Fork Revalving - Shims and Stacking

[James_Dean]

I decided to pull out the fork compression valve on my '00WR to see what the shim stacking arrangement was. Thought that you guys might like to know and maybe give a little insight as to what it does. The forks were removed and turned upside down to remove the valve without a complete disassembly. ?

The shims are flexible washers that cover the holes in the compression valve and provide speed sensitive damping. The faster the fork compresses the more the washers flex to let oil flow through the valve.

There are 2 sets of shims. The one closest to the valve is the low speed (LS). There is a small diameter "crossover shim" next and then the high speed (HS) stack. The low speed stack flexes at lower speeds up to the point where it bridges the crossover (spacer) gap and starts to push on the HS shims - at faster fork compression speeds.

----------------------------------

Starting from the compression valve -

6 LS shims - 24 X .1mm

1 shim - 14 X .1mm (crossover)

HS shims - 24 X .1mm

22 X .1

20 X .1

18 X .1

16 X .15

14 X .15

12 X .15

11 X .26 (base shim)

Backing plate 18 X .5

--------------------------------

I'm looking to soften the ride over rocks and roots for woods riding this winter. The plan is to reduce the HS stiffness and a little bit accross the range. I will also raise the fork oil level 1/2" to compensate for the decreased damping.

-----------------------

Pulling one or more from the HS stack is a start. A good option would be to remove the 16 X .15. But instead I will pull out and reuse the 12 X .15.

Adding space to the crossover pulls the HS further away from the valve which lets it open more freely. So to do this I plan to move the 12 X .15 into the crossover gap.

This also makes a smaller support for the LS shims. They will then overhang the crossover by 6mm instead of 5mm ( (24-12)/2=6 )

---------------------------

Proposed stack:

6 LS shims - 24 X .1mm

1 shim - 14 X .1mm

1 shim - 12 X .15 (added this as a crossover)

HS shims - 24 X .1mm

22 X .1

20 X .1

18 X .1

16 X .15

14 X .15

11 X .26 (base shim)

Backing plate - 18 X .5

----------------------

It takes one shim to make a big difference.

Any one else tried to do any revalving on your WR or YZ?

It would be interesting to compare.

James Dean

[This message has been edited by James Dean (edited 11-13-2000).]

[James_Dean]

See www.ccycle.com/main.html

For a view of a damper in motion look at the shock demo.

The compression stroke side has 2 crossover shims if you look close. The rebound side has 1 crossover shim. The low speed shims are shown in black when it stops.

[Drehwurm]

Servus James,

I think it is not only the shims which cause the harshness on fast movements with the WR fork. One limiting factor for the oil flow is the valve design itself (I had great success with Gold Valves) and the "mid-valve". It doesn't help softening the hs-comp on the base valve, when the mid-valve is not modified! As I said, the Gold Valves did wonders to my forks (98 WR400) and there is still room enough for experimenting for guys like you ;-)

BTW, when installing the Gold Valves the mid-valve is disabled!!!

Michael

[James_Dean]

Michael,

Have you tried lowering HS compression without altering the mid-valve or was this something from another source?

The ports on these valves are shaped much different than years past. Nice round and contoured, not that they will flow that much more at high speeds.

I have had Race Tech Gold Valves before and found that they still needed some altering from the recommended settings. Suspension performance is very rider specific.

James

[William]

Hello, Dean, thanks for the info i fully understand the only part i don't understand is the part after you said, " i decided "

------------------

2000 WR400F

2000 EC 300

2000 TTR 125L

2000 TTR 90

1999 750 Katana

[James_Dean]

William,

Glad you got that part ?

James

[Drehwurm]

Originally posted by James Dean:

Michael,

Have you tried lowering HS compression without altering the mid-valve or was this something from another source?

I'd better be careful here, because I put in the GVs as soon as poosible after I got the bike. There was a feeling like hitting a hydraulic stop in the forks when going over sharp edges and this was completely gone after installing the GVs. Even though the shop who did the installation put in way too much HS-comp at first. After a recommendation from MX-Tuner I reduced HS-comp way down and have been a happy camper since.

Since then I've ridden a 1999 WR400, 2000 YZ426 and 2000 Yz250 on my home track and all of those forks had the same 'hydro lock' effect. So I figured it must have to do with the mid-valve. Nevertheless I've no proof!

Michael

[Guest Guest]

The problem is the mid-valve. My shop removed the mid-valve completely and now the forks are silky smooth in the woods.The total cost of the re-valving and re-assembly was $150 Canadian (dirt cheap).

[James_Dean]

Willy,

Are you certain the compression valve was left untouched? The compression valve has to come out to get the mid-valve out.

The 2 damping circuits act independently and in parallel. If either is harsh, altering the other will not cure the problem. If it is the combination of both, then either one can be altered.

Taffy had to go back and have his GV's redone because it was still harsh on the first setup. Not sure how much??

[Outlaw]

James,

I think all this talk of shims, crossovers, et al is just a bunch of hooey and that yer' just trying to confuse everyone.

Me, I just drained my forks and put in automatic transmission fluid. It should work really good when I go riding tomorrow. Probably run away from that WR you own.

S.

