Somewhat Verified

[Chrisj CMA]

So the somewhat controversial idea is that our inverted forks on our Valkyries can build up air pressure and therefore a leak not necessarily associated with a bad seal.

So the bike has been sitting for over a week due to bad weather and some crazy cold temps (for Florida anyways).  Two days ago I noticed a teaspoon amount of fork oil on the floor under the left brake caliper.

Weird since there was no wetness at all after the last ride. I would have noticed that on the wipe down after the ride which happens every time. Also no oil blown back on the timing cover like it would have been if it was leaking while riding.

So I surmised the cold shrunk the seal and allowed some leakage. I decided to do the seal mate thing even though I didn’t think the seal was bad or dirty. When I got the seal mate in a forceful gush of oil came out. I cleaned that off and repeated. No gush of oil the second time just a small ooze compared to the first time.

This same scenario happened last year on the right side and I suspected pressure build up was the culprit.

After an aggressive test ride today all is dry so the seal isn’t in need of being replaced.

I’m convinced pressure build up is responsible for many Valkyrie fork leaks.

[Avanti]

Would that mean as the forks extend they are creating an internal vacuum bringing in the air that latter becomes pressure as the forks settle causing a leak.

[Chrisj CMA]

I’m not sure, I’m no scientist. What you say makes sense. I just know that for the last two times I had an apparent leak. The tool caused a much bigger gush of oil on the first pass compared subsequent passes.

[WintrSol]

If the forks were fully extended when they were closed up (seems likely), putting weight on them would compress the air in them, creating some pressure. This all seems normal, except fork oil sitting above the seal, but because of the nature of them, I can see how they could hold the oil there.
Next time you go to use that tool, lift the weight off the front wheel.

[f-Stop]

Not trying to throw a red herring at this thread, but...

...the CRF250X in my garage has pressure relief screws on top of each fork.  These forks have compression and rebound damping adjusters and are somewhat different animals than what's on the Valk, but they do operate on the same principle.  They're even inverted like the Valk's.

Also, it is recommended to release the air pressure after each ride and while the forks are fully extended.  It's an easy procedure.  The pressure relief screws are small flatheads and a quarter turn out relieves the pressure.  Takes less time to do than to say.

I looked in the CRF250X's shop manual as to why pressure builds in the forks, but there was no explanation to be found.  The manual does say that the forks will get "stiffer" as air pressure builds which affects the bike's handling.

Don't think I've ever noticed Hildr the Valkyrie's handling changing over the coarse of a ride!  Nevertheless, I do think pressure does build in the forks.  Maybe the volume size of the forks compensates for any air pressure increase.  Or maybe the fork design doesn't create much pressure.  Eventually, that pressure has to go somewhere...

 

[WintrSol]

Unless there is a way for more air to get in, the pressure at the same conditions - mostly temperature, but also weight on the forks - should remain the same. Pressure will increase, some, during a vigorous ride, as the forks get warmer from use, but should return to 'normal' once they cool back down, if ambient temperatures remain the same. Going from a cool garage to a hot afternoon is probably a bigger factor, unless there IS a way for air to enter, and not leave, the forks. Can someone explain how more air could get in?

[Chrisj CMA]

I can’t definitively say how air can get in. But I can say definitively that pressure was relieved when I ran the tool the first time. Would it have done that immediately after a rebuild?  Meaning the pressure was always there from  the beginning and didn’t build up over time. Who can say.

What I can say is that if your forks start leaking do the seal mate or seal doctor procedure before forking out the dough to replace the seals. Pun intended. lol

[Jess from VA]

Couldn't pressure inside the fork be created from temperature (and humidity) changes inside the fork, and not actual air intrusion.

Say for instance, bike sitting in cold damp weather, then a ride in warmer weather, added to some degree of warmth created from actual use of the fork action (which is like a pump)?  Heat expands.

I don't suppose there's all that much empty space in there.

I've used a fork Sealmate (crummy) and the Fork Doctor (better), and got oil out every time, but don't remember ever having a pressure release event at startup of clean-out.

I also remember cleaning one bike's forks so many times I was afraid I would be short of oil, with reduced function.  But function was never noticeably reduced.  Rebuild was finally paid done, as it's beyond my skill set (and patience).  

[The emperor has no clothes]

Couldn't pressure inside the fork be created from temperature (and humidity) changes inside the fork, and not actual air intrusion.

If pressure is 0psi at 68 degrees F and the temperature is raised to 104F,  the pressure increases to 1psi.  Is this significant?

And if the forks are sealed, the humidity can not be changed by external conditions.

[Chrisj CMA]

So, if I read the scientific information here correctly it seems if the amount of air inside the forks is constant then changing environments is unlikely to account for significant pressure increase. So that leaves the idea that somehow additional air gets sucked in a tiny bit at a time  over months  of riding. I don’t discount this as possible.

[98valk]

good details here

https://crfsonly.com/howto/230f/fork-air-valves/fork-air-valves.php

[Chrisj CMA]

good details here

https://crfsonly.com/howto/230f/fork-air-valves/fork-air-valves.php

Ok so if the amount of air can’t increase then a leak must form as the strength of the seal decreases either from age or environmental conditions like temperature. Since there are no adverse affects to the ride quality with  pressure released I think closing the fork caps with the forks compressed (weight of the bike) would be a good way to prevent a premature leak. Less air, less pressure.

[The emperor has no clothes]

Back in the day, some of my motocross bikes had air shraeder valves on the forks. They were for fine tuning the dampening. I don’t recall ever having an issue with them.

[WintrSol]

good details here

https://crfsonly.com/howto/230f/fork-air-valves/fork-air-valves.php

Ok so if the amount of air can’t increase then a leak must form as the strength of the seal decreases either from age or environmental conditions like temperature. Since there are no adverse affects to the ride quality with  pressure released I think closing the fork caps with the forks compressed (weight of the bike) would be a good way to prevent a premature leak. Less air, less pressure.

If the forks are sealed with weight on them, there would be brief periods of lowered pressure as the forks extend. If the seals are normally one-way, that is, are meant to contain positive pressure, but not negative, air could be pulled in, thus producing a small positive value, maybe nearly the same as if the forks were sealed while fully extended. In any case, a fluid leak would indicate the seals are weakening, allowing fluid to squeeze past, or the forks are pitting. Using the tool to release this small pressure would allow more fluid to pass the seals, of course.

[f-Stop]

good details here

https://crfsonly.com/howto/230f/fork-air-valves/fork-air-valves.php

That's a good "how to" article.  I've bought a bunch of stuff from that website (CRF's Only) for my CRF250X.

So, it seems that our aging Valks -- which means aging fork seals -- may have occasional fork oil "burps" caused by various factors including temp changes.  I replaced my seals a while back upon the first sight of oil, but maybe that was just a burp.