35mm Marzocchi Caps

[Chrisbo]

Can anyone tell me if all the 35mm Marzocchi fork caps were the same and more importantly, How they work. I was looking at one of the mangled up ones that were in the top of my forks and it looks like from the underside there is a small hole with a ball bearing and spring in it. From what I can see from the top side there is a brass screw or something at the bottom of the hex.
Is all this normal and if so what's it all about as I don't see what any of it does [?] [?] [?] [?]

Oh yeah and can anyone tell me what size of hex is supposed to be in the caps as mine are that badly mashed I can't work out the size!!!!

Thanks for any help guys
Cheers
Chris

[454MRW]

The hex size is the same as the swingarm bolt, 12mm. I hope someone else can answer your question about the check valve, as I have the same caps om my 38mm forks on my 1980 250 and my Project 77 MC5 drag bike. Mike

Michael R. Winter
1974 250 Harescrambler
1975 250 HS Project
1977 250 MC5 Project
1978 250 MX6  
1979 250 KTM Project
1980 250 MX KTM

[Chrisbo]

Thankss Michael, At least I know what size the hex is now As for the rest of it I don't see what the ball and spring under the screw at the bottom of the hex is acheiving

Cheers
Chris.

[rob w]

Hi Chris,

Because trapped air acts as a anti-bottoming device.
The small screw in the fork cap is to access the spring and ball below, which (is suppose to) work as a check valve for bleeding excessive air that is sucked in thru the fork seals and builds up inside the fork chamber.
I'm sure it was designed to work automaticly, although it was'nt without some failure. I think that's why drilling and tapping for a Schrader valve in the cap became popular. Instant release...pissshh.....ahhh!

Rob

[firstturn]

Chrisbo,
  It is supposed to work like a pressure relief valve.  Most of the ones I take apart are in very poor shape and haven't worked in a long time.  I hope this helps and welcome again to the Penton Owners Group.

Ron Carbaugh

[rob w]

Chris,

Do you know Mad Max ?

Hi Ron

Rob

[Chrisbo]

Thanks for all the replies guys, I just don't see where the pressure can go as I've now managed to get it apart and all it is, is a ball bearing at the bottom with a spring on top and a countersunk screw decked out at the bottom of the hex so any air can't actually escape or is this not how they are meant to be [?] [?] [?]

Rob, I don't think I know Mad Max. I'm from Scotland in the U.K. but I have seen the three films

[OUCWBOY]

On the side of the cap should be a very tiny hole that the pressure is released from. If they are in bad shape the hole could be covered with dirt/oil or buggered up from improper wrench size.

Donny Smith

[Chrisbo]

I know it's a how long's a piece of string sort of question but where about on the side is it Donny and how does it connect with the hole that houses the ball and spring [?] because mine are in really bad shape, So bad i couldn't work out what size of allen wrench fitted them [xx(] [xx(]

Cheers
Chris.

[454MRW]

Chris,
I took one of my fork caps aparts that was in very good un-corroded condition and cleaned out the seating area underneath the screw, and it appears there are very small ridges that keep the screw from completely sealing off the opening to the threaded screw hole. It allows a very very slight amount of air to pass by the screw even when fully tightened down, which would allow air to slowly vent after it reached the point of pushing the check ball off of the seat and escaping through the internal hex opening. This very small amount of clearance would keep dirt from getting in. I think it is an interesting approach to maintaining a small amount of air in the forks which might also help keep dirt from being drawn in past the fork seals. Mike

Michael R. Winter
1974 250 Harescrambler
1975 250 HS Project
1977 250 MC5 Project
1978 250 MX6  
1979 250 KTM Project
1980 250 MX KTM

[Chrisbo]

Thanks Mike,

I've actually got one of mine lying on my desk and after reading your post I went and carefully cleaned away the inside at the bottom of the hex.You're right, I think I can see the remainder of the little raised grooves you are talking about. I'd still like to know about the type Donny was talking about with the little hole in the side as it sounds like it would work a wee bit better.

Cheers
Chris.