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F800GS - RXV Shiver'ed Fork Conversion

Discussion in 'Parallel Universe' started by Gangplank, Jul 25, 2010.

  1. MannyM

    MannyM Adventurer

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    Thank you cbleroy !!

    I notice on the drawing that the depth dimension for the 31.3 mm is only referenced from the 8 mm shoulder that remains from the original design. Is this 8mm crucial for setting up the proper length of the forks? I would thing that this depth would be really important in setting the length of the shock with the new innards? Just a question - I don't see to much mention of dimensions throughout the posts other than spacers and travel... and those discussions are really hard to follow ?
  2. cbleroy

    cbleroy Adventurer

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    You're welcome !

    The 8 mm is to respect the positioning of the compression valve toward the holes inside the inner cartridge.
    When fork compresses the oil flows according the blue arrow in the pict below.

    In the drawing given to the mechanical shop I have written 8mm+-0,1 to avoid them asking me what tolerance I need.
    Obviously the tolerance doesn't need to be so strict, in the posts it seems most relied on their mechanical shop for this positioning, and all are happy with their modification !
    But I think this 8 mm is the right spec to give for the modification.

    I found 8mm from my donor fork (WR250) and appears to be the same measuring the picture from the Marzocchi manual .
    When you have your own donor fork, you may check this measurement too.

    pied de fourche 8mm.JPG
  3. cbleroy

    cbleroy Adventurer

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    The length of the fork is a different topic. You address this by adding a spacer.
    In my case I made it machined, some other just used a spring for it.
    The red arrow says where it goes.
    Coupe detendue.JPG

    upload_2018-1-19_19-8-33.png

    In my case having it 34mm long makes the fork keeping the same travel as the stock.
  4. todd900ss

    todd900ss Been here awhile

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    Did I miss it, or is there a list of bikes that are confirmed donors for the shiver forks?
  5. cbleroy

    cbleroy Adventurer

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    Thanks to Gangplank there is a list in the post #122
    MannyM and todd900ss like this.
  6. cbleroy

    cbleroy Adventurer

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    Question to the ones who made similar spacer design as mine, do you experience some "click-click" when the spacer is pushed up and down by the oil flow ?

    I already mounted the fork, and the spacer is free of vertical movements.

    I'm thinking I should have locked it using the top out spring.
    Below the drawing of a possible modified spacer.
    I've not done it, maybe in a future upgrade if the movement of the spacer within the fork is too strong.

    Sharing in case it can help others.

    Attached Files:

  7. todd900ss

    todd900ss Been here awhile

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    Nice modeling work!
    Someone posted using a spring instead of a spacer, wonder if that would help?
    I think it was motolab.

    Curious if you revalved your forks?
  8. cbleroy

    cbleroy Adventurer

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    Well, yes, making a spacer using a spring is definitely an option, but I didn't see real benefit of doing so, except if it would replace the top-out spring.
    In the spring-style spacer design, there is apparently also washers and both ends of the added springs. These components could also probably move vertically doing some "click-clicks" noise !?
    I also wondered if the added washers could damage the rod...
    My considerations are maybe purely theoretical, and the click-click may anyway be fully covered by engine noise...I just asked the question.

    I designed a spacer that will never cover the small hole in the rod involved in the rebound ajustement and that would keep the rod safe.
    The drawing I attached in my post is an (untested) improvement of the rod I have currently mounted. The improvement is that the spacer should lock itself to the top-out spring and thus not move inside the fork.

    I did revalved the fork.
    I have considered the Husky WR250 shim stacking donor fork as reference and I used the restackor software to estimate what change should be done when going to a 0,64kg/mm spring.
    Honestly, I admit I am not sure this is the right baseline, but I couldn't find a better starting point. I'm anxious to see how it will behave.

    Here are the graphs of the base valve.

    Base valve.JPG
    Bli55 likes this.
  9. MannyM

    MannyM Adventurer

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    I’ll admit to needing some help. From the drawings above I cannot comprehend the spacer and travel discussion.

    I have received my donor forks (from a 2007 GasGas 300 - note: original owner had springs changed and forks revalved for a 190 lb / 86 Kg rider - perfect fit for me)

    I have disassembled both forks after taking all external measurements. As expected, the donor forks are longer and appear to have more travel.

    Now what is my next step??

    I see multiple posts where inmates have disassembled the original BMW components- why? I understand the requirement for machining the bottom of the BMW foot to accept the donor compression valve, but I cannot understand the discussion on springs and spacers?

    Someone please point me to what I need to do next ?

    Below are the photos of the dissembled forks.

    Thanks again from Canada.

