Fork Air Caps....

[viclioce]

What would these be worth, and how, exactly do they work besides putting air in the forks? I mean the only thing they need is a little cleaning. Even the O rings still look good. Victor

[BrianZ]

All will be revealed:

http://hodaka-parts.com/sub-category.as ... 3&cID=1954

Brian

[viclioce]

OK so it says 40 psi with synthetic 20w or 30w fork oil as a starting point & 7 ounces of oil in each tube but no less than 6 ounces. My question becomes what does the air do to handling besides making the forks stiffer? Is it just a start at 40 psi and reduce until you like the way the bike handles? Victor

[Bullfrog]

The air fork mod is for tune-ability. Particularly at an MX track, the rider could increase or decrease air pressure - even between motos.

NOTE: It is a system which works without the coil springs in the forks (which reduces un-sprung weight and total weight on the machine).
Ed

[viclioce]

That’s interesting Ed! So you’re saying you just remove the springs from the fork tubes and use air pressure in place of the springs? I sent them to Alan to use on his Super Combat for Vintage Racing! So I’ll pass this info on to him! Victor

[bcruder]

Tuning damping-rod forks with air pressure...

First, be sure that the existing seals can tolerate 200-300 psi and are positively located to prevent them from being pushed out of the fork sliders. The original seals or even NOS replacements that have been ageing since the 1970's are likely to fail.

The static air pressure sets the ride height while the oil volume sets the progression. More oil leaves less air volume so that the pressure rises more rapidly with each inch of fork compression. Neither is changed that often during competition because one keeps notes regarding the specific track/course and sets them before leaving home.

If one's initial static height with springs is sufficient, one should not add any pressure and does not need caps with Shrader valves. Oil volume could still be used to set progression.

For light riders, the standard springs might already be stiff enough without the need for additional oil. Back in the 1970's, we often switched to lightened springs to allow the air tuning or at least reduced the preload on the standard springs.

Some tried tuning without steel springs at all. I found that to be far too progressive. Enough oil to prevent bottoming made the first few inches of compression somewhat mushy. Thick enough oil to avoid too-rapid (pogo stick) extension after bottoming prevented the forks from ever fully extending in use.

For tuning the progression, with or without springs and with or without static pressure, one removes the springs, fully compresses the forks and adds enough oil to reach a specific distance from the top of each tube. The common starting distance is 6 inches or 15 cm. Ebay and Amazon have tools that allow one to add excess oil and then suck some out to set a specific level.

Ebay and Amazon also list hand pumps that can pressurize each fork leg and then be removed without losing pressure. Starting pressure is typically 15 psi. Simons forks from the 1970's demand one use no lower than 15 psi. Regular air seldom contains enough moisture to cause problems and we change fork oil often enough to avoid oxidation. We do not need dry nitrogen.

Honestly, I have valves on all of my bikes and lightened springs on two of them. None ever needed more than 20 psi and one starts out with no pressure at all. Even the heaviest did not need shorter than 5 inches of air volume above the oil to avoid bottoming. Maybe I was just a slow rider...

[dirty_rat]

bcruder, you gave a real good explanation. I used to run air forks on my Hodaka back in the 70's. At first I ran without springs, just air pressure. Found that was hard to find a happy medium between too hard initially or bottom too easy. I went back to springs with less air pressure to adjust to different tracks etc. Worked much better. Also, if you keep the springs in and one or both of the forks loose air pressure, you still have fork action. With only air, you get a leak and your forks are useless.