shim shuffle - KTM WP forks

[drehwurm]

Servus,

I have a shim stack here, some ideas of how to change it and would like to get some comments from you guys.

The bike is a 2001 KTM 520EXC with 43 WP USD forks and we are talking about a fast outdoor MX track. If the suspension works on this track, I also like it for enduro riding.

Problems with forks (the rear PDS works surprisingly good):

1) severe headshake when braking hard over braking bumps and not being over the rear of the bike
2) deflecting off sharp edges when accelerating
3) bottoming
4) fork soft on LS-comp, but I don't want to go in to far on the comp-clickers - IMHO oil has to flow.

Springs are balanced and seem fine to me.

Shim stack:

24 x 0.1 2x
12 x 0.15 1x (crossover)
22 x 0.1
20 x 0.1
18 x 0.1
16 x 0.1
14 x 0.1
10 x 0.3

Ideas:
1) widen gap in middle of HSC-stack to get rid of the deflecting
2) add shims ( 12x0.1, 11x0.1 at end of HSC stack to stop bottoming
3) add 24x0.1 shim in LSC stack to make fork a little firmer and fight headshake

Idea No. 1 has been realized with exchanging the 18x0.1 and 16x0.1 shims with a 19x0.1 and 17x0.1 shim. Oil level has been raised by 10mm to fight bottoming, but due to lack of shims idea no.2 and 3. could't be realized so far.

The deflecting is gone, maybe also due to the change to Öhlins no.5 fork oil, but bottoming has increased (not surprisingly because of the weaker HSC). Next steps would be idea no.2 and 3. and I would like to hear comments on this one please.


Michael

* 2001 KTM 520EXC *

 

[Shaw520]

Drehwurm, I have the same feelings about the front suspenders. The rear works fine, but the front seems to deflect a bit more than I like, and seem a bit soft through the longest part of the stroke. Dont want to increase comp clickers in fear of increased deflection. Please post your proceedures and results, I dont have any previous experience working on WP forks.
Thank You.

 

[marcusgunby]

A few suggestions are try using Mobil1 ATF its about 7.5wt and should do what you want.Ie stiffer with the ability to run the clickers fairly open.Also possible is to run stiffer springs.Im going to try 0.4kg/mm in my 125sx with less proload and less low speed comp-i will relay results-most jap bikes have alot stiffer springs.Also possible is to look at the midvalve as its fairly soft and tends to let the fork hand down in its stroke.Good luck and a word of warning i dont consider myself a suspension expert.

 

[drehwurm]

Servus Shaw520,

Well, just follow the thread. The problem is, that what is working for me is not very likely to work for others also. Rding style, terrain of riding, skill level and so on play a very important role in suspension setup. I doubt that if I just post my settings here, many people would be happy with the same settings.

The only thing I dare to say so far is that changing to a different oil CAN have very positive effects on the fork. The stock WP oil seems to be thicker than common 5 weight oils and I have had good results with Öhlins 5wt fork oil.

Michael

 

[drehwurm]

Servus marcusgunby,

Also possible is to look at the midvalve as its fairly soft and tends to let the fork hand down in its stroke.

I wasn't aware that the WP forks have a midvalve also; thought this is only found on Kayabas?

As for the Mobil ATF I don't think we get the same mixture here in Europe, so I'm reluctant to try it. 7.5wt seems a little heavy to me also!

Michael

 

[marcusgunby]

Didnt see you were a fellow european as i assumed everyone else is from the US.I adgree 7.5 wt oil may not be the best way to go.The fork does have a midvalve like a kayaba the 125 has 4 24*0.2 shims from memory.My opinion is the fork is undersprung and overdamped.So i would go up on the spring rate and reduce the damping some.Also alot of people run the oil height as low as 160mm with stiffer springs.Keep us updated on your progress.

 

[Shaw520]

My thoughts also Marcus, undersprung and overdampened. The dampening I can deal with, cause it actually helps at speed. I'm going to get higher rate springs, I'm thinking that'll lessen the dampening effect at lower speeds cause It'll be riding higher in the stroke.

