Fork shim stack styles
- Thread starter jeffro847
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marcusgunby
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Hi jeffro as a bit of a way of making it interesting, what are your thought and feelings on the different types.Dont worry about any mistakes as we learn the most from these.
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- #3
Actually Marcus, I am unsure really.
I know in the past that the forks I had revalved were a single stack, and
I know this from when I cleaned them, changel the oil, and got inside there and checked it out.
Those forks worked reasonably well too.
My new bike now is a 02 YZ250, and I dont like dampening on the forks.
Is it a single stage stack or two??? I don't know yet.
I was gonna do the shims my self this time to experiment, have fun, and also save me 2 hundred bucks that I dont have to spend on forks right now.
I've been reading and reading and reading any post or website with info on different valving or shim stack styles.
It seems to me that alot of you guys go with a two stage stack.
Now from what I read on the Race Tech gold valve instructions, two stage stacks are softer and more for motocross/enduro/desert riding, and single stage is for agressive motocross/supercross.
What I want from my dampening is more bottoming resistance since I'm a big fast guy and my forks slam off bigger jumps if I over or under jump something....(I'm no pro, I make mistakes) It hurts my hands and wrists real good and I have to slow down afterwards...ouch...
I was thinking of putting in a single stack with an eye for more high speed dampening... thicker small shims(.15's or .2's) and .10's on the bigger shims.
I also got a suggestion to stiffen up the mid valve a tad to keep my forks from dropping into the travel too much over bigger bumps.
Oh yeah, I do have stiffer springs!!!
So Marcus, can I make myself a 2 stage stack thats supple for small breaking bumps and square edges, but nice and stiff for big air landings?
I know in the past that the forks I had revalved were a single stack, and
I know this from when I cleaned them, changel the oil, and got inside there and checked it out.
Those forks worked reasonably well too.
My new bike now is a 02 YZ250, and I dont like dampening on the forks.
Is it a single stage stack or two??? I don't know yet.
I was gonna do the shims my self this time to experiment, have fun, and also save me 2 hundred bucks that I dont have to spend on forks right now.
I've been reading and reading and reading any post or website with info on different valving or shim stack styles.
It seems to me that alot of you guys go with a two stage stack.
Now from what I read on the Race Tech gold valve instructions, two stage stacks are softer and more for motocross/enduro/desert riding, and single stage is for agressive motocross/supercross.
What I want from my dampening is more bottoming resistance since I'm a big fast guy and my forks slam off bigger jumps if I over or under jump something....(I'm no pro, I make mistakes) It hurts my hands and wrists real good and I have to slow down afterwards...ouch...
I was thinking of putting in a single stack with an eye for more high speed dampening... thicker small shims(.15's or .2's) and .10's on the bigger shims.
I also got a suggestion to stiffen up the mid valve a tad to keep my forks from dropping into the travel too much over bigger bumps.
Oh yeah, I do have stiffer springs!!!
So Marcus, can I make myself a 2 stage stack thats supple for small breaking bumps and square edges, but nice and stiff for big air landings?
bclapham
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hey jeffro, we have quite a bit in common here, sounds like we are both big, but unfortunately i am not fast! i am also doing some experiments with my yz250 forks. where abouts in CA are you, ive been riding gelen helen and cahuilla recently, maybe we should meet up.
i have gone (with quite some help:)) to bring the midvalve into play more and reduce the basevalving quite abit, for the reasons you talk about, i am waiting on engine parts though so i havent had chance to try the setup properly. i am in the good posiotion, in that before i started, i got a spare set of forks! so this should help me try out a few things very quickly.
cheers
Bruce
i have gone (with quite some help:)) to bring the midvalve into play more and reduce the basevalving quite abit, for the reasons you talk about, i am waiting on engine parts though so i havent had chance to try the setup properly. i am in the good posiotion, in that before i started, i got a spare set of forks! so this should help me try out a few things very quickly.
cheers
Bruce
marcusgunby
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jeffro im fairly sure your fork has a single stage, super stiff base valve and a single stage mid with loads of lift.It is similar in its setup to a 02KTM fork in some ways-and they ride similar as you have found.If it wasnt for the cylinder valve(acts as a bleed on the cartridge) IMO your fork would not move at all.
Onto styles of stacks-im not the worlds leading expert (by a long way)but i will try to tell you what i believe.
What ever stacks you use is not as important as if you are close on the base/mid valves and amount of lift on the mid vlave.On any fork on any terrian, its the valving that makes a fork to within 10% of perfection.The last 10% maybe achieved by different styles of stacks/pistons/special seals and bushes, cannisters etc.
So a 2 stage stack is generally used for woods and a single stage for mx/sx.My main concern is with a 2 stage stack you sometimes get the fork using a little more travel and so when it hits a large bump it will run out of travel.Jer uses a different setup called non independant cross overs.
eg
24
22
20
24
where as a nomal cross over looks like
24
24
24
12
24
22 etc
i think jers is probably the better way as i can see how the 2nd example may blow through the stroke more.
For simplicity im using single stage stacks that are lighter than my previous ones(i used to use 2 stage base and mid) so far im very happy with the performance.On the 03 KX they are close in performance to my previous 02 forks with low flow pistons.
Not that it helps but the YZ fork is all wrong as it comes from the factory.I would suggest you stick with the std midvalve(even though it could be alot better) and just concentrate on the base valving.Buy your self one of those 12v impact wrenches($20) go to the track and keep trying stuff till you make progress.Make big changes at first as you wont feel any difference otherwise.
Onto styles of stacks-im not the worlds leading expert (by a long way)but i will try to tell you what i believe.
What ever stacks you use is not as important as if you are close on the base/mid valves and amount of lift on the mid vlave.On any fork on any terrian, its the valving that makes a fork to within 10% of perfection.The last 10% maybe achieved by different styles of stacks/pistons/special seals and bushes, cannisters etc.
So a 2 stage stack is generally used for woods and a single stage for mx/sx.My main concern is with a 2 stage stack you sometimes get the fork using a little more travel and so when it hits a large bump it will run out of travel.Jer uses a different setup called non independant cross overs.
eg
24
22
20
24
where as a nomal cross over looks like
24
24
24
12
24
22 etc
i think jers is probably the better way as i can see how the 2nd example may blow through the stroke more.
For simplicity im using single stage stacks that are lighter than my previous ones(i used to use 2 stage base and mid) so far im very happy with the performance.On the 03 KX they are close in performance to my previous 02 forks with low flow pistons.
Not that it helps but the YZ fork is all wrong as it comes from the factory.I would suggest you stick with the std midvalve(even though it could be alot better) and just concentrate on the base valving.Buy your self one of those 12v impact wrenches($20) go to the track and keep trying stuff till you make progress.Make big changes at first as you wont feel any difference otherwise.
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- #6
Hey Bruce, I live in OC and ride mostly at Elsinore.
I used to ride alot at Saddleback too and Glen Helen sometimes.
Its over those big tabletops that if I dont land just right on the downside, my forks slam.
I even let my friend who is way smaller than me ride my bike and he could really notice my forks slamming through the travel...
I think with my big weight, I may have worn out the stock mid-valve shims.
Either way, I think my plan of stiffening up both should help the problem.
My concern though is how the bike will feel over the small choppy stuff.
After I stiffen up, I may be able to jump fine but my hands might hurt just the same from braking bumps.
I do have a idea though, make my forks stiff for going fast and jumping, and install Fasstco flex bars for the small stuff....... I just dont wanna spend 290 bucks for handlbars!!! Maybe after next years tax return...........
I used to ride alot at Saddleback too and Glen Helen sometimes.
Its over those big tabletops that if I dont land just right on the downside, my forks slam.
I even let my friend who is way smaller than me ride my bike and he could really notice my forks slamming through the travel...
I think with my big weight, I may have worn out the stock mid-valve shims.
Either way, I think my plan of stiffening up both should help the problem.
My concern though is how the bike will feel over the small choppy stuff.
After I stiffen up, I may be able to jump fine but my hands might hurt just the same from braking bumps.
I do have a idea though, make my forks stiff for going fast and jumping, and install Fasstco flex bars for the small stuff....... I just dont wanna spend 290 bucks for handlbars!!! Maybe after next years tax return...........
- Thread starter
- #7
Thanks for the thoughts Marcus.
I think what your saying is - I'm probably getting hydralic lock and that going stiffer wont help..... Maybe I'm wrong....
I do know that I tried heaver wt. fork oil and it helped alot.
7/10 wt. instead of the 2/5 wt.
Thats why I'm thinking stiffer valving.
Only the heavier fork oil only lasted a few rides before the performance diminishes.
Maybe I gotta change my fork oil after every other ride.
Either way, I'm gonna buy some shims from Mx-Tech and experiment with my valving.....starting with the base valve first.
Marcus, do you by any chance know what the stock YZ shim sizes are??
It would help to know before I order so I can buy different sizes and thickness shims compared to the stock stack... that and more of the same.
I think what your saying is - I'm probably getting hydralic lock and that going stiffer wont help..... Maybe I'm wrong....
I do know that I tried heaver wt. fork oil and it helped alot.
7/10 wt. instead of the 2/5 wt.
Thats why I'm thinking stiffer valving.
Only the heavier fork oil only lasted a few rides before the performance diminishes.
Maybe I gotta change my fork oil after every other ride.
Either way, I'm gonna buy some shims from Mx-Tech and experiment with my valving.....starting with the base valve first.
Marcus, do you by any chance know what the stock YZ shim sizes are??
It would help to know before I order so I can buy different sizes and thickness shims compared to the stock stack... that and more of the same.
bclapham
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if the 02yz250, is anything like the 01 yz250 and 426f forks that i have had apart, then yes, they probably have a quite stiff single stage basevalve and a single stage midvalve with lots of lift. the rebound is 2 stage, and identical on both forsk btw.
jeffro, how much do you weigh? have you gone up with your spring rates? have you added oil to help against bottoming? these are all things to think of before you hvae them apart.
and as for the bars, i this would be a bandaid fix rather than the source of the problem. i doubt you have worn out the midvalve shims though! it takes a bit more effort to get to them though if you want to modify the midvalve, but it did it OK first time, so its definately doable.
bclapham
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marcusgunby
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jeffro im amazed 7.5wt oil helped and also it went 'off' so fast.Good oil should last 20 rides at least.Im guessing your cv has gone soft and its bleeding off damping too much.As far as i know the 02 has a large midvalve lift and so it shouldnt be over stressing the midvalve shims.If its like the 02YZ250f it also has a 0.4mm plate before the midvalve shims to stop them bending too much.
Bruce makes some well thought comments :)
go for the basics and then work onto the harder stuff.
So you have 2 issues-one is the forks performance in general ie is it working like when new?
and if it is the same as a perfect working std 02 fork ,the valving/springs etc need adjusting.
Back onto 2 stage stacks
if you imagine the example i gave before
24
24
24
12
24
the three 24mm shims will bend over the 12mm shim fairly easy-so on small fast impacts the 24mm shims bend and give a supple ride, on a harder/faster hit the 24mm shims bend far enough to touch the 24mm shim under the 12mm shim.This then makes the damping as stiff as the 2nd stack and the 1st stack combined.
On a single stage stack all hits cause the whole stack to deflect/open and so even if you add some stiffness to the high speed part of the stack it will increase the low speed strength as well.People think in terms of HSC and LSC on a single stack stack, but really the 2 are almost inseprable.Increase one and you increase the other.And decrease one and you decrease the other.
Bruce makes some well thought comments :)
go for the basics and then work onto the harder stuff.
So you have 2 issues-one is the forks performance in general ie is it working like when new?
and if it is the same as a perfect working std 02 fork ,the valving/springs etc need adjusting.
Back onto 2 stage stacks
if you imagine the example i gave before
24
24
24
12
24
the three 24mm shims will bend over the 12mm shim fairly easy-so on small fast impacts the 24mm shims bend and give a supple ride, on a harder/faster hit the 24mm shims bend far enough to touch the 24mm shim under the 12mm shim.This then makes the damping as stiff as the 2nd stack and the 1st stack combined.
On a single stage stack all hits cause the whole stack to deflect/open and so even if you add some stiffness to the high speed part of the stack it will increase the low speed strength as well.People think in terms of HSC and LSC on a single stack stack, but really the 2 are almost inseprable.Increase one and you increase the other.And decrease one and you decrease the other.
bclapham
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what would cause the CV to go soft? how would be repair it, it looks well sealed to me!:)
i wonder if these forks just need cleaning- a proper clean by stripping down all the way, maybe there is just a load of dirt built up between the valving causing the forks to blow through the travel?
i wonder if these forks just need cleaning- a proper clean by stripping down all the way, maybe there is just a load of dirt built up between the valving causing the forks to blow through the travel?
