USD Shim Questions

[Jeb]

RE: what would the holes accomplish otherwise - heck, I don't know! For dummies like me to gaze and wonder? Point well made and taken, guess a 6mm end mill is in order. I guess "6mm" is enough of a description? I don't see dimples though so it'll be interesting to see how this turns out.

I did pose the "how to disassemble" question on SN to see what is brought up there. I did a search and found reference to the possibility of knock off CVs that are VERY cheap for replacement purposes if need be (OEM = $200 per bikebandit), 'need to find out more.

Yes, I tried to remove with just heat - no go, and given the suspected pins/stakes I'm resisting overdoing it. I treated the heat gun with respect, but I did manage to lacerate the webbing between my thumb and index finger on my left hand so I do have one bandage!

So, whilst I wait - the good stuff. The shim stack that fell out of the partially disassembled CV goes like this (all are 0.10mm thick, 8mm ID): (4) 27mm, (1) 12mm - huh?, (1) 20mm, (1) 18mm, (1) 16mm, (1) 14mm, (3) 11mm. Washer that came out after the nut is 20mm OD, 8mm ID and almost 2mm thick.

If I eventually change this config, I think I can do the same for the CV that I haven't mutilated without needing to tear it apart. If I can manage to secure the rod with it pushed all the way down (so the rod doesn't move up and out of the midvalve), the nut, washer, and shims should fall out. Then when I reassemble I just need to be creative in getting them back on the rod end.

[canyncarvr]

Re: 'I guess "6mm" is enough of a description?'

No.

Google the term 'end mill' and you get stuff like:

http://www.carbideconnection.com/

The post reference earlier specified the type..a two flute. Whether cobalt, nitrided, or carbide I don't know. Tip types vary.

I would suspect it would be next to never getting the job done with a vise and a hand-held drill. If you don't have a drill press, I'd suggest not even trying it. Yeah...prolly everybody has a nice floor stand unit 'cept me.

Re: '(4) 27mm, (1) 12mm - huh?, (1) 20mm, (1) 18mm, (1) 16mm, (1) 14mm, (3) 11mm.'

Huh what? You're looking at a two stage stack. LSC at the 'top' HSC the other one. The 12mm is supposed to be a separator 'tween the two, generally referred to as a 'transition' shim (I think). Obviously it still DOES something oil control-wise.

Any time you're handling shims in a stacked configuration, use some sort of indexing device..a punch/nailset/rod through the holes to keep them correctly stacked. It's REAL easy to misplace a shim. They may stick together even without oil on them and it's virtually impossible to look at a stack and see what its makeup is.

So...lay the stack out the way you want it, make notes of what it is, skewer the whole mess to keep it that way. To put on the post, hold the stack, put the tip of your indexer on the stud, drop the whole mess at once.

'Clean' is a big deal. Keep it all spotless!! No lint, hairs, fuzz, grit, dirt, pet dander or flea poop!!

That's pretty basic stuff..but had I not SEEN someone do it, I don't know that it would have occurred to me.


Hey! Are you sending me an email address for that valving doc? Am I in the right thread??

[IdahoCharley]

CC wrote "You're looking at a two stage stack. LSC at the 'top' HSC the other one. The 12mm is supposed to be a separator 'tween the two, generally referred to as a 'transition' shim (I think). Obviously it still DOES something oil control-wise. " Your correct as usual - well almost anyway - 99.9% correct in technical world = 120% correct in virtual world.

I believe "cross-over shim" is a more specific term referencing the shim in question. "Transition shim" is more speicific to an inverted shim stack arrangement where the shim stack taper transitions from a converging taper to a diverging taper.

The cross-over shim's purpose is to allow the shims against the face of the piston to react to slow velocity hits over a longer distance. i.e. the high speed valving is not enaged as soon since the low speed shims can bend or be displaced further. In a two stage stack one of the fine tune variables you can play with is changing the size of the cross-over shim: both in diameter and thickness. A larger cross-over shim (or thinner shim of the same diameter) stiffens the low speed circuit and engages the high speed portion quicker: A smaller diameter shim (or thicker shim of the same diameter) will entend the initial low speed valving circuit.