    522B7FA4-290C-4BE0-A2BE-614451D872D1.jpeg

    9E425F32-AEAC-4CB4-96CD-071716F0AB4F.jpeg

    C2D57CFF-EB79-4451-9DA8-FB39E93E21AB.jpeg

    Attached Files:

  10. cbleroy

    cbleroy Adventurer

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    You will have to open your donor fork and take some mesurent of inner parts.
    I'll sketch something out to explain.
  11. MannyM

    MannyM Adventurer

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    Thanks cbleroy, - I'll buy you (several) beers.

    I have read all of this thread... and the missing photos from the early posts commenting on spacers and springs and 40mm and 10mm... they are tricky to follow.

    But this spacer discussion may not be of any interest to me... I see on several posts that those who did not want to reduce their donor forks travel (300mm) to the original BMW travel spec (230mm) did not use a spacer. My intent for this bike is to be a more capable off-road machine. If I am installing a steering stabilizer and raising the handlebars... I am completely OK with having the tops of the forks extend through the top of the triple tree ? More travel is better for my purposes. Do I still need to disassemble and install a spacer?

    Thanks again,
    Mike
  12. todd900ss

    todd900ss Been here awhile

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    I agree the spacer you designed is a better option than a spring. Just trying to figure out what direction I'm going.
    Curious how Restackor works for you.
    What are the WR stock shim stack numbers?
    I have a Husky CR250 donor fork I’m working with.
  13. MannyM

    MannyM Adventurer

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    So much spring and spacer and spring vs. spacer talk without any pictures of spacer and/or spring and its component location... The original posts from the 2010 period no longer have their photos available.

    IF i were to install a "spacer", where does it go and what are its dimensions?
  14. cbleroy

    cbleroy Adventurer

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    Here is some cut and past exercice to help for understanding.
    It represents the F800GS my shiver conversion. Dimensions have been setup based on my measurements. the Leg feet are not representative in shape.
    What you can see is that without the spacer the fork will have a longer travel.
    In my case I preferred to keep the same travel a stock in order to keep the geometry of the F8GS unchanged.

    Is you have or install the free software Inkscape you can play with the fork and measure dimensions in mm. I can share the .svg file but I don't know how, advrider site refused to upload the .SVG extension.

    Just updated the picture to show the main spring and the preload spacer.
    ScalingShiverF8GS.png




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  15. cbleroy

    cbleroy Adventurer

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    Here is my compression configuration. As I told you I'm not sure it is the right baseline:

    ----- INPUT FILE -------
    DAMPER GEOMETRY:
    D.rod D.valve w.seat Vspec
    12.000 26.000 1.000 BVC
    VALVE GEOMETRY:
    r.port d.port w.port N.port
    5.420 5.890 3.620 4.000
    h.deck d.leak N.leak d.thrt N.thrt
    2.260 1.000 1.000 2.800 4.000
    OIL PROPERTIES:
    Toil cST40c cST100c SG15
    20.0 34.0 9.3 0.884
    SETTINGS:
    n.click, F.max u.wheel
    23.0 8.0 6.0
    NEEDLE CONFIGURATION:
    D.bleed MAX.clks
    2.8 23.0
    HSC CONFIGURATION:
    Preload D.hsc K.hsc
    0.00 0.00 0.00
    DYNO PARAMETERS:
    Offset cf.stk xLsat dToil
    0.00 0.00 -0.01 0.00

    STACK:
    ID Float
    8.000 0.000

    N Diam Thickness
    1 23.0 0.15
    2 23.0 0.15
    3 12.0 0.10
    4 23.0 0.10
    5 21.0 0.10
    6 19.0 0.10
    7 17.0 0.10
    8 15.0 0.10
    9 13.0 0.10
    10 10.0 10.00
    todd900ss likes this.
  16. MannyM

    MannyM Adventurer

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    YES!!! thank you cbleroy!! I think I now understand...

    This drawing makes sense! Thank you. From this drawing I can clearly see how a spacer will alter the preload on the fork spring. NOW I can see why people are messing with springs to find their optimum "sag".

    Does this make sense to those who know...

    1) My donor fork was a 300mm stroke Shiver that had been set-up by a really good a pro shop (Factory Connection) for a 86 kg MX racer / rider (Springs and valves set for this rider) I am 86 kgs on bike.

    2) My goal is to use this bike for 100% aggressive off road riding. It will get airborne ... lots. (I have cars and another bike for the gross paved stuff... )

    3) I should be able to simply machine the fork feet and install the donor cartridge and protrude the fork tubes up through the triple tree a small amount (25-35 mm) and maintain the same fork geometry and gain some nice fork travel.

