shim shuffle - KTM WP forks Part 2

[James Dean]

marcusgunby,

Are you trying to say that a stack on the face of the compression valve of something like:

24X.1 (4x)
16X.1
14X.1
12X.1
11X.1
18X.3

will be softer than:

24X.1
22X.1
20X.1
18X.1
16X.1
14X.1
12X.1
11X.1
18X.3

Is this what is trying to be conveyed? Just trying to clarify.

The first looks firmer not softer.

James

 

[c3hammer]

Mace:

Your idea works great. Turn it all the way upside down.

Just bring a big piece of carpet to flip the bike on. This keeps your levers, grips, master cylinder and rear fender from getting scratched up.


Drehwrum and friends:

I have absolutely no experience with the KTM forks, but your shim stacks look really weird to me. I would run something like:

24x0.1 x6 (+3)
12x0.15 x2
- 22x0.1 (-1)
20x0.1
- 18x0.1 (-1)
16x0.1
14x0.1
- 13x0.1 (-1)
12x0.1
- 11x0.1 (-1)
11x0.1
18x0.3 base plate

This would firm up the low low speed, stop the bottoming, get rid of a bunch of high speed sharpness and eliminate most of your head shake by keeping the fork up higher in the stroke. How big are the orifices in the piston? It must have relatively small orifices to only need 2 or 3 24x.01 low speed shims.

The only problem with the above is that it dances around on steep rocky uphills. Some of this can be solved by removing some preload from the front if there is any.

And for another really wierd suggestion. Put a two shim-face shim against the valve to help keep the low low speed really plush. This is a 24x.01 shim that has a 12mm ID with a 12x.01 shim inside of the bigger one. Don't ask me how it works, but it does soften up the really slow stuff, but stays firm enough for the big hits.

Just my $0.02

Pete

 

[James Dean]

c3hammer,

Where do you get shims like that from? What bike have you experienced this on?

I've seen it before on an older Yamaha, but with the outer shim being thicker to apply a "seat pressure" to the face of the valve.

The KTM compression valves have relatively large ports but they also have large 14mm cartridge rods that pump more fluid.

Mace's idea is a novel approach. Be sure and take a picture of your USD forks RSU on the USD bike.

James

 

[marcusgunby]

Hmm it seems im showing my inexperience here, i thought the first stack would be softer but i guess my reasoning of shims bending over the smaller ones is incorrect.Im starting to see that if the shim is smaller- its edge is stiffer(like JD pointed out)i suppose my mistakes help teach myself and others.

 

[drehwurm]

Servus,

Oh Boy this gets out of hands! I went testing my #3 stack today, solved one problem and found antoher, found that I'm stupid, stupid and stupid and now c3hammer comes up with this new stuff. Ok, lets get this into an order:


*1) I'm stupid (but also lucky ;-): Just take a look at this sentence and switch on your brain (like I didn't) and you'll see the light right away:

I replaced the 16/18 shim with a 17/19 to open a gap in HSC to get rid of the deflecting

Cheese, what was I talking about here? This 'gap' has absolutely no effect, the 17/19 stack is just a tad stiffer on HSC than the 16/18 and that's it. No magic or exotic damping curve, just stiffer!

How I found out? Well, when riding today the forks were suddenly deflecting on sharp edges at high speeds again - it was less severe than with the original stack, but it was there again. Changes from stack #2 were the replacement of the 10x0.3 shim with a 11x0.15 and replacement of the 17/19 with the stock 16/18. Stack #1 was even stiffer than #3 and there was no deflection problem so it can't be the 11x0.15 shim.

Okay, here is my theory: My problem was never too much HSC, but too little! When hitting a sharp edge the forks were just blowing through their stroke. Out of luck I increased HSC with the 17/19 shims and that helped to cure the problem. I have the following options (shims) now to prove this point:
1) replace the 16/18 with 17/19 shims like it already worked
2) go even stiffer on HSC with replacing the 18/20 with a 19/21 combo
3) go even more stiff on HSC with replacing the 22x0.1 with a 22x0.15

1) is boring, 2) is tempting and 3) has some resemblance to marcus' CR stack - I don't know yet!


*2) With replacing the 10x0.3 shim from the overly soft #2 stack with a 11x0.15 I finally did something right. This is just what I intended to do - overall firmness is now to my liking. Controlled, stable and not tiring - that's it.


