800GS shock bolt design flaw?

Discussion in 'Parallel Universe' started by johngil, Jul 16, 2009.

  1. easyman05

    easyman05 Been here awhile

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    the wife's F650GS is at dealer - asked to check the shock bolt today and yes, it is slightly bent. No jumps, hard off-road or/and overload of the bike - her weight with helmet, boots and gear does not exceed 50 kg. She rides without panniers. Will check my F800GS next - will keep you informed.
    #81
  2. Lion BR

    Lion BR I'd rather be riding

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    What is the role of this brace just to the left of the shock?
    When the bolt bent, did the brace fail as well? Did the brace break at the weld? What is the structure behind where the brace is welded to? Or is it not structural? If structural, I would think it helps "shorten" the length of the bolt and hence give it strength.
    Lion


    #82
  3. DockingPilot

    DockingPilot Hooked Up and Hard Over

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    Mine is not bent, that photo was for John to look at.

    John this from a suspension guy when asked about this situation:

    "Frank,
    The bushings on all shocks I know of are split. They have to be inserted ½ half from each side.
    If his bolt is bend it is from bottoming out very hard and has nothing to do with the bushings being out of one piece or not.
    All the high end shocks have spherical bearings and half bushings, usually out of aluminum.
    The bushings are stepped, with the smallest diameter a press fit into the bearing against a shoulder in the bushing, than another step to provide a seal against the O-ring. Than the outer step or collar which is to take the place of a washer. The measurement across the outer collars has to be the exact width of the clevis of fork in the frame.
    The BMW have a top bolt (Torx head) with the head being a precise fit in one of the fork shanks, to allow lateral movement for expansion etc. If the nut is tightened to spec, it will pull the shoulder of the Allen head against the collar of one of the ½ bushings, against the inner race of the bearing, against the other ½ bushing and against the shank of the other fork on the other side where the nut is tightened. This is a solid assembly. However, I have seen bent top and bottom bolts (mainly on GS’s) with Wilbers shocks. It happens when the bike comes crushing down after a lift off and the shock bottoms out. This should not happen with a Hyperpro shock/spring. The progressive spring is so stiff at the very end, that it is almost impossible to fully compress it under these conditions."
    #83
  4. johngil

    johngil Reseda, CA

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    I have a hefty spring on my Ohlins as well. The valving seems pretty progressive as well. I doesn't bottom hard, if at all. The elongated hole on the frame tab is going to cause any setup to bend in my opinion. If the cross tube were not bent,,, a simple fix could be as easy as welding in a bushing in the enlarged original hole providing there was enough meat left to weld on. The bent cross tube is what is complicating matters for me.
    I was disappointed that BMW didn't contact my dealer Friday. That means no contact w/ the dealer until Tuesday.
    #84
  5. DockingPilot

    DockingPilot Hooked Up and Hard Over

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    Dam, Keep on your dealer to pressure them to show up. Thats aggrivating for sure. For all of us really. We want to know how they will treat you on this.
    Keep us posted John.
    #85
  6. kmueller_gs12

    kmueller_gs12 Adventurer

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    @JoelWisman and all the other f650/800gs riders

    one hour ago i checked the situation once again as you wrote
    i have splashed a little bit wd40 between the rubber and the bush and pulled the rubber to the left.
    then i trie to torque the bold and what i see, the bush turns with
    so i take a wrench and hold it while torque the bold up to 100nm

    everythine ok

    my conclusion:
    the work instruction "changing the rear shock" is very bad. ther is no word about this eventality.
    so now my dealer have to give back the spare parts

    thank you to all

    regards klaus:clap
    #86
  7. itsatdm

    itsatdm Long timer

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    That is the left mounting flange, the right flange is welded on the right side of the frame visible in the pic. The tube the left flange is welded to is a frame crossmember. The silver cylinder object to the left of the left flange is threaded and serves a nut for the bolt that holds it together.
    A bent bolt is fixable, but in this case, it appears that after it bent, the left flange took more force that it was designed for and bent the crossmember. From the pictures it looks like the way the flange is cantilevered rearward, it acted as a lever twisting and bending the crossmount.
    #87
  8. PackMule

    PackMule love what you do Super Moderator

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    :beer Klaus
    #88
  9. Gangplank

    Gangplank Advenchaintourer

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    I dunno know about this. I ride mine really hard. Seems to me its fine. If your was bent when you went to put on the after market I would think there is something wrong with the bolt.

    I have 4k mi already. Others have 20k.... haven't even heard of this other than this thread.
    #89
  10. johngil

    johngil Reseda, CA

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    Gangplank, thanks for posting. That was my mission when I started the thread. So far I have only found 3 other bent bolt/frame problems. It's not a lot by any measure, but it helps me and possibly BMW or Ohlins in the end.
    I guess when people say they ride hard, it is rather subjective.
    I feel I ride at a moderate pace, not hard. That is why I am looking for answers.
    My confidence in this bike is low, however.
    #90
  11. Lion BR

    Lion BR I'd rather be riding

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    That's a lot of damage.

    #91
  12. johngil

    johngil Reseda, CA

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    Sorry for the hack job, but this is what Gary is describing. As the tab bends (in red) the cross tube arches (in yellow).

    [​IMG]
    #92
  13. Lion BR

    Lion BR I'd rather be riding

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    I take it that a lot of force was pushed through the system to bend the bolt, the sleeve, the tab, and the cross tube. Wow.


    #93
  14. Lion BR

    Lion BR I'd rather be riding

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    Either that or the materials/design in question need to be revised.

    #94
  15. Bruno T .

    Bruno T . N8YQ

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    Agreed.

    The question here is how much force will cause the above to happen on a GS 800. It may be unacceptably low. We have no way to know and compare with other motorcycles' designs.

    Wouldn't that impart nearly the same force on the bolt, ears and cross tube ?
    #95
  16. Gangplank

    Gangplank Advenchaintourer

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    Yeah it would. Compressed is compressed. Just be cause it doesn't bottom like a pancake doesn't mean its not transferring forces.

    I bet bad bolt that bent frame parts. Any others have this issue?
    #96
  17. Lion BR

    Lion BR I'd rather be riding

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    So hitting with same force, a rubber mallet and a regular hammer with same mass, would effect same indentation on a given surface?

    #97
  18. Gangplank

    Gangplank Advenchaintourer

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    Huh? Not a great example. More like comparing two different rubber mallets. If you hit hard enough to fully compress the rubber mallet... Then theoretically one that is more absorbant would transfer less force than one that is less. If you put on a different shock with a stiffer spring it will transfer mire force. If it stiffer and very progressive... It will absorb, sure but it will also transfer more forces than less stiff and less progressive up to the point of bottoming out. At bottoming the one that is fully compressed transfers more.
    #98
  19. ]I)Money

    ]I)Money D NOT I

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    If it's not fully compressed, it's not bottoming.

    that's the point of stiffer springs, after all.
    There is a big difference between running out of force to continue to compress a spring, and running out of compression. In the first instance, deformation of hard parts will not occur at the same point as it will on a softer spring that bottoms.
    #99
  20. Lion BR

    Lion BR I'd rather be riding

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    Well, I went to the extreme example to dig for the rational for why different shocks would be more likely to transfer more or less force to the bolt and cross member. It seems like you are saying that different shocks may absorb differently and hence may transfer forces differently. If that is the case, we are in agreement.
    Lion