USD Shim Questions

Questions and comments about converting to beefier forks..
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Jeb
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USD Shim Questions

Post by Jeb »

I had this posted in the "KX Fork Conversion" but thought I'd put it here - maybe there's some unwritten rule about non-KX forks being there or something . . .

'Got the YZ KYB forks apart yesterday evening . . . some differences between the Kayaba disassembly instructions sticky Inda has for us and my model but the sticky was definately a good guide. I took a bunch of pictures and I'll get 'em loaded up for reference. I ended up being able to fabricate a custom tool to get the compression valve separated from the cylinder: a piece of 1" PVC pipe (leftover from preload spacer making - HA!) with some notches.

Here's the compression valve stack setup from the top of the assy:
-nut, cup (lip pointed down), and spring
-checkvalve plate & sleeve
-valve
-Shims (all 0.125mm thick): (10) 24mm, (1) 22mm, (1) 20mm, (1) 18mm, (1) 16mm, (1) 11mm
- Two base plates 18mm & 0.5mm thick

Questions:

-Suggestions on a good stack config? I've read where removal of some of the largest of the shims makes things plusher. Comments?

-Looked over both of the valves and saw that one assy was different: there was an additional 11mm shim but was not part of the shim stack. Instead, it was sitting in the recess on the valve top such that the sleeve was resting on it, i.e. the cup ends up higher over the checkvalve plate & valve (by about 0.125mm). Any good reason why one of the assy would be different from the other? Any reason why you'd need that there in the first place?

-Where would one actually purchase shims like these? *** EDIT ***
Moto-Pro Suspension offers them, I'll call if I need 'em.
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Jeb
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Post by Jeb »

Yeah, I'm kinda answering my own question . . .

The Suspension Network looks like a decent resource - on the surface.

And I do see on gp-racing where the shims can be purchased.

I'll see what they have to say . . .
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Post by krazyinski »

take all but four of the 24's out of the base valve
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Post by Jeb »

>|<>QBB<
krazyinski wrote:take all but four of the 24's out of the base valve
You do mean all but 4 of the 24's on each side, right?

What little I understand about how the shims work, you're suggestion makes sense - thanks!

:grin:
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Post by canyncarvr »

??

A tool to remove the compression valve from the cylinder?

I guess you are referring to the base valve? What with the 'taking apart' comments I thought at first you were referring to the midvalve?

Why not take the base valve out (loosen it anyway) before the spring is out?

I'm missing something.

Do you have bradf's stack info? He used 4-24x10s on his...for the 24 part of it anyway. If you don't have it and want to peruse his setup, I'll email it to you. He was willing to send it to whomever..I'll save him the time if you're interested.

Yes, 4-24s on each side.

I'm curious about the .125mm part...I haven't gone looking for .125mm shims..but have seen only .10s and .15s (.004"/.006") for active shims. ..that's what SN has for sale, too.

That 11mm piece..doesn't your cupped washer have holes in it? So...that washer blocked those holes?

No, I don't know why it would be there or what its perceived function would be. The rebound control is up in the midvalve, so the purpose of anything restricting flow 'after' the check valve flow-wise isn't apparent to me. Now THERE is not something to wonder about.....

Going to take the midvalve out, too? Might as well...you're this far.

Let me know about bradf's valving .doc.

BTW...what's the inside diameter of your shims?

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Post by Jeb »

^
RE: I'm missing something. No, 'only thing missing is my fork vocab. But you're right, it's the base valve. The PVC piece holds the "cylinder" from the top while you unscrew the base valve at the bottom of the fork. I actually did loosen the basevalve prior to doing anything else (I compressed the fork tubes while they were on the clamps as you described from another posting) but I didn't take 'em all the way out for fear of damage (not that there would be any, just my ignorance of the internals).

RE: bradf stack info - LOVE to have it!

RE: 4-24s on each side - thanks ('thought so, just makin' sure!)

RE: 0.125 thickness - I was wrong, 0.10mm, thanks again . . .

RE: 11mm piece - no, the washer doesn't block the cup holes. Look at pic below (click
here for subalbum) - it's a pic of the valve with the checkvalve plate resting on top. See where the sleeve would sit inside the ID of the checkvalve plate and into the recess on the valve top? The cup sits on the top of the sleeve, so all that this 11mm piece does is raises the sleeve and thus the cup. The 11mm shim itself (removed from the recess in this pic) would be hidden underneath the sleeve and doesn't interfere with the cup or the cup holes (you probably knew all of this but were confused by my description).

Image

RE: perceived function - I believe the only change the 11mm shim that jacks up the sleeve and cup would be 1) to increase the distance between the valve and the cup, probably nothing and 2) preload the spring ever-so-slightly less, probably nothing. Having stated "probably nothing", I would say the same about what that tiny stack of thin shims below the valve had I not learned that they are indeed pretty important! Which is why I asked the question, I don't really know my way in these forks too well . . . but the mystery is starting to unravel.

RE: ID of shims - 8mm

RE: the midvalve, too - only after your inquiry did it dawn on me that I should have a midvalve in that cylinder somewhere (at first thought it was just a piston in there). So this evening I proceeded to disassembe . . . and I'm stuck! I could see the nut on the bottom of the midvalve assy through the bottom end of the cylinder so I secured the rod and loosened/removed the nut. Following the nut was a washer, then followed the midvalve shims all stuck together, then . . . nothing. Duh!! The midvalve won't come out because the bottom end of the cylinder is tapered.

OK, no sweat . . . right? Well, try as I may I cannot get the "top" off of that cylinder. I've tried to clamp the cylinder in place and twist the top off to no avail - it doesn't want to budge. Look here and open the picture entitled "zoom on cylinder". See the tiny holes near the top end? It looks like that shiny aluminum piece through which the rod pertrudes is threaded in the cylinder, but it don't budge! ANY IDEAS? HEAT MAYBE? Right now whatever midvalve assy pieces above the midvalve are now rattling inside the cylinder!! :blink: So, the cylinder must come apart.

Image

BTW, thanks for the feedback, I could NOT do this without the help!!
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Post by scheckaet »

If I read your post correctly, you have the rod stuck inside the cartridge.
To get it out you have to remove this:
Image
have you checked this link?
http://kdxrider.net/Kayaba.htm should help
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Post by Jeb »

^ yeah, scheckaet I looked through the link. And I believe you're right to the extent that I need to remove that top piece, but the piece looks different (different forks).

Just the same, thanks!
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Post by scheckaet »

got any pics?
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Post by canyncarvr »

scheckaet's pics should be pretty close.

It's some combination of nuts and split rings that hold the two together. Well, KX-wise anyway.

Take a look at the BuyKaw site for a set of Kayabas to see if anything looks similar.

I do NOT know to what extent Yamaha KYBS would be 'completely' different. Not THAT much I would expect.

Re: 'See the tiny holes near the top end?' Is it pinned in? If that 'shiny' metal is flush with the cylinder, it's pinned.

'My Kingdom for a set of KX KYBs!', the man said! :wink:

But NNnnoooo.....you had to use yamahammer forks!!

Sorry. My 'sperience with forks has to do with forks I've owned and worked on..not this/that/other variance between brands and OEM manufacturers.

Read THIS!!

Of any use? Someone's been here before methinks......

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Post by Jeb »

RE: tiny holes - no pins

RE: more pics - here's a couple, somewhat different than the KX version

Image

Image

The "ring" around the notches on the top piece is removeable.

RE: KX vs. "yammahammer" - your point certainly has validity, why make it hard on one's self, right? Well . . . I can't help it, I guess. But this will get figured out, I'm certain. I think your thread is on the money but I'm gonna go looking before I really start twisting . . .

THANKS GUYS, I'LL GET THERE!
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Post by scheckaet »

I believe you have to drill the pin in the tiny hole (not all the way trough but just to get it undone).
I'll check tonight to be sure
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Post by canyncarvr »

Curious...if you look sidewise into that hole can you see anything that looks like a thread? It would have a taper to edge you would see if the hole was on a ridge, you could see the adjacent ridge if the hole happened to be in a valley.

