F800GS - RXV Shiver'ed Fork Conversion

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

  1. cbleroy

    cbleroy Adventurer

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    Hi MannyM,

    Sag is not a major obsession by itself, i believe at the end it is mainly to keep the available travel of the fork.
    In my case I expect not to compromise the on road behaviour, while improving the off road characteristics.
    For the on road, my obsession is more on the geometry (experienced shakking already based on a wrong geometry). The starting point of the geometry is related to the race sag and the position of the fork in the clamps.
    The sag is related to spring rare and the spring preload.
    So the things shall be considered together I believe.
    At last are the rebound and compression settings, as soon we have choosen the springs we may define a baseline for the shims stacks. Then it is about experimentation and eventual corrections.
    Am I wrong in the approch?


    Sure I could share the excel, but i should first figure out how. Anyway, you may rebuild it in 10min since I displayed all used formulas...
  2. MannyM

    MannyM Adventurer

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    NO! - your approach is awesome and makes perfect sense! I am impressed with your efforts.

    I am keeping it simple. My donor forks fortunately have been sprung and valved to a near perfect matched pilot mass... I'll try without any extra work because I believe that IF I keep the travel longer (as per the donor), I may be all set. I may also be wrong! Worth a try.

    For me, my bike is a dirt bike. I am spoiled because I have a pavement bike (Triumph Thruxton... that has been turned into a semi-scrambler). The F8 is a dirt bike to me. The geometry is all dirt bike and this cannot ever be changed. Just the size of the front wheel alone (21") says that this bike will never behave on the road like a "road" bike should. So to me... and only me, I choose not to fight it. My F8 is a 450cc enduro bike that has put on some permanent "winter weight" (like me!) but is still strong as hell. Despite all of the popular criticism this site will give me for wanting to thrash my F8 at high speeds and on trails where anything with 4 wheels cant get to.
  3. cbleroy

    cbleroy Adventurer

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    clear, objectives are slighly different, so are the approches,
    What springs-spacers will you use?
  4. MannyM

    MannyM Adventurer

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    hey cbleroy - sorry for my long winded rants above.

    1) I will be using NO spacer. That is the point of most of my above comments. No spacer. I want to try the longer travel. I suspect it will be fine and I can adjust the tubes in the trees if I need to.

    2) The springs and the valving in my donor Shiver fork was set by Factory Connection (https://www.factoryconnection.com) for the previous owner who was an 86 kg rider (I am also 86 kgs). I completely realize it was on a different bike (yes, a MX race bike)... but I suspect the spring is in the 0.5 - 0.55 kg/mm range and it may work for me just fine. I am not going to disassemble the donor fork components. I am simply going to clean the parts very well, install new SKF seals in the original tubes, and try the forks.

    No spacers, no changing springs yet... machine the feet, install the donor components and then see how the bike performs. If I need to make changes after the install and trials I will do them then. Keeping it simple and doing work only after I have tried the simple stuff first.

    M
  5. cbleroy

    cbleroy Adventurer

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  6. cbleroy

    cbleroy Adventurer

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    UOTE="cbleroy, post: 34142287, member: 402098"]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.

    View attachment 1083759 [/QUOTE]

    Hi MannyM,

    I answer here since I could't attach the picture as direct answer.

    My analysis is that you should consider only the dimension "1" as relevant. Did you succeed to measure it on your donor fork?
    fork leg shapes.PNG
  7. MannyM

    MannyM Adventurer

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    Thanks for reply ! I think I understand what you're indicating.

    The reference to dimension #1 is a little out of an ordinary form for a machinist.... they usually only want to know what size to cut, and how much to cut it. Giving them finished "remaining" dimensions could be trouble - especially trying to measure that inside lip dimension. Would need a miniature machinist with a miniature set of verniers.

    I know that there is a lot of speak throughout this post indicating that this was done in a lathe, but turning this piece and the additional steps for using a lathe to literally "drill" one through hole and one counter-bored hole is mill work.

    All that need be done is one 28mm dia. through hole and then one counter-bored 31mm dia. to a plunge depth of dimension #2 + dimension #3. You cannot effect the inside (or left most position) dimension of dimension #1. All that is needed is #2+#3. One set-up in the milling machine. One bit change. Maybe 30 minutes work in a small mill. The machinist will just touch the end mill to the face of the fork, zero the depth readout, and then plunge to the depth of #2+#3...


