KYB fork revalving tips? Mid-valve get out?!

[Techfreak]

Hello Guys, hello Jeremy!
At first please excuse my English. Hopefully you understand my questions.
I ride a ’97 YZ 125. OK, it’s not the newest but the rider has more effect on lap times …
I want to revalve my suspension at home because I’m really interested in the technology (how it works) ...
The Fork is too hard at the begin of the damping stroke. The fork gives all bumps to my hands … I guess the mid-valve is the reason. It restricts the oil flow to much through the valve on the damping rod … Maybe that’s one reason why race tech recommend to rebuild the mid-valve to a normal check-plate-design when they install a gold valve. Race Tech also recommend 10mm spring preload. (because the fork dives in deeper than before, so the preload will avoid it?!)
If I would rebuild the mid-valve to a check plate valve. The check plate lifts up round 1.7mm during the damping stroke. (So here is no more a damping effect. The oil can flow relative unrestricted and all the work is on the base valve.)
Is this opening not too much (it gives away all damping possibilities on the active valve) ? (I guess trough the base valve flows lesser than 1/5 of amount of oil than through the valve on the damping rod during the damping stroke!?! … )
How can I revalve my base valve in order to compensate this lost of damping?
I guess the spring preload has effects on the rebound damping. So should I reinforce the rebound stack?
Other bike brands use Kayaba too. Do they also use mid-valves?
I have no possibility to compare my compression stack on the base valve to others. So I hope someone can help me with tips or a list of his own compression stack. Much thanks ahead.
My stock compression stack on the base valve:
5x 0.10mm 24x8 (number, thickness, outer diameter in mm, inner diameter in mm)
2x 0.10mm 22x8
1x 0.10mm 20x8
1x 0.10mm 18x8
1x 0.10mm 16x8
1x 0.15mm 14x8
1x 0.25mm 11x8

 

[marcusgunby]

I would work with the std pistons and midvalve and just work on the base(passive) valve stack-you can lighten up the base valve to compensate for the midvalve.

You shouldnt need to revalve the rebound as the clickers should be able to compensate.Have you got the correct springs for your weight?

 

[Techfreak]

One more time much thanks to MarcusGunby!
My fork spring is a 0.41kg*mm-1^or 23lb/in. And it should be OK for my weight of 77kg in complete MX-outfit.
I will use the std pistons. But if I don’t lighten the active mid-valve I’m not sure if the revalved base valve is enough for a good sensibility at the begin of the damping stroke. Because I guess trough the mid-valve flows more than 5 times amount of oil than trough the base valve. So if the mid-valve is to stiff the room over this valve will filled too slowly (speed depend). So the fork is harsh over bumps. But at higher speed the fork will be softer. That’s not my aim. I want my fork soft at the begin and it should get progressive harder at half way point with good bottoming resistance. Softer at lower speeds, harder at higher speeds.
What do you think about this???:
I rebuild the mid-valve to a check-plate-design but with only round 1mm opening. (Add spring preload) So I hope that I can save some HSC with a softer feeling at low-speed (over many kinds of bumps) and a harder one at higher speed (stability). Maybe this setting requires not to much changes on the base valve because I can’t compare it to others. A lot of potential for wrong decisions. I know I must add some (thicker) shims at HSC and maybe also some on LSC if the clickers aren’t enough. (I don’t have tested anything of this. That’s all in my mind. So maybe something could be wrong.)

 

[JTT]

I would agree with Marcus, leave the midvalve alone and work with the basevalve first before doing anything drastic, like removing the midvalve. You will find, I think, that you can get most of the improvements you want with just the base valve settings, then, if necessary, fine tune with the midvalve.

When you refer to "softer at lower speeds, harder at higher speeds" are you referring to bike speed or suspension speed?

 

[marcusgunby]

Yes i think you will be able to get enough sensitivity with just the base valve-i can almost get a 02Cr125 dialed in with just the base valve and that has a stiff midvalve with no lift at all.You really are making the job hard by changing the midvalve-one change at a time only, or how will you know what to do if it feels wrong when riding.
Just work at removing some LSC.

Keep the shape of the stack the same.

