Replacing Fork Seal (oilhead)

Discussion in 'GS Boxers' started by Carlos M, Oct 7, 2003.

  1. Carlos M

    Carlos M www.motoxplorers.com

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    I've busted another (it's the 2.nd in 4 months) fork seal and I intend to replace it myself. I've searched the wisdom here and it looks simple. Just to make sure, can the wrench gods confirm the following steps:

    a) With a 15 mm and a 19 mm loose the stanchion from the top triple clamp

    b) once loose, the stanchion will move down inside the slider.

    b) remove the plastic black band at the top of the stanchion.

    c) unscrew the cup (is it a sort of dust seal ? is it screwn in?)

    d) remove a retaining clip

    e) pry the busted seal off. (anyone knows standard seal dimensions?)

    f) Install new seal, reverse the rest of the operation

    g) take front wheel and axle out, take air purge plug at top of stanchion out and drain fork leg at bottom drain plug.

    h) fill 0.47 l of SAE 5 susp. oil.

    Is it something like this or am I totally wrong? Why do these shites blow if there's no susp internals inside? Are we supposed to purge the air regularly like on real forks?

    TIA
    #1
  2. jdiaz

    jdiaz .

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    Don't remove the slider at all. Just remove the fork brace bolts, the axle, and the brake caliper, and the fork lower drops right onto the garage floor. At least, that's how my memory remembers it. I do know that there is nothing positively attaching the slider to the lower fork leg.

    The rest of your procedure sounds fine, although I wouldn't even bother changing oil.

    Jon
    #2
  3. Carlos M

    Carlos M www.motoxplorers.com

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    John,

    Thanks.

    Sorry, it may be my english. I am calling stanchion to the inner fork tube (attached to the top triple clamp) and slider to the outer tube (attached to the bottom triple clamp / telelever arm).

    So do I need to loosen the lower (outer) fork leg? I though that, by releasing the inner from the top triple clamp, this inner would move down inside the (outer) bottom fork leg, allowing me to take the seal out by the top part. Hum... maybe a drawing...
    #3
  4. OUtback UFO

    OUtback UFO GLOW IN DARK SPACEINVADER

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    I just redid my left fork seal, and the upper (shiny part) of the left fork, today for the 2nd time since doing both in Achorage early this May, I tried to do it with out taking the entire fork out of the mounts. But it will save you time and knuck skin if you just take the bloody hold thing out. Rememer to re-aline the front axel before putting the tire back on. i tighten the bolts that #4 on preivioius pict. withthe axel in then put the tire back on.

    as for replacing the fork seal. by taking the entire lower fork off you will have the ability to remove the bad seal easier. they are really tigith fit. also be very careful on putting the new one back in not ot damage the inner seal ring part of the seal. I used a large socket for to evenly get the seal to sit flat on the metal o-ring that goes below it. I had BMW Anchorage show me how to do it with their BMW speciality tool, I used a large socket that just fit into the lower fork section. If you have a friend with mechanic shop they should have a large enough socket. .

    in addition, i put a bit of extra grease on the top cap to help keep dust getting into the seal and wearing it out quicker. To get old seal out is a pain and you need a L shaped hook type of tool to pull it out. that is why i take the lower section, so i can use my feet and legs to get a good hold on the fork to pull the seal out.

    thing to check while doing seal replacement
    take the tiem to clean out any grime in the bottom of the fork lower section, i use a little but of desiel fuel as a solvent and clean inner part of the fork of and grime fork oil that did not drain out.

    the uper part of the fork (shiny part) will slide in easily if the seal is sitting flat on the lower metal o-ring. also take out the tiny hex bolt on the top of the upper part of the fork to let air in as you re-insert the lower part back onto the upper part. and then when everything is at the right place tighten the tiny screw back to seal the fork.

    In addition, you should check you upper fork section to see if there are any fine scratches... i had some bad ones from all the dirt roads i ride in Colorado, that could be the reason you seals are wearing out so quickly. And buy a pair of fork covers.
    #4
  5. PartTimeTravel

    PartTimeTravel Been here awhile

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    You should clean up the slider surface also - is it called honing?
    #5
  6. Carlos M

    Carlos M www.motoxplorers.com

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    :thumb Now I got it... I think. I'll shoot some pics and I'll post them when done.

    Thank you very much.
    #6
  7. Noggin

    Noggin blissfully ignorant

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    My experience is much as described above - Much easier to bite the bullet and remove the lot!

    Buggest problem I had was removing the ABS sensor as it had become one with the casting :splat

    Take your time and all will be well, my local parts shop also recommended replacing the plastic dust seal also, makes life easier if you don't have to worry about damage when pulling it out!
    #7
  8. kevbo

    kevbo Rubbery-Lip Flappin' PHI

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    Ive done it both ways, by lifting the top pice out, or dropping the lower piece. I recommend the later. It is a real pain trying to work on the seal inside the beak area.

    It is more work to get the lower leg off, but much easier to work on the actual seal once you have it in hand. To change the oil you'd have to pull the axle anyhow. (to get at the plug) When you have the lower leg in hand, you can just dump it out the top.

    Don't forget to put the spacer (washer looking thing) back under the seal BEFORE you install the seal...hard to pry the seal out to put in without damaging seal. DAMHIKTIJD.

    Nothing threads on. Just slip/friction fits and the snap ring.

    When I did mine, it didn't "take"...still leaked even after doing it twice. Fork leg looked and felt near perfect, but I pulled it off, put it on the lathe and polished it.

    I used Cerium Oxide optical polish (basically buffing compund without the wax) on a piece of chamois. Jewler's rouge, Semi-chrome, or even toothpaste sould probably work just as well. I think ANY sandpaper or emory paper would be too coarse.