- Thread starter
- #13
Thanks for all the feedback guys.
I got my bike used here in Dec. and it appears stock.
I already changed the oil the quick way(no dissasembly) and put in my stiffer springs.
But who knows??? Maybe something was done to it before....
I'll just have to take it apart and look at it.
This will be a fun learning experience for me amyway!
I got my bike used here in Dec. and it appears stock.
I already changed the oil the quick way(no dissasembly) and put in my stiffer springs.
But who knows??? Maybe something was done to it before....
I'll just have to take it apart and look at it.
This will be a fun learning experience for me amyway!
marcusgunby
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bruce is again right on:) could be all sorts in the base valve holding the shims open.
As for the cv going soft-well i have never seen one apart but it sounds like a shim stack in reverse(ie it is clamped on the od of the shim and the id bends)so after time the shims can 'set' and stay open.Also if any dirt has got stuck in them it might cause trouble.The CV if broken will i suspect cause big problems.Trouble is testing the cv sounds like trying to juggle sand.
As for the cv going soft-well i have never seen one apart but it sounds like a shim stack in reverse(ie it is clamped on the od of the shim and the id bends)so after time the shims can 'set' and stay open.Also if any dirt has got stuck in them it might cause trouble.The CV if broken will i suspect cause big problems.Trouble is testing the cv sounds like trying to juggle sand.
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- #15
Once again guy's, Thanks for all the input.
I still just really want to know about wich is a better style stack?
Or are there merrits to both styles.
Of couse, I want more bottoming resistance without hydrolic lock for my forks.
I'm really getting a lot of new info here from you guys.....thanks!
I still just really want to know about wich is a better style stack?
Or are there merrits to both styles.
Of couse, I want more bottoming resistance without hydrolic lock for my forks.
I'm really getting a lot of new info here from you guys.....thanks!
marcusgunby
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Yes both stacks have good and bad points so its not really a case of better.All suspension settings are a compromise.Its finding the least compromise.Your needs are very hard to meet as you want to get good air but still be able to pick up the small stuff.Thats a tall order.Also you need to ensure the forks are working properly before making a alteration, as otherwise the std shim stack will not teach you anything.I would strip them down, and if nothing is wrong try building a 2 stage stack for the base valve.
If you find alot of dirt holding the shims open on the base valve i would measure them and rebuild it, the same as std and give it a try.It maybe the performance of a good std fork is a good compromise for you.
The last alternative is to order up some self install kits, these are a big help as they give you the shim stacks and the backup advice if you dont like the results.
If you find alot of dirt holding the shims open on the base valve i would measure them and rebuild it, the same as std and give it a try.It maybe the performance of a good std fork is a good compromise for you.
The last alternative is to order up some self install kits, these are a big help as they give you the shim stacks and the backup advice if you dont like the results.
Last edited:
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- #17
Hey Marcus, I've been reading and reading and got to thinking......
What if I add a slow speed stack to the top of my stock valving?
It would give me more high speed dampening and maybe soften it up at the beginning of the stroke.
Am I thinking right on this?
24
24
24
12
????
What if I add a slow speed stack to the top of my stock valving?
It would give me more high speed dampening and maybe soften it up at the beginning of the stroke.
Am I thinking right on this?
24
24
24
12
????
marcusgunby
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You could give it a try and report back to us.
Everybody touched on some good points. Here is my two cents worth, touching on both Jeff's and JTT's questions.
Hope it's helpful.
Not much has been said about oil level. Oil level is critical in controling bottoming.
Two stage stacks offer a little more adjustability. The benefits are, you can adjust the low speed softer and the high speed stiffer than a strait stack. But, making the low speed softer doesn't always translate to a plushness. The forks push thru the upper part of the stroke to easily and then hits the middle.
With a single stage stack, you can target the low speed without effecting the high speed, (to a degree) and vise versa. Going to thicker shims doesn't target the high speed.
On the above mentioned two stage stacks, the 24mm low speed shims will make contact very quickly with the high speed shims if the separator diameter is 12mm, and the base shim diameter is also 12mm. (approx .004"), but if you go to a larger diameter separator shim the contact point becomes greater. (for example, .007" for an 18mm diameter and .012" for a 20mm diameter) This offers even more adjustability.
Hope it's helpful.
Not much has been said about oil level. Oil level is critical in controling bottoming.
