KTM LC4 Fork Oil Change

Discussion in 'Thumpers' started by Gary, Mar 26, 2003.

  1. Gary

    Gary Another Adventure Rider

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    Can anyone offer a 1-2-3 or outline a quick method of changing the fork oil on KTM USD 43's ('01 LC4E).

    I found and downloaded the manual on the forks but by the time they get to pouring the oil out, they have disassembled beyond what I think would be necessary for just an oil change.

    Theres a bit on KTMTalk.com for an '03 450 but it sounds like the design might be different than mine.

    This is my first set of Upside Down Forks, and I've been used to pulling a plug or two and refilling out of a measuring cup.

    I can see that I'll probably have to pull fork tubes and get one of those nifty fill level sucky things.

    Any tips would be greatly appreciated!

    Gary
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  2. mcomstock

    mcomstock GS==offroad

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    Gary, this isn't specific to an LC4, but in general for USD forks, you remove the forks from the triple clamps, remove the spring keeper cap in the top of the fork (there is light pressure from the spring on it, so be careful as it pops open.) Remove the springs and any shims that are present. Turn the fork top side down and pour the oil out, then pump the fork until you hear the fork sucking air to make sure you get all the trapped oil out. This can be messy if you don't do it slowly.

    Refill with the specificied cc's of your favorite fork oil, if you have the spec and nifty sucky thing then measure the distance from the top of the fork to the oil level to get it exactly setup for your preferences.

    That's the the general process. The complete disassembly drill in the manual is really more for inspection of fork internals for wear and/or valving changes.
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  3. Randy

    Randy Long timer

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    what mcomstock said but i will add one small hint: break the fork caps loose before loosening the triple clamps. you also don't really need the special float tool although it may be worth having. i've always gotten by with a ruler and small flashlight. just pour in the approximate amount of oil, with the forks fully collapsed without springs and measure oil level from top of tube to top of oil. adjust as necessary. i just use a large syringe with plastic hose to suck out excess if necessary.
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  4. Gary

    Gary Another Adventure Rider

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    Thanks MC and Randy for the tips. This is making sense to me now.

    Where you you find the fork oil setting/measurement. The WP manual refers to an initial filling to 25mm below the 4 holes in the inner tube with the outer tube extended, but to "adjust" the oil level after pumping to fill the cartridge.

    And do you use 5w oil as I noted in the manual?

    Gary
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  5. Randy

    Randy Long timer

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    well, i don't have experience with your forks specifically so i can't say. but unless someone else has a better method to offer or you can't find out in the literature then i would suggest you loosen the fork caps, remove the forks, remove the caps, carefully remove the springs (keep them clean), collapse the fork and measure the oil level from the top of the fork tube. without better info, this should get you in the ball park. you may also want to drain the oil into a container then meaure the original amount so you have an idea of the quantity required. again this in case you can't find the fill volume listed somewhere. good luck.
    i would stay with the oil weight listed for the forks in the manual unless your planning to revalve to some spec that requires different viscosity.
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  6. Flanny

    Flanny Flanny-it-up!

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    Hi Gary,

    I just did this over the winter, and it seems to have worked out.

    1 - Loosed fork caps (while on bike)
    2 - remove forks
    3 - Remove caps, pull out spring assmbly a few inches (It did not come out completely)
    4 - empty oil out of each leg and compress/extend forks until comletely empty and sucking air (as indicated in prev. post)
    5 - take recommend amount of oil (was it 450cc for each leg? can't remember) into a measuring cup, and pour into fork leg. Extend/compress a few times each while filling.
    6 - Put caps back on
    7 - put back on bike
    8 - bleed air our with screw in top of cap.
    9 - go for a ride.

    I used the 5W recommended, and it all worked out great. Fork is as good as it was before.

    I too was confounded by the process, but the somply way I did it seemed to work ok. If there is something wrong with how I did it..i sure would like to know...but it seems fine.
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  7. GODSPEED

    GODSPEED finger lickin' good

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    coppertone bump


    just a friendly service reminder :D
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  8. Esteban

    Esteban Banned

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    Flanny,

    Your method will work but - it is better to measure the oil height in the tube rather than the milliliters (CCs) of oil you are putting in. Slight air volume variations have a very noticeable effect of fork function. Measuring the oil height/air volume is a more precise method to achieve desired results.

    Steve
    #8
  9. creeper

    creeper Still alive...

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    As Steve indicated, the amount of oil determines the remaining air capacity of the fork. As the air in the remaining "chamber" acts as a spring, the oil level can alter the rate of the air spring... at the very least, getting the oil levels equal is a good thing.
    You can also adjust the oil level (within limits) to alter the air spring rate... not the same as changing a coil spring but more of a "fine tune" capability.
    #9
  10. meat popsicle

    meat popsicle Ignostic

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    bookmark.

    thanks godspeedy :D
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  11. GODSPEED

    GODSPEED finger lickin' good

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    That's what I thought, hence the bump for us newbies. :thumb
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  12. Velocibiker

    Velocibiker Adventure Antagonist

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    Instead of the "spiffy (expensive) fork oil level tool", the easiest way is to buy/use turkey basters.

    Measure from the tip of the baster to the proper fluid depth and make a nice visible mark.

    Fill fork with oil. Stick in turkey baster to mark and start sucking. When nothing else gets sucked up, you have the correct amount/level of oil.

    Quick. Simple. Cheap.
    #12
  13. markjenn

    markjenn Long timer

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    Make sure you have the spring removed and that you pump the cartridge full of oil before checking the level.

    - Mark
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  14. creeper

    creeper Still alive...

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    I vote for osmosis... it's slow, but reliable. :lol3
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  15. ChrisC

    ChrisC Amal sex?

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    Your cell walls are too impermeable for osmosis, what do you think you're made of...fuckin' Goretex?

    Mornin' Crappy.... :wave
    #15
  16. creeper

    creeper Still alive...

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    Mornin' Kissy Chrissy...

    Not me you boob... see, you make a mark on a dish towel you steal from the kitchen... then you shove X amount of mm into the fork leg... then... nevermind. :lol3
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  17. meat popsicle

    meat popsicle Ignostic

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    that's "wicking" you wacker :D
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  18. creeper

    creeper Still alive...

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    Ooops...
    My bad. :lol3
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  19. meat popsicle

    meat popsicle Ignostic

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    It is also defined as flow from areas of low concentration to areas of high concentration - almost applicable except the main force of movement in the towel case is surface tension right? :dunno

    Or you could go for the "learning thru osmosis" definition (just reading Chrissy's posts makes me dumber... :pot) but that is more of a stretch.

    back on target, is their some indications that fork oil might need to be changed? :ear
    #19
  20. creeper

    creeper Still alive...

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    Karma has a lot to do with it.
    Still Karma.
    How black... is your Karma?
    #20