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I got around to dissasembling my '03 KX forks today, and something doesn't look right with what I think is the shim stack. In the pic, on the top is the nut; then a cupped washer; below that is a shim that is .010" thick, and is .982" in dia.

Is that my shim "stack"? One shim doesn't seem very "stacked" to me. As you can see they have gold valves.

Can anyone confirm what I am saying is correct, and also recommend a ball park stack for a 190+ lb geared-up guy in western mountainous terrain with some cautious use on MX tracks?

I always thought these forks were soft, they use all of the travel when I'm going at a good pace. they still handled way better than the stockers , but I wouldn't want to jump on an MX track with them. I plan to figure out the spring rate but would like to know a starting point for the damping. I'll also be tearing into them to figure out if the bladder was removed or not.

Uh... where's your shims?

Dude... that is not right! Better order some shims and rebuild them. That is a blow through....

ok, I looked at the KYB sticky again and it looks like what I thought was a shim is really the "check valve plate". To be clear, the shims would go below the gold valve then?

What that looks like to me is someone replaced the shim stack with a check plate sysytem. I know that this was a very common half ass fix for the mid valve where they would eliminate the MV entirely and put in the old fashioned check plate system which is a heavy washer type shim and a spring with a certain amount of "lift", usually around 2.5 mm. But I have never seen this in the BV before nor have I ever heard of it. I think someone screwed up by getting their info wires crossed and messed with the BV and that is why the forks were sold. You could send them in to MX-Tech with your seals and bushings and when you get them back they will be perfect.

The shims are on the opposite side of the piston than the cup and nut. You should have a few 24's anywhere from 11 to 4 ea, one 22, one 20, 18, 16, ... that would be a "normal" shim stack.

Thanks Brad. I took the GV off and there are shims below that. I measured them in thousanths let me convert that and compare to what you are saying. Above the GV, my parts on the compression assembly match the KYB service sticky layout.

Mine go:
Low speed - (5) 21, (1) 12

High Speed - (1) 21, (1) 17, (1) 14, (1) 12, (1) 11.

I was looking on the Ractech site, and can't believe how much the shims cost ($16 for ten!!). Anybody got a better source? it would be nice to have an assortment to play with, if you had to buy a ten pack each, of a good variety of sizes you'd be up to what the forks cost.

I measured my fork spring rate and got .42 Kg/mm . Racetech thinks I oughta be around .425 . Usually I think they're pretty high on their estimates for trail riding, but maybe not in this case. I guess I'll see what it feels like with fresh oil and go from there.

trail riding with the KX forks is much nicer with springs on the softer side of the scale than the stiff side.

Trail riding or street riding or MX/SX is a lot nicer with spot on shock valving. Tuning for slow or sharp edge bumps using spring rates is NOT a sound suspension technique. Spring rates are to suspend the sprung weight of the vehicle and to keep it from bottoming on slow bumps. There is a range of acceptable spring rates on any bike as long as it falls within the acceptable sag parameters. Control of the moderate and fast motion of the wheels over sharp edge bumps is all valving and a very very tiny bit is the spring. You can take exact forks; one with say .38’s and the other with .44’s and both forks may just fall within the acceptable sag parameters. The .44’s can be plusher than the .38’s on the trail simply because of the valving. The rider feels valving on the sharp bumps, not spring rate.

MX-Tech has the best prices on valve shims and will sell them individually with a standard handling/shipping charge. They package them in sealed plastic identified bags which is also excellent.

CM, usually, mind you "usually", the first shim(s) covering the piston face are 24 mm. It could be that the Race Tech piston only needs a 21 though. This is something different.

bradf wrote:Trail riding or street riding or MX/SX is a lot nicer with spot on shock valving. Tuning for slow or sharp edge bumps using spring rates is NOT a sound suspension technique. Spring rates are to suspend the sprung weight of the vehicle and to keep it from bottoming on slow bumps. There is a range of acceptable spring rates on any bike as long as it falls within the acceptable sag parameters. Control of the moderate and fast motion of the wheels over sharp edge bumps is all valving and a very very tiny bit is the spring. You can take exact forks; one with say .38’s and the other with .44’s and both forks may just fall within the acceptable sag parameters. The .44’s can be plusher than the .38’s on the trail simply because of the valving. The rider feels valving on the sharp bumps, not spring rate.

TAKE IN MIND WE ARE TALKING ABOUT A CONVERTED KDX.
EVERY THING CHANGES WHEN YOU CHANGE THE WAY SOMTHING IS ENGINEERED.

SOME TRUTH AND SOME FALSE. WITH THE SAME RIDER SAME BIKE HOW WOULD YOU GET EXCEPTABLE SAG? I JUST TOOK .43 OUT AND PUT ..40S IN. ON THE SAME EXACT FORKS. THERE IS A DRAMATIC CHANGE IN THE WAY THE BIKE FEELS. THE .43 MADE THE BIKE FEEL STIFF AND HAD ME CONSIDERING SENDING THE FORKS OUT FOR REVALVE . WITH THE .40 SPRINGS THE FORKS ARE RIGHT ON THE MONEY NICE AND PLUSH.

I should clarify.
Lowering spring rates for slow plushness on rocks and roots is a common fix. But in doing so can drastically affect the suspension at higher speed conditions where the forks travels more into the stroke. I needed to be more specific when I said "slow". If they are hit relatively slow (slow wheel deflection) this would be very affective as they are not high speed hits. Hitting sharp edged bumps like rocks and roots at higher speeds (where the wheel deflects much quicker) will shoot the forks through their travel if the valving doesn't control it. The springs rates have little affect on the control on hits like this. Then there is the problem of getting the wheel to rebound quick enough and that is where the spring rate and rebound valving come into play. Spring rates will vary according to rider preference but the sag must be maintained within specs.

Sorry Mike.. I still can't see the shim stack .....

In the picture, the silver line under the gold part. It's way thinner than I expected it would be, these shims for the most part are .004" thick, and I only have 11 of them. So it's easy to miss .04" total thickness in the photo.

Being a total newbie to suspension valving I thought the shims would be much bigger, and the stack would have a pronounced cone shape. I thought oil flowed around the cone. Apparently the shim stack appears to make a springy resistor to the oil flowing through the orifices in the valve.

I would really like to see an animated cutaway view of the internals to understand how the oil flows on compression and rebound.

it appears from the research I've done that the aftermarket valves simply provide much larger holes in the valve to eliminate and constriction in the valve itself, and rely on the shim stack to control oil flow, then (at least in the case of Race Tech) they not-so-simply provide you with various recommendations for constructing a shim stack that suits your riding style.

Brad, the check valve washer I have completely covers the holes in the GV, so I think it's fine.

CM, I had an animated diagram I found on the web. I will try to find it again. Have you looked at your mid-valve (MV) stacks? There could be 1 shim stack on the end of the rod and another check valve CV) just above that.

bradf wrote:Trail riding or street riding or MX/SX is a lