2002 KTM EXC 250 fork length mystery

Discussion in 'Suspension' started by jmil, Jul 17, 2017.

  1. jmil

    jmil When are we riding?

    Location:
    San Francisco
    Name:
    Jeremy
    2002 KTM EXC 250

    Rebuilt forks (new seals and bushings) with about 5 hrs on them. At the time of rebuild, everything went together fine.

    Put new fork springs in last weekend. Initially I noticed the front axle was difficult to remove. Springs went in fine.

    Now the forks are different lengths. The R fork is about 2cm longer than the left fork. Bounced them both several times to see if something was sticking. No parts were removed other than the springs, which was without drama. Nothing is leaking out. We pulled the new springs out and swapped them between forks, no change. Thinking back, the difficult-to-remove axle suggests that the change happened sometime between the fork rebuild and spring replacement. In that time, the front wheel had not been removed. Triple clamp bolts have been tightened to correct spec with a torque wrench each time.

    I'm thinking it's witchcraft or some kind of curse, but if anyone has a logical explanation, I'd love to hear it. In any case, I think the course of action is the same: tear down, inspect, replace (if needed), rebuild. Am I wrong?
     
  2. EricB

    EricB Modulator

    Location:
    San Jose
    Name:
    Eric
    Is there an end collar on the bottom of the spring that has gotten dislocated?
     
  3. jmil

    jmil When are we riding?

    Location:
    San Francisco
    Name:
    Jeremy
    There is a ring that the spring sits on (part #48600021), but there's really nowhere for it to go. If it were seated unevenly, the spring would have flexed to one side when compressed, which it did not. In any case, a spacer out of place would add preload to the spring, but wouldn't change the overall length of the fork.
     
  4. KTMJack

    KTMJack Cheese cutter

    Location:
    Sunnyvale
    Name:
    Jack
    You were having problem with a leaking fork. Is the valving on that side tight or Before you put the top on did you back nut all the way down on the Damper rod then screw the cap down
     
  5. jmil

    jmil When are we riding?

    Location:
    San Francisco
    Name:
    Jeremy
    The leak was a bottom bolt with failing seals. It was replaced. Both bottom bolts are fully seated.

    How would valving affect fork length? I assume they're the same, but wouldn't know how to tell except ride the bike. Even then I'm not sure.

    I didn't loosen either nut from the dampening rod, just loosened and removed the fork cap while holding the nut still. It's possible one of them moved a little (I recall it looking normal), but that couldn't account for 2cm.
     
  6. Ankur

    Ankur Well-Known Member

    Location:
    Cupertino
    Name:
    Ankur
    Just to be sure: you measured the fork lengths with the forks off the bike right? Else they may just be sitting uneven in the triple clamps?
     
  7. KTMJack

    KTMJack Cheese cutter

    Location:
    Sunnyvale
    Name:
    Jack
    The lock nut has to be all the down before you put the cap on Then bring the nut up to the cap .
    Call me if you need help
     
  8. jmil

    jmil When are we riding?

    Location:
    San Francisco
    Name:
    Jeremy
    No need to measure. It's quite visible standing the forks up next to each other.
     
  9. jmil

    jmil When are we riding?

    Location:
    San Francisco
    Name:
    Jeremy
    Now you've got me confused. On both forks, the lock nut (the one that requires the thin wrench) was seated against the dampening rod, I threaded the fork cap down by hand until it seated, then held the nut in place and tightened the cap.

    The. I'm supposed to back the nut out against the cap?
     
  10. KTMJack

    KTMJack Cheese cutter

    Location:
    Sunnyvale
    Name:
    Jack
    My number is in sbr information
     
    jmil likes this.
  11. KTMrc

    KTMrc Dino

    Location:
    San Jose
    Name:
    Randy
    Most likely the fork cap is not screwed onto the damper rod far enough.
    front fork.JPG
     
    jmil likes this.
  12. KTMrc

    KTMrc Dino

    Location:
    San Jose
    Name:
    Randy
    This video shows how the forks come apart.
    The important part is that the hydraulic stop ( black plastic part) has to be threaded all the way down the piston rod otherwise the fork cap will not thread all the way until it bottoms against the piston rod. It is possible for the piston rod to spin in the hydraulic stop when threading the fork cap on which will result in the fork being longer when the fork is assembled because the fork cap is not threaded down far enough but it still contacts the the top of the hydraulic stop.
     
    RobertHaas and LoopDuplicate like this.
  13. jmil

    jmil When are we riding?

    Location:
    San Francisco
    Name:
    Jeremy
    Yeah I reinvestigated that. On both forks the fork cap threads down until it hits the hydraulic stop with the same amount thread showing before putting the cap on. I suppose that means the hydraulic stop is too high, but it also means the difference in fork length is not caused by the position of the fork cap. I can't take them apart any more than that at my house, so I'll have to figure something else out.
     
  14. Ankur

    Ankur Well-Known Member

    Location:
    Cupertino
    Name:
    Ankur
  15. DaveJ

    DaveJ Well-Known Member

    Location:
    Los Gatos
    Well...something is wrong, and if I were you I would not ride this bike until you fix it, because something internally might be coming apart and if and when it does, things will get ugly really quick.

    Most likely the caps are not seated correctly and/or coming off the rod.
     
    Andy likes this.
  16. jmil

    jmil When are we riding?

    Location:
    San Francisco
    Name:
    Jeremy
    Oh I would not ride it like this. The caps are seated evenly (though perhaps not fully). The problem is in the bottom.
     
  17. tgroenbeck

    tgroenbeck The Deer Hunter

    Location:
    San Jose, CA
    Name:
    Tom
    Why don't you let Dave fix it? If you pay double he let's you watch. :runaway
     
  18. KTMrc

    KTMrc Dino

    Location:
    San Jose
    Name:
    Randy
    Could be a broken rebound spring on the damper rod. Part 44 in the parts diagram. Minute 4:24 in the video shows the rebound spring next to the white spacer.
    The rebound spring stops the fork from hammering the damper when the forks extend completely.
    The broken spring would allow the fork leg to extend farther and may account for the fork leg difference in length.
     
    DaveJ likes this.
  19. DaveJ

    DaveJ Well-Known Member

    Location:
    Los Gatos

    It would be a little odd for this to happen, and I have never seen it happen, but everything here is correct. If a top-out spring broke the fork would extend further than stock.
     
  20. DaveJ

    DaveJ Well-Known Member

    Location:
    Los Gatos
    It is also possible that the rod is completely disconnected from the cap. I've seen this happen, mainly because the rod jam nut is not secured properly.

    In this case, the one fork leg would hang down lower, but due to the vacuum in that leg, it would not completely fall down.

    You could test for this by seeing how much more you can extend the fork by pulling on it. If it still has a hard stop at the end, then something like the top out spring is busted. If you can pull it down further, then most likely the rod has come off the cap.

    I sense that since this happened right after a service that it is a rod/cap issue, and most likely a very easy fix with little to no damage to the internals.
     
    Andy and Ankur like this.
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