800GS shock bolt design flaw?

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

  1. Lion BR

    Lion BR I'd rather be riding

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    In other words, would a bolt and cross member bend without a full compression of the shock if even if the compression is non linear?

  2. Lion BR

    Lion BR I'd rather be riding

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    And since I got your attention, another variable in this equation is the distance a shock can travel before full compression. The longer it is, the more gradual this compression can be, the higher rate of possibilities for absorption. Perhaps a contributor for the flaw (if it is proven to be a flaw) is on the length available for the shock to compress for the weight of this bike.
  3. johngil

    johngil Reseda, CA

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    Joel, I really appreciate your input and it would stand up as truth in a court of law. I'm sure the engineering works out to a gnat's ass and combines function and economics that will serve 99.6% of the riders out there in the real world.

    My personal uneducated opinion is that the design sucks. For the intended (advertised and otherwise) use of the bike it is a stretch. This bike is aimed at a market that includes or even targets the 950/990 KTM's.
    If you are a dealer, which is what I gather, then it would not benefit you in any way to say anything other than this is a great design.
    I have come to the adventure bike/riding world straight from racing desert in southern California and doing so on KTM's. I have never in over 100 desert races bent or mutilated a structural member of my race bikes, ever.
    I'm not looking for BMW to wipe my ass. I do think they went out on a limb w/ this design. I have not hidden a thing from my dealer or BMW. We will see how this plays out.

    I have never crashed this bike or even bent a rim.
    I am not the guy who wins raffles or could score some $$$ on a lottery ticket. What ever happens is what it is.

    Most owners of these bikes would never know there was a bent bolt or frame to begin with. That isn't a knock, just the truth.

    Whether my frame is replaced by BMW or I run it through my insurance, I don't trust this design. I will check the bolt after every off road ride.
    If I have to fabricate a fix on my own, I will check it once or twice and forget about it.

    Something is not right here.
  4. johngil

    johngil Reseda, CA

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    All parts replaced and torqued to spec. Covered under warranty.
    Ride 175 miles the next day and bend bolt.

    How many times do I have to do this?

    By Wednesday BMWNA should be in contact w/ me. Patience is a virtue, but is hard to come by when a few thousand dollars are at stake.
    Joel, you and I would be sitting down shooting the breeze if we lived nearby. Thanks again for your input.
  5. ROYAL COACHMAN

    ROYAL COACHMAN Long timer

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    A question for Joel; In this design is the hardness of the bolt or the torque more important?
  6. johngil

    johngil Reseda, CA

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    While I can't answer for Joel...
    The hardness of the bolt and the torque are engineered values and specified by BMW. They work together.
    Ohlins has unofficially advised me to find a harder bolt. That doesn't seem like a good option, yet.
    In my case I have already added a few variables. I won't be adding any more unless told to do so.
  7. ROYAL COACHMAN

    ROYAL COACHMAN Long timer

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    John I feel your pain!
    I recently had a very costly failure on my F8 and I know what you are going through.
    In the end, BMW took care of me ans I hope they do the same for you!

    Glen
  8. big adv

    big adv I need supervision

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    So they already replaced the frame once 'all parts replaced' 'bent the next day'?
  9. johngil

    johngil Reseda, CA

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    I should have been more clear. The shock mounting hardware was replaced .
  10. Bruno T .

    Bruno T . N8YQ

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    Why would "others" be torquing the upper shock bolt ?

    How do you know it works on 99.9% of the F8GS's out there ? I'm sure you haven't come to that conclusion based solely on the insignificant number (in relation to overall production) of F8's you have personally inspected.

    You don't know, and neither do i.

    When you say; "the seat comes off" , does that mean that you are removing the seat bench locking system and exposing the upper shock mount for inspection ?

    I'm not surprised that there are few reports of bent rear suspension components on F8's.

    Out of the F8's that are circulating, what percentage do you think are ridden in a manner that might compress the rear shock enough to bottom it with significant force ?

    Even if one were to bottom his shock, why on earth would he go dismantling his motorcycle to inspect the shock mounting hardware. I don't know of anyone that would do that.

