??Fork Pressure Release

[wildbill]

I have read on other threads about the fork seals weeping,and the fixies.Why bike a 78E has the same problem.The fork seals have been replaced recently but after the bike has been rode for say 10-30 miles then they start leaking.It`s like the forks are pumping up with air and the only place for them is the fork seals.What I`am asking is this,can one put bleeder screws in the fork caps to let off the pressure{say like on a dirt bike }I don`t see as this would hurt anything,might help in long run.There are kits to do this but on my bike would have to change fork caps.Any Ideas? Thanks.

[TopCatGr58]

Hey there Bill,

The Specials have an air inlet in their caps, cause the forks are designed to provide air pressure assist to adjust the dampening/preload of the front shocks. I never add any air to mine, just run them at atmospheric pressure.

Did you inspect your tubes/uppers to ensure that they were perfectly round, vs. flattened on one edge/side or slightly bent?? Were you sure that the little holes in your dampening rod were open, not clogged so that the fork oil could get by/thru them during their action, allowing the pressures both hydraulic and air to equalize?

You can take the cap off the offending upper, and then compress or load up the front forks a little before replacing/sealing the cap back on, and then check to see if you still get the weeping, if so then I would think that the air pressure isn't doing it as much as either a damaged/faulty seal, or upper tube!? Good Luck!

T.C.

[wildbill]

Hi TopCat, When I replaced the fork seals I checked everything pretty good.I will have to check it again when warm weather gets here again.Why I started this thread was I took the fork cap off one fork and heard air leaking out,so something is not quite right.When first starting out on a ride the forks are stiff and they get stiffer from there and in 10-30 miles the forks are weeping again.That`s when I thought about bleeder screws.On a dirt bike you bleed the pressure off before and after each ride,if you don`t the forks pump up and you run the risk of blowing a fork seal at worst, a harsh ride the least.My bike has the slot on top where you adjust spring preload.The bike is down right now and the weather is going down hill anyway.Making a list of things I need to do to the bike.Any ideas? Thanks

[MartyA]

I am not a fork expert, but I do have a 78E, I don't recall ever having air build up in there. When my springs finally gave out this spring, I was in and out of there a few times, never heard air escape. Gotta be sucking air in without letting it out, maybe a tiny area of the seal not sealed? Fine crack below the oil level? The leak must be microscopic, it takes 30 minutes to build up enough pressure for you to notice. Interesting.

[wildbill]

Originally posted by MartyA
I am not a fork expert, but I do have a 78E, I don't recall ever having air build up in there. When my springs finally gave out this spring, I was in and out of there a few times, never heard air escape. Gotta be sucking air in without letting it out, maybe a tiny area of the seal not sealed? Fine crack below the oil level? The leak must be microscopic, it takes 30 minutes to build up enough pressure for you to notice. Interesting.

The forks act like a pump and build up air pressure.Could be in seals or something.Frankly this has me stumped and the bleeder screws seemed to me a simple fix.Still might try that if nothing else works.I`am useing 10wt. fork oil at service book amount{would have to look it up again}.Any ideas,suggestions? Thanks

[Ken Talbot]

I don't think the forks are really pumping up pressure and forcing the oil out. For that to happen, the seals would have to be working like some kind of one-way valve as the lower tubes slide up and down. Then, the oil would have to be sitting above the air somehow for it to be forced out and not the much lighter air?? I think all that's happening is the seals are leaking, regardless of how new or old they are.

When the inner tube is forced down into the outer such as when braking, hitting bumps, etc, it is coated with a light film of oil. Upon rebound, the oiled tube comes back out with its light film of oil. When the front end goes down the next time, that light film is wiped off the inner tube like being squeegeed. Do that enough times, and you have a build-up of oil visible all over the inner tube and seal.

Now, if we could just figure out why the realtively new seals are leaking...

[TheDjost]

But in normal operation, the oil should be "squeegeed" DOWN back into the tube as the inner tube rises. My seals are at least 5 years old and do not leak a smidgen of oil. Even after riding on some very bumpy roads(hey I live in Quebec), the tubes are *almost* dry.

Did yuo use yamaha selas, or did you go el cheapo the last time you changed them? I'd think that you got bad seals if they did not last. If they are not tight enough, they may be leaking in air as they compress, and not when they expand, just like a one way valve. This would account for the pressure build-up.

The solution is not to bleed out the pressure, but to get rid of the bad seals, and replace them with working ones.

-Justin