Maybe?

A couple of other items of btw: What is the diameter of that cartridge? I've read that Yam KYBs are considerably larger than KX KYBs. They both supposedly have the same rod size..so the swept volume of the Yam forks is considerably larger. Yes..I understand that cartridge size effects midvalve 'volume' and rod size effects base valve 'volume'.

I digress....

What year of YZ?

The drilling part I think has to do with models that are STAKED (dimpled). You have to remove the dimple to take the cylinder parts out without thread damage. Holes don't = stakes.

**edit**
Wait a minute...is it a HOLE in the material, or is it a DEPRESSION made by something pressed INTO the material? Now THAT (the latter) would be a 'stake'. Looking at the 'hole' if you see the cylinder material all the way around and in the bottom of the 'hole', it's been pressed in and must be 'drilled' out. If you see the material of the top 'nut' through the hole..well, you get the idea.

In the picture, it's a bit blurry, but it looks to me that the material of the cylinder is indeed pressed 'in'.

BTW..the drilling part isn't done with a drill BIT. Use an end mill:

Image

From a DRN post regarding staked cylinders:
(attributed to) J. Wilkey wrote:-Using the light to moderate heat warm the area around the now milled
stakes. This is important to relive tension and locking agents used in
assembly from the factory.
-Using the CV holder place the components in a vice.
-Using a appropriately sized screw driver or round stock turned to the
hole diameter, unthread the cylinder form the CV. Uses a back and forth
unthreading technique to help prevent thread galling.
That from HERE!

'CV' is 'Cylinder Valve'.

DO read through the link above (where the quote comes from)..important info about HOW to remove those stakes. Real easy to 'drill' TOO DEEP..and fork problems WILL result.

I've seen in more than one place a reference to heat, locking agents and threads in forks that (as near as I can tell) are similar to yours.


Need MX-Tech's address? :wink:

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Post by kawagumby »

I used the shim stacks from an 03 yz250f. It also had 10 24's each side. Removing only 3 shims from each side was more than sufficient to get plush action. My forks are VERY compliant, throughout full stroke...so you might want to start more conservatively at first.
Last edited by kawagumby on 03:21 pm Feb 06 2007, edited 1 time in total.
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Post by IdahoCharley »

Good information CC.

Low to moderate heat necessary to break the loctite bond (using a hand held propane torch) will have the fork oil starting to smoke (when the flame is not in contact with the tube). Hope that makes sense and helps. :?

Be careful recommending or directly applying fork shim stacks from the KX to the YZ forks. As you are seeing - they may be all KYB units and possibly even the same year forks, but the internals are different and thus require different shim stacks/configuration for similar performance. Active valve piston design and inner cartride rod diameter play a hugh role in valving the mid-valve/rebound circuits and also the passive compression valve and its shim stack.
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Post by canyncarvr »

Stacks...shims...rebound...compression...staking...cylinder valve....base valve....cylinder diameters...rod displacement volumes...mid-valve float...drilling..tapping and....ZZzzzZZZzzz...boring. :shock:

Rip 'em apart, change a lot of stuff, put 'em back together with a good dose of JBWeld (everyone knows THAT is the tuner's *secret*.

I say...thassa JOKE, son!

Yeah..the forks are obviously not at all the same. Kind'a like tuning recs for your Ford Focus applied to a GT...apples to zebras.

kawa: Did you reconfigure the mid-valve at all? I don't recall if you mentioned it or not..seems you did not. ..and, your shims are .10 or .15?

Jeb: Looking at the gallery pic: 98_YZ125 KYB 46mm - details on "top" end of base valve assy

...and what that 11mm shim is doing...

How is that NOT the check plate? Funny how reading something and seeing a pic gives (me anyway) sometimes a completely different 'understanding' of what's going on. IF the layout in the pic is the way the thing came apart..that washer is simply a check for rebound flow.

Well, about the time I'm sure of something is about the time my mind is closed to other 'obvious' options..but I don't see what else it's doing. Then...it's obvious enough (again, seeing the pic) that I wonder why there was any question about it.

Another me 'missing something' I s'pose.

Compare where that washer sits on the piston to the check valve below:

Image

The check valve part is the brass colored part...by defintion on the opposite side of the compression stack, controlling flow in the opposite direction of the compression flow.

**edit** Whew...write too much for too long and sooner or later (or always) something is going to get buggered.

THIS just occurred to me: In the pic above (my '99 KX250 base valve) I fanned the compression shims so they could be seen in conjunction with the other parts. It IS obvious, isn't it??...that the LARGE diameter shims go AGAINST the piston? You could conclude from the pic that assembling left to right, the SMALL shim looks to have been faced to the piston. If I fanned them correctly as they came off, you wouldn't SEE the smaller shims.

That is SO obviously wrong, it never occurred to me that anyone would figure other than correctly. After looking at the pic a couple dozen times, it JUST dawned on me that the wrong impression could indeed be deduced from the pic.

OK.. Enough excuses from me for now.

**end edit**

Sorry, Jeb. I had looked at one of your links, didn't think to put them all together. How is that washer NOT rebound control? By 'control' I mean it allows oil to flow through the piston to the mid-valve where the ACTIVE rebound components are..it doesn't really DO anything rebound-wise, if you take my meaning.

Good luck, Jeb.

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Post by kawagumby »

>|<>QBB<
canyncarvr wrote: kawa: Did you reconfigure the mid-valve at all? I don't recall if you mentioned it or not..seems you did not. ..and, your shims are .10 or .15?
The only changes I made were the compression valve stack and oil height. The shims were .004 thickness. My earlier post was wrong, I pulled three not two from the orginal yamaha stack (I edited the post).

The KX500 forks I use may behave differently than some other forks - they have less travel than most 250 forks, about 9.5" wheel travel, so overall damping oil movement may be catered to fit that kind of design also...they sure work well though.
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Post by canyncarvr »

For the casual reader....

FTR....004" is .1mm in shim-land (not in critical math-land!), commonly denoted as '10' or '.10'.

15 or .15 is for .15mm, or .006".

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Post by Jeb »

RE: threads vs. pins - I've stared at and down into the pinholes - there's four of 'em equally spaced - and I'm convinced that I'm looking at threads. There's nothing sticking out from the inside into the hole so I don't believe there's anything to drill out.

RE: offending 11mm shim - it's NOT shown in any of the pictures! The checkvalve plate is the washer that sits on top of the valve in the picture provided above. I probably corn-fused anybody reading/participating in this thread. The very fact that it's confusing is probably proof enough that it means nothing - it was a big surprise finding it there (and it wasn't on the other one). I'm just gonna remove it. :grin:

The forks are a '98 YZ125 vintage. I looked through various years on buykawasaki and can't find anything comparable (although I will say that Kawasaki provides MUCH better drawings than Yamaha).

When I was at work today I looked into heating the piece. I signed out a heat gun that is able to reach 1000F (yes, three zeros), above the "release" temperature of Loctite. Talked to a Loctite rep and he said Loctite - the company - recommends a heat gun to release all three versions: blue, red, and purple. Of course, I'm assuming that Loctite or similar was used!! Surely they wouldn't make things "irreversible", would they? :blink:

Torch? I'm figuring that's gonna be rough on that soft aluminum, bigger chance of melting things.

Anyway, gonna give it whirl this evening - I'll holler back . . .

and many, many thanks for all of the feedback.

And when this is all done I'll heavily document for the next Yamma-hammer victim!! (I like that . . . Yamma-hammer)
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Post by canyncarvr »

One more repeat...but having nothing sticking OUT of the hole may mean it's not PINNED, but doesn't mean it's not STAKED or punched.

What would the holes accomplish otherwise?

So...you CAN see a metal difference? The tube being a soft aluminum and the threaded 'thingy' NOT being aluminum, I'd think the shiny factor would be fairly evident.

Looking forward to what the post is going to look like with you pounding on the keyboard with bandages up to your elbows after employing that little heat gun.

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