    I realize that you don't have personal knowledge of many cases of bent rear suspension components on F8's, i don't either, but that's far from being able to say with certainty that the assembly is adequate for its intended use.
  11. ]I)Money

    ]I)Money D NOT I

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    Possibly, but not at the same force level, ie, if you took the same exact hard landing on both setups, the bottoming shock would bend parts before the stiffer sprung shock. The fly in this particular ointment is that the hard parts had already bent once, which weakens them for future stresses.
    In other words, that first bend and failure (root cause yet to be determined) contributed to the subsequent bend. The aftermarket shock is, I think, a red herring in this discussion.
    My guess is that it probably slowed the rebending, but couldn't completely prevent it.
  12. tmex

    tmex Long timer

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    I agree with your analytics relative to the bottoming versus the linear compression of a stiffer shock. Not sure about the aftermarket shock being a red herring. When someone is having a problem with their bike my first question is always "what did you do last"? It is usually the right question to ask.

    With respect to John, I know his wrenching skills are good and it is hard to suspect Ohlins. It would seem unlikely that the aftermarket shock is the culprit, but I would really like to examine the upper shock mount bushing before ruling it out completely. It would also be interesting to track down some other Ohlins customers for this bike/shock combo to see what their experience has been.

    As far as a dealer not seeing the problem, I would be suspicious of the data integrity. You cannot see the affected area without taking stuff apart, and there would be no reason to do that unless the customer reported an issue. I just don't see dealers even inspecting this area without a very good reason.
  13. mookymoo

    mookymoo Mookish Mook

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    The forces transmitted by the shock (which are affected by spring weight and damping) during normal operation are nothing compared to those transmitted when the shock bottoms out.

    Rather than the energy being stored by the spring or dissipated by the damping, when it bottoms its absorbed by flexing/bending metal. Usually, shocks have some kind of bottoming control (rubber stopper) as a last-effort to prevent a metal-to-metal contact. Im not sure what the stock shock components are like - but if it was metal-to-metal contact you would certainly hear it.
  14. johngil

    johngil Reseda, CA

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    In this photo, the evidence of the bending bolt is hard to see. The red oblong outline is way out of proportion, but it shows what the steel bushing on the stock shock is deformed.
    The small yellow arrow shows the opposite side of the bushing and indications of the bent bolt.

    [​IMG]

    This is the proof I have at this point, along w/ dated ride reports and other photos showing the stock shock.
    I don't know how the Ohlins will come into play.
    I was handed off to the "next level" by BMWNA today. I don't know what this means, but it's something.
  15. Bruno T .

    Bruno T . N8YQ

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    Bottomed out in Central America;

    [​IMG]

    I'm sure you can guess what that did to the upper (and lower . .) bolt.
  16. Bruno T .

    Bruno T . N8YQ

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    Perhaps they are reading this thread and thinking that they better check the torque on the bolt in question, seeing as you suggest in one of your earlier posts it may have been improperly torqued from the factory ?

    That would simply tell us that a few people who happen to be following this thread decided to check the upper shock bolt torque on their F8's. That's hardly an indication of any significant number of owners having under-torqued the bolt, as you imply.
  17. Lion BR

    Lion BR I'd rather be riding

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    The problem with 99.9% is that you need to see 1 failure in 1000 to obtain that number (assuming there is not a half-failure on this). If you've seen one failure in 10, your sample is 90% non failure. One failure in 100 is a sample providing you with 99% non failure. If you've seen zero failures, your sample is 100% non failure until you see a failure.

    The second question is "how representative is your sample". More precisely, if we are going to use statistics properly, and also be strategic about it, I would like to see what is the number of failures with the original shocks on bikes that were "untouched" after factory assembly.

    Second, of those, I would know what is the failure rate on bikes where suspension has been bottomed out.

    Third, I would like to know what is the failure rate on bikes with after-market shocks.

    However, one could say that someone who bothered to invest on an aftermarket shock is really using this bike in ways that are probably at the edge of the performance envelope. Which may approximate it to the second group above.

    And one can go on and on on this.

    Curious to know more about this.

    Lion


  18. ]I)Money

    ]I)Money D NOT I

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    I don't think I was very clear. I called it a red herring because the original bending happened with the stock shock in place. My opinion is that, once bent, the mount is pretty likely to bend again, even with a theoretically better shock in place.
  19. Y E T I

    Y E T I Unpossible

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    John, the FIRST time it bent, was the stock shock on the bike? i.e. at the time that the bolt bent the first time, had you ever touched it? What I'm getting at is this: Ift hefirst time it bent, it was as it left the factory then perhaps Joel's idea is correct, i.e. that it wasn't properly torqued at the factory.

    I think it's safe to say that once metal (the shock mounts) bends, it is weaker and more likely to bend again.
  20. johngil

    johngil Reseda, CA

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    The first time I discovered any damage was when I was removing the stock shock to install the Ohlins. The bolt bent before I had ever taken a wrench to the shock area of the bike.