    4) Although the donor bike was a GasGas 300, it was setup for a rider (an MX race bike) of my mass. Despite the differences between the two bikes, the fork springs should be close... our GSs handle their weight (gas tank and rider) on the back shock... and MX guys will have heavier springs for the abuse? For my first tests, because the springs and valving on the donor fork "should" be close to my rider profile, I should just try the donor cartridges as they are (installing no spacers) and see how it feels?

    ... basically install it with the top cap sticking up through the trees and see how it feels?

    Thoughts?

    IMG_6641.JPG

    IMG_6639.JPG




  17. todd900ss

    todd900ss Been here awhile

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    Manny
    The spacer in the pic is to limit the fork travel or stroke. Making the stroke the same as stock f800gs, 230 millimeters. Therefore not needing to slide the forks up in the clamps.
    If you are not going to use a spacer and slide the forks up into the clamps you need to make sure under full compression that the wheel/fender will not hit the lower clamp or body work.
    MannyM likes this.
  18. MannyM

    MannyM Adventurer

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    Thx todd900ss - throughout this (old) thread ... there appear to be a few that welcome the additional travel and have not reported any issues? I'll for sure be checking for interference issues... Just can't help but try the conversion without the additional work if (in my case) it is unnecessary. Consider that tiny extra bit of travel as a good insurance policy.

    Let's be honest... people don't like the "look" of the tubes protruding up through the trees... get over it... go look at any cafe racer.

    As far as suspension "balance" and geometry goes... peaople just want the numbers to match front and back IMO. I would challenge anyone to ride a bike with more travel in the front (offroad) and see if they can find any ill effects? Mountain bikes (which are far far far more sensitive to suspension tuning... because we pedal them) have commonly had more front wheel travel than rear (the fork eats the hit energy, the rear has chain tension and power and paniers full of Starbucks to interfere with its travel and needs to climb the terrain).

    In short, I wonder why the spacers started being installed and I suspect it only was out of our human need to match numbers and not experimentation. Most of the post here say that "their guy" made the spacers because they wanted it to match the OEM travel numbers. There was no testing done. Not in any case of these 36 pages of threads have I found a single "their suspension guy" who rode the bike before and after conversion. The past effort that was done and done and done and done by the countless previous inmates on spring rates and arguing over methods of sag measurement and which fork oil manufacturer really measures in the "proper" centistokes... All report on "feel" and concrete data like "dive" and "went around the block once" and "way better". Maybe they would have had exactly the same feel(ing) if they were a little longer ??? :)

    Just a note. Ride it and try it. And as always - I could be completely wrong! That is the fun part of experimenting.

    And just like the stock suspension on these bikes being absolutely terrible... the stock duckbill fender may actually be worse - it is an ugly duckling. High fender is being installed.

    M
  19. cbleroy

    cbleroy Adventurer

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    You are right and I'm curious to see your experiments results.

    Here, this is winter time and I've not the bike insured, this is part of the Women Acceptante Factor.
    So I have time to make the best guess using the theory. Hopefully this will speed up the experiments.

    Bellow is on more contribution from my side. The table is a tentative to anticipate the sag figures.
    If you are interested you can make this very simple excel at home; I've written the formula used.

    I would be curious to see if it matches other's experiments.

    SagCalculation.PNG
  20. MannyM

    MannyM Adventurer

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    Untitled.jpeg cbleroy! This is awesome!!! Good work

    I have the same "type" of wife... that's why my mechanical engineering and project manager mind speaks in her voice saying ... "is that reeeeaaaally needed?" and if so "why?"

    Your calcs are very cool. I'd love to have it so I can play with it?

    My main comment is on this obsession with sag. As the originator comments so many times and repeats it over and over and over again, the SAG is good to choose your ideal spring. That's it... your spring. After that, the system is DYNAMIC and valving and oil weight is adjusted to the riders requirements.

    Your calculations rely a lot on the estimated value cell B3 (43%)... the ratio of pilot and bike weight on the forks... this value changes every 0.00000012323432 seconds when riding the bike. And this dynamic performance in my opinion is the WHY of why we are changing these forks. Not sag. Sure, we can measure sag. We can adjust preload to change it. We can look in books and find arguments over when our sag isn't ready to "race". We ride terrain other than flat surfaces that make us rock on the pegs like riding a horse. When riding really gnarly off road terrain, riding smooth means light on the controls. Input to the forks is as little as possible unless you need to use the fork (trying to make cell B3 < 5%). Hit the gas and float. Weight back and let the fork run up and down. Using the fork and rider weight to force the wheel into a turn or pushing the fork spring and blending the throttle/blip to match the rebound in order to loft the wheel off the ground.

    Just more of my thoughts regarding this conversion... I could be wrong!!

    It's snow season here too. Forks to be machined this week and I'll check to see how the static measurements measure up!

    Attached Files: