stiffening up a Kayaba shock

jaguar · Jun 13, 2004

My bike came setup for enduro, but I'm using it for motocross. So I want the rear valving to be stiffer by installing a stiff washer in the shim stacks. The Kayaba on my KDX200 has a 14mm shaft.
Anyone know the necessary inside diameter for the stiff washers?
I was thinking of putting the washer at about the third shim. comments? suggestions?

marcusgunby · Jun 13, 2004

I would just use a bigger clamp shim(smallest one in the compression stack)

jaguar · Jun 13, 2004

Since I don't have any other shims, do you think it would work to replace the smallest shim with a stiff washer the same diameter?
Hey, do you know the inside diameter of those shims?
thanks

DEANSFASTWAY · Jun 14, 2004

12 mm

marcusgunby · Jun 14, 2004

If you remove the last shim, the clamp shim becomes the next smallest and this will stiffen the entire stack by a reasonable amount.

DEANSFASTWAY · Jun 14, 2004

Marcus whats the Vcash thingy?

dbrace · Jun 14, 2004

If it's been revalved for enduro you will need to increase low speed to help keep it up in the initial part of the stroke . Do you have it apart? How many crossovers does it have?
IMO just changing the clamping shim will only really work if it is a single stage stack, which isn't really what you want anyway.

marcusgunby · Jun 14, 2004

dbrace ive been working on the assumption the clamp will increase the overall stack strength including ls.Do you work on the same idea.If its a 2 stage or single i cant really see how this changes anything.The bigger clamp will make the ls shims pivot over a wider footprint and so are effectively stiffer.

jaguar · Jun 15, 2004

thanks guys. I'll dig into it soon once I receive the new bottoming bumper.
Right now the compression adjustment is too stiff for small bumps but has filled in the needed stiffness for jump landings.

dbrace · Jun 15, 2004

Right now the compression adjustment is too stiff for small bumps but has filled in the needed stiffness for jump landings.

If it's been setup for enduro i'm surprised its too stiff for small bumps. More than likely it's riding too far into the stroke which is why it feels too stiff. What spring are you running and what are your sag numbers.

As far as the clamping shim:I do agree the clamping shim will stiffen up the stroke but much more so on a single stage stack. eg a pds shock.
But if the stack is running crossovers the shims above are greatly influenced by the size, number and thickness of the crossovers in the initial part of the stroke. The initial part of the stroke and how it performs has a big effect on how the rest of the stroke acts.The way i see it if you,re too soft initially the suspension will just blow thru the stroke and build up too much speed and momentum resulting in a loss of dampning control that no clamping shim can control.

That is why the midvalve in forks is so important as it also plays a big part in what happens in the initial part of the stroke. Run a check plate and you have lost all of your low speed control. Then you need to rely on too much basevalve dampning to try and control a fork that has built up too much momentum. This results in a harsh fork.

D.B.

JasonWho · Jun 15, 2004

jaguar, do you have a picture of your disassembled piston assembly? I am curious as to what it looks like in an '89 - '94 model.

jaguar · Jun 16, 2004

Just whats in the manual. I don't have a good camera to take a picture with.

JasonWho · Jun 16, 2004

Have you already had the piston assembly disassembled or were you just looking at the valving without grinding the peening away and taking off the nut? If you have disassembled it, can you tell me what the valving shims are (how many, what size, tapered or straight layout)?

Thanks.

DEANSFASTWAY · Jun 16, 2004

DBRACE I agree with your point on crossovers to some degree but what Marcus says is has merit. Its also the size of the crossovers that comes into play .If you add smaller crossovers than clamp shim it will bleed off damping Larger cross or clamp =more damping. I try to keep in mind that valving is not position sensitive its velocity sensitive. .To some extent on a regular shock a possible position sensitivity part comes into play on a shock when the Shaft travels into the shock body and past the comp adjuster and depresses the bladder .Only on a PDS is there really a true device (Needle ) that comes into play that is truly position sensitive and tunable. On forks there might be some devices like bleeds drilled into cartridge tubes or fluted tubes ,Marzocci likes that .Another position sensitive part on forks is the comp ratio(oilheight) . I think on twin chamber Showa partly the ICS spring rate.

jaguar · Jun 17, 2004

Jason, I've had it completely apart before for maintenance. The valve shims vary in diameter. They are widest closest to the piston, and narrowest farther away from it. The ones closer to the end of the shock shaft are the rebound shims. The ones on the other side of the piston are the compression shims.

JasonWho · Jun 17, 2004

jaguar, thank you for the information.

Anyone: Is this what is called a tapered stack? Is this a single stage stack?

Thank you

marcusgunby · Jun 17, 2004

Jason heres some shim stacks for you
40.2(10) -40mm* 0.2mm thickness and 10 of them
30.1
26.15
40.2
38.2
36.2
34.2
32.2
28.2
26.2
24.2
22.2
that is a 2 stage tapered stack
a single stage tapered looks like
40.2(10)
38.2
36.2
34.2
32.2
30.2
28.2
24.2
22.2
the last shim( the 22) is called the clamp and this affects the stiffness of the stack above it, think of leaf spring in a car suspension.

Most suspension nowdays uses 2 stage stacks to try to get plusness and bottoming resistance.

DEANSFASTWAY · Jun 17, 2004

Whats the VCASH?

JasonWho · Jun 17, 2004

marcusgunby: Thank you very much for the information. That helps. Are all normal clamp shims very close to the same diameter as the shim before it?

vCash is for betting. You can bet on sports games, MX races and events in motorcycling. Recent events are:

Lakers vs. Pistons
Southwick MX
Will James Stewart ride a 125 or 250 4-stroke at Southwick
various baseball games

You may need to search around some. There is also a BET link toward the top where it has User CP, Garage, Arcade, etc.

Hope this helps

marcusgunby · Jun 17, 2004

normally yes they go in nice equal jumps(eg 2mm bigger each shim)-it makes the stack look more symmetrical.

JasonWho · Jun 18, 2004

On the rebound side, normally, what is between the clamping shim and the shaft nut? My '87 KDX200 rebound side has (from piston to shaft nut):

(quantity, inner diameter, outer diameter, thickness)
8 12mm x 26mm x .25mm
1 12mm x 14mm x .4mm
1 12mm x 20mm x .5mm
1 (looks like a regular washer) 12mm x 26mm x 3.2mm

marcusgunby · Jun 19, 2004

are you asking what the std shim stack is? as i dont have it im afraid.On the washer they use them to space things out-as long is its bigger than the clamp shim its ok.

JasonWho · Jun 19, 2004

No, no. I am not worried about any specifics on a particular stack. I am curious as to what is between the shaft nut and the rebound shim stack. Is the clamping shim considered part of the shim stack? What is between the clamping shim and the washer on top of the shaft nut? Is there just a shim stack, including the clamping shim, which is the last one in the stack, plus one washer. then the shaft nut? Sorry to bug the pi$$ out of you with simple questions.

As always, thank you very much.

marcusgunby · Jun 19, 2004

normally you just have the piston face-then the shim stack(including the clamp shim) then the spacers then the nut, the spacers are there to make the nut work on the threaded partof the shaft , as without the spacers the nut would bottom out on the threads and not compress the stack against the piston face.

hope that helps.

JasonWho · Jun 20, 2004

Hi. That helps a lot, and I fully understand it now. Is it the same for the compression side, just with no nut? Is a washer/shim put at the start of the compression stack to keep the compression clamp shim from flexing? It is intended that the clamp shim not flex, right?

stiffening up a Kayaba shock

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