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'10 KTM 450EXCR Deflecting Fork

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My 2010 KTM 450EXCR has a horrible deflection at high speed.  It is as if the fork totally stops moving halfway through its stroke.  It is ok on low speed trails.  The bike is actually the Champion's Edition which I believe means it has '09 valving.

 

I am 172lbs without gear and the bike has the 21L Acerbis tank.  I installed 0.48 springs which helped but they still have that deflection.

 

Shims are as follows:

 

10450EXCRBaseValve_zpsadf815c1.jpg

 

.25x16

.3x10

.1x12

.1x14

.1x16

.1x17

.1x18

.1x19

.1x20

.1x21

.1x22

.1x23

.1x24 x 7

 

10450EXCRMidampRebValves_zps6a9e4ce9.jpg

 

Mid from spring:

.4x11

.1x16

.1x18

.1x20 x 3

.1x18 x 2

 

Reb:

.1x18 x 3

.1x12

.15x16

.15x14

.15x12

.3x10

.25x14

 

Any suggestions?  What would the recommended oil height be?

Edited by bkoz

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No love for the OC WP'S?

 

How does the mid valve tie into the base valve on this fork?  Does the mid valve come into play after the low compression side of the base valve is activated?

 

Is it possible the mid valve is too stiff causing the harshness?  I tried running the compression clicker in and out trying to tune out the harshness and neither way made a difference.  

 

The specific problem I am having is when hitting a root or a rock in 3rd gear or so.  Instead of soaking the hit up the front end just deflects.  

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What springs did you ride before?

The stock springs would be just fine for your weight and woods riding.

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What springs did you ride before?

The stock springs would be just fine for your weight and woods riding.

 

The stock springs, either .42 or .44.  

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According to my notes, the stock springs are 4.6 N/mm, which would be 0.47 kg/mm.

 

Personally, I dont like the stacks you posted.

I would start from a new baseline.

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According to my notes, the stock springs are 4.6 N/mm, which would be 0.47 kg/mm.

 

Personally, I dont like the stacks you posted.

I would start from a new baseline.

As far as I know they are the stock stacks.  I have never touched them.  But I am the 2nd owner.  Do you have the stock stacks handy?  

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I do have the 2009 stacks and they are exactly the same as yours.

So I would say these are the stock stacks, yes!

 

How does the fork react to small trial trash like rocks, roots and such in 1 and 2 gear?

Does it also deflect or is it plush?

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I do have the 2009 stacks and they are exactly the same as yours.

So I would say these are the stock stacks, yes!

 

How does the fork react to small trial trash like rocks, roots and such in 1 and 2 gear?

Does it also deflect or is it plush?

Plush, the slow speed stuff is plush.  

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Try this:


 


BV


24 (6)


22


20


18


16


14


12


9.5 x 0.30


16 x 0.25


 


MV


18


20 (3)


18 (2)


12


16 x 0.15


11


Float 0.60mm


 


Reb


20d (3)


12


16


14


13


12


10 x 0.30


14 x 0.25


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Okay, I assumed that.

 

According to my notes the float height of your current setup should be 0.4mm, can you confirm that?

 

Plush, the slow speed stuff is plush.  

 

 

The stacks posted by cactusone are the latest EXC stacks with an altered midvalve.

I like these stacks more than the ones you found in your fork.

Try and finetune them!

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Okay, I assumed that.

 

According to my notes the float height of your current setup should be 0.4mm, can you confirm that?

 

 

 

The stacks posted by cactusone are the latest EXC stacks with an altered midvalve.

I like these stacks more than the ones you found in your fork.

Try and finetune them!

 

Ok, bear with me.  I have never measured the mid valve float and I thought I would post some pics.  In case other beginners are tuning in:

 

2014-02-10%2014.34.15_zpsmtddbt2m.jpg

 

Measured the height of the shaft where the shims ride.  I actually flipped the piston upside down and measured between the piston face and the shoulder

 

2014-02-10%2014.35.42_zpsq6xz0i34.jpg

 

Measured the depth of the piston recess = 1mm

 

2014-02-10%2014.36.54_zpsgquopujr.jpg

 

Measured the entire mid valve shim pack thickness

 

So: 2.55mm - 1mm - 1.15mm = 0.4mm

 

2014-02-10%2014.48.30_zpsl8jsodpc.jpg

 

I also did the feeler gauge check.  With a 0.406mm feeler on each side of the piston I got similar drag to checking valves.  

 

Any comments from the more experienced guys?

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Now just to compare cactusone's new and improved shim stacks to my crappy originals just to help with my learning curve.  Cactusone, I am not second guessing your shim stack. Just trying to increase my knowledge of the black magic.

 

Old bike breaker vs New and Improved:

 

BV

24 x 7                      24 x 6                      

23                           22

22                           20

21                           18

20                           16

19                           14

18                           12

17                           9.5 x 0.30

16                           16 x 0.25

14

12

10 x 0.30

25 x 6

 

Am I right in saying that the BV is softer on both the high speed and low speed?.  And is it correct that I will be replacing the six 25mm shims with one 16mm x 0.25mm shim?

 

MV

18 x 2                     18

20 x 3                     20 x 3

18                          18 x 2 

16                          12

                               16 x 0.15

11 x 0.4                  11 x (0.10?)

Float 0.4mm           Float 0.6mm

 

And the MV is softer.  And with the increased float that would mean that it comes into play later in the suspension stroke?  Or comes into play at a higher speed of fork movement vs the old stack?

