BMW R80 G/S Fork setings ?

Discussion in 'Airheads' started by Caddy82rats, Jun 15, 2009.

  1. Caddy82rats

    Caddy82rats Long timer

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    Hello

    my G/S fork seems to had something like a too soft spring ?
    When I put my weight on the bike, the fork go down of 5 centimeters (2 inches), I've set the rear Olhins for 2 centimeters (a litel more than 1 inche)
    Oil is 10w the previous owner had changed fork springs for new BMW.
    Any draw back about some progressive springs ? I want to stay with this fork, his dual disc and BMW fork brace

    [​IMG]

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    The entire bike

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    Thanks in advance for all reply
    #1
  2. Rob Farmer

    Rob Farmer Long timer

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    I keep trying progressive springs in various bikes but cannot get on with them. Most folks seem to like them though.

    I've got similar issues to yours with my G/s since fittng a Wilbers rear shock a few months ago. I'm going to try fitting preload spacers to see if it helps.
    #2
  3. PaulRS

    PaulRS Dutch fool

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    Give these guys a call;

    http://www.hobbyist.nl/

    They make their own set of springs, 46,50€ with 6 months return garanty.

    I've fitted them on several older airheads with good results.

    Paul.
    #3
  4. Caddy82rats

    Caddy82rats Long timer

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    I think spacer's do the job for your shock, a good aloy "washer", this is OK if the spring isen't too soft, the spacer only place at an other point the time where the bike go down with your weight, if the spring is too soft, the chock stay too smouth.
    Apologizes for my poor english :D
    #4
  5. PaulRS

    PaulRS Dutch fool

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    Shortening the spring will make it stiffer.

    Just cut-off, say 2-3 cm and add a spacer of similar lenght, testride.
    Repeat if neccessary. :D

    Paul.
    #5
  6. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Springs too soft and too much sag are two entirely different things.

    If the forks don't bottom out, then I'd think they're stiff enough.

    Sag is handled with pre-load spacers. The travel on these forks is supposed to be close to 8 inches, so 2" of sag should be about right.

    Why are you using 10wt oil? Spec is something like 5 or 7.5 - if you are using stiffer springs, stiffer oil would be necessary, but otherwise it would make for a harsher ride.
    #6
  7. Caddy82rats

    Caddy82rats Long timer

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    Springs are BMW ones changed 2 years ago
    Oil, I've put 10W because it was stiffer and in my storage :D, but the result is not better.
    The fork doesn't botom out but act lik if I was having 2.5W oil and weak springs
    #7
  8. StephenB

    StephenB G(/)S ... what else!

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    So, it is bouncy (bouncing)?
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  9. Caddy82rats

    Caddy82rats Long timer

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    Not really bouncy but for me terribly not enough "brake" on botoming (or going down) the fork never botom on normal use.
    Afrer reading reply and wrinting my feeling I suspect a bad oil, it was in closed botle in my storage but I suspect it to be out of order
    #9
  10. StephenB

    StephenB G(/)S ... what else!

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    This is a linear not progressive spring, so the "braking" when getting closer to the bottom doesn't happen. Before you open it up, try 15W or even 20W oil to see what happens. I had the same problem with my G/S and made a very successful experiment. Read here:

    http://www.stephenbottcher.net/BMW/springrates.htm

    Maybe that helps. I still got a couple of pieces of springs left over. You are welcome to it. I still owe you for the KTM tacho (which I never got to work right).

    A bientot.
    #10
  11. Caddy82rats

    Caddy82rats Long timer

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    Thanks Stephen
    In first I'm going to drain the fork oil and to put some Bel Ray in it and see whats hapends. After that progressive springs could be an interesting try
    #11
  12. ChromeSux

    ChromeSux Un-plated and Unscrewed

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    some say a good rule of thumb is that the springs are correct if when in the real rough stuff you bottom out every now and then but not often.
    i like my suspension to have sort of a plush ride, i have noticed that when on a real rough jeep road or single track with steep areas with ruts etc that it does bottom out sometimes.
    #12
  13. One Less Harley

    One Less Harley OH.THAT'S GONNA HURT

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    Caddy-looks like you've been spraying some paint on the old girl. Looks good.
    #13
  14. Rucksta

    Rucksta SS Blowhard

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    Try increrasing the volume to 225ml or even slightly more but not past 250ml as this is where hydraulic lock willl start to happen.

    Spacers and spring amputation work well but this is a no cost reversible modification.

    The effect of more oil is to increase the compression damping mainly at the compressed end of the stroke without effecting the rebound. ATF (auto tans fluid) about 7.5 wt depending on brand and type works well for me and is cheap.
    #14
  15. PaulRS

    PaulRS Dutch fool

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    Nope. (sorry :D )

    By adding more oil, you reduce the volume of air above the oil and by doing so the trapped air will act like a spring.

    Adding too much oil will eventually push that airpressure op to a level the forks will not compress anymore and feel rockhard. (like your hydraulic lock)

    Paul.
    #15
  16. Rucksta

    Rucksta SS Blowhard

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    Paul the air will keep on compressing until it either liquifies or blows the fork seal. The Increased air pressure on compression does as you say increase the spring rate progressivly but also increases the damping as it is harder to move the oil into a higher pressure chamber.

    When I ran a stock front end on my R80G/S I used 230ml of ATF and was happy enough with the results(for a stock front end). The manual says 200ml +/_ 10%. 250 ml gave me lock up at about the same point the forks bottomed which was before the coils bound. I found 250ml stiff over medium bumps , bowling ball size rocks would cause the front to skip sideways but 250ml was very good under hard braking on road.
    Increasing the level above the 250ml mark reduces the amount of travel available and risks damage to the internal fork components under max load.

    Give it a go. As long as you don't exceed the parameters you can always drain the oil out if you don't like it.

    P.S. oil level below 180ml caused cavitation on rebound and frothing of the oil, not good.
    #16
  17. zenben

    zenben all roads are one

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    Of the three G/S that I've owned, all had the right side damper rod assembly come apart during use.
    The damper rod unscrews from the top retaining portion, so that retention of the fork slider and damping are both handled only by the left side of the fork.
    This is probably a tad dangerous, but easy to both check and fix.
    I've put both the current damper assemblies back together with a helping of loctite to prevent this situation in the future.

    Unfortunately, even with both dampers working, fork performance is still lousy.
    Heavier oil helps a little, as does increased pre-load, but the sad truth may be that these just aren't very good forks. :dunno
    #17
  18. Solo Lobo

    Solo Lobo airhead or nothing

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    with a fork brace, alu top triple and racetech emulators they are decent, not great, but decent.... the R100GS with a brace and an emulator are better...
    #18
  19. StephenB

    StephenB G(/)S ... what else!

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    +1 ... a lot!
    #19
  20. Caddy82rats

    Caddy82rats Long timer

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    yep the old girl was nacked some time ago : after a broken valve, the best was to put out the angine to clean it

    [​IMG]

    during the rebuilding process

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    you can see at the back ground some kind of "cooper" rings
    this is part of aircraft ball bearings I use to put hot pans on the table !!! And of course a botle of french alcool
    #20