800GS shock bolt design flaw?

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

  1. GravyEater

    GravyEater n00b

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    I started to install the BestRest brace on my 2016 F700gs today and had a problem removing the subframe torx bolt. I tried 2 different 50mm torx bits and they both seemed ever so slightly loose. When applying pressure with my ratchet it spun out and didn’t budge the bolt. I only tried twice because I didn’t want to strip the bolt. The bolt stripped a little but there’s still meat on it. I stopped trying so I wouldn’t it totally strip it out. Any ideas how to get that bolt out? Would an air impact wrench help or would it strip it faster? Any problem using an air impact on the frame? Any ideas greatly appreciated.
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  2. malloy

    malloy Long timer Super Supporter

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    Try some PB Blaster, Kroil or similar penetrant. Soak the thread end and let it sit for at least a couple of hours. Then again and again and eventually let it sit overnight with the penetrant. Can you get some heat on the thread end?

    Another trick is to try to tighten the bolt before backing it off. Actually get some tightening torque on it then give your tool a whack with a hammer.

    I'd be shy of an air impact wrench. Maybe others wouldn't be.

    If the torx was "ever so slightly loose", that suggests the next size up.

    I've forced an oversize Torx head into a stripped out Allen head. Would the reverse work? Just a thought.
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  3. Tom D

    Tom D Been here awhile

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    i've read many of the post here and have given it much thought and have concluded that the problem is not the bolt, but the rider's lack to adjust the suspension.

    bolts are design to work in tension not shear. i will however agree that if a bolt is not properly tensioned then any force applied perpendicular to it's axis could cause it to bend.

    first off..... everybody thinks they know that a tight suspension is a good suspension and so for general road work they dial in way too much rebound dampening. then when they head down a terrain requiring massive suspension articulation they fail to change the dampening. the result is that the shock can not extend quick enough for the next impact and so it compacts becoming more of a strut then a dampener, jackhammering across the diameter of the bolt.

    point being.....adjust your suspension to the terrain being ridden, that and a overly stiff suspension is not good....on any terrain.
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  4. Rider 101

    Rider 101 Time poor

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    I would dispute your theory to a degree. I have an aftermarket shock as I tend to ride more off road than on tar. It has been serviced and modified by a highly reputable workshop here in Oz. I have it set up for my weight ( including gear ) and riding style. I have the BestRest brace and the 12.9 bolt and have replaced it several times as they still bend. It is an outright design flaw from BMW. No amount of adjusting your suspension to suit your riding will totally alleviate the problem.

    It would be interesting to see the top mount of the new 850!

    Funny I have never bent a bolt on any of my WR450s, 250s, Cr250s etc etc
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  5. Tom D

    Tom D Been here awhile

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    ^ i'm not going to disagree with you because i can't, you make a good argument.

    however, assuming it's a design flaw, then is the flaw due to an engineering oversight or was it an oversight of how the bike would ultimately be used?
    =o&o> likes this.
  6. shuswap1

    shuswap1 Long timer

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    Any engineer worthy of the title would design the rear suspension to easily handle predictable uses and the force required to bend these tabs and bolts falls within a predictable range, given the shear volume of failures. A careful look at the design would raise questions in mechanically-minded people. Most would assume the engineering of such a critical component would follow sound engineering principles.
    MITOK likes this.
  7. BMW-K

    BMW-K F800GS FTW!

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    I haven’t posed this but...

    Is it a design flaw? Or, are we using a bike beyond its parameters? No, really. Consider that for a brief moment. What exactly are the design intentions of the F8GS? I don’t mean YOUR intentions,,,but BME’s.

    Maybe the real issue is in framing the challenge correctly.

    (*mind you, I have both a Best Rest brace and Touratech Extreme Shock/forks on my. 2010...)
    =o&o> likes this.
  8. Woody2627

    Woody2627 Grey Wobbler

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    ^^^^^^^
    :fpalm
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  9. malloy

    malloy Long timer Super Supporter

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    Sold as a "dual sport adventure bike" means riding off road with gear. Should be able to do so with no problemo.
    Indy's fix and the Best Rest are good stop gaps. Looking at the original design, it's not too hard to see how it could have been corrected years ago at the factory given all the complaints. Sort of disappointing that BMW has ignored it through several iterations.
    ultane likes this.
  10. Motoriley

    Motoriley Still riding like crap after all these years.

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    DesIgn flaw for sure.
    It is not sold as a street bike. BMW uses them in their own GS Challenge events as well as many others they run. The official BMW riding schools use them for off-road. The saddest part is how easily they could have changed the design. I’ve looked at a bunch of upper shock mounts since this started and the are simple designs. The lower mount for the 800 is a crappy design as well. Looks like a case where someone tried to really smart and come up with a new design instead of following the tried and true. The Indy kit I installed wasn’t perfect but there was no way it was going to bend.