Two stage stacks offer a little more adjustability. The benefits are, you can adjust the low speed softer and the high speed stiffer than a strait stack. But, making the low speed softer doesn't always translate to a plushness. The forks push thru the upper part of the stroke to easily and then hits the middle.
With a single stage stack, you can target the low speed without effecting the high speed, (to a degree) and vise versa. Going to thicker shims doesn't target the high speed.
On the above mentioned two stage stacks, the 24mm low speed shims will make contact very quickly with the high speed shims if the separator diameter is 12mm, and the base shim diameter is also 12mm. (approx .004"), but if you go to a larger diameter separator shim the contact point becomes greater. (for example, .007" for an 18mm diameter and .012" for a 20mm diameter) This offers even more adjustability.
marcusgunby
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Kevin it seems so strange for you to write in metric and imperial, at the same time-we will have to teach you guys how to go all metric;)jeffro the examples i gave were, on purpose not really specific(ie no thicknesses) and i wouldnt often use a 12mm cross over.I really didnt want to give actual stack settings as i feel it goes against the unwritten rule(which is no shim stacks asked for, or given)this isnt me bagging on you just explaining that i wouldnt use those shims i listed.
This is a little different question but still along the same lines as it has to do with the effect of adding/removing shims. On the midvalve stack on my '00 YZ250, let's say (since I can't remember the specific stack) is:
(2) .1X24
(1) .1X22
(1) .1X20
(1) .1X18
(1) .1X16
(1) .1X14
(1) .1X12
Now let's say that I removed the .1X16 (because it was bent when I bolted the whole mess back together without first checking that it was sliding down the spring guide).
What would be the general change in dampening and why?
(2) .1X24
(1) .1X22
(1) .1X20
(1) .1X18
(1) .1X16
(1) .1X14
(1) .1X12
Now let's say that I removed the .1X16 (because it was bent when I bolted the whole mess back together without first checking that it was sliding down the spring guide).
What would be the general change in dampening and why?
marcusgunby
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If you remove one leaf of a truck rear spring what do you think the change will be?
bclapham
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i will take a shot.
by removing one shim, the spring strength of the shim stack will be lesser and as consequence the damping will be lesser.
depending on which shim is removed, this will either decrease low or high speed compression.
now, back to the 2 stage.
the first part of the stack bends (LSC), it then bends past the crossover and contacts the shims that control the HSC which then bend. this is the part i dont quite get, but here is my take. becuase the LSC shims are bent further to contact the second stage, they essentially have more preload on them and as consequense this makes the second stage of the stack stiffer, thus we will still expect plushness with the first stage and the second stage will deal the big hits/fast impacts, so this might be a good thing for a heavier rider that is not that fast, plushness when needed, but the big weight off a jump is taken care of also.
so imagine this basevalve stack, a bigger guy, not that fast, likes the feel/ride, but on a good day he is riding better and the suspension isnt dealing with the bigger/faster hits
24.1(5)
22.1
20.1
18.1
16.1
14.1
12.25(clamp)
my guess would be 12.1 inbetween the 22.1 and the 20.1
where would we put the crossover and what shim would we use? (i suppose that is the million dollar question, and if you told me then you would have to kill me right?)
by removing one shim, the spring strength of the shim stack will be lesser and as consequence the damping will be lesser.
depending on which shim is removed, this will either decrease low or high speed compression.
now, back to the 2 stage.
the first part of the stack bends (LSC), it then bends past the crossover and contacts the shims that control the HSC which then bend. this is the part i dont quite get, but here is my take. becuase the LSC shims are bent further to contact the second stage, they essentially have more preload on them and as consequense this makes the second stage of the stack stiffer, thus we will still expect plushness with the first stage and the second stage will deal the big hits/fast impacts, so this might be a good thing for a heavier rider that is not that fast, plushness when needed, but the big weight off a jump is taken care of also.
so imagine this basevalve stack, a bigger guy, not that fast, likes the feel/ride, but on a good day he is riding better and the suspension isnt dealing with the bigger/faster hits
24.1(5)
22.1
20.1
18.1
16.1
14.1
12.25(clamp)
my guess would be 12.1 inbetween the 22.1 and the 20.1
where would we put the crossover and what shim would we use? (i suppose that is the million dollar question, and if you told me then you would have to kill me right?)
