A question of forks

[fatblokeabroad]

Good morning all,
Having just changed the oil in my forks I noticed a `hissing' coming from the right fork leg cap. It appears to be coming from the counter-sunk machine screw in the cap recess. Below the screw is a spring and ball-bearing that looks like a pressure release. I cannot find any reference to this screw in the blue book (it only shows the cap as one piece). can someone please tell me; Is there supposed to be a seal or o ring under it and if it is an adjuster of some form what are the recommended settings?
Many thanks in advance.

[George 350]

There is no setting as far as I know. Have always assumed that it acted as a one way valve such as let's air out when forks compress, but stops air going back in.
In 45 years ownership, I've never even thought of 'why' until your post, but I suppose it might have a technical benefit of keeping oil in the forks as the seals will grip tighter.
George

[Fastmongrel]

I services my forks recently and shed gremlins stole one of the pressure release spring and ball valves. There's a seal under the screw I replaced mine with Orings which I think the original seals were before flattering with age I lightly coated the rings with red rubber grease before installation.

When I fitted a new ball and spring valve I was told to tap the ball into position using a drift and a light hammer. The aluminium can get dirty and worn clean it with a blast of brake cleaner let it dry then find a drift that's about 2/3rds the diameter of the ball. Give it a tap with the hammer you are only trying to get the ball seated your not trying to deform the aluminium.

Fit everything and try pressing fork down you shouldn't hear any hissing the valve is a blow off valve that works only if you bottom the forks at high speed. If it does hiss give it another tap with the drift and hammer you wont damage the ball it's about ten times harder than the aluminium. Equally the aluminium is soft so tap but don't swing the hammer like your forging Thor's hammer

[Fastmongrel]

https://classicandvintagesuspension.co.uk/

Very good shop that sells hard to find parts for 35mm Marzochi suspension. Ben is a very nice chap and he can sell you some shiny new top caps.

[fatblokeabroad]

Thanks for the replies,
Whilst I was waiting I ultra sonic cleaned the caps and their internals, all manner of gak came out so I guess the ball was not seating properly. I gave everything a good blow through with compressed air and replaced the outer O-rings. I looked at the recess where the counter-sunk screw fits and it appears to have slight channels cut in the faces, I am guessing that these are for the air to escape under max compression so, I am thinking that placing an O-ring on the shaft may prevent this from working. I will see how it goes without for now.
Everything has been polished to a ridiculous shine, refitted and no longer hisses under compression. It's a shame in a way, I was trying to justify a huge array of new stuff from classicandvintagesuspension.co.uk. I will have to wait until my next project I suppose.
Thanks again!

[Daddy Dom]

Mdina Italia is also listing fork tops, for future use.

I'm sure classicandvintage are lovely folks but to a point Mdina depends on us and we on them!