Air is easy to adjust but sensitive to moisture
I use it for my KYB Fork.
These parts are designed to prevent the air inside the fork from expanding and contracting as the temperature inside the fork changes during the ride, changing the effectiveness of the air spring.
This is a convenient way to operate the Breeder with one push of a finger instead of using a slotted screwdriver to turn it.
Most motorcycles have a manual air capacity adjustment when the fork is fully extended, meaning the wheel is floating.
So in most cases, the temperature of the fork will rise while driving, and when the internal pressure of the fork rises, I think it is the way to use according to the manual to float the wheel and release the large air.
By the way, when I actually used it, I think that the change of the internal pressure by the difference of the temperature of the morning and the daytime is Large as well as the change during driving. Especially, it is remarkable in summer. The empty plastic bottle and the empty can "Pop. It seems that the same thing is happening inside Fork.
And there is another way to use this Parts, because it is easy to bleed air with One push, so if you bleed air while riding 1G’, you can get the effect similar to lowering the oil level, reducing the amount of stroke, making Damper effective, etc. while driving.
It is only a pseudo, but our feeling is that it is generally 'There will be less Strokes. Less lumpy ride, Damper extension from near Full Bottom works so you can easily use it depending on the running scene.
By the way, I tried to measure the sag by retracting the FFork as much as possible in the state of riding 1G’, but the value was hard to become constant even if Damper was set to the weakest. This is probably because it is in a halfway state, with 1G’ at the center, negative pressure works in the direction of extension, and reaction force is applied in the direction of contraction.
Other factors such as Spring rate, Initial, etc. are also involved, but it is necessary to take this air pressure into consideration when setting out, otherwise you may fall into a trap.
Also, this Parts is very vulnerable to moisture penetration. Is it possible that the moisture is coming from the Button part? Is it?
This type of KYB's fork cap has a hollow top. The top of the fork spring will be roasted if it is not good.
I applied a lot of silicon grease to the O-ring of the part that is inserted into the fork top cap to make it seal a little bit. If the O-ring is screwed in too tightly, the O-ring will be torn to shreds, so you need to be careful about Torque management. By the way, it seems that the air tightness is kept enough even by hand tightening.
As an added bonus, when I wash the car, I carefully air blow the water away and when I store it, I cover the entire Top Bridge with a Vinyl bag.
As you can see in the image from the side, it juts out from the Top cap, so there is a limit to how far it can stick out and the direction of the cap, and when disassembling the fork, it takes a little more work.
However, it is a unique Parts, so if you are interested in it, please try it.

