advantages of KYB's cylinder valve?

[Bud-Man]

Jeremy (or anyone else that may have experience with this item),
What are the advantages of the cylinder valve, mounted in the top of the cartridge on recent ('98 and up) KYB forks.....particularly those on Yamahas. I'm just curious why KYB would make the cartridge flow oil from the top and bottom unlike a more traditional approach were the primary flow is from the bottom and out the base vavle. Does this setup increase the pressure differential from one side of the rebound piston to the other, thus making the midvalving more sensitive?
Thanks in advance!

 

[shaggy829]

the cylinder valve functions as the cartridge seal and doubles as a high speed pop of valve for extreme high speed hits :)

take care shaggy

 

[Bud-Man]

shaggy829,
At one point I thought that as well but now I don't believe so. If it was only the high speed stuff, then the rest of the speed range would be too stiff. For example, look at the passive valve stack for an '02 YZ250
Piston Face
24.15 (4)
22.15
20.15
18.15
16.15
13.15
11.25
Now that's one burly valve stack if you put it into a KX's KYB fork. So the cylinder valve has to pass fluid at many speed ranges. I've also seen a disassemble CV and it didn't appear to have a blow off mechanism. Instead it appeared to clamp the "shims" on the outside and allowed them to flex on the inside. Unusual to say the least. In the end I'm still puzzled at what they were trying to achieve that they can't to with the passive valving on the base valve.

 

[podia]

This is a single stage valving?

Hmm..:think

 

[Jeremy Wilkey]

Bud,
Intresting thread, everytime I read this, or something like it, I get pulled off into almost thinking there is more to it.. But when you diagram it out the purpose is not that exciting.


First of the Major thing your forgetting is the fact the KX has a 28mm cylinder and a way stiffer midvalve. The mid-valve and base-valve work togther to produce a "joint-damping coefient"

The earlier model CV's did leak at lower speed ranges, the 99 and older models have gotten progressively stiffer. The shim stack is yelid, pop-off stack by nature of its design. That allows it to not impact fluid flow to a certain range (based on internal pressure) and then open and blow off..

Well are there some other intresting observations? How about rebound? How does the rebound of the CV equiped forks change? It would be a potentially larger volume going through the same valve, with a speed based restriction for a smaller volume?

Regards,
Jer

 

[Jeremy Wilkey]

Another thought

I was Talking with James Hunt today and this related story came up....

Thinking about this one some more, I can make a comment that may have a purpose here. Last Spring I rode the wheels of a buddy of mine's KTM 125SX for about 3 mounths.(thanks Glenn) It was a 99 model with the Extreme fork. Well the compression and rebound adjustment althought seperated operated very normally. The passive compression was adjusted by limiting of fluid volume displaced by the rod, the only unusual part was we adjusted a big hole (makes sence as we are adjusting for 2). Well I valved and valved that fork but allways found that I could never get the bike to pick up little roles, and it had bad mid-corner grip. We ultimatly had to run bleed on the base-valve to get evrything working right. The path of the oil out the rod is analogous to the CV... And something that has me curious to this day..

Regards,
Jer

 

[Bud-Man]

Jer,
Thanks! I wasn't aware that the cylinder valve had been update over the years. So it's basically going to blow open an allow a lot of flow when the speeds are high....sort of like preventing a hydro-lock situation. How does the blow off mechanism work? is it spring loaded or is it just a figure of speach (meaning the shims seal the valve until they deflect, which opens up a large volume passage way). Also, I've notice a wide variety of leakage from the cylinder valves, how do you account for that in your valving without using a block off plate or something to eliminate it?

As for the rebound issue I'd think that the valve would open up under rebound damping, as the pressure would be much higher than that created by the damping rod under most situations. Do they have a stop or limiting divice that prevents the CV from opening up too much and disableing the rebound damping?

 

[Jeremy Wilkey]

Bud-Man,
Actually its still normal... Just the valving has gotten way stiffer.. The CV works with a yeild point. As for the leakage issue we rebuild them if they leak..

Here's something to think about.. when a valve is set-up to regulate a volume and you increase the volume by 3 or 4 times the valving even becomes stiffer and less effecting to the total range.

Regards,
Jer