02 KTM520SX - Playing with valving

Good day to everyone.
First, I'd like to take this opportunity to thank Jeremy and the entire DRN team for sharing their passion with us... I've been enjoying these forums for quite a while now, and I thought I could also share with you my latest experiments... This 1st post is going to be a bit long, but I believe it might be of interest for some KTM riders out there.

Well, here it goes. I'm the happy owner of a 2002 KTM520SX, which we all know doesn't have the best suspension settings in stock form. As I live in Cyprus for the moment (little island in the Mediterranean), I can't send my suspensions to Europe or USA easily for a revalve. There is no local suspension guru here either, so I decided to give it a try myself... first with the fork.

The stock setting of the fork is a real nightmare for me! The ride is very tiring. No plushness for the 'choppy' stuff, yet not firm either to handle hard breaking (front-end dive) or hard landings (bottoming). Yes, and like many other KTM riders, I have to deal with headshake too... Here are the specs:

The rider: 1m80 - 85kg - Fast intermediate
The terrain: Mostly hard clay, dusty, slippery, with rocks. Flat or bermed turns (no ruts) and a lot of man-made jumps.

The bike: With the stock valving and springs, I ended up with the following settings:
- oil type: ATF
- oil level 85mm (to fight bottoming, but it is harsh),
- external pre-load 1 turn IN
- LSC 32 clicks OUT (well, full 'soft'...which is not soft at all!)
- LSR 13 clicks OUT (a bit slow to compensate the high oil level)
- Front tire: Metzeler MC4 (intermediate) at 12 to 13PSI

Stock BV stack
(7x)24.1
22.1
20.1
18.1
16.1
14.1
11.25
18.25
Note: On both BV's, the needle circuit was partially obstructed (I would say as much as 30 to 40%) by the peening process on top of the nut. I had to drill it open to its original 3mm diameter. That could explain why the opening of the clickers didn't do much change!

Stock MV stack
Compression
(4x)24.1, with a lift of 1.5mm
Note: the 1st 2 shims (those that bottom against the rod end) were found heavily marked by the repeated impacts and bent.

Rebound
(4x)D.1 (D=delta shim, I think diam. 22mm... forgot to note...)
14.1
20.1
18.1
16.1
14.1
14.1
10.3
16.25

Now, I'm no suspension specialist. Not even close. So go easy on me here! According to data I collected in previous posts, it seems that I had to go in the following direction: better balancing BV and MV by
- softening the BV stack for more LSC control,
- reducing the lift on the MV stack so it kicks in sooner,
- strengthening the MV stack to compensate for the softer BV.

So not knowing really how to start, the 1st mod went like this:

Modified BV MV compression MV rebound
lift=0.5mm
(3x)24.1 (3x)24.1
14.1 14.1 (4x)D.1
14.1 14.1 20.1
22.1 22.1 18.1
20.1 20.1 16.1
18.1 18.1 14.1
16.1 16.1 10.3
14.1 10.5 16.25
11.25
18.25

I decided to set the oil level first at 105mm (ATF) and tested the bike this morning. I can tell you that I went real slow on the 1st lap. Man, I was scared to fly over the bar in the 1st turn!

Unfortunately, I didn't have much time to play a lot with the clickers, oil level and fork pre-load. But the results are not bad, not bad at all. Plushness is definitely improved. The bar doesn't 'vibrate' as much on choppy stuff and the ride is much less tiring. I also have now better control of the front wheel in the turns. It doesn't wash out so easily. I could take tighter inside lines without the front end jumping around and pushing me to the outside. I was also more relax in the breaking bumps or on a rough straight before a jump. Now, I can even feel how the shock works...

But bottoming resistance has not been improved.
I hope to test the bike again tomorrow on the same track. Now that the fork has more plushness, I can probably increase the pre-load and oil level and see how bottoming/plushness progress. We will see after that about the next valving mod...

In the meantime, feel free to share any remarks or ideas. I'll be back soon with more test report.

