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johnmeasures

Fork bleed screw lets out oil

9 posts in this topic

The bike is a YZ450F '05. Good racing 2day at Toddington, UK. 2 holeshots, 3 wins by my sponsored rider Robert Barney. I did the prep & checks between each moto. The forks have started leaking so we will replace the seals in the week. However, when I bled the air from the top of the forks the left one let oil out of the bleed screw. I have not seen this before. Any ideas why? Thanks. :D

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my 05 YZ250 did this also....but just once. The forks have been apart for a revalve but this happened several months after. Only happened once though. Maybe just excess pressure build up because of the heat? (at least in my situation...) :D

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my 05 YZ250 did this also....but just once. The forks have been apart for a revalve but this happened several months after. Only happened once though. Maybe just excess pressure build up because of the heat? (at least in my situation...) :D

True, it was hot today. I have the sunburn to prove it! I got panda eyes, only RED!

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no kidding...I am right there with you. We raced today and by the time the second moto came around it was 97 degrees with a 102 heat index..... :D

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The '03 fork has a steel spring seat sleeve under the cap that is made in such a way that it is nearly sealed off from the rest of the fork. Oil can get trapped above it and only very slowly work its way back down. The '04 fork is not like that, but there could be something in the way the cap/spring seat is configured in the '05 that produces a similar situation.

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no kidding...I am right there with you. We raced today and by the time the second moto came around it was 97 degrees with a 102 heat index..... :D

O/T.....102 is what we ended up with? I felt it!

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The '03 fork has a steel spring seat sleeve under the cap that is made in such a way that it is nearly sealed off from the rest of the fork. Oil can get trapped above it and only very slowly work its way back down. The '04 fork is not like that, but there could be something in the way the cap/spring seat is configured in the '05 that produces a similar situation.

Hi Grayracer, I was hoping you'd see my post, thanks for your help. I have learned to replace fork seals by the "monkey-see monkey-do" method & although I understand the physics of how liquids & gases behave under pressure I know very little about fork construction. I will take a closer look at the cap etc.. when I take the forks apart later this week. I am a little disappointed that every Yamaha I have campaigned, that's 5 in the last 3 years, has had flimsy fork seals. They have all failed within the first 5-10 weeks of use from new. I clean the seals using a piece of 35mm film negative so I doubt whether the failures have been due to neglect. Also I am careful not to direct the power washer jet directly onto the seals. Any ideas on replacement seals that might perform better than the originals? Thanks

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Ive had the same leaking seals, my solution which has worked all season, take the rubber seals down to the bottom of the fork, get a tear off and cut it into strips 3cm by 1 cm and insert them vertically in between the fork and the metal bush, rotate around fork for one third of a turn and remove and wipe with clean cloth, repeat on the next third, remove and wipe and continue until any dirt or grit is removed, you will be surprised what can come out, next pull the rubber seal away from the fork gently and place a clean piece of cloth between for and seal and rotate the seal to remove any dirt from there, next put some white grease in the seal ( approx half fill it) to collect any grit that gets through and replace the seal in the fork casing. Job Done and next time clean out the grease and replace, Dependant on use do this every 2 weeks. Good Luck

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Any ideas on replacement seals that might perform better than the originals?
Some people swear by these:

http://www.synergyseals.com/

I haven't tried them, but they look like they might work really well.

Any time you have to replace a fork seal, check the surface of the tube for nicks, chunks of stuff sticking to the surface, and vertical scratches. If you can feel them, they'll cause a repeat seal failure. You can usually remove these small blemishes simply by sanding the tube "cross diagonally" with 320-220 wet/dry sandpaper. Normal wear will restore the polish to the tube in a few weeks time. If there is a serious blem, you can have the tube replated.

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