Hopes this helps in the quest for the perfect forks.

[scheckaet]

A larger cross-over shim (or thicker shim of the same diameter) stiffens the low speed circuit and engages the high speed portion quicker: A smaller diameter shim (or thicker shim of the same diameter) will entend the initial low speed valving circuit.

? ok now I'm confused

[canyncarvr]

Re: '"Transition shim" is more speicific to an inverted shim stack arrangement where the shim stack taper transitions from a converging taper to a diverging taper.'

Sounds good to me. I knew it was called sumthin' like that. I should'a stuck with a 'separator'. More likely several. They're good!

scheck: Think of the shape of the stack and the direction of flow..and IC's comments will dawn clear upon 'ye.

Well...it makes sense to me. Don't ask me to repeat it and still make sense of it next week.

Thank you Mr. Idaho!

[Jeb]

RE: Clean - I'll make every attempt, but the flea poop's gonna be tough.

RE: LSC vs HSC; description of cross-over shim - great descriptions, thanks. This stuff is starting to make some sense.

A question about the midvalve - are you guys "converting the midvalve back to the checkvalve plate design" per the Kayaba fork service bulletin Inda has posted? What exactly is done?

BUT . . . before I can put this stuff into action I need to resolve my little dilemna with the CV. I ended up calling MX-TECH with intentions of having a very brief conversation with one of their techs - and ended up talking to da man, Jeremy Wilkey. What a nice guy! I think he actually cared even though he didn't know me from Adam - guess where my future suspension business is going? Anyway, out of respect for his time I tried to keep the conversation to a couple of minutes and in that time we surmissed that the greatest likelyhood was . . .

. . . that the dimples were already drilled out, hence the holes w/no dimples and the ability to see the thread. Further, I didn't notice a peen on the nut at the bottom end of the rod when I removed it. Meaning that work had previously been done most likely (there WAS mx-tech stickers on the forks when I got them so, I wonder). Meaning that my attempt to remove the top was just flat out lame (he didn't say that but . . .). Sounds, though, that it's not an easy task and requires the right kind of tools so I'm going to give it another shot with some improved method. If that doesn't work - and I won't push it too hard - I'm gonna' send the CV to MX Tech for reassembly (we figured less than an hour so no more than $40 which is << a new one).

So, there's light at the end of the tunnel . . . and I'm headed toward a great set of forks thanks to the help!!

[canyncarvr]

Re: 'Sounds, though, that it's not an easy task and requires the right kind of tools...'

Like.....????? A bigger heat gun?


I could'a told you Wilkey is a good guy. Well, I have already here and there.

It's from him I got the three sets of springs I used in deciding what I was going to use on my OEM forks. He ended up sending me XR springs complete in red-winged wrappers!

I did spend a lotta bucks with them...and I did get a lot of service/work/help in the process.

It would be a simple decision to choose a tuner next time..MX-Tech!

[kawagumby]

The cross-over shim's purpose is to allow the shims against the face of the piston to react to slow velocity hits over a longer distance. i.e. the high speed valving is not enaged as soon since the low speed shims can bend or be displaced further. In a two stage stack one of the fine tune variables you can play with is changing the size of the cross-over shim: both in diameter and thickness. A larger cross-over shim (or thinner shim of the same diameter) stiffens the low speed circuit and engages the high speed portion quicker: A smaller diameter shim (or thicker shim of the same diameter) will entend the initial low speed valving circuit.

Excellent post!

I have a fork-tuner friend, a professional, and that is exactly what he does to further tune 2-stage stacks for off-road...and he tunes for some of the quickest cross-country riders around here, including my nephew (an ISDE vet) - who also often works for him.

