fork tuning for enduros

Taffy · Oct 18, 2006

the latest shimming is available on the ktmtalk.com site. they have long threads on it already. i also have found that the shim nearest the piston is the first to lose it's shape!

however, i have now done two sets and it's only the 'check plate' set up (same as you 4 x 24)that has had the trouble. the ZP3 set up is now on two bikes and i'll soon know whether it does the same with that set up.

thanks for getting involved. it's always nice to have someone else's view.

regards

Taffy

Smorgasbord · Oct 19, 2006

It was not that easy to find out about the latest ÃƒËœ14 piston rod OEM shimming. They are all on about the ÃƒËœ12mm piston rod shimming now. If I get it right the ÃƒËœ12mm produces higher cartridge pressure for the same damping force,which would allow a higher share of the load to be born by the MV than with the old ÃƒËœ14 rod. And that exites them.
Not on that level I'll try something with my old stuff to see what it does and with some luck learn something.
Going 2006 OEM to start with, plus the free mods two holes and MV tap, and only then changing things just one thing at a time.
BV will be the easiest to reshim as needed. MV would theoretically be done within in an hour in the garage without removing fork legs from bike, or dropping much oil, at least after some practice.
Spring is stock and may be the right choice for my lanky corpus.
Maybe something like this:

BV, in the table is the 2000 OEM shimming, new is an Idea that I had, and there is the 2006 EXC OEM shimming (mikst).
The table is aligned at the breakover shim so that low and high speed stacks can be compared directly, respectively. All shims in the BV are .1mm thick and with a ÃƒËœ6mm hole unless otherwise noted.
2000 /new1/2006
- / - /24
24/24/24
24/24/24
12/12/14
22/24/24
20/24/24
18/22/24
16/18/22
14/14/22
12/12/20
10.3/10.3/20
18.2/18.2/18
- / - /16
- / - /14
- / - /9.6
- / - /18.28
BV post

Rebound stack:
This is the 2000 OEM rebound stack. I was thinking in terms of keeping it, but might just as well uppdate to the latest stack to get a proven starting point. There seem to be a lot of consensus on the 2006 stack, VIKINGs notes in this thread on how to manipulate cornering beaviour with the rebound stack are very interesting. While people have exprimented a lot with compression stacks and each found their own favourite, there is little to be found on rebound stacks. All shims are .1mm thick and with a ÃƒËœ6mm hole unless otherwise noted. "d" for delta.

2000/2006
Piston
24d/24d
24d/24d
14/24d
22d/24d
20/16
18/20
16/18
14/16
10.3/14
16.25/10.3
- /16.25
nut

MV:
All MV shims are .1mm thick and with a ÃƒËœ8mm hole.
Piston
old/new
24/24
24/24
24/24
24/24
-/22
-/20
-/18
Aiming at a 1mm play or less, not totally sure yet. If much more free play it will become a second high speed stack.

The free mods:
Will do a mod turning down the rock solid ÃƒËœ16.5mm outside the coil spring to a level 2mm lower than the central ÃƒËœ10mm, as contrary to the present same level. Updating the MV stack is pointless unless the tap is modified to look like the new ones.
The bypass holes will be left alone.

Might drill the two additional holes in the chrome for the internal venting of the fork bearing inclusion. The four large holes under the lower leg bearing bushing will easily let out air from the inclusion, the two mod holes are probably to drain some of the pressure/suction caused by hydrodynamic drag as the lower leg moves?

Thanks for the inspiration Taffy, VIKING, ktmlew and other gurus.

No idea where this is going to end.

ktmlew · Oct 20, 2006

Last try...

Stock 04 200SX forks

24 X 0.1
20 X 0.1
18 X 0.1
16 X 0.1
14 X 0.1
13 X 0.1
11 X 0.1
9 X 0.3
18 X 0.25

Mid-Valve

Stock-Float 0.61 mm
24 X 0.1
24 X 0.1
24 X 0.1
12 X 0.1
22 X 0.1
20 X 0.1
18 X 0.1
16 X 0.1
11 X 0.1
11 X 0.2
11 X 0.2
11 X 0.2
22 X 0.1

Rebound (D=Delta shim)

Stock
24D X 0.1
24D X 0.1
24D X 0.1
24D X 0.1
16 X 0.1
20 X 0.1
18 X 0.1
16 X 0.1
14 X 0.1
10 X 0.3
16 X 0.25

I suspect this is a pretty darned good stock fork aside from the triple bushings?

ktmlew · Oct 20, 2006

What the hello is with the "alien's in my post?

LeFrog · Oct 20, 2006

Add a space somewhere. It's just recognized as an imoticon.

Smorgasbord · Oct 20, 2006

I got a mail with some very good advice. Thanks!

:thumbup:

The pictures are from Taffys "the Doc". On the left the zp3 modified. On the right a "later model" piston tap. Looking from the top. the first step is the one that the piston rest against. The second step is what the MV shims will rest against during compression.
The third step (with the hex) may be what is limiting the MV shim stack flexure during hard compression hits. What years are the ones of the right model? On my old 2000 WP43 the third step is flush with the second, causing immediate limiting, letting only the 4mm of shim sticking out flex under the pressure and flow. Not very much different than a solid CP I suspect. It looks like the third step on the tap is about 2 mm lower than the second step. Is that right?, Is it possible for anyone to check it?

This piston tap third step looks like the one on the right hand side above.
I Might modify to the later tap before going all the way to zp3. That way there are greater numbers of tried stacks to consider. Also, zp3 beveled the second step, letting the shim stack bear on the very inner edge of the poor shim already being battered by the valve and getting sucked out of shape by the ports in it. While gaining some minor flexure I have not hardened my heart enough yet to be able to do it, poor little shim.
Another thing, everyone seems to run a lot heavier return stacks than the ones in my forks. IÃ‚Â´ve been quite happy with them as I like a fast return but if they could hold back rebound just a little bit more after the forks are returning from fully(ish) compressed I'd be even more happy not getting sent aloft to such heights. That is why I was on about adjusting the ceiling height shim thickness to control rebound "speed limit". The newer shimming might do just that? Regards and thank you all gurus.

ktmlew · Oct 20, 2006

I finally got the other post to work. I'm not a fan of the 23mm shims on the mid-valve for ZP's mod or only running (2) shims. There is another way to get the pivot even smaller...

Smorgasbord · Oct 20, 2006

The ports in my piston are at ÃƒËœ22.7mm. That leaves a 0.15 overlap radially with the ÃƒËœ23mm shims. You don't know how little 0.15mm is. Two layers of paper. I do not trust them to be that well centered and do not dare to use ÃƒËœ23s, they'll likely get sucked out through the valve ports. The same goes for the BVs. I'll stick to ÃƒËœ24mm.

ktmlew said:
There is another way to get the pivot even smaller...

Yes there is!, when you think of it, you clever man! Why didn't I think of that myself?
I do not really know your actual solution to the problem but was thinking that if you put an o-ring on the second step it would support the shim more kindly and flex to make the shim look like it was pivoting somewhere INSIDE the ÃƒËœ8mm tap! You'd have to machine a nice seat for the o-ring or use a suitable flat rubber washer instead of it. Or remove the second step and replace it with a stiff short spring.

But why would you like to decrease the pivot dia.?

Regards.

Taffy · Oct 20, 2006

smorgy

in the second page of this thread i believe that viking lists all the changes to the forks over the past 6 or so years. it reads like the man never takes a breath but it is there!

i asked my engineer to copy the photo and what i found was that he machined the first shelf - the one for the piston. leave this alone and you'll have float of about .5mm which isn't enough. most make tiny shims that are 6mm id - 8mm od and use them to stack out the float to get it right.

i'm currently on 1.25mm and i think that even if people disagree - it's still a good start point. viking likes 1.5mm and many others like 0.8 - 1.0mm like ZP3 himself does.

nice to have you over here lew...

regards

Taffy

ktmlew · Oct 20, 2006

Taffy said:
smorgy

in the second page of this thread i believe that viking lists all the changes to the forks over the past 6 or so years. it reads like the man never takes a breath but it is there!

i asked my engineer to copy the photo and what i found was that he machined the first shelf - the one for the piston. leave this alone and you'll have float of about .5mm which isn't enough. most make tiny shims that are 6mm id - 8mm od and use them to stack out the float to get it right.

i'm currently on 1.25mm and i think that even if people disagree - it's still a good start point. viking likes 1.5mm and many others like 0.8 - 1.0mm like ZP3 himself does.

nice to have you over here lew...

regards

Taffy

Bonk, Bonk, Bonk my head against wall...something is wrong...I understood all of this as I usually need this when taffy speaks! :shock:

Taffy · Oct 20, 2006

ha ha ha ha !!!

well it is rare for me i know!!!

regards

taffy

ktmlew · Oct 20, 2006

Smorgasbord · Oct 23, 2006

The WP 2000 CP on the tap. Not much shim sticking out that can bend really.

About to cut down the CP support 2mm.

On the left the 2000 OEM piston tap, on the right 2mm removed from the CP support ring and the hexagonal part beveled 30 deg.

It was fun removing material so I decided to bevel 45 deg.

Now at 45 degrees the bevel would allow even more shim stack flex. Not that I think they are ever going to flex that much. The old one to the right for comparison.

Finished former Husabergh 2000 OEM now modified to resemble modern taps. And a bevel on the hex, almost like the zp3 mod but not quite.

The modified tap with the CP on it. Lots of freedom for the shim to flex. And yes, it IS Taffy in the background!
Does the coil spring fit in the recess without interfering with the shim stack at full storm? The answer is yes, but there is no picture showing it.

