Sunn Obsys 40 set up. SORTED OUT!

Hi all,

I'm having trouble setting up some bouncy forks for my Sunn.

When I'm not on the bike, they are at full extension. When I get on it, they drop down to the stop. When I ride and lift the front, I get that horrible top out clunk!

I've set them up as per the recommendation below

http://xcrosseur.09.free.fr/Vtt/meca-obsys55.html

With around 3.5bar in the r/h leg, (slightly more than I need) and 5w oil in the l/h one, up to 12mm below the top after some up and down with the stanchion to get oil in the lower part.

The 'air' leg is not leaking either.

Hmmmm :?

There is no preload of any kind. Just a screw in the l/h leg top that doesn't seem to do anything except stop the oil coming out. I have tried adjusting it anyway, but no change. Would thicker oil cure this?

Can anyone help?

Thanks folks

Mike

Re:

Anyone?

I'm thinking, - uh-oh , the oil leg for compression damping, air leg for rebound damping ?

Mike

Re: Sunn Obsys 40 set up. HELP ! !

I was thinking perhaps there's no oil in them any more, but then ... I have very limited knowledge of these matters (I've rebuilt one set pf Rockshox only), so really don't have a clue.

Re:

Thanks mate,

I've just sorted it out. Drained the 5w oil and replaced with 15w. Loads better!
If anything, I may need to do a blend. I shall see how they perform on the trail soon

Would love to run them with cantis, but will have to drill a hole in the brace for a cable stop. Hmmmmm

Mike

Re: Sunn Obsys 40 set up. HELP ! !

I was under the impression that you were supposed to have air and oil in both legs. If you're having to put something above 5w in them, either you or the fork are wrong somewhere. I rode a friend's pair of carbons years back, he used 7.5w or thereabouts for racing, they were more rigid than the rigid steel forks.

User's manual here (in french)

http://www.ruwenzori.net/mtb/obsys.pdf

Re:

There is only one leg that has an air valve.

You may be right about both legs having oil though, looking again at the link I put at the top of the thread

:?

Mike

Re: Re:

Mike Muz 67":3v9aq6ij said:

There is only one leg that has an air valve.

Click to expand...

Are you sure about that? There should be a little screw covering the valve. 1.5mm allen key or something equally ridiculous, if memory serves. The valve itself is, as I'm sure you're aware, just a chunk of 8mm OD silicone rubber with a very fine hole poked through it.


If you've got an actual valve there, one of the legs has been modified. Does the "no valve" cap look like this (with or without small allen screw)?



Looking back at the user manual

"It is very important that the pressure be equal in both fork legs"

[edit] 2mm allen key, according to the manual.

Re:

Yes, you're right, Tufty! Cheers

They just had different screws in. 2mm allen is correct. And I have two spares now.

15w drained :facepalm: 5w back in. Now to do the air :roll:

Watch this space

Mike

Re: Re:

Mike Muz 67":1upwl2te said:

Yes, you're right, Tufty!

Click to expand...

Yay! Get yerself onto the french sunn forum if you're not already, there's a group buy for obsys joint / seal /valve kits in action.

Re:

The r/h one is good. sealed nicely after pumping up. The l/h one leaks as soon as I take the valve out. So , guess i need to work out how to make another one :roll:

Thanks for your help T

Mike