 

[Magoo]

I don't really have anything to add to this thread (I'm pretty much an idiot when it comes to understanding shim stacks), but I do remember a thread not too long ago titled something like "Rocky, Rooty Trail Settings." If I recall correctly there was a HUGE discussion about shims, shim stacks and altering the fork action to acheive a desired result. I think the stack changes were chronicled and reported on in some detail -- good info for those that are able to make sense of such things...

------------------
Magoo
Fear is Temporary, Regret is Permanent!

[This message has been edited by Magoo (edited 12-18-2000).]

 

[drehwurm]

Servus Magoo,

I'm pretty much an idiot when it comes to understanding shim stacks

Well, make that two of us ;-)

James Dean has posted parts of the thread you were referring to over at ThumperTalk.com, but I'm not a fan of the "crossover" tactic. Nevertheless it was very interessting reading - thanks!

Michael

 

[drehwurm]

marcusgunby, Shaw520

My thoughts also Marcus, undersprung and overdampened.

Are we talking about 2001 forks here? The 2001 suspension seems to be much better than the years before.

Michael

 

[JTT]

Originally posted by drehwurm:


Idea No. 1 has been realized with exchanging the 18x0.1 and 16x0.1 shims with a 19x0.1 and 17x0.1 shim. Oil level has been raised by 10mm to fight bottoming, but due to lack of shims idea no.2 and 3. could't be realized so far.

The deflecting is gone, maybe also due to the change to Öhlins no.5 fork oil, but bottoming has increased (not surprisingly because of the weaker HSC). Next steps would be idea no.2 and 3. and I would like to hear comments on this one please.


Michael

* 2001 KTM 520EXC *

Michael, I am no expert, but how do you figure that with the shim change you made that the HSC is weaker? Wouldn't the change you mentioned make it slower (ie: stiffer)(ie: more resistance to flexing)?

The other thing is not to forget about rebound. I have read that often headshake is caused by too slow rebound. Have you already tried this avenue?

As for bottoming, be sure that it is the HSC you want to change....

Curious to hear Jer's response, at least to see if I am on the right page.

JTT

 

[marcusgunby]

I am talking about the 2001, as far as i can remember the only difference from 2000 is the 2 strokes got the 8.5mm cartridge holes.Interestingly the 4 stroke appears to have less damping than the 125 and in my opinion works better than the 125 so the theory of less damping seems to be right.

 

[drehwurm]

Servus JTT,

Michael, I am no expert, but how do you figure that with the shim change you made that the HSC is weaker?

Good point - the goal was to open a gap in HSC to reduce defelecting from sharp edges. Unfortunately we also changed the oil so the effect of the shim change can't be isolated, but the defelecting is gone now! Still I'm of the oppinion that the shim change is mainly responsible for this. The probably lighter, slicker oil might be responsible for the bottoming though. But back to your question, yes in going from a 16/18 shim to a 17/19 HSC must have increased!

The other thing is not to forget about rebound. I have read that often headshake is caused by too slow rebound. Have you already tried this avenue?

I'm already very light on rebound and it helped. Nevertheless the KTM RFS have a problem with headshake while braking hard and my Scotts damper will finally fix this. BUT before mounting the Scotts I want to have the suspension dialed in as good as possible.

As for bottoming, be sure that it is the HSC you want to change....

I'm sure, but it wouldn't be the first time I'm wrong! That's why I'm asking here.


Michael

 

[JTT]

I said that because in most cases, bottoming is actually a LSC problem. I assume you mean bottoming off large jumps and such?

As a side note, don't be afraid to try M1 ATF. Don't let the "estimated" viscousity rating scare you. I tried it and found it to be excellent, not effecting valving, but giving a much greater range to clickers. Besides, it's relatively cheap, and an oil change is quick and easy....no harm in trying.

 

[James Dean]

Michael,

Why not go in on the LS clickers?? Yes, the oil has to flow, but the valving shims are there to open for the high speeds.

If the deflecting is gone, you now have some room to adjust before it gets too firm.

Whether you want to add a crossover to the middle of the HS stack or just expand the existing crossover is a matter of preference. Whenever I expand the existing crossover it is always done with also turning in the LS adjustment screw to keep a firmer low speed damping than you might expect.

Option #1 still looks good to me.

