Schrader valves on forks and rear shocks

The fork ones allow you to bleed out any pressure that might build-up, that's about all and that's a good thing, there was a time when adding pressure was done, you could buy tiny syringe type pumps and even kits that linked both forks so even pressures could be added. All it did was make the forks harsher and blow seals easier. The valve on the shocks takes nitrogen, which inflates a bladder that separates the gas from the oil and reduces any cavitation in the oil, that's tiny gas bubbles that form as the oil is agitated cursing foaming and loss of damping. these rubber bladers do deteriorate over time allowing the gas to pass through, that's why you're supposed to get gas shocks rebuilt every few years.
 
Not sure about the SFC1000 but the forks on an RGS have very rudimentary valves in the fork caps; they supposedly relieve pressure within the forks under compression I guess to reduce the risk of blown fork seals. I drilled my fork caps out and araldited a set of Shraeder valves in. Have been able to run only one fork seal in each leg without blowing them.
 
There are 2 RGSs with Fournales fitted in the NSW club, I had a day run on one. After the pressures were upped I couldn't see any issues, it felt pretty good to me. But now that Mr Frog, I forget his name, La Parisian bloke has passed away doing rebuilds might be an issue.
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Legs said:
Not sure about the SFC1000 but the forks on an RGS have very rudimentary valves in the fork caps; they supposedly relieve pressure within the forks under compression I guess to reduce the risk of blown fork seals. I drilled my fork caps out and araldited a set of Shraeder valves in. Have been able to run only one fork seal in each leg without blowing them.
Click to expand...

The fork seals are there to hold the oil in and water out, however they can be inclined to let air in as the forks extend. This additional air can build up to form pressure on top of the oil level, acting as pneumatic spring in addition to the main fork spring stiffening up the compression stroke.
Schraeder valves will release this build up of pressure when released.

On the other hand this pneumatic spring can be used to great advantage when understood.
When the forks are fully extended the air on top of the oil can be adjusted to improve dive under braking.

When I change the oil in the front forks I use the following technique;
  • Springs out and forks fully compressed,
  • Add oil to give a gap of say 150mm from the oil level to the top of the fork tubes.
  • extend forks and replace springs.
A 150 to 160mm air gap will produce a plush ride with controlled diving under brakes.
This air gap can be reduced to 130-120mm for more spirited riding and braking without inducing hydraulic locking on full compression whilst minimising braking dive.
Adjust the air gap to suit your riding preference.

Periodically release pressure build up with shraeder valve with the forks fully extended.
 
I had Ohlins dampers with schrader valves and recommended 140psi pressure. I used to pay to get them filled with nitrogen until Ohlins said to just use air. I couldn't tell the difference.
 
The air we breath contains 78% nitrogen. Given that nitrogen molecules are larger than oxygen the oxygen will escape first leaving pure nitrogen.
Cheaper by far.
Nothing wrong with putting a little pressure in the forks provided the seals are up to it.
 
I thought the use of nitrogen was to avoid water vapour in compressed air, but I am no Ohlins tech. I think you can get water vapour catch tanks on air compressors used in Spray Panting, just had a thought can most compressors get to 140psi?
 
Thanks for replies. I did search the forum prior to posting with no results so at least others will now have this on record. I do remember the bicycle pump thing for the forks from years ago. As I am now a Fairweather town rider when good weather opportunities arise in London. I shall depressurize the forks and put a little air in the rears.
 
Vince said:
I thought the use of nitrogen was to avoid water vapour in compressed air, but I am no Ohlins tech. I think you can get water vapour catch tanks on air compressors used in Spray Panting, just had a thought can most compressors get to 140psi?
Click to expand...
Pure nitrogen is just that, no moisture.
Air that we breath, the same air that compressors use contains moisture that can build up in compressors.
Nitrogen is used to inflate racing bike and car tyres because it doesn't contain any moisture.
moisture in tyres will expand exponentially when heated thus increasing air pressure,
Nitrogen containing no moisture will not increase as dramatically as air.
Nitrogen is a gas and is still affected by changes in ambient temperature (about one psi for every 10° Fahrenheit). Nitrogen filled tires will require pressure adjustment as ambient temperature varies.
 
The Marzochi's on my 1200TS have little balls and biro type springs in the centre of the fork top nuts under a drilled screw, this relieves air pressure on cmpression,when it is great enoiugh to overcome the biro spring, i.e not a lot, works for me. I recently saw one with the ball and spring one side and nothing at all the other side (under the screw) the rider didnt seem to notice.
CLEM
 
That's what I found Clem, very agricultural. Replaced with 'upside down' Schreaders, haven't had a blown seal for donkey's years. Works for me :)
 
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CLEMTOG said:
The Marzochi's on my 1200TS have little balls and biro type springs in the centre of the fork top nuts under a drilled screw, this relieves air pressure on cmpression,when it is great enoiugh to overcome the biro spring, i.e not a lot, works for me. I recently saw one with the ball and spring one side and nothing at all the other side (under the screw) the rider didnt seem to notice.
CLEM
Click to expand...
Same spring and ball on SF1 Cerianis.
 
My 1985 Ducati MHR came with schrader valves in the fork caps (Marzocchi) as well as on the reservoirs of the Marzocchi Strada rear shocks.

I think the rider's manual said something like 4 psi max in the forks and around 25psi in the shocks. I might be mis-remembering the numbers, but whatever they were, they were impossible to achieve without a special hand pump and gauge. Even then, the volume inside is so small that you'd lose half the air in the "pssssst" when you take the pump fitting off. Totally impractical.

I just used the valves in the forks to occasionally vent them to atmospheric pressure. They never built up much pressure in anyway.

I fixed the Strada shocks by chucking them in a box and fitting some decent shocks to the bike.
 
Dellortoman said:
My 1985 Ducati MHR came with schrader valves in the fork caps (Marzocchi) as well as on the reservoirs of the Marzocchi Strada rear shocks.

I think the rider's manual said something like 4 psi max in the forks and around 25psi in the shocks. I might be mis-remembering the numbers, but whatever they were, they were impossible to achieve without a special hand pump and gauge. Even then, the volume inside is so small that you'd lose half the air in the "pssssst" when you take the pump fitting off. Totally impractical.

I just used the valves in the forks to occasionally vent them to atmospheric pressure. They never built up much pressure in anyway.

I fixed the Strada shocks by chucking them in a box and fitting some decent shocks to the bike.
Click to expand...
Same here. I messed about for ages trying to get the pressure right in my Stradas. They leaked oil on the very next ride. Immediately ordered new Nitrons.
That was a good day 👍
 
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