 

[Techfreak]

At first much THANKS to all who answered me!!!
To JTT: I meant bike speed.
To MarcusGunby: You are right that it is a lot of work if I would change the mid-valve then testing then changing again … I just thought about the problems and I haven’t no experiences in revalving (it’s the first time). So I’m really grateful for the tips!
My normally mid-valve doesn’t lift too. And it seems stiff. You suggested that I should leave the mid-valve alone. So I will only think about the base valve revalving. Here is just one pyramid. If I understood you right I should only remove some of the bigger shims (with the bigger diameters) - step by step.
You also suggested that I keep the shape of the stack. So I should hold on on my one pyramid – no transform to a LSC-pyramid and a HSC-pyramid? (I could add a smaller shim (maybe 16mm) between the second and third big shims in order to lighten the LSC?! But I guess it lightens the HSC too.) Right or wrong?

 

[marcusgunby]

Sounds good to me-you seem to have alot beeter grasp of the theories than i did when i first started.
You could add a cross over shim but again it adds a whole new dimension to the thoery.
A 2 stage stack should be more forgiving and i generally run them on the CRs even with expert mx riders.In fact you will end up with almost the stack i fitted to my friends 02.

total HSC is the sum of all shims strength-so if you increase LSC or HSC you will increase total HSC.

 

[Techfreak]

Every time if I got a new reply I learn more and more. I really appreciate that. Especially much thanks to MarcusGunby!
I think I will try the stack with a crossover shim (0.15mm 14) in third position. The first two shims would bend more and earlier (lesser LSC) But the stiffness of the whole stack decreases, right?! OK I will see what happens. Or has anybody a better idea (before I start the work)???

It’s no problem to remove the base valve alone (without an opened end cap, spring and oil out and so on). But can I install it also this way? (to use a air pressured driver – I don’t know the right technical word.) So the compressed spring holds the damper rod assembly on the axle holder and so I can tighten the base valve?!? Good idea or bad idea???

 

[KTM-Lew]

I usually tie the bike down and break the base-valve loose with a rachet. Do my work and then re-tighten it the same way. I have seen the base-valve come out dis-assembled after using air tools. You then have to go fishing for all the parts. :eek:

Get it as tight as you can with the rachet and then gently bump it tight with the air gun. :yeehaw:

 

[marcusgunby]

KTM s are bad for the base valves coming apart using air tools-KYBs arnt a real problem as long as the nut is tightened to the correct torque and threadlock applied-i wouldnt use a air tool on a WP fork-it isnt worth the hassle.

Tell us how the fork responds with the cross over shim.

 

[Techfreak]

(almost the same text like in the KYB Shock revalving - Thread)
OK, I finished the work. And tomorrow I'm going to ride. I'm really exited how my suspension will work.
Also in thread: much much thanks to everyone who answered me especially to MarcusGunby!!!
And I will told you how my suspension feel. At this time my home track is soft and muddy, so stayed tuned. You get an answer ...
THANKS, THANKS, THANKS!!!
(I installed the crossover shim 14mm 0.15 in third position)

 

[Techfreak]

So the first ride is finished. And I try to tell you how my suspension felt. The track was not too bad. So I guess I need more testing time. First impressions:
My fork was better because it soaks up more bumps. (my handlebar doesn’t hops or hits in my hands as much as before during I ride trough bumpy sections) It was easier to hit and hold the right lines. Bottoming is also no problem (with std oil height). At the end of this test I got a little problem with headshake but only on one part of the track. I will lower my fork in the clamps and test again.
I guess it could be more softer because the adjuster is relative wide open and my friend’s bike is much softer than my. And he is faster and his bike weights more but it also doesn’t bottom too often. OK, his fork felt to soft in bumpy braking zones…
Maybe I will remove two 24 .10mm shims. One before the crossover shim and one behind of it. And to save HSC I could remove the 11mm clamp shim. So the 14mm shim would be the new clamp shim?!? There are some options... What’s your opinion?

 

[marcusgunby]

Dont forget the clamping shim affects the entire stack strength so if you use a 14mm you will stiffen the LSC.