pyromaniac

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Jun 25, 2000
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I have had problems with my twinchamber forks on my bike being too harsh. I installed gold valves and set the recomended stack and it was a big difference but still too harsh. I already ran almost the softest setting and it was bottoming so i though i couldnt go softer. But today i went out of the valving chart and made my own stack. I added more oil in hope it wont bottom but yet be soft in the 1/2 on the stroke. Havent tried in on the track yet.

I also changed the low speed "base plate"(i forgot its name) that is the same size and thickness on every stack. From .15mm thick to .10mm. What i have done i dont think is recomended as no setting is like this so i would like to know what i have really changed. What aspects on the suspension do the different parts affect? Can i get a very plush 1/2 of travel and yet not bottoming and being overall good by doing what im trying to?
 

marcusgunby

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Jan 9, 2000
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Dont be afraid to experiment and make big changes-ive heard of people saying the RT stacks are too stiff-your use of 0.1mm shims will make it a good deal softer-which is what you want-get the desired plushness and then add oil to prevent bottoming.
 

dbrace

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Oct 30, 2002
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If it is the clamping shim (the bottom shim on the stack) that you have changed from .15 to .1 it will make the stack harder.
 

marcusgunby

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dbrace is correct-i didnt read it well enough-you should always use a thick clamp shim.This allows the stack to flex over clamp but not hit the valve body.
 

JohnScott

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May 22, 2001
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Marcus, I've been playing with my shims recently (RT GVs). I use a 18X.5 as the clamp shim. But, above that, I am thinking of trying a 12X.25 instead of the normal 12X.15. What effect will that have? I was thinking it would make the whole stack softer as it gives the entire stack .10mm more room to flex, or open. What do you think?

John
 

bclapham

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Nov 5, 2001
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john: if you are using a 18.5 clamp shim (more like a washer) i cant see how putting anything above that will make that much difference- even if in theory the shims have got 0.1mm room to bend, thats not a lot on the yz forks- like running 0.5 vs 0.6 mm lift.

as for the twin chamber forks, i am a bit tentative on a RT check plate set up- my rm forks have gone from OK to terrible to excellent with only a couple of shim changes on the midvalve.
 

marcusgunby

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Jan 9, 2000
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I think we are getting confused with clamps and spacers-the clamp is the last shim in the stack that the stack bends over-in scotts case this is a 12.15, i think in scotts case i would increase this to a 12.25 or even 12.25(2)
to give the stack room to flex-alot depends on the stack build-a stacks with all 0.15mm thick shims will probably not bend over the clamp shim and touch the base-however a stack something like
24.1
22.1
20.1
18.1
16.1
14.1
11.2
will possibly bend over as the 14 is a big jump up from 11.

To be sure i would always use a clamp at least 0.25mm thick and often double them up to 0.5mm thick.
 

pyromaniac

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Jun 25, 2000
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The shim i was referring to is the one closest to the valve. It doesnt make sence if a thinner one would make the forks harder since in the chart they add more .15 shims to make it harder.

I would think the low speed stack acts when the oil is passing slow through the valve and when the oil is going through faster it starts to bend the high speed stack aswell. But is there any difference changing a big shim rather than a small shim or is it the total resistans the onlything that matters? Does the midvavle still have ANY affect after doing the "midvavle mod" recomended by racetech?
 

marcusgunby

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Jan 9, 2000
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The shims closest to the valve have a huge effect-a 0.1mm shim is three times softer than a 0.15mm-so if you are after a softer stack this is the way to go.
We were getting confused with the terms-in my example the 11.2 is the clamp and the 24.1 is the one that touches the valve.

On the question of big or little shims-the little ones are termed high speed and the large are considered low speed-so you need to decide which ones you are having problems with-high or low speed.And make the appropiate changes.

Once you do the RT mod the mid isnt considered part of the damping.
 

pyromaniac

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Jun 25, 2000
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Its now even softer but still im not happy with it. Its still harsh in the top stroke while the mid or last part of the stroke feels almost too soft. When i last from jumps it feels like it almost bottoming and doesnt absorb much. What can i do about it?

Its far away from the bikes i've ridden with good suspension. They feel almost "swampy" compared to mine, yet no hard landings. Like the '04 cr250f, really nice suspension. I want mine like that. They feel like its floating on the track while im bounching. Im gonna talk to a suspension company tomorrow and hear if im gonna get it revavled, front and rear.
 

marcusgunby

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Jan 9, 2000
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its still confusing what changes you have made, why dont you post the stacks you have used and how they felt and members can look over them to give guidance.
 

pyromaniac

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Jun 25, 2000
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Originally posted by marcusgunby
pyro could you list the stacks as i dont use the charts myself.

Sure, i just didnt have them in my head at the time.
All are 0.10mm thick from the vavle and out:
21
12
21
17
14
13
12
11
9
 

marcusgunby

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Jan 9, 2000
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pyro, yours is a 2000 model which i have never worked on or heard about, but i remember them to be harsh std.Your valve stack looks soft enough, so why is it firm to start with then blow through the travel?? it could be too little low speed damping but you had more before-so lets discount that, you have fitted new bushes and so thats not the problem.I think you have looked into fork alignment previously as this is what i would think of next.

I would ask you to completely stip the forks and inspect them very closely-maybe you have done this already. If so im at a loss as to what the problem is.

Another thing to look out for on the RM forks is the rebound is very fast at the top of the stoke-it uses a big bleed and so they tend to pogo a bit, i have tried going to 3 clicks out on rebound and it didnt feel any different.
 

terry hay

Member
Nov 8, 2003
200
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pyro
your dilemma is not an uncommon one for twin chamber forks. Your attempts to find a solution will only result in confusion unless you include more info. How much do you weigh? What type of riding? Oil weight and height?
Originally posted by pyromaniac


Sure, i just didnt have them in my head at the time.
All are 0.10mm thick from the vavle and out:
21
12
21
17
14
13
12
11
9
 

pyromaniac

Member
Jun 25, 2000
378
0
Im around 63kg. I ride motocross, 5w oil, level is just above the "shulder". The twin chamber is two separate systems where the oil isnt shared right? How does the oil level affects the action in the two systems?

I'm seriusly thinking about getting both forks and shock tuned by a suspension company. They will change the "cone" as he explained it, in the forks. They want $510 and it should be a huge difference if im gonna be happy with it.
 

KTM-Lew

Member
Jan 26, 2002
428
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The oil level in the "outer chamber" is what controlls bottoming. Maybe your oil-level is too low?

I just noticed you list 5wt oil.....I thought they used 2.5wt in the inner-chamber? The heavier oil would be 'harsher' on little stuff than the 2.5wt. If you have removed the mid-valve and changed to a check-plate it will tend to blow thru the stroke very easily...maybe that is why you think it feels harsh.

I would put an o-ring on 1 of the tubes to indicate travel used and then just split your next ride into sections. Do a track section that you have previously felt the fork was harsh and see how much travel it is using. Is it using 7" of travel on 4" bumps......and so on. Or you could have someone video you and watch it in slow motion......that is probably the better way.

I am very interested in what you find as I have a set of 96 model forks, they have essentially the same internals, that I will be trying for off-road use. :think: :scream:
 
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pyromaniac

Member
Jun 25, 2000
378
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The "cone" is probably not the bottoming cone as it would cost $70 buck extra to the rebuild. Its probably the tube reparating the two systems.

I added a little oil in the innertube to prevent bottoming and it seemed to help but i should have added in the outer tube i guiss. Well i guiss i can change to 2.5w in the innertube and add more oil in the outer to prevent bottoming but yet i dont think it will help me too much.

I dunno quite how to explain the problem, i can feel small bumps and stones no matter where in the travel the forks are in. Yet its not like its too much compression. I would think this is the result you would have if you had alot of stiction but i cant see that i have that.

The oil level should be just above the "shulders" in the innertube right? What effect would it have if i remove some or even pretty much oil, like 5cm?
 

russ17

Member
Aug 27, 2002
301
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Pyro
I think if you are using the GV with the stack you have posted. It is a very light stack for a high flow piston and feel are blowing through the stroke. Also with the very little low speed that you have posted you are in all reality riding down in the harsher part of the stroke and thats why you are feeling this on small stuff IMO.
Russ
 

KTM-Lew

Member
Jan 26, 2002
428
0
From what I understand, the oil-height in the inner-chamber has to be right at the shoulder......if it is lower it could suck air (foam the oil). The inner chamber is basically a long shock stuffed inside the outer tubes. There shouldn't be much room for error on fluid quanity/level.

I agree with Russ that with no mid-valve and the very light stack you are probably riding too low in the stroke......that's what i was trying to say in my last post. :silly:

They probably ARE refering to changing the bottoming cone. :thumb:

My problem with these is I don't understand what the IC spring does?
 
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russ17

Member
Aug 27, 2002
301
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KTM- Lew
Think of the TC as a shock. on a shock the gas pressure aids in resistance.
The Ics spring acts in the same manner but in a machanical manner.
Russ
 

KTM-Lew

Member
Jan 26, 2002
428
0
Russ

Ok....got it! That's why the compression assembly is so tough to get back in. When you are pushing it in the TC spring is resisting. A lighter spring would be like lowering the pressure on a shock.

I had the comp assemblies out to see what shim stack it had. Thought the forks had been done by FC but apparently they hadn't as the nuts were still peened. Changed the clamp from a 9X.20 to an 8X.20. I want to try them before I completely tear them down.

Thanks :worship: :thumb:
 
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