[bradf]

Converting the MV "back" to a check plate is indeed "backwards". It was a viable simple alternative initially when KYB came out with the bladder and confused the tuners. A well stacked MV for HSC is better than good, way more efficient than the check plate in fact. Jeremy is one of the few tuners that took the time to experiment with the bladder system back then. When he finally said "enough", it was because all the logical modifications to rid the mid-stroke harshness while retaining the bladder were tried and the science of the bladders was found to be lacking. MX-Tech has proven that they understand the complete system and when they make a change it is a system change not just a shot at correcting a single symptom. My stack is NOT complicated at all. It is nearly a stock configuration. Jeremy advised on the bleeder shim in the HSC and I figured out a simple fix on the restrictive barrier and bladder removal. The forks are exactly what Jeremy said they would be, even better. Now I know what the factory GNCC riders had. If Jeremy wanted to load my forks with flea poop and paint them with whale piss I’d let him do it.

[IdahoCharley]

Ok - so here we go again. Not picking on you JEB (well maybe but just a little bit) but using you as an example of what has happened many times on this forum and others. Lots of peeps have done the same thing as you are doing - but that doesn't make it right!!

New forks to JEB - marked with MX-Tech sticker which may or may not mean anything. Pulls forks apart since they are well - new to him. Its winter and Jeb wants to set them up for his KDX. Spring rate selected - oil changed ; as received oil height measured ????? viscosity known????

What I don't understand is the valving changes and discussion about removing or installing a MV/CP and other hoopla. Sending cartridge valve assembly to MX-Tech for disassembly and then will change shim stacks based upon what - experience of other forum members??? (Not dissin any forum members here but still trying to make a point that we all have different backgrounds, experience, aggressiveness, terrains, abilities, and yes - most importantly - our forks for the most part vary from one another)

MX-Tech will want to know JEB's weight, riding style, experience, terrain and Jeb's dislikes with the present forks. Well so far the dislikes are fork tubes have a few scratches, hard to get the cartridge disassembled, etc.

I'm trying to make the points:

1. We only know the best forks that we have personally have ridden.

2. If we purchase some forks that appear to be in decent shape why are not we trying them out prior to tearing into them and fixing them??? What are we fixing??? (It should go without saying - I agree in selecting and installing a set of springs for your weight as a given prior to attempting a performance evaluation)

3. Lets consider the possibility that these forks - as they arrived - and if the spring rate was close to what you need: could have been the "best forks that you have ridden." If you had dislikes with their performance then you would have information that MX-Tech could use to help you out!!

I have a very high regard for JW at MX-Tech and he will treat you fine but has your money been well spent? i.e. If you had a complaint about high speed harshness, blowing through the stroke, deflection off trail trash, diving in corners, pushing to the outside during cornering, etc. etc. then JW could really help you get a better set-up. With no performance compliant information you get the 'standard' set-up based upon what he thinks you may need.

Sorry about the RANT .

[canyncarvr]

I thought he was taking them apart just to check them out? ..to see what was going one in th'ar!!

My mention of bradf's valving wasn't to intend that everyone do theirs like he did his. His write up and graphical representation of the setup is educational is all (well, was for me).

Jeb said: 'If I eventually change this config....'

The point of this post is two-fold: Jeb, if you were looking for stack recommendations or advice on what to change to...I missed it. Any comments I made were meant to be taken more in the 'general' realm of things and not anything particularly to be done valving-wise. Well..if you'd had 10-22x.10s all stacked together I'd probably vote for offing some of them for starters, but that wasn't the case.

Secondly, IC is exactly correct. All sorts of changin' everything here and there without having ANY idea what you're starting from doesn't make any sense. If your ARE Mr. Tuner and KNOW what you want to get done, then get it done!

Again, that is not the situation in this case.

[bradf]

I think I stated this a long time back in a thread far far away. There are (were) many approaches to fixing the old KYB bladder forks. JW did so much work with them back in the day and he put in a lot of time and effort to fix the mid-stroke harshness. He finally found what worked using solid suspension knowledge and physics. JW possesses so much in depth knowledge from trial and error, like the scientist that came up with formula 409, 408 wrong tries till #409. JW's stack info, spring rate, bleeder shim removal for me, and oil type and height was all taken into consideration with my weight and type of riding. JW could have told me to send them but he took the time to listen to my ideas and in the end, I got a wealth of FREE MX-Tech info. The point is that I did NOT have the time to go through all the suspension testing and changing. I did that for years and I am simply tired of it. I am sure I would have arrived at the same stack, or very close to it. Most of these forks don’t need all that much besides correct springs. You can look at 2 different stacks and tell what the difference will be to a point. Sorta like removing all but 3-5 of the 24's on the BV. Or removing the bleeder in the HSC. Or you can spend 3 weeks on a shock dyno making all sorts of changes. Or you can go straight to the man. JW already knew exactly what would work for me after our talk. It is a different stack than what I would have gotten if I were still riding in WA. It is JW’s proprietary knowledge that makes MX-Tech so valuable to me. The basic science of the HSC MV is a very good progressive system, a system still used in Penske shocks at all levels of racing. When I heard other national shops say they would put in a check plate, which to me is a cop out, I knew I would not do business with them. They were taking the backwards approach.

If Jeb’s friend KNOWS what to do, then by all means Jeb, let him do it. There is a significant difference between good and nearly perfect. I decided to shoot for nearly perfect right off and JW was the answer. My slight mod to the RB was just a simpler redneck grinder approach that works, quite well.

[Jeb]

I DO intend on ending up with a primo set of forks. And I just may be getting into the gory details eventually - after I get the chance to play for a while, race in some good 'ole Kentucky harescrambles. IF I need to change things. And I probably will. Even if I don't need to!!!

'Kind of the point for me and this KDX - I've been fascinated with it since day one, pretty much. It's been kind of a WOW thing for me, something I can sink my teeth into, tweak, and enjoy immensely . . .

and the forks - had to start somewhere, right? So I'm really just doing the obvious things. Like change the horribly-leaky seals. Oil height - 108mm roughly (wonder how much leaked out before I made that measurement). Viscosity - no clue, just looked really yucky!

Shim stacks? 'Seemed reasonable to start with what's been working for people, cutting back on the huge stack of 24s makes sense. For starters anyway. The midvalve thing? I've done a BUNCH of reading on a couple of sites about this and am thoroughly convinced that its as much art as science - the "seat of the pants" thing.

But again, just a matter of a starting point, wanting to see what YOU guys thought about midvalve stack vs. making the thing a checkvalve. And, yes, read some stuff on another site where Jeremy Wilkey expressed his thoughts on what the midvalve can do for a rider if done properly.

The whole idea with sending the CV to MX-TECH was to fix my mess, not to go rearranging the stacks. UNLESS I knew ahead of time how I might ask them to shift things around a bit if there's a general consensus about some things . . .

Yeah, I've got a LOT to learn - but that's the fun of it!

More than anything, though, I'm truly having a ball with this and thank ya' all for your time and thoughts!

[IdahoCharley]

If I came across too strong for anyone, it was not intended that way, and I apologize if my rant sounded harsh or pointed.

I believe most of us that frequent these forums like to tinker and although I don't tinker with the bikes as much as I use to; I still like to mess around and try a few different approaches to fix or make the bikes better for a given purpose.

I've met many more motorheads on the forums than in my "real" world and I do appreciate and respect them.

I may be just doing through motorhead withdrawal - sucky low snow winter and can't ride the sled anywhere decent within a couple hours drive and I haven't ridden a bike since last Oct with Clutchcover.

[scheckaet]

last Oct

And I was complaining about not riding for the last 4 weeks...I feel your pain. Hang on! the good weather is coming and it'll be SWEET!

[Jeb]

. . . I may be just doing through motorhead withdrawal - sucky low snow winter and can't ride the sled anywhere decent within a couple hours drive and I haven't ridden a bike since last Oct with Clutchcover.

It IS tough, ain't it?