*3) c3hammer, could you give us some info on this stack like which bike, which use (MX, trail, ...) and how it worked? Looks like a Gold Valve stack MXTuner once recommended to me; very little HSC for my taste! Though I liked it very much back then, but I was also slower ;-)


*4) Hmm, I should come up with a #4 stack, but I'm just not sure - need some time off I guess.


Michael (stupid, stupid, ...)

 

[c3hammer]

Sorry JD and Michael, it's from a 94 YZ250. I ride everything, with a preference for fast whoops, puppy jumps, rocks and very narrow single track. I'm also a little guy. 5'7" and about 145 lbs.

The stack I listed is basically the same as what I use in my KYB forks. It came with the shim inside of the shim against the piston. I took it out and liked it much better before in some ways.

I hate it when the bike spikes my wrists or punches the rear end over the bars on the high speed hits. I'd much rather have it bottom occationally (uncontrolled tavel).

The overall firmness, I think you are refering to, I don't believe has anything to do with the small high speed shims, IMHO. In fact I can't figure out what most of the high speed shims ever do :)

Mace, didn't you run a shim stack that had no high speed stack at all once? I think the low speed is totally uncontrolled without the HSC, but it takes very few of them to keep the LSC from blowing through before you want it to.

In other words, start with the LSC that will work for the "feel" you're looking for. Then add HSC as needed to control the LSC shims at the higher suspension travel speeds encountered on the faster/sharper hits.

How's that for some real B.S.?

Pete

 

[c3hammer]

Hey Marcus:

Sorry, I missed your post.

I think the first one will be much stiffer than the second until the speed increases enough to blow open the 24x0.01 shims. Then it will move faster / with less resistance at those speeds of travel, than the second, relatively.

Does that sound right?

Pete

 

[PT564]

Notice no comments from Jer.... Hmm -- why do you think that is?

Mabe Rob can chim in and ad something instead...

 

[marcusgunby]

i just rechecked JD's 1st stack and didnt notice the 1st stack has 4 24.1 shims as opposed to the 2nd with
24.1
22.1
20.1
the 2nd stack does look softer but im confusing myself now.

[This message has been edited by marcusgunby (edited 02-23-2001).]

 

[JTT]

Originally posted by c3hammer:
And for another really wierd suggestion. Put a two shim-face shim against the valve to help keep the low low speed really plush. This is a 24x.01 shim that has a 12mm ID with a 12x.01 shim inside of the bigger one.

Sorry Pete, I'm a little dense. I just can't get a picture in my head of this arrangement. Do you mean, use 12mm ID (on a 14mm shaft) shims, 24x.01 and 12x.01 (in that order) against the piston face, before adding remaining stack?
------------------
JTT
Logic Over Hype Coalition

[This message has been edited by JTT (edited 02-23-2001).]

 

[KawieKX125]

I kindof understand it, but really need to rack my brain. When I pull the valving on my KX in the future, I will post for help :D.

------------------
Aaron's web site

 

[c3hammer]

OK, I think I blew the description of this two shim / shim.

Here's what it looks like. Draw a circle 8mm OD, then one outside that 12mm OD, then another 24mm OD. Color between the inner circle and the middle circle red. Color between the middle circle and the outer circle blue. The red is the shim inside the blue outer one. They both are 0.005" +/- 0.0002" thick.

They both sit flush against the piston. I misspoke this as a valve in my original post.

I think what is going on, is that this shim inside a shim is much more flexible than a standard 24mm OD x 8mm ID x 0.1mm shim.

When you put 5 to 7 more 24mm x 0.1mm shims behind it, what happens???? Why does is feel so much more plush on large gravel size rocks at speed???? With the shim in a shim, all that disappears from the front. With a single solid shim you can feel the little stuff like that.

Pete
[email protected] http://www.vert.com/dirt/

 

[drehwurm]

Servus,

BIG NEWS: Just got off the phone with my dealer and learned the following: even though I have a 2001 model, the early 2001s still have the 2000 spec forks. Now there is an update kit for ~USD120 with completely replaces the base valve, base valve body and several other parts. New stacks are out as well, but I won't have the exact info before I get the kit (hopefully next week). This should put the forks in another league (don't believe till I see) and can be also fitted to the 2000 models - JD are you listening. Sorry Marcus, too late for you ;-)

I've ordered the kit and will give it a try. If I don't like it, I'm sure I can fit my ongoing project stack to the new parts.

Back to the ongoing discussion!

