Fork Seals Blown Again

12 replies to this topic
  • 426F

Posted April 01, 2005 - 07:36 AM


Last fall I replaced the fork seals and fork oil in my 2000 YZ426. It sat for about a month before I was able to ride it and the first time out they are blown again. Both legs are leaking very heavily. Does anyone have any ideas why this would have happened. It was my first time doing fork seals but I did exactly what my manual says. I need some help please!

  • big t

Posted April 01, 2005 - 07:47 AM


Seems like alot of people are having a problem with this. If it was sitting maybe they dried out. Does anybody know of after market seals that are better?

  • mkporn

Posted April 01, 2005 - 07:58 AM


There are so many reasons why...... It could be one of a hundred things. I would say that something was done incorrectly. Not to bag on ya, but I think you are on to something with the "it was my first time" and the fact that both seals are blown the first time out.....

Are the seals in correctly?

To much oil?

Did you stroke the fork tube to get oil between the the two tubes?

What kind of seals did you use? (don't use the leak proofs, they are junk)

Are you sure they were the correct seals?

Wrong oil?

There are a number of reasons. Tear them down and do it again. My guess would be that the seals are in up side down...

  • Scotty426

Posted April 01, 2005 - 08:06 AM


2 issues I'd look into.
1. Did you cover the metals with plastic or at least lube them with fork oil when you slid them down? It's easy to rip out a piece of the oil seal as you slide it over the metals (personal experience).
2. My local suspension guy says it's easy to bust a seal when you twist the forks. When you dump/crash it and the tire doesn't line up straight with the front fender, the tubes are twisted in the triple clamps. Stop riding and fix it. The cure is to loosen the axle hold bolts (4) loosen the bolts on the lower triple clamp (4) straighten the wheel/handlebar alignment (hold the tire with knees while you move handlebars), push the forks full stroke bottom so they align the axle, then re tighten everything. He says miss-alignment busts more seals than anything else and I believe him. I don't loosen the top triple because I don't want to have to readjust fork height (mine are dropped 10mm for better turning).
Did you ride it and then it started leaking or was it leaking at rest the whole time? Are any of the tubes nicked? Did you run a piece of thin plastic under the seals to make sure a chunk of dirt isn't holding the oil seal away from the inner (aluminum)tube? I'm sure you got the right seals, right? 426s have 46mm tubes and late 450S went to 48mm tubes. Were the metals worn out? Do you regularly vent the air from the top of the fork. When it gets hot air pressure really goes up and can force the oil seal. Are you sure you got the oil level right? The dealer can tell you the approximate cc's that go in there, and I fine tune with a brake bleeder and a 105mm wire rig I made up. I bet way too much oil will defeat the seal as well (though some guys run a bit higher than stock). I'm no pro, but I have done it a couple times including once on my beloved 426. You have me curious. Good luck to you brother and let me/us know what you find.

  • 426F

Posted April 01, 2005 - 08:22 AM


1 - I did use a plastic bag lubed with oil on the lower tube before I slid the upper tube on.
2 - I am fairly sure that I got the oil level correct. I did measure it but do not remember what height it was set at. I set it per TT members recomendations.
3 - I used K & S fork seals and dust seals. Good or bad I don't know?
4 - It did not start to leak until I went out and rode it.
5 - "Did you stroke the fork tube to get oil between the the two tubes?" Explain this alittle if you could.
6 - the forks are aligned and I did not have any spills that day.
7 - "Do you regularly vent the air from the top of the fork" Explain this alittle if you could.

Thanks for all the quick replies!!!

  • grayracer513

Posted April 01, 2005 - 09:58 AM


5 - "Did you stroke the fork tube to get oil between the the two tubes?" Explain this alittle if you could.

7 - "Do you regularly vent the air from the top of the fork" Explain this alittle if you could.

5- When filling the fork, the first step should be to fill the tube nearly full (with the tube and damper fully compressed) so that the oil is higher than the row of oil holes near the top of the inner tube. Then work the outer tube, not the damper a few times to work oil into the gap between the tubes. After that pump the air out of the damper and set the level.

7- Air pressure can build up in the forks, and you should release it after each day of riding (or each moto even) by loosening the two vent screws. These are the small screws off of center in the fork caps. They have o-ring seals on them, BTW. Do this with the bike on a stand so the weight is off the fork.

Things to consider for this problem:
> Dirt under the seal. Run a piece of thin material such as a 35 mm film negative under the seal and go around a couple times to get trapped stuff out of the seal lip.

> Worn fork bearings. The manual calls them "metals". If there's too much clearance, the seal won't be able to hold well.

> Scratched fork tubes. It doesn't take much. See if there's anything that catches a fingernail. You can sand out the smaller ones with 600-800 grit wet/dry and some oil. If they're bad, look into re-plating at a suspension shop.

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  • Scotty426

Posted April 01, 2005 - 10:32 PM


Hey 426f, the bag trick is for sliding the oil seal over the metals. This takes place before you join the tubes. When you drove in the new seals, did you do it with a seal driver or cut the old seal in 2 and plastic hammer it? Some people get rambunctious and dent the rod. The fact that it doesn't do it at rest makes me think you have a scratch on the tube somewhere near the down end of the stroke (doubtful) or you got some debris between the seal lip and the tube (likely). I would try the film trick O &YZR recommended next. Good luck.

  • Slowmotion426

Posted April 01, 2005 - 10:57 PM


What about the compression valve in the forks? If it's clogged with foreign materials (like small metal particles/shavings) it's gonnna cause a lot of back pressure.

  • felony

Posted April 02, 2005 - 04:14 PM


chances are your fork bushings are shot,if you have a 2000 and havent replaced them you can bet that the teflon is wore off on them causing excess play of the forks in the tubes,i had the same can buy a complete kit with inner/outer bushings,seals and wipers for like $60.good luck

  • MXof21

Posted April 03, 2005 - 06:34 AM


You may have tried this but I always start by assuming some small particle of dirt worked it's way into the seal. Remove the dust cover, clean everything out well with carb cleaner or something similar. Take an old 35mm film negative and wrap it around the fork and work the corner up into the seal, you should be able to get in 3/4 to one inch. Work the negative around the fork and do your best to clean any foreign material out of the seal. When done clean things up again, push the dust seal back in and give it a try. I have had this simple procedure stop oil leaks many times.

  • 426F

Posted April 04, 2005 - 04:21 AM


Thanks for the replies! I am picking it up from winter storage this weekend and will be going to work on it asap.

  • sirthumpalot

Posted April 04, 2005 - 05:25 AM


If new seals keep blowing right away, personally I would box them and send them to a suspension shop to be checked for wear. As mentioned above, worn bushings can cause things to leak and a 2000 can easily have enough hours on it to require some new parts in there. Tackle it yourself if you have to tools. Let us know how it turns out!

  • felony

Posted April 04, 2005 - 08:57 AM


fork bushing are easy to replace,you have to remove them when you replace the seals which you have done on several occasions,easy to do

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