Front Fork Springs

[jaan]

How long the front fork springs will last?

I don't know the correct English word but I mean that how many years they work well before getting worn out, slack?

What do you think about the front forks with fork top nuts inc. pressure relief valves? Are they much better than standard front forks?

[peterb]

Hi Jaan,

You are probably referring to the schrader type air valve fitted to the fork top nuts on the 70's Montesa's. They worked on the Monts but were not really taken up by other trial manufacturers, I think about 12 psi was used to assist the springs, which really sagged without the air assistance. In engineering thoughts, there would be less friction with pure air versus springs, which may bind on the inner fork tubes. Depending upon use, a set of fork springs could last over 20 years or more - hard to put anything definate on springs.

Bye, PeterB.

[feetupfun]

Hi Jaan,

You are probably referring to the schrader type air valve fitted to the fork top nuts on the 70's Montesa's. They worked on the Monts but were not really taken up by other trial manufacturers, I think about 12 psi was used to assist the springs, which really sagged without the air assistance. In engineering thoughts, there would be less friction with pure air versus springs, which may bind on the inner fork tubes. Depending upon use, a set of fork springs could last over 20 years or more - hard to put anything definate on springs.

Bye, PeterB.

Yes there is no friction at the spring/tube surface if you have no springs, but the friction at the fork seals goes up dramatically with increasing air pressure which is why very few manufacturers used air springing on its own. Most had air and steel springs together. Any bike with sealed fork caps is making use of the air inside as a spring, whether the caps have the facility to adjust the pressure (schrader valves) or not.

Jaan, you can buy new springs for the Cota 348/349 but most people just add a bit more preload to the spring. When the springs get so sagged that to get the preload right, you have to put in enough spacers that the coils touch each other before the forks bottom, it is time for new springs.

Sagged single-rate springs have the same spring rate as new springs, they are just shorter overall when relaxed - hence needing longer spacers to achieve the same preload force. In the case of my 1976 348, I have about 10mm more spacer length than standard, and ride with the pressure set at atmospheric pressure with the forks topped out. Be careful when comparing settings from one 348 with another 348 because some came with higher rate springs than others. If you have the low rate springs, as Peter says, you will need to run some air pressure in them.

[jaan]

--- You are probably referring to the schrader type air valve fitted to the fork top nuts on the 70's Montesa's.---

I mean this:

France Trial Classic

[feetupfun]

I can't see much of the fork caps in that photo but the caps look like they are of modern manufacture to me rather than made by Montesa. Schrader valves are simply the type of valves that are used on car and bike tyre tubes and act as a non-return valve to hold the gas in and you push a litle pin in the end to let the gas pressure out.

A different type of gas valve was used in the fork caps of a few old trials bikes like Bultaco Sherpa Ts and Kawasaki KTs. These are called vented caps.