James

 

[drehwurm]

Servus James,

Why not go in on the LS clickers?? Yes, the oil has to flow, but the valving shims are there to open for the high speeds.

I don't want to go in farther than 1/3 of the available clicks! Why? I'm of the oppinion that LSC added by shims and LSC added by going in with the clickers is not the same!

Whether you want to add a crossover to the middle of the HS stack or just expand the existing crossover is a matter of preference.

No, I think we are talking about different things here. When you widen the crossover gap, you are influencing the shim stack BEFORE the HSC stack comes into play. I'm talking of altering the HSC stack itself - the effects cannot be the same!

You wanted to make the forks more compliant for rocks and woodsriding, I'm aiming at reducing deflection at high speeds and sharp edges.

Michael

 

[James Dean]

Michael,

Your points are well made when searching for a perfect solution. My comments were made hoping for good discussions.

***Keep in mind those WP forks have 14mm cartridge rods. They push more fluid through the valve and are more sensitive to pressure than a 12mm rod. (36% more fluid compounded with 36% more area on the rod)

-Low speed clickers work in parallel with the LS shims. They overlap within a range. There is a point where I would aggree with your arguement and for me it is more like 1/5 rather than 1/3. This may just be 5 clicks vs. 8 clicks to increase LS-comp and help reduce bottoming. Not an ideal answer though.

-The crossover expansion should be looked at with the 14mm rod in mind. An expanded crossover gap from .15 to .20 will not be nearly as noticeable as on a 12mm rod fork. Also, the effect of reduced stiffness on the HS stack will match the damping of an increased crossover gap WITHOUT reducing the HS stack stiffness at some "uncertain" velocity. My point is to look at tension vs. deflection instead of stiffness alone. The 2 stackings will have similar damping, although to be precise you are correct that it's not exactly the same.

That said, here's my suggestion-

24 x 0.1 2x
15 x 0.1 (a little more support for the 24's)
12 x 0.1 (total gap now = .2)

22 x 0.1
18 x 0.1 (remove the 20 x 0.1)
16 x 0.1
14 x 0.1
12 x 0.1 (this just looks better on paper

)
10 x 0.3

If I were a KTM engineer for a day, the SX would use the current compression valve and the EXC/MXC would get a valve with 40% greater port area. They should have different valves for their intended uses IMHO. Square ledges are HS damping at 20mph just as much as rounded are at 50mph. Gut feeling is this design is never going to be as plush as the Marzocci's of years past.

---------------------------------------
***** The pro's on the forum will disagree, for certain. The party line is generally a soft single stage, maintaining shim seat pressure as best possible on the stock piston and use the port restriction for high speed damping. It works for the 12mm rods, but will it for the 14mm?? It didn't for me 3 years ago so why should it now?

A different suspension tuner was involved and the promise of relief from square edges was never achieved despite their valve mods. I made lots of shim stacking tests along the way too. All the way to mush, and the HSCD harshness was still there.

-------------------------------------

BTW - Christmas was good this year, a '00 KTM 250EXC found it's way into my garage. YAHOO!!

(already had the comp valve apart and it had shims just like yours plus the 12 x .1 in the HS stack)

James

[This message has been edited by James Dean (edited 12-28-2000).]

[This message has been edited by James Dean (edited 12-28-2000).]

 

[drehwurm]

Servus James,

Ok, lets see:

24x0.1 2x

At first I though of adding another 24x0.1 shim, but after looking at my Gold Valve chart this seems too radical a change.

15x0.1
12x0.1

You are a good salesman ;-) I would have changed the stock 12x0.15 to a 13 or 14x0.15 to stiffen LSC a little, but your suggestion seems very interesting. Besides, I'm also curious how the enlarged crossover gap works. Sold!

22 x 0.1
18 x 0.1 (remove the 20 x 0.1)
16 x 0.1
14 x 0.1

Nope, I like the 22x0.1, 20x0.1, 19x0.1, 17x0.1, 14x0.1 very much so far, so I won't change it this time. Maybe removing the 20x0.1 from this stack, but that's something for later.

12 x 0.1 (this just looks better on paper

)

I want to go even more radical like 14x0.1 (or 14x0.15), 13x0.1, 12x0.1, 11x0.1 to fight bottoming after large jumps without raising the oil level to its maximum.