Oups!... sorry! The modified valving stacks did not show the way I expected in the above post. So here it goes:

New BV stack
(3x)24.1
14.1
14.1
22.1
20.1
18.1
16.1
14.1
11.25
18.25

New MV compression stack
New lift=0.5mm
(3x)24.1
14.1
14.1
22.1
20.1
18.1
16.1
10.5 (spacer)

New MV rebound stack
(4x)D.1 Delta shims
20.1
18.1
16.1
14.1
10.3
16.25

The second day of testing was really good. Same track, same conditions. It was not necessary to increase the oil level. I just increased the preload on the fork springs from 1 turn to 2 and than 3 turns IN. The fork remained "plush". Dive was reduced under hard breaking ... and I didn't experience any headshake at all! It is like riding a totally different bike!
I am sure I can benefit from stiffer springs (0.46kg/mm probably).

Bottoming resistance is quite good too. I slightly overjumped a table-top (length=15m, height=2.5m). The landing area is steep and short and the front wheel landed first just about 1 or 2 feet before the flat part. While in mid-air, I prepared myself for some pain upon landing, but it did not happen. The fork went through its entire stroke smoothly and barely bottomed.

I'll keep this setting for some time, at least until I hit a faster track where I can really test the high speed setting.

Considering my total lack of experience in valving, I really got lucky to find a setting that is "rideable" and, in my opinion, better than stock.

Now in theory, do those valving mods make sense to you?

Take care
Yoken

For the base valve, the idea of using the 0.2mm cross-over came from earlier posts . In 2000, an Austrian rider (Drehwurm) was trying different BV settings for his EXC... James Dean gave the idea but with
(2x)24.1
15.1
12.1

For the mid-valve, it is just pure imagination (except for the 0.5mm lift, which comes from you Marcus in previous posts). I spent several hours assembling different stacks and comparing them to the original one...hum... by pushing on the shims through the piston ports ...hum... with a toothpick! Now you are all laughing at me here, I am sure, but that is what I used to "feel" the different shim stacks.

Like you, I expected this kind of setting to be too soft and "divey" for my SX.
But I decided to try it and work my way up from there. It is just a surprise that it works well for me... on that particular track (medium speed, tight turns, hardpack, rocky. slippery, choppy, dried ruts...). I must try the bike on faster tracks now to have a better judgement.

Questions:

With 0.5mm lift and the 0.2mm cross-over in the MV setting, does the high speed stack have a chance to be solicitated? In other words, can the LSC stack have enough deflection to even reach the HSC shims?

Is a 2-stage stack a bad idea on MVs?
I don't remember reading any posts on that subject.

The original seating area of the MV shims is 14mm diameter (please correct me if I'm wrong). This is where the shims get in contact with the rod base when fully deflected. That 14mm diameter seat is a pretty large area for the 24.1 shims. There is not much room to flex. In order to reduce the lift, I have used a 10x8x0.5mm shim at the base of the stack and I assumed that the smaller seating area (now 10mm) would allow the stack to flex more and therefore offer more control. Does that make sense?

Why did WP use a 2-stage stack for the rebound?
In my opinion, the rebound stack is mainly related to the spring. The more energy stored (and consequently released) by the spring, the higher the damping. It looks like a linear relation and it sounds more like the job of a single-stage stack. What is your opinion?

Yoken

Originally posted by marcusgunby
i use a 12.15mm shim under the 11.2 thats fitted to the BV, this spaces the 11.2 to give the stack more room to flex.

Click to expand...

Marcus,
Do you mean a 0.35mm cross-over like this:
11.2
12.15 ???

Thank you guys for your input.

Drehwurm, thanks for the link. I remember reading it a few months back, but forgot about it when I set up my shim stacks... am an idiot!

Yes, the 0.2mm cross-over gives up a lot of control. It makes sense...
I need to hit faster tracks now before I can make further changes.
My problem is that I have never ridden a bike prepared by a specialist. I have absolutely no idea how it feels like. So I dont know what to target.

Now, similarly, may we consider that the 0.5mm MV lift gives up control too?
Could we envisage a MV without lift and a shim stack progressive enough to do the job?

Being overseas, I thought of buying the piston + other spares from Jeremy (he is no1 on my list so far). But I might move to the US (Nashville-Tenessee) in 6 months... looks like people ride a lot there! So I might have the chance to have Jeremy do his magic...

Take care,
Yoken