Forks hold air, but not fluid

[Razzamatazz]

Please explain to me how this can happen. I had a leaking fork seal on my MNS, figured the air was gone too. When i took the plug out, the fluid shot out about 8 feet. Don't quite understand how it can be.

[DEEBS11]

Did you do this while the bike was still fully assembled? If so, it was the weight of the bike pushing the fluid out the lower drain hole.

If the fork was on the bench then the seal was still good enough to hold a few PSI but not hold oil under the load of the bike over bumps.

Also, too much air in the forks will surely kill a fork seal. It causes a condition called stiction in which the seal has too much pressure around it and it grabs the fork which causes increased friction. It didn't take long for Japanese manufactures to figure this out and get rid of it. Then, dumb Ol' Harley Davidson put it on all of their dresser bikes for years.

I have changed hundreds of fork seals on every manufacturer of bike on the planet. I hate air forks. I rebuild an air fork with a small PVC preload spacer (about 1") and tell the customer to never use air again.

The original Standard XS11 has a cool no-air preload spacer and it is a superior fork for seal longevity.

[Mathh]

The air sits above the oil level which is above the oil seal. So it can not reach the oil seal.

[jetmechmarty]

It’s my understanding that these will not fit the Special due to thread differences. Standard forks were built by KYB. Standard forks were built by Showa.

[DEEBS11]

The air sits above the oil level which is above the oil seal. So it can not reach the oil seal.

Math, oil can easily reach the seal under the pressure of riding which is evident in a fork seal leak.

Also, when you remove the threaded top of any fork and look inside it is wet with oil. You are correct that at rest, the fluid drips down to the bottom but it certainly moves around once you ride the bike.

[DEEBS11]

Marty, yes, the tops are different. The Standard gets the KYB. However, there are other differences when they went to air forks. The first picture is a Special fork top with Schrader valve hole. The second & third is from my 1980 Standard. None of these fork tops interchange so the fork tube is also different.

[DEEBS11]

From a 1980 Standard

[DEEBS11]

The Special has the same part number. But you can see it is the shorter part. Something ain't right. Perhaps again, KYB VS. Showa?

[DEEBS11]

See, the larger fork top number is 3H52311100. That's what is on my 1980 G front end.

[jetmechmarty]

I don’t like my Special fork caps, even a little. The hex head adjustable is far superior. My XS650s have KYB forks with preload adjustable caps.
My Eleven Special is fitted with straight rate springs and Race Tech Gold Valve Emulators. It is superior to stock and I’d love to lose the air caps.