change the bearings anyway, and would prefer to avoid buying 70 dollars worth of pivot pins.

    I know I have to mod the rear brake switch also, but unfortunately, the instructions on this forum have lost all the pics that used to be there.
    #1
  2. DoktorT

    DoktorT BigBrowedNeandereer

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    #2
  3. Boxer Metal

    Boxer Metal Mad Scientist

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    Screw the original ones in and see if they bottom out and you can still get the jamb nut on. If you can then use them:D
    #3
  4. wirewrkr

    wirewrkr the thread-killer

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    You can use the bearing and seal and spacer setup from the earlier style if you want.
    Especially since those late model bearings will set you back around $130.00!!
    Don't forget the grease retainer on the one side.
    For the brake light setup, you'll have to get creative.
    #4
  5. Max Headroom

    Max Headroom lost in the '70s

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    As it happens, I've just about finished installing a big-tube swingarm on my R90S, and it appears to me that the earlier pins will work with the later bearings. I haven't adjusted and tightened them yet, but they seem to fit OK at this stage.

    The brake light switch is a bit more of a fiddle. I trimmed about 10mm (or 3/8" in the old currency) off the mounting bracket with a Dremel to clear the new swingarm, and then re-mounted the switch as close to the muffler bracket as it would go. I was fortunate to have a matching foot brake pedal, as It has a deliberate kink at the "switch end" where it strikes the switch when compared to the earlier style which is straight. If you're stuck with the earlier brake pedal, you'll probably need to fit a little tab to meet up with the switch. There's probably several ways of dealing with this issue, hence the advice to "get creative" from Wirewrkr!

    I didn't take any photos. sorry. I could take some later today if it helps, but everything is assembled and I'm not sure if the photos would reveal anything meaningful.
    #5
  6. Boxer Metal

    Boxer Metal Mad Scientist

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    I too am installing a big tube swing arm on an R90S. I have it loosely fitted. I'll take pictures as I go.

    [​IMG]

    BTW- Use the early drive shaft. The spring breaks in the later ones.
    #6
  7. xavier296

    xavier296 Alaska n'Back

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    Thanks for the timely input gentlemen! I am trying to be a good little builder and install everything now before I have everything painted and powdercoated, so I think I have enough info to just try to install the new swingarm with the parts I have. I took a good look at the brake light switch earlier, and can see that cutting the mount and reinstalling the switch closer to the ear would be the answer. I have an earlier pedal, so I will have to make up something to push the switch closed.

    I am hesitant to install my solid driveshaft into the new swingarm as I hear it is quite a pain to install. Don't you need a special press?
    #7
  8. Boxer Metal

    Boxer Metal Mad Scientist

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    I had someone with the proper tools swap it out.
    #8
  9. Solo Lobo

    Solo Lobo airhead or nothing

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    "Proper tools" Pffft...... (not that I would advise anyone else to use the method below :D

    [​IMG]
    #9
  10. Boxer Metal

    Boxer Metal Mad Scientist

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    Got the rear brake switch figured out today using a BMW brake switch. I'll do a full tutorial soon.

    [​IMG]

    [​IMG]
    #10
  11. Boxer Metal

    Boxer Metal Mad Scientist

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    #11
    GCCR likes this.
  12. xavier296

    xavier296 Alaska n'Back

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    Thanks for the great article euro. What type pivot pins did you end up using?

    My new swingarm is waiting patiently:

    [​IMG]
    #12
  13. Boxer Metal

    Boxer Metal Mad Scientist

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    You're welcome. The early pivots appear to work fine.
    #13
  14. Jon-Lars

    Jon-Lars Jon-Lars

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    This setup works best with the use of the later, wider-race bearings that are specified for the later swingarm.
    The wider race puts the load closer to the frame, reducing flex.
    #14
  15. Boxer Metal

    Boxer Metal Mad Scientist

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    Do you know what the width difference is between the 2 bearing? Since either bearing race bottoms out in the swing arm I am curious.
    #15
  16. Jon-Lars

    Jon-Lars Jon-Lars

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    The dimensions are listed on Max BMW's catalog page.

    According to them, 3mm.
    #16
  17. Boxer Metal

    Boxer Metal Mad Scientist

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    Interesting. Well bigger is better! I do like the seal set up on the later ones as well.
    #17
  18. xavier296

    xavier296 Alaska n'Back

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    So, BMWeuro, you used the original sized (larger) bearings of the "big tube" swingarm with the longer (earlier) pivot pins (my question seems redundant, but I am just making sure)?

    Also, how do you test a swingarm bearing?

    My swingarm bearing and seal setup doesn't really look like any of the ones from the microfiche.
    #18
  19. Boxer Metal

    Boxer Metal Mad Scientist

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    So, BMWeuro, you used the original sized (larger) bearings of the "big tube" swingarm with the longer (earlier) pivot pins (my question seems redundant, but I am just making sure)?
    I did use the wider bearing and the early shorter pivots. I got everything adjusted and torqued down tonight ans ran the swing arm through it's travel and it worked great

    Also, how do you test a swingarm bearing?
    I removed the bearing and the race, Cleaned everything very well and did a visual inspection.

    My swingarm bearing and seal setup doesn't really look like any of the ones from the microfiche.
    The info from the fishe sucks. I ordered a bunch up parts and most turned out to be wrong. The seal let up has seals that you can clean and reuse.
    #19
  20. brocktoon

    brocktoon Been here awhile

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    THREAD, RESURRECT! :pope

    So, a year on:

    For those that have done the big tube conversion, have any issues arisen using the earlier style bearing, spacer, seal and pivot pin setup? I have a big tube swing arm for my /5 coming back from the powder coater on Thursday. Like others, I'm loath to kick down an extra $130+ for the exotic bearing setup. Is performance the only thing lost from using the earlier bearing setup?
    #20