Fork install guide

Discussion in 'Japanese polycylindered adventure bikes' started by Motociclo, Aug 21, 2017.

  1. Motociclo

    Motociclo Long timer Supporter

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    This is a bit of a guide that can be used for any fork.
    I was going to add pics, but i think anyone reading this will be able to understand what I am trying to explain. It is a bit involved and requires a bit of double handling, but the results could be certainly worth while. I have done this with my bikes, and I think it works well.

    To start off with, check fork tubes for straightness then re-assemble forks only with bushes in place, no seals or dust seal. For USD forks, can put dust seal and oil seal on inner tube, don't locate them home at this time.
    Check for any excess play in fork bushes by trying to move legs around.
    It is not a common practice, and i haven't used it, but people have shimmed the slide bush with shim stock or feeler gauges. Start very thin, 0.001" or 0.025mm thin.
    Can try it, there has been success with this in the past, but is a fine line. You don't want to have so little bush/tube clearance that it causes binding.
    Install fork internals, minus spring and put fork cap on as though it was a final assemble.
    Put a fork in triple clamps and tighten to spec, a lot of debate goes into what the right specs for clamps are, I don't care what you use, I just know what i use. I start with left fork first.
    Put other fork in, clamp should have enough grab too hold in place.
    There are 2 things we are trying too achieve here. Check for fork bind and axle bind.
    First, adjust the height of last installed fork leg, so the axle spins freely inside its own clamp area. If axle is bent, no amount of aligning will fix, ensure it is straight.
    When axle is spinning freely, torque up triple clamp bolts to spec. There may be the slightest height difference at top of clamps between the fork legs, this is less important than ensuring axle is properly aligned.
    Nip up a clamp bolt on axle to hold in place. Move forks through stoke a couple of times to feel for binding if none your probably all good. Next, push fork legs up through travel to the top and release. They should lower under they're own weight, if not we may have a binding issue.
    Process of elimination, start with lower clamp bolt torque.
    Loosen lower bolts off totally and try again. If this sorts it, then we know bolts are too tight. I have largely always used stock specs, but you may find you need to drop bolt torque down considerably. I leave the numbers you choose up to you. This info here really only relevant to USD forks, but next bit useful for all types.
    Got bolt torque sorted, tube alignment may be the issue.
    Two things that can effect, triple clamp alignment and bent tubes. Bent tubes is fairly unlikely. Fork tubes are made very well, but still could be defects during manufacture that could cause binding.
    You may need to loosen off top triple clamp and stem nut and re-install fork legs to ensure it is all straight. You can use a flat/ straight edge across the fork tubes to check for alignment, if the flat edge rocks on a diagonal axis, it is out of whack.
    If clamps and forks are aligned, loosen off triple clamps for one fork tube and rotate 90 degrees, continue with the drop test and rotation of tube until they lower by themselves.
    At the end of this you will need to leave some marks so you can align everything up.
    Permanent marker or paint pen will do. Leave some marks on triple clamps and fork tubes.
    Now you can remove forks, disassemble again if required and install seals if they're not on inner tube already, ( USD forks), add springs and oil, then reinstall. Go through the motions for the axle alignment again, but if you put marks on everything, it should be pretty right.


    Last step is to install front wheel.
    Most every bike has an axle clamp. Usually on right leg, sometimes both.
    Install front wheel, axle, brake calipers. Torque axle or axle nut to spec, and if there is a clamp on the left leg, tighten also.
    Take bike off stand, make sure you have pumped brakes if needed and hold front brake on and push down on forks a few times.
    This ensures fork is sitting where it wants to naturally, then tighten the right side clamp.
    If axle was aligned properly earlier, it will be pretty close, but do this step regardless.
    This may seem a bit involved, but after installing new bushes or seals, it may just be worth it.
    Modern forks are pretty well made, most of this just might be a time waste, unless you do it, you won't know.
    Hopefully it helps someone.
    #1
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  2. CrStep

    CrStep Been here awhile

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    You are awesome for sharing your knowledge and experience with us. Thank you.
    #2
  3. Motociclo

    Motociclo Long timer Supporter

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    No worries. I hope you get some value out of it.
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  4. Dillo

    Dillo Almost Awesome

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    Do you have any images to help make this a bit more clear?
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  5. Motociclo

    Motociclo Long timer Supporter

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    Not at present. Waiting on my fork tubes to come back. I will take some pics when I reinstall for clarity.
    #5
  6. road_apple

    road_apple Hit the Trail

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    Not completely in the same realm but look up Dave Moss on Youtube. Take the time to go thru all his vids and suspension becomes clearer.
    #6
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  7. Motociclo

    Motociclo Long timer Supporter

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    Here are some pics of putting shim behind bush to take up slop in tube.

    20170918_125136.jpg

    Shim material, bang on 0.05mm.

    20170918_150856.jpg

    Have cut material into a 19mm by 136mm strip, this wraps around nicely with gap. Don't want overlap.

    20170918_151346.jpg

    Slide bush on a bit, and hold shim material in place. You can nearly slide bush all way on, and material stays in place nicely.
    Have dressed the bevelled edges on bush with 1200 sand paper. There were quite noticable rough edges.

    20170918_151522.jpg

    Here are the numbers. Outer tube ID is 47.06mm, glide bush od without shim is 46.81mm. This is 0.25mm clearance.
    What I have found is 0.10 to 0.18 is about what you need for bush/tube clearance.
    With 0.05mm shim, we get 46.91mm od for bush, this gives 0.15mm clearance.
    Massive reduction in slop in tubes. Still enough to just be able to feel it though.
    This will ensure bush sits flatter against inside of outer tube.
    #7
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  8. Motociclo

    Motociclo Long timer Supporter

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    If you now go back to the top post and read through, you can check for binding of axle and fork tubes.

    20170918_152541.jpg

    Tubes moved beautifully with no binding and slide down under they're own weight. I torque lower clamp to 12nm, and top one stock at 22nm.
    Fork lengths pretty well identical, so no height difference at all. Axle rotates smoothly.
    I have run oil level at 50mm fro top WITH spring installed. This is same as stock.

    The video posted above by the road apple, gives good visual on what I finish first post with how to tighten axle nut and clamps.

    Excuse the dirty bike, but here it is finally after 8 very long weeks and my incessant ramblings. Tomorrow we ride!!!!

    20170918_165059.jpg

    I think i have covered everything. Will add more if needed.
    #8
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  9. Dillo

    Dillo Almost Awesome

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    If you have the right kind of scrap material lying around, you should take a piece of chromed steel and put a mark on it with the same marker you used to mark the tubes and then leave it in a cup of fork oil. If after 5000km of riding the mark is missing from the fork tube it might be because the ink dissolved in the oil. If the mark is still present on your control sample but missing from the fork tube then you know it had to have been worn off somehow.
    #9
  10. Motociclo

    Motociclo Long timer Supporter

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    I'm not expecting to see ink left when I check. I did have a paint pen, decided not to use. The idea is sound, just need a medium that, like you say won't dissolve.
    If there is any contact between inner and outer tubes there will likely be witness marks. Heres to hoping not.
    #10
  11. todd900ss

    todd900ss Been here awhile

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    Nice work, keep us updated.
    #11