Taffy · Oct 23, 2006

smorgy

if you get the chance could you do a DEFINING measure of the difference in height between the inner post shelf and the outer ring over the hexagonal nut. you'll need to put together a shimstack first and measure the float. only i haven't got a defining measurement.

regards

Taffy

Smorgasbord · Oct 24, 2006

Taf, here are some dimensions taken on my 2000 OEM piston tap.
First shelf to second is 3.6mm, second to third is now 2mm (was 0mm). On the first shelf there was a D8 d6 t0.3mm washer, didn't see it at first until it fell out of the piston body recess, the other one, from the other fork leg, had to be pryed out with a scissors. The depth of the piston recess is 2.08 on one side and it reads the same on the other fork leg. It may have been supposed to be 2.1mm and I'm not accurate to anything better than .02mm using a vernier (nonie) caliper. Anyway, the gap for the stack to play freely in will then be 3.6 + .3 - 2.1 = 1.8mm, minus the thickness of the stack then of course, which was 4x.1mm, and that leaves us with a 1.4mm free play. And luckily, that's exactly what it was found to be when measured before it was all taken apart!

Regards

Edit: The two ***** Miss Pelling and Miss Typing were here and an attempt was made to chase them out, at least to get the numbers right.

The gap is 1.8mm.

Taffy · Oct 24, 2006

smorgy

then what i suggest is the same as they do on k-talk and that is that we recommend a gap between the ledges of 3.5mm. with a recess of 2.08 and around 4 x .1mm = .4mm that means the float would be 1.0mm which is accepted as the minimum.

to pack the float out (to the largest float i've heard of as being 'right' (1.5mm) people can add shims inside the piston recess. in general it's around 1.25mm. i had zero float and luckily a ring of 1.3mm solder tapped in the recess beautifully and i now have 1.3mm float checked after the solder was tightened down!

by the way the english is vernier caliper.

thanks smorgy. keep up the good wrk and i REALLY, REALLY, REALLY hope that we can give good feed back here as we set up the suspension. don't forget to add your weight, bike and year each/most times.

you never know, viking might even get involved again although i think he's probably disgusted with me!!!!

ANON
while i'm here i'll mention that after two tests (although on 43mm and at that a katoom 520) the 34mm top out springs have been a nice success! i can feel them on flicks and switchbacks giving a softer feel to the front wheel. can't say it's made me quicker coz i'm on a new machine but when i test them on mine soon then i'll have double the confirmation!

the 520 is an '02 and has as said 43mm fronts and the PDS rear. the bikes are a similar weight but the shock angle is different on the rear.

so far i've tried the old 81/99 PDS8 i had and it was better than the standard PDS2 at 75/97 and this last weekend i tried a straight 95. the spring is made by the same people who make the WP springs even though WP don't make this spring for their catalogue. the katoom only has one rear comp and not LSD and HSD. it felt a lot stiffer, which it will as i've gone up two sizes essentially. (the PDS's went up 5 each time from 71 to 76 to 81 to 85.5). i may get the PDS4 off my bike and do a straight back-to-back this weekend, my last race of the year.

on the front, i have essentially copied my own forks but haven't done the drill mod, have gone 24, 24, 18, 14 on the MV. the rest is essentially the same bar the springs which can only be bought up to .046s (again from k-tech here in the UK and made by the same people as WP get them done by).

the forks are very good but i'm only just getting the clicks right having added oil to get a 125/130 air gap. after this sunday i'll know where we are.

regards

Taffy

VIKING · Oct 24, 2006

Hi taffy
No i am not disgusted with you Ive been too busy to chat got a new bike so there is
allot of details fix and this weekend is the 25 hour race this just takes time
the new fork is very good stock it is as good as a 06 showa and it is better in slow speed
the new frame geometer perhaps plays a part in the good feeling
the frame is much better in down hills than the 04 it feels like 00 FC501 but with better
steering
there is only so much you can do with the MV with out sacrificing reliability
I looked at Ktalk the other day and ktm lew made some recomdations on shim stacks for the new 07 fork that looked like too drastic change for a fork that is decent
that said I don't know what berg fork have but I have a suspicion that they are fairly
close in shim stacks
so long VIKING

Taffy · Oct 24, 2006

viking and all?

has the frame geometry changes again for '07? i'll have to check up on the details of the '07 model sometime. more bloody effort required!

regards

Taffy

Smorgasbord · Oct 25, 2006

The swing pivot point lowered, at least so i've heard.

ktmlew · Oct 25, 2006

VIKING said:
there is only so much you can do with the MV with out sacrificing reliability.

I looked at Ktalk the other day and ktm lew made some recomdations on shim stacks for the new 07 fork that looked like too drastic change for a fork that is decent that said I don't know what berg fork have but I have a suspicion that they are fairly close in shim stacks so long VIKING

I was shooting from the hip and completely missed the target!!! My boss is riding his 07 300XC box stock with only a change to a 8.0 shock spring. He says he weighs 205 but I think it's closer to 235!

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