Marcus, don't think so complicated. Shims are not working like a lever!!! The thicker the stiffer, so if you add a shim with a larger diameter you also add material => thus becoming stiffer. Reasonable?

c3hammer, due to my understanding your stack does exactly what you want. Lots of LSC for the whoops, little HSC for the rocks. Not what I'm aiming for. We don't have whoops here, but fast special tests and MX tests. I want a very progressive stack with lots of stability and emergency damping when hitting unexpected high speed obstacles. The idea behind the stack of marcus' CR looks very appealing to me. BTW, you said you liked the '2-piece' shim mostly - what didn't you like?

JTT, he is talking about a shim inside the shim - 12x0.1 inside a 24x0.l with a 12mm ID. Hmmm, anybody going to try this?

Proposed stack #4:

24x0.1 3x
12x0.15
22x0.1
21x0.1 new, instead of 20x0.1
19x0.1 new, instead of 18x0.1
16x0.1
14x0.1
13x0.1
12x0.1
11x0.1
11x0.15

Michael

 

[KawieKX125]

Are the bigger diameter shims for HSC or LSC??? Also, what is the .3 shim at the end of the stack and what is its purpose and what would happen if you changed its diameter or thickness? Does the modified shim stack have to have the same total height as the origional? Do the shims closest to the piston have to have the same outerdiameter as the valve to control the initial oil flow through the valve? The way I figure it, if you used a smaller diameter valve at the piston, you would get"oil leakage" around the circumference of the piston where the valve would no longer cover. I am right eith this or have I just guessed at a way that LSC is reduced dramatically? Valving doesn't seem too complicated, it is just alot of commensense and patience. As a favor, could someone post a picture of some different kinds of dissasembled and assembled valving do that I can get a better idea of how it appears assembled? It would be greatly appreceated.

------------------
Aaron's web site

 

[James Dean]

drehwurm,

What is the part number and cost? My dealer was in the dark on it. Very interesting.. :)

Kawie, (too many questions) 1- HSC mostly 2-bottoming, change HSC, 3- NO, 4-First only, 5-Yes 6- See www.penskeshocks.com/8900%20Motorcycle%20Manual.pdf

c3hammer, did you replace this "non-shim" with a "real shim" while leaving everything else alone, thus adding stiffness?

James

[This message has been edited by James Dean (edited 02-23-2001).]

 

[c3hammer]

Michael:

Sounds like you've got my stack pretty well figured out.

I believe the 2-piece shim will always be good in my fork. When I go back to it, I'm hoping I'll have a little less LSC for the tight rocky single track with my clickers all the way out.

The other thing the 2-piece shim does, is allow the LSC to "bleed" a little more under braking and in hard cornering. In otherwords a little more dive in the front. I believe I'll be able to tune this out with the clickers. It will get the clickers back toward the center from way out now.

You could try to look up a guy named John Reising from Oregon. He has a KTM that is set up much like what your talking about. I rode with him in Idaho last year. He's wicked fast. Also a little sadistic when it comes to watching other people suffer on the really technical stuff.

Good luck with your quest.

Pete

[This message has been edited by c3hammer (edited 02-23-2001).]

 

[KawieKX125]

I have taken apart an old 89 cr250 shock that I had in the basement and this is the valving and how I figure it would ride, correct me if erong.
Compression valving, starting at piston
38X.15(7X)
30X.15
23X.15
22X.3
38X.3(2X)
34X.3(2X)
30X.3
26X.3
22X.3

This valving seems very stiff to me by waht little I understand. I think that the seperation between the HSC an LSC in between the 22X.3(end of LSC) and the 38X.3(start of HSC) The HSC doesn't seem too unreasonably stiff to me, but the LSC seems very firm because of the 7 38X.15 shims. That shock seems like it would be very, very firm with an abrupt transition to HSC. It does not seem very progressive to me at all. The LSC stack is very flexible though when installed and the HSC stack is very stiff. Does this valving make any sense? Please correct me since I am trying to learn how to valve correctly.
Thanks

0




------------------
Aaron's web site

 

[Blue Smoke]

If I be you....
This looks very similar to the valve stack that I liked from my 97WR 250, so I suggest you leave the 21 & 19mm shims in place and try increasing the 13, 12 and only (1) 11mm to .15mm thickness. This worked well for my app. but I also shuffled the midspeed valving (or "active Valving" as Jeremy calls it)

Originally posted by drehwurm:
Servus,
Hmmm, anybody going to try this?
Proposed stack #4:
24x0.1 3x
12x0.15
22x0.1
21x0.1 new, instead of 20x0.1
19x0.1 new, instead of 18x0.1
16x0.1
14x0.1
13x0.1
12x0.1
11x0.1
11x0.15

Michael

 

[drehwurm]

Servus Blue Smoke,

I actually forgot to mention the 18x0.3 shim which sits on the end of the stack and makes the 11x0.25 (11x0.1 + 11x0.15) necessary - I have the feel, that with the thickness of the 11OD shim and the 3rd stage 18x0.3 shim I can controll SHSC (Super High Speed Comp)very nicely. No need to go thicker on the 11,12,13 shims.