So after I receive the shims I've on order my stack will look like this:

24x0.1 2x
15x0.1
12x0.1
22x0.1
20x0.1 (candidate for removing)
19x0.1
17x0.1
14x0.l
13x0.1
12x0.1
11x0.1 (probably useless)

Gut feeling is this design is never going to be as plush as the Marzocci's of years past.

That's one of the problems here - once you have ridden or owned a bike with great suspension, you are spoiled forever. This was with my 1998 Yamaha WRz400 with Gold Valves (valved after a recommandation from MX Tuna - thanks) and an Öhlins shock revalved by MH Racing. This bike worked for me being fast or slow, doing MX or Enduro, just everywhere! I won't stop experimenting with the KTM till the suspension works either as good or I sell the bike!!!

Nevertheless I'm very hopeful because the stock suspension works so well (surprisingly). None of the KTMs I've ridden previously, including my riding buddies 2000 KTM 250EXC after 2 revalves, came even close. Hope you have more luck with yours!

BTW, when the suspension is fixed we can start the "needle-thing" - again ;-))))

Thanks a lot for sharing your ideas and experience - just too bad you can't go for a beer on the internet.

Michael

 

[drehwurm]

James, I forgot:

already had the comp valve apart and it had shims just like yours plus the 12 x .1 in the HS stack)

Can you post a picture of the valve? I'd like to see if the 2000 and 2001 valves are identical.

Michael

 

[James Dean]

Michael,

Can't give you a picture right now, the valves are already back together in the bike. The part number in manual is #4860.0047. Does this match yours?

The shim stack was put back together as was suggested except for a bigger crossover -
15x0.1
12X0.15 (total gap now = .25)

Time will tell how good it will perform.

For your perspective: This is a woods bike only. It will see lots of rocks, roots, some whoops, and narrow 2nd/3rd gear trails with the bars skimming bark off the trees. Rarely will it see a jump. I'm considered a to have a smooth riding style and don't bottom out very often. Basically an old fart in good shape. Running 2 marathons every year, last one took 3hrs 12 min.

James

 

[tonyr]

Gentlemen, I have read this topic with a lot of interest. I have a 00 200EXC with the same stack as drehwurm listed with the addition af a 18 x.2shim at the bottom, below the 10mm x.1. My question to drehwurm or james dean is: Have either of you rode the bikes with the mods that were mentioned? I too ride tight trails and I am very interested in how these mods worked. I had coinsidered similar stacks, but your discusion has me reconsidering what I was going to do. I would love to hear your comments.
BTW James your posts on the needle info has been very helpful.
Thanks Tony

 

[drehwurm]

Servus tonyr,

I have a 00 200EXC with the same stack as drehwurm listed with the addition af a 18 x.2shim at the bottom, below the 10mm x.1. My question to drehwurm or james dean is: Have either of you rode the bikes with the mods that were mentioned?

I've ridden a 00 200EXC and didn't like the forks at all - same with all the 00 KTM 2-strokes I got a chance to ride. The 00 4-strokes and all the 01 KTMs differ in one (IMHO a critical one) point from your bike: the bleed holes in the cartrige have been enlarged from 7mm to 8,5mm. So even if we have the same shim stack, the forks will work differently. Oil weight and brand is critical also.

James does have a 00 250EXC so his experiences should be more comparable than mine. Besides I'm still waiting on my shims to come. I'll post the results as soon I have them.

The 'shim' on the bottom normally works as a base plate - it should be thicker than 0.2 though. (we are talking mm here!)

Michael



[This message has been edited by drehwurm (edited 01-17-2001).]

 

[cp380sx]

On my '01 380sx forks all I have done is replace the soft .41 springs for stiffer .46 and they work great for MX. The faster you ride the better they work.

CP

 

[PT564]

Hey,

Where are you guys finding the best pricing on shims? I bought some from WER and they were a bit on the pricey side (1.39 ?).

PT

 

[drehwurm]

Servus PT564,

Take a look at http://www.ccycle.com/main.html

The offer shims for 99cents, but I have no experience with them.

Michael