    Thanks for your help. I'lll triple check my measurements and cut (twice...).
    And send me your email- I'll send you beer!!

    Thanks again!
    Mike
  8. Bayner

    Bayner Long timer

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    I will also caution against using a measurement based on the bottom of the fork leg (#2+#3) The most critical dimension is indeed at #1 in both diameter and depth as this is what seals and locates the valve stack into the damper tube.
    Different fork bottom lugs may have different external dimensions and thereby result in different widths of the measurement #1 if #2 & 3 are simply transposed from one fork leg to another...
  9. MannyM

    MannyM Adventurer

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    gotcha Bayner- thanks. It is just not generally how things are dimensioned but all and everything can work.

    I still need help... and I think that maybe the hairs we're splitting are too fine... above in cbleroy's drawing and in your mention, you both comment that the dimensions of #1 are critical to locate the holes... Because the valve and the cartridge body are connected, the important part is that the valve bore in the foot of the fork be deep enough to ensure that the holes in the cartridge are far enough into the leg that the FOOT does not impede oil flow and the valve body holes are where they will function with the orfices.

    The dimension is not to make the original damper hole locations be in the same vertical position as the new donor cartridge holes location.

    yes?

    From the photos I have just taken, it appears that it is not possible to have the cartridges positioned so that the holes from the original damper and the donor damper can be in the same position within the fork tube. As long as the cartridge holes are far enough up into the tubes that they can "breath" the oil and let the shims tickle the flow appropriately... than we're all flowing good, and I'm not flying over the bars because of their marshmallowy plushness.

    The total bore thickness of the stock feet is ~ 25mm. I will counterbore at 31.10mm (+0.01/-0) dia. to a depth of 17mm (which is also the measures bore depth for the stock cap screw). The through bore will be 28.15mm (+0.05/0) dia.


    Make sense?

    IMG_6861.JPG IMG_6859.JPG IMG_6860.JPG
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  10. Bayner

    Bayner Long timer

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    Hmm, not sure how to best express myself here...
    That dimension is not so much related to the placement of the holes in the damper tube but more about the proper relationship of the two pieces when assembled together.
    The two 'female' parts (being the damper tubes external dimensions) need to be at exactly the same placement. So take the male parts out of the equation and bring the tube on the right up until it's flush with the other one, and then screw the valve assembly into it. But it's going to have to have a gap rather than being screwed all the way in, and that gap is the dimension #1. That's the one that you need to be exactly matching the donor fork.
    Someone please jump in if I'm failing to express this properly...
  11. cbleroy

    cbleroy Adventurer

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    Hi,
    I suggest to "forget" for a while the F8GS cartridge tube in this discussion, you won't use it anymore...
    There is no easy way to get the Shiver cartridge oil holes at the same position as the F8GS cartridge holes (within fork) - it is not the main goal; In my drawings I was referring to the relative position of the shiver cap within the shiver cartridge that shall be kept.
    Yes, the shiver cartridge holes will be in a lower position within the fork compared to the F8GS cartridge oil holes, this is due to cartridges different constructions.
    It seems there will be still room around the cartridge to let the oil flowing ; anyway, this is the same for all converted shivers forks done so far, you cannot do much about that !

    By measuring, you should be able to transpose the #1-8mm into a #3 measurement you need to machining.
    It it not easy to measure from the inner bore, but even if this 8mm dimension is, by principle, important, the tolerance is probably not so strict.
  12. MannyM

    MannyM Adventurer

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    Yes yes yes - agree completely with all of the above. Again - thanks for talking this out with me.

    The confusion (completely on my part!!! Sorry;), began for me from the hand drawn sketch transposing the two forks together (the blue and black hatching). It shows that the machined foot that accepts the donor cartridge places the magical shoulder #1 much further into the fork than the “original” shoulder for the stock socket head cap screw. It does not. They are actually in the same location within the fork. Following that, the drawings were regarding oil flow out of the damper orfices ... and I got confused - sorry!