How did you modify the midvalve?

Michael

 

[drehwurm]

Servus JD,

What is the part number and cost? My dealer was in the dark on it.

Cost is around USD120 (we have 20% tax), but I don't know the part no. so far. The guy I spoke with actually is the WP importer for Austria. Even though the KTM factory sits here in Austria, all WP spares are going through his hands :eek:

As soon as I get my hands on this kit I'll post details. Wonder if Marcus is right.

Michael

 

[JTT]

Originally posted by drehwurm:

24x0.1 3x
12x0.15
22x0.1

Is this the "12 inside of the 24" that you were referring to? ...sorry the "inside" terminology threw me. Looks kind of like an other stage to valving. I would think that this should fairly significantly speed up low speed, at least until shim bends and hits the 22...or maybe just the ultra small hits...like the gravel...hmmmm?

I too would like to understand the "midvalve" thing better...I think I'll start a new post, so we don't loose the original direction of this one....sure I'll see you all there. :D



------------------
JTT
Logic Over Hype Coalition

 

[drehwurm]

Servus JTT,

Is this the "12 inside of the 24" that you were referring to?/QUOTE]

No, when referering to the '12 inside 24' I was just giving an example of my understanding of c3hammers proposal.

I too would like to understand the "midvalve" thing better...I think I'll start a new post, so we don't loose the original direction of this one....sure I'll see you all there.

Yup!

Michael

 

[drehwurm]

Servus,

Today I got to test my latest stack and the updated base valve parts (3mm bleed hole and larger comp-clicker needle). To make a long story short I went into the wrong direction. With the updated parts there also came instructions for new stacks from the SXS 43mm enduro forks, which lead me into the wrong direction. LSC and HSC on those stack are considerably stiffer so I figured to try the following:

24x0.1 4x (+1)
12x0.15
22x0.1
21x0.1 new, almost same like 2x 22x0.1 or 22x0.15
20x0.1
18x0.1
16x0.1
14x0.1
12x0.1
11x0.25
18x0.3

My forks were dancing on the high speed stuff and it felt like the bike wanted to twist from underneath me - couldn't find a straight line. After a few laps my elbow-joints began to hurt and headshake was felt even though I had my Scotts damper. I don't contribute this to the stiffend LSC (+1 24x0.1), because the new parts have a considerably larger range of adjustment on the LSC clickers and I could easily go from stiff to soft on the LSC part. At least now I think I can determine the difference between being too stiff and too soft on the initial part of the HSC stack. Too stiff - dancing forks - too soft - 'hydrolock' jolts. Coincidentally a friend brought his new, completely stock 520EXC from the latest batch, and his forks felt like mine in the beginning - controlled and plush, but delivering severe jolts and headshake on the high speed stuff (sharp edges, accel. bumps).

On Monday I'll leave for a week of MX/Enduro training in Hungary and this will be my stack:

24x0.1 4x
12x0.1
22x0.1
21x0.1 instead of 20x0.1
19x0.1 instead of 18x0.1
17x0.1 instead of 16x0.1
14x0.1
13x0.1
12x0.1
11x0.25
18x0.3

Result in Part 3 when I'm back in one piece hopefully!

Michael

 

[DEGBERT]

How did your last shim stack work?

 

[drehwurm]

Servus Degbert,

How did your last shim stack work?

I do like the HSC part, I'm too soft (probably way too soft) on the LSC and I still have the headshake problem, which could be because of too soft HSR.

During the last weeks I could do lots of riding in very different conditions with some video taping, probably developed a shock problem and got me a cast :confused: for two days. I'm faster on this bike than on any before, but I'm far from the perfect suspension setup. Hopefully I'll get my shock fixed, stiffen LSC (adding some 24x0.1 shims), install the updated rebound parts together with stiffer valving and let my body heal (only minor stuff). Should be back to testing in about 2 weeks and will post more experiences in part 3!

Michael



[This message has been edited by drehwurm (edited 03-21-2001).]