 

To achieve the 0.6mm of float I would now have to replace my 11 x 0.4mm spacer with a 11 x 0.1mm spacer?  (7 x 0.1mm shims + 1 x 0.15mm shim + 1 x 0.1mm spacer= 0.95mm) (2.55mm - 1mm - 0.95mm = 0.6mm float)

 

Reb

18 x 3                     20 x 3

12                          12

16 x 0.15                16

14 x 0.15                14

12 x 0.15                12

10 x 0.30                10 x 0.30

14 x 0.25                14 x 0.25

 

The rebound will be slightly softer with the 1.5mm shims being replaced with the 1mm shims.  Am I right in assuming the 18 x 3 triangle shims are the same as cactus ones 20 x 3 triangle shims and I just measured them wrong?

 

I guess to sum it up the fork now has less MV compression and the MV will come into play later now.  The BV will now be softer and will be used sooner because of the changes to the MV.

Edited by bkoz

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Make the 16x1.5 and the 14x1.5 0.1 thick.

What is your measured spring preload? What is your oil level?

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bkoz: Very good analysis for a beginner! :thumbsup:

 

But its not 100% :rolleyes:

 

You are right about the base.

The mv and reb ist the tricky part.

The 2x18.1 on the OEM setup give you lots of freebleed on reb and comp, so the OEM reb stack is quite stiff to compensate for that.

The newer mv still has some freebleed over the 18.1, but is less than with 2x18.1.

However, I would use a slightly stiffer reb than cactusone recommened.

maybe like this

3xdelta

14.1

18.1

16.1

14.1

13.1

12.1

10.3

16.25

 

But I would use a 1.2mm bleedhole in the piston too and you use a stiffer spring!

So a stiffer reb doenst sound to bad, ha?!

 

The mv is a tuning paraemeter which is hard to judge.

There are so many variables to consider...

All you can do is to break it down to the individual components and compare them back to back.

 

However, I would give the stacks a try with a stronger reb.

 

As E-tech remarked, the preload and oil level plays a role too.

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bkoz: Very good analysis for a beginner! :thumbsup:

 

But its not 100% :rolleyes:

 

You are right about the base.

The mv and reb ist the tricky part.

The 2x18.1 on the OEM setup give you lots of freebleed on reb and comp, so the OEM reb stack is quite stiff to compensate for that.

The newer mv still has some freebleed over the 18.1, but is less than with 2x18.1.

However, I would use a slightly stiffer reb than cactusone recommened.

maybe like this

3xdelta

14.1

18.1

16.1

14.1

13.1

12.1

10.3

16.25

 

But I would use a 1.2mm bleedhole in the piston too and you use a stiffer spring!

So a stiffer reb doenst sound to bad, ha?!

 

The mv is a tuning paraemeter which is hard to judge.

There are so many variables to consider...

All you can do is to break it down to the individual components and compare them back to back.

 

However, I would give the stacks a try with a stronger reb.

 

As E-tech remarked, the preload and oil level plays a role too.

 

Thanks very much for that explanation.  The softer MV stack with the reduced bleed makes a lot of sense!  Will your rebound stack work without the bleed hole?  What is the advantage of the bleed hole?  

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Make the 16x1.5 and the 14x1.5 0.1 thick.

What is your measured spring preload? What is your oil level?

 

E-TECH are these shims in reference to the rebound stack?

 

As far as the spring preload I cannot find it in my notes anywhere.  I will have to recheck when the forks are back together.  

 

I was thinking of working with the stock 5w oil @ 110mm

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Try this:

 

BV

24 (6)

22

20

18

16

14

12

9.5 x 0.30

16 x 0.25

 

 

Cactusone, 

 

I will be heading to the local suspension shop today to try and sweet talk some spare shim's from them.  Just to clarify I will be replacing my original low speed six 25 x 0.1mm shims with one 16 x 0.25mm shim?  

 

Thanks

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You posted your original BV and Mid Valve stacks upside down. Cactusone has posted the stack the more common way starting with the low speed, then the hi speed and ends with a new 9.5x0.30 clamp and the 16x0.25 spacer.

He suggested a new BV that uses (6) 24x0.10 low speed comp shims.

Your stock base valve that you posted had (7) 24x0.10 shims, new low speed is one less shim.

Edited by Van Wick

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You posted your original BV and Mid Valve stacks upside down. Cactusone has posted the stack the more common way starting with the low speed, then the hi speed and ends with a new 9.5 x 0.30 clamp and the 16 x 0.25 spacer.

He suggested a new BV that uses 6x 24mm OD low speed shims.

Your stock base valve that you posted had 7x 24 x. 10 shims, new low speed is one less shim.

:banghead:  Thanks for the clarification.  

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1. Yes, the reb stack I posted will work fine with the bleedhole, bleedshim and stronger spring

 

2. the bleedhole gives some additonal freebleed and will make the responsive over small stuff. However, with the bleedshim installed some would say you dont have to drill it.

It's my way of thinking to say that a bleedshim does indeed add bleed, but a bleedhole makes it in a different way. To state i quite simple: the bleedhole cant flow more oil after a given rod speed whereas the bleedshim gives even more bleed. Hard to explain...

 

3. the suggested stack isnt softer as you current. its firmer! the 16.15 will provide more HS damping compared to your current stack, which can bent till it hits the tap.

You may want to get some additional shims to get the float of 0.6mm.

You are smart, you will figure out what needs to be done, dont you ;)

 

4. check all mv shims. some may be bent.

Edited by Vietze

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