    QUOTE="BMW-K, post: 36624019, member: 10295"]I haven’t posed this but...

    Is it a design flaw? Or, are we using a bike beyond its parameters? No, really. Consider that for a brief moment. What exactly are the design intentions of the F8GS? I don’t mean YOUR intentions,,,but BME’s.

    Maybe the real issue is in framing the challenge correctly.

    (*mind you, I have both a Best Rest brace and Touratech Extreme Shock/forks on my. 2010...)[/QUOTE]
  11. MITOK

    MITOK Adventurer

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    You answered your own question in the post you made prior to this one. The bolt should be in tension, holding metal faces together so that friction forces between those faces bear the brunt of the shear.

    Think of a bolt that goes through a lap joint, where the ends of two pieces of wood are placed one atop the other like jenga pieces. The bolt holds the wood together, but when a shear force is applied, the friction between those two wooden members resist that shear force. They are pressed together and their surfaces provide friction where the tensile stress of the bolt contributes the normal force. If shear strain in the wood is minimal, the bolt could theoretically see zero shear stress.

    The inherent problem with the BMW design is that the bolt is used as a bending member instead of a tensile fastener. Imagine using a long 10mm bolt as your front axle without tightening it down on the bearings and bushings. That's essentially the design of the rear upper shock bolt.

    Stated differently, the bolt in the upper shock mount is placed under bending stress to constrain the axial motion of the shock, which is a poor application for a fastener.
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  12. malloy

    malloy Long timer Super Supporter

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    "the upper shock mount is placed under bending stress to constrain the axial motion of the shock"



    I just love it when you talk like that, MITOK:rofl
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  13. Frapple

    Frapple Been here awhile

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    Just purchased a Husqvarna Nuda (road bike) to convert to adv purposes . Basically same frame design . Bent bolt .
    Lets say they copy someone else's (everyone else's!) design and put the upper brackets directly on either side of the shock bearing . Problem solved . May have to add support to the top tube . It is an incredibly stupid design . Bottom bolt on the gs is not much better .
    Whether you have well set up aftermarket or standard suspension , eventually you will bottom your suspension regardless of its intended purpose . It will happen sooner with stock suspension . Do it once will bend the bolt . Doing so repeatedly will wreck the frame .
    Some may have had no issues but that does not make it in any way an acceptable design . That just means that you have never bottomed the suspension .
  14. shuswap1

    shuswap1 Long timer

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    Bit silly to say the bike is damaged as a result of using it beyond what it was designed to do. We aren't jumping motor-homes over buses here. This is simply poor design, poor engineering. I really enjoy the almost 'hooligan' capabilities of my F7 but will always wonder how they got so many really nice details right while missing some basic fundamentals.
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  15. cgguy09

    cgguy09 Scientiæ Cedit Mare

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  16. MCMXCIVRS

    MCMXCIVRS Long timer

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    Refunds for us early buyers :D:lol3:lol3.
  17. MontanaPaul

    MontanaPaul Adventurer

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    I'm about to put on a shock brace (as soon as my new TFX res shock arrives from Ted's Beemershop). I did not order the "upgrade bolt", as it seems the brace will provide all the support needed. However, I was Googling to see if the bolt could be sourced locally, and ran across this interesting article (http://www.boltscience.com/pages/the-stronger-the-better-is-not-necessarily-the-case-for-fasteners.pdf) on bolt strength. Worth the read, but the Cliff notes version is that the highest tensile strength bolts (12.9) are more susceptible to hydrogen embrittlement during manufacture (eg during thread rolling and machining due to breakdown of lubricants). Thus, they are more susceptible to fatigue cracking in service. The article also points out that the fatigue endurance of a 12.9 bolt is the same as for a 10.9 or even 8.8 fastener. Lastly, comparing the yield strength, class 10.9 is 940 MPa, and class 12.9 is 1100 MPa (just 15% higher).
    So the characterization of the stock bolt as "buttery soft" is misleading, and in fact the stock bolt grade has several advantages.

    The problem is not the bolt, but the long unsupported span. The brace reduces the unsupported span by a large amount.

    I don't yet know if my stock bolt is bent (unlikely), but if it is and needs replacing, I'm staying with grade 10.9 and adding the brace.
  18. BuiltnotBought

    BuiltnotBought Perpetual Project

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    Corp BMW riders ride their F800's way beyond what I can mine. Its not a matter of riding beyond what the bike was intended.

    BMW has never been ready to acknowledge problems with their bikes - consider the notorious "stator issue" on the first gen F8's. BMW never acknowledged a flaw, but they did change the design in the next generation and guess what? big surprise, no more stator issue...:bluduh
  19. ultane

    ultane sqeezin the bag

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  20. Buzuka

    Buzuka drz400e \ f800gs

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    Can anyone make a drawing with dimensions? because the price of this part is too high.