[James_Dean]

Went riding with "Outlaw" today and the forks worked really well. Found myself flinching for sharp rocks that used to give me trouble, but not today. The forks weren't mushy but had excellent control with less harshness. Allowed me to look further ahead and increased my speed a little while keeping it upright all day. ? Hung in there with the KTM 520's all day, except when the WR stalled, that KTM E-button's not fair!

--------------------

Shim stack was:

5 shims - 24 X .1mm (1 fewer LS shims)

1 shim - 14 X .1mm

1 shim - 12 X .1mm (new and smaller)

HS shims - 24 X .1mm

22 X .1

20 X .1

18 X .1

16 X .1 (new softer replacement)

14 X .15

12 X .15

11 X .26

18 X .5

This was an easy change to make by pulling the compression valve out the bottom with the fork upside down..

James

[This message has been edited by James Dean (edited 12-05-2000).]

[Guest Guest]

when the shop removed the mid-valve they also modified the shim stack on the compression. I haven't pulled the forks apart to check on the exact arrangement yet but plan to start my winter teardown in the near future.

I'm not sure how much this info will help you though since I weigh in at 250lbs and the valving is adjusted accordingly.

[James_Dean]

Alright and thanks for the inputs.

James

[mcarp]

James-

I wanted to thank you for posting all your helpful info.

I'm interested in hearing any additional experimentation you have done with your shim stack or any additional comments of your proposed stack vs. the stack you posted last.

WR400_Jay (now KTM250 ? is going to help me make some changes to allow for what sounds like a similar setup-softer in harsh bumps, perhaps uses slightly more stroke but still has the same or better bottoming resistance.

Was the new 16 X .1 HS felt at all? Is this part of magic?

Also, I am considering using 2.5W fluid to help the fork react quicker. Do you think raising the level by an add'l 2-3 mm from your spec would do it? What weight are you running with your stack?

I was going to measure what I have currently, add 10-12mm to compensate the lighter revalve, then another 2-3mm for light weight oil. Sounds reasonable?

Thanks again for all your help!

[James_Dean]

Mcarp,

This sounds like alot of changes at once. The rebound will be affected when you go to lighter oil. It may work ok, just keep it in mind. The extra crossover gap shim of 12 X .1 was most important in my view, then the reduced (5) LS, and then the thinner 16 X .1mm. All of these have an influence in the same direction - softer at higher speeds. Note that a correction was made in my final HS stack (just had the posting wrong). I made lots of changes all at once myself, so make your best guess and give it a try. It's not really magic you know. ?

I like the idea of increasing the oil level at the same time. Maybe another 5-10mm for the light oil making it 20mm higher.

BTW - I am still running the original oil in the fork with only a few ounces extra using 7wt Spectro.

Note that Moto-Pro was great about sending me valving shims in the mail 1-800-277-5089. Shims are dirt cheap $.89 each.

James

[This message has been edited by James Dean (edited 12-05-2000).]

[Shane Denner]

On 11/13/2000 at 6:55 PM, James_Dean said:

I decided to pull out the fork compression valve on my '00WR to see what the shim stacking arrangement was. Thought that you guys might like to know and maybe give a little insight as to what it does. The forks were removed and turned upside down to remove the valve without a complete disassembly. ?

The shims are flexible washers that cover the holes in the compression valve and provide speed sensitive damping. The faster the fork compresses the more the washers flex to let oil flow through the valve.

There are 2 sets of shims. The one closest to the valve is the low speed (LS). There is a small diameter "crossover shim" next and then the high speed (HS) stack. The low speed stack flexes at lower speeds up to the point where it bridges the crossover (spacer) gap and starts to push on the HS shims - at faster fork compression speeds.

----------------------------------

Starting from the compression valve -

6 LS shims - 24 X .1mm

1 shim - 14 X .1mm (crossover)

HS shims - 24 X .1mm

22 X .1

20 X .1

18 X .1

16 X .15

14 X .15

12 X .15

11 X .26 (base shim)

Backing plate 18 X .5

--------------------------------

I'm looking to soften the ride over rocks and roots for woods riding this winter. The plan is to reduce the HS stiffness and a little bit accross the range. I will also raise the fork oil level 1/2" to compensate for the decreased damping.

-----------------------

Pulling one or more from the HS stack is a start. A good option would be to remove the 16 X .15. But instead I will pull out and reuse the 12 X .15.

Adding space to the crossover pulls the HS further away from the valve which lets it open more freely. So to do this I plan to move the 12 X .15 into the crossover gap.

This also makes a smaller support for the LS shims. They will then overhang the crossover by 6mm instead of 5mm ( (24-12)/2=6 )

---------------------------

Proposed stack:

6 LS shims - 24 X .1mm

1 shim - 14 X .1mm

1 shim - 12 X .15 (added this as a crossover)

HS shims - 24 X .1mm

22 X .1

20 X .1

18 X .1

16 X .15

14 X .15

11 X .26 (base shim)

Backing plate - 18 X .5

----------------------

It takes one shim to make a big difference.

Any one else tried to do any revalving on your WR or YZ?

It would be interesting to compare.

James Dean

[This message has been edited by James Dean (edited 11-13-2000).]

Bringing up a really old post, but is this referring to KYB forks? The same as the 98 WR? I’m revalving my forks as well and am stumped. thanks y’all