Fork oil seal replacement
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  1. #1
    Member canadainshiver's Avatar
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    Probably best to completely disassemble forks and examine parts, but, I'm wondering... Would this method work?



    Part 1

    [media]http://youtu.be/5ksdXTL_PH4 [/media]



    Part 2

    [media]http://youtu.be/uRtjQjNjBxA[/media]



    Couldn't water be used as the fluid to create necessary pressure?
    1991 TW200 Hidden Content

  2. #2
    Senior Member r80rt's Avatar
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    Yep, that old trick works well. I wouldn't use water but it might work, the thickness of the oil will push the seal out a lot better.
    Only a fool would attempt it, and God help me, I am that fool!

  3. #3
    Senior Member lizrdbrth's Avatar
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    It works, but it's no substitute for complete disassembly where you can inspect the legs, inner seals and stanchions for wear, pitting and rust. Unfortunately this tube was cleaned up a bit before I decided to grab a pic of it. If you let your oil get to the "gray gack" stage like the guy in the video has you're looking at a total disassembly to get all the rust off the inside, outside and the orifices in the tube. If you don't the rust will end up in suspension with the oil and eat that little white teflon seal at the top of this tube and score the bores of your fork legs.



    Just my .02. If you haven't changed your fork oil at least once annually yours looks far worse than this one and the holes have very likely at least partially rusted closed.









    The pic also shows why fork oil level is so critical in these forks. The little holes in the top of this tube are your rebound oil flow holes, the ones on the bottom control compression damping. If you're even 5mm low on fork oil the holes at the top will cavitate (suck air, instead of oil), your forks will bottom and they'll oscillate like a jackhammer. If it's too high or if the holes have rusted shut you'll reduce the air gap and your seals will blow, which is the same principle the guy in the video is using to remove the seals. Air is compressible, oil is not. Sumpin' gots to give.





    Also, it's best to use an actual fluid height measurement taken with a ruler rather than the measuring cup method to fill your tubes. The manual shows both, but the stated amount listed for the measuring cup method is wrong and will result in underfilled forks.



    Make the depth measurement WITHOUT the springs in the tubes and the forks fully compressed (bottomed out).



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  5. #4
    Member canadainshiver's Avatar
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    Thanks! Sounds like I'm on the road to a complete dissasembly so I know everything is good, as I have no idea the history of the bike and I would probably be correct in assuming the fork oil has never been changed in any of my bikes.



    You said change the oil once anually?... really?...
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  6. #5
    Senior Member lizrdbrth's Avatar
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    Really. This has nothing to do with the oil "wearing out" from use. Fork oil doesn't ever wear out. There isn't enough friction and heat activity going on in a fork to ever break it down. Almost any oil will serve as fork oil for this reason. Back in the day they used fish or even veggie oil.



    The viscosity of the oil is what matters in simple conventional forks like ours. Thicker oil is harder to force through those tiny holes and slows or stiffens fork action. The reverse is true with lighter oil.



    What kills fork oil is contamination (the gray gack). Moisture from the air gets to the oil and emulsifies, creating acids which then combine with the water. This stuff is constantly condensing and recombining inside your fork tubes and when the bike is at rest it all settles to the bottom of the fork legs, causing rust.



    Basically it's always "raining" inside your fork tubes. Like any other oil the more often you change it the better. If your oil is already gray it's potentially too late, and at least worth a look.



    I can completely strip a set of forks in far less time than it took that guy to pop his seals out, anyway. But you do need the proper tool to hold the tube still while removing the bolt. I have one that I welded up but I also have one that anyone can easily make from scrap without a welder. I'll post a pic of it later.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  7. #6
    Senior Member lizrdbrth's Avatar
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    Here's the poorboy version of the fork tool. Basically just a giant allen wrench used to hold the inner fork tube still while you back off the bolt in the bottom of your fork legs.



    Nothing more than a piece of half inch copper water pipe bent on one end. A bolt with a 19mm head on it is inserted into the end of the tubing, then a hole for a fairly beefy cotter pin is drilled through both:











    The fork tool is used to engage the socket in the head of the damper rod. Looks like this. You don't want to turn the rod with it. Just use it to keep the rod from spinning inside the fork leg while you undo the little allen bolt in the bottom of the fork leg. Your fork will literally fall apart once the bolt is out. That's right. One short little bolt is all that's keeping you from changing your fork seals in 20 seconds:







    My welded version is made from a steel tube with bolts welded into both ends so I can just hold it with a ratchet. It's loaned out at the moment (actually it's been over a year. Bring it back. You know who you are). But you get the general idea.



    If you commit to makling a welded-up version consider making it at least 2 feet long. Overkill for a TW but a lot of other forks with longer tubes share the 19mm hex and you'll be able to use it on a wide range of bikes. Obviously the guy in the video didn't have the tool. There's nothing necessarily wrong with his method, it's just a Rube Goldberg PITA compared to having the ability to pop the lower leg off. His seal driver is flippin' ingenius, but you won't need that, either.



    I generally will break the fork caps and the bolt on the bottom of the tubes loose while the forks and front wheel are still on the bike. Saves a wrestling match when they're off the bike and and harder to handle. Putting them in a vise is an unnecessary risk which will often result in scarred fork tubes or lowers.



    I've wanted to do a "How works the front fork" writeup, but I'm no draftsman. I found this page on the internet:



    http://racetech.com/html_files/DampingRodForks.HTML



    Some folks aren't terribly good with drawings or written explanations. But if you're remotely mechanically inclined while you have your forks apart, compare the drawings and written explanations with the actual hardware and try sliding the parts in and out to see how the pieces interact. The bell might go off in your head and you'll see how truly simple they are. Things like fork oil weight and fluid height may make a lot more sense when you have the hardware in your hands.



    Upside-down forks, cartridge forks and emulators scare the hell out of most people. But once you realize that they don't function much differently than our simple damper rod forks (aside from the fact that you can change the size of the "holes" at will) you'll be an instant expert on those, as well. Fluid in, fluid out.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  8. #7
    Member budgar's Avatar
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    What is the depth measurement for fork oil before dropping in the springs? And I assume using the stock 10wt, I weigh 170. Rebuilding forks this weekend if the new boots show up. Thanks.

  9. #8
    Senior Member lizrdbrth's Avatar
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    OOPS!



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  10. #9
    Member budgar's Avatar
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    OOPS!



    What does that mean?

  11. #10
    Senior Member lizrdbrth's Avatar
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    "OOPS!" means I screwed up and double-posted.



    The fork oil level procedure is in the service manual. I set mine 5mm higher than the factory numbers. I find I get better rebound action out of it. We're around the same weight, so try it if you're into it, ignore it and stick to the manual if you ain't. Don't get too carried away with it or you'll end up blowing seals or your fork will become too stiff in compression. 5mm either way have a definite effect. Try to be as exact as poss.



    You can always add or subtract fluid with a turkey baster later if you want to see if you like the result.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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