    Yes! Thank you for clarification! The location shoulder to sandwich the valve to the same locations will leave ~ 8mm shoulder length inside. But my drawing that I’ll give the machine shop will not have this 8mm dimension on it whatsoever. Machinists only have gauges on their machines to read the tool travel as the tool cuts and removes material.

    Know that I finally understand my own confusion... I’ll do a drawing and post it for any future inmates.

    Thanks again to both !!
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  13. piero.favero

    piero.favero n00b

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    Hi guys,

    may I ask you which are the pros and cons of a shiver conversion instead of buying drop-in cartidges?
    In the past I believed shiver to be superior compared to many road-dedicated cartidges and truly considered the conversion. I would have bought a second hand shiver but I have been told that the mod was only advantageous when no drop-in cartidge kits were available, as these are now superior.
    As an alternative, I am considering the matris cartidges, which preserve full stroke of the fork and have compression and rebound damping regulation, plus the preload regulation (as far as this is truly useful).
    Use would be 50% off road and I am interested in smooth riding and comfort. Perfect attitude and race setting are not in my desires.
  14. MannyM

    MannyM Adventurer

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    Hey Piero,

    We each would have our own opinions on this mod. For me, it was primarily on cost-logic. If a bike is worth $10k... I struggle with the logic that 25% of the bikes total worth is in a set of fork cartridges ($2500 Canadian is a set of cartridges from the trendy T company) ... so for a few hundred dollars (less than $500 Canadian total), I had exactly what that expensive option would offer to may bike and I personally had a great time bonding with my bike during the cold winter months. But I could have not do that because of this thread and the ability to convert the fork internals. I will openly admit to being a hypocrite and purchasing a canned rear suspension because there are no options (I went with a Nitron custom rear shock).

    It’s all what you fancy. I love tools and have machine shop capabilities. The suspension on these bikes suck if you want to take the bikes off and beat the beaten path. Both options help remedy.
  15. piero.favero

    piero.favero n00b

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    Haha I think you are right. Matris are not cheap, but they come for 800 euro about. Shiver conversion comes for at least 500 euro, as I have to buy a new shiver and find a workshop that machines my forks and makes a couple of chocks...
  16. todd900ss

    todd900ss Been here awhile

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    In the same boat at the moment. Problem is all the donor Shiver 45’s I’m finding in the US are starting at $300. Add $150/200 for machining, $130 for springs let’s say another $125 for oil, seals and some shims. And your getting close to a set of drop in cartridges.
    If I could find a set of donor forks for $75-$100 this is the route I would go.
    May still go this way as I like to tinker!
  17. Bli55

    Bli55 -

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    Thanks guys, really interesting and insightful discussion the last couple of pages!

    I know most of the better shiver forks state they have 300 mm travel, had anybody gone and measured/confirmed that?

    What i did on mine was remove the spring, then screw the top cap back on fully.

    I assume this will yield the true travel because the fork will bottom out at the metal-on-metal contact point?

    I additionally used the pressure release valve so i could compress the forks without fighting the increasing air pressure.

    Also made sure to force the travel through the bottoming out hydraulic circuit until there was definitely metal contact.

    On the other side though, the fork just extended by itself and i couldn't really pull it much further out.

    So please educate me, did i make a mistake in some of these assumptions/measurements?

    Because...the total travel i measured was...

    288 mm.
  18. Bayner

    Bayner Long timer

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    While I can't say for certain, different donor bikes will likely have come with different fork travel lengths. Unless you're building a custom shock to match the additional travel it is not a necessary feature for the BMW.
  19. piero.favero

    piero.favero n00b

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    Also consider that the longer travel in this case comes for a reduced overlap between fork legs and stanchions. Maybe this is possible on a hundred chilos enduro, but not on a 250 fully loaded GS...

    Bye
    Piero
  20. Bli55

    Bli55 -

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    Understand, I'm just saying that my forks were also specified as 300 mm, and that 288 is an oddly odd number...

    And most other forks are described in this thread as 300 mm, but i didn't come across anyone writing on if they measured the travel themselves.

    In any case, were my measurements and assumptions explained a few posts above correct?

    Or is my number of 288 simply incorrect because i measured wrong?