shim shuffle - KTM WP forks

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#1
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

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#2
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

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#3
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.
 
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#4
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
 
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#5
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
 
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marcusgunby

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#6
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

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#7
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

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#8
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).]
 
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#9
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
 
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#10
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
 
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JTT

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#11
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

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#12
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.
 
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#13
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
 
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JTT

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#14
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.
 
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#15
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
 
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