    Anyway, no leak after polishing.
    #8
  9. Carlos M

    Carlos M www.motoxplorers.com

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    Thanks for the information. Mine has bottomed a lot lately. I am waiting for an Ohlins but I can't stop myself to pop a few wheelies meanwhile. Doing it off-road, where you don't have enough road to land it smoothly, invariably ends up in bottoming.

    I am almost sure that the blowing of my seal is related to abuse/bottoming. That had me thinking: If there's no vent in the fork is the air inside working as a spring?

    I'll get some neoprene fork boots anyway...
    #9
  10. cRAsH

    cRAsH Banned

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    I'd be willing to bet that you've bent your slider tube.
    Which means you MAY have bent your telelever a-arm.
    When you have it apart, try rolling the slider tubes on a flat surface to see if they are bent.
    If they are, you'll keep blowing seals. And you probably have a bent a-arm as well. Have a look under the a-arm ball-joint nut cover - it's the plastic bit on the top of the a-arm.
    If you see any cracks in the paint, it's bent... :(:
    #10
  11. R-dubb

    R-dubb Dubbious Adventurer

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    This is a great thread. While I'm not leaking, I have pretty good notion that my tubes are bent. The bike tracks perfectly, but I can't perfectly center the forks. Even when loosening the pinch bolts at the bottom and at the tele, the steering yoke won't square up as well as I would like.

    Good info here on how to tear the front-end down. I've been told that by loosening the pinch bolts and rotating each fork tube, it is possible to check trueness without extracting the tubes. Mine will turn but not easily.

    :dj
    R-dubb
    #11
  12. Carlos M

    Carlos M www.motoxplorers.com

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    OK the job is halfway. I have removed the seal and it looked OK. Shit. Crash is right. For dummies, here goes:

    Remove front wheel and brake callipers:
    [​IMG]

    Loosen the inner top from the top triple clamp:
    [​IMG]

    Loosen the pinch bolts on the bottom triple clamp:
    [​IMG]

    Lower the fork tube in the lower triple clamp, let the cup(dust seal ) rest agaisnt it and push down to extract the dust seal.
    [​IMG]

    how it looks once out:
    [​IMG]

    Now remove the air purging little bolt from the top of the inner tube. Then pull the inner from inside the outer. Beware oil spillage!

    Now remove circlip:
    [​IMG]

    Then pry the seal out with a big flat blade screwdriver. Protect the top of the outer tube with some plastic piece or something:

    [​IMG]
    [​IMG]

    Bellow the seal there's a large washer (rusty in my case):
    [​IMG]


    Where it all seats (once cleaned):
    [​IMG]

    All in pieces:

    [​IMG]
    [​IMG]
    #12
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  13. simonm

    simonm Stealth Adventurer

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    ....for the pics Carlos.

    They made this thread a lot clearer.
    How's your telelever arm?
    #13
  14. Carlos M

    Carlos M www.motoxplorers.com

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    Now, when I took the inner from the outer I saw that the seal didn't have any visible damage. The inner is also in good aparent shape without scratches... humm.. I begin to suspect crash is right. Let's put the inners in the truing stand:

    [​IMG]

    Shit. Crash is Right. About both inner tubes.

    [​IMG]
    [​IMG]

    I didn't have my feeler gauges handy. But I had a book 1 cm thick and a 100 pages :): . I can slip 2 pages but not three bellow the middle of the inner. So I guess it has a runnout of 2 to 3/10 mm. Is this acceptable? I can turn the inners inside the outers with no effort...

    The Telelever A-arm looks OK. (Apart from the fact that it hits the Hepcko & Becker crash bars :splat.

    [​IMG]

    I can't see the dreaded cracks in the paint.

    [​IMG]
    [​IMG]

    So Crash, what have you done? (bought a KTM?)
    #14
  15. Jim Moore

    Jim Moore Harsh and colorful

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    I've changed a few fork seals and I've never seen a rusty washer like that. I would replace it. I'll bet that the rust is messing up your fork seals. Or maybe the bent tubes are allowing moisture to get beneath the fork seal and cause the rust. Thanks for the pics. BTW, the fork seal is easier to remove if you heat it over the stove first.
    #15
  16. B-art

    B-art Been here awhile

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    That rusty wacher is more common than you think, it is because of the water passing the seal while traveling up and down.
    Brush the wacher with a wirebruch and re-use.
    But do clean the inside of the inner and outer fork leg, change the oil. Oil is hygroscopic (do you spell it like this?), and must be changed every ????km(see manual) to prevent damage to the fork.

    Honing is not nesesery becaus the glyding buches are teflon coated->softst part.

    B-art
    #16
  17. kevbo

    kevbo Rubbery-Lip Flappin' PHI

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    I'll reiterate that I still had leakage with two new seals,
    fixed it by polishing even though the fork leg LOOKED and felt fine.
    #17
  18. Carlos M

    Carlos M www.motoxplorers.com

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    I guess I should have RTFM in the 1.st place... permissible runnof is 4/10 mm so I should be inside spec.

    I'll give the tubes a good polishing session and I'll replace the dust cups also. Hope it will hold.

    If any of you disassemble your front fork for seal replacement I would be curious to know the runnof you find.
    #18
  19. kevbo

    kevbo Rubbery-Lip Flappin' PHI

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    When I polished mine on the lathe, I grapped the upper hex with in the three-jaw, and made a butt plug for the live center to run in.

    I doubt there was as much as .005 runout, and most of that was at the chuck end, so ecentric chucking or hex rather than a bent tube.
    #19
  20. OUtback UFO

    OUtback UFO GLOW IN DARK SPACEINVADER

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    an additional thought about replacing the fork seals.

    put a but extra grease on the inside of the dust cap... this will help catch dust more if it gets inside the dust cap to help lessen wear on the seal.
    #20