[Carnaza]

i don`t know how to explain it.. but i`ll try..

Today before i went to ride i put like 120-130 psi in the fork (wc 09) but after 9 runs in my local trails i rechecked the pressure and it was 150 psi...

any ideas how is this possible... and how can i fix this?

thanks

 

[AlCapone]

I'm not a suspension expert or anything, but because the fork moves when you use it, the friction it uses causes heat. As you probably know, when air heats up, it expands, which causes the pressure to go up. I believe this is one of the reasons why air shocks aren't used for DH very often. Since they have a lower air volume, the pressure increase is magnified.

 

[Carnaza]

yes i know about that....

but this is the 2nd wc i have... and with the older one i didn`t have the problem.... even with the new one the problem appeared like 1 month (never before)... when i replaced the oil seals... i just removed the lowers, change the seals and put the lower back and set 130 psi as always...

it`s weird, it doesn`t make sense at all... if it loses air makes more sense to me....i`ll take it apart and rebuild it... but i wanted to know what part or building process could be wrong, to check it when i build it.

thanks..

 

[DirtyMike]

Hmmm, gaining air pressure, only two things I have ever known to cause that is altitude, and heat build up.

 

[Udi]

Nope, it's not heat or altitude (the change can't be that significant, especially once chambers equalize). There's also very little heat buildup in the air spring (likely due to its high volume) - at the end of a long run, the air stanchion usually won't even be warm whereas the damper leg will be.

The cause for pressure increases usually involves pressure from the negative chamber leaking into the positive chamber and/or chambers not equalizing properly. It can usually be traced back to an o-ring or lubrication issue.

My suggestion would be to pull out the solo air cartridge, clean everything, replace all o-rings (you can get them matched at a seal shop, cheap), and carefully inspect all sliding/mating surfaces for scratches or damage. Don't forget to replace the o-ring under the solo air piston (after you remove the circlip at the top of the piston). Remember to put in 3-5ml of oil in to lubricate it, but no more.

 

[Udi]

Also, keep in mind the solo air leg equalizes pressures at topout, so make sure you top your fork out a few times (hold the wheel and pull the bars up) while pumping it up. It's strange it only started happening after a rebuild, has the problem occured multiple times after you've reset it to 130psi?

Anyway, if it keeps happening and you replace all the o-rings, make sure you replace the ones at the base of the stanchion too (including the one that the air shaft slides against).

 

[miuan]

Udi, I had the same issue happen to me at my recent muddy race. I had been riding whole weekend. Just some 2mins. before my race run I discovered the fork acted like there was no neg air in = harsh topout. I deflated the fork yesterday and inflated it again, pulled it up several times, but it is still very firm at beginning stroke, like old marzocchi air forks with no neg air. I do have a Boxxer service kit so I will strip it all apart and replace the o-rings anyway. My question is, how long do the Boxxer WC solo air o-rings last? I don't ride a lot and my solo air was only 1 year old. I change the oil 2-3 times a season and use prep-m grease + 5ml oil for solo air. And I have a non-honed stanchion (Ride converted to WC).

Edit: I rebuilt the solo air, changed all 4 o-rings (used original RS ones), and the damn thing still tops out pretty hard and is all but supple on initial stroke. I'm afraid the negative chamber just doesn't bleed properly, or at all. During the rebuild I also replaced the small wavy washer under the tiny c-clip and made sure the piston moved when compressed by the bumpers upon topout. I inspected the seal seats, all seems flawless. But still, it's real bad. Am I missing something? Should I stretch the small spring washer to get less preload so the valve actually opens?

 

[miuan]

Any advice boxxer geeks?

 

[toodles]

Replace the O-ring under the negative air chamber... Mine was doing the same thing. when the fork compressed, the negative air chamber moves into lower than atmospheric pressure and combined with the higher pressure in the fork lowers it was pulling air in.

Forks slowly pumped up.

 

[miuan]

Toodles, I did replace all O-rings after I encountered the problem. I also believe that air is not escaping from neg. chamber to lowers because I burped them while fork was compressed and they stayed burped well after inflating the fork. I will try again though, it makes some sense since the neg chamber si very small. I may also try to modify the conical bumpers so they have more intense contact with solo air piston, but they did push the piston just fine before, so the issue must be somewhere else.

 

[miuan]

Problem solved. I pumped it to 180 psi and went for some small hucks and curbs to run the fork in. Eventually air found its way to where it belonged. The fork is still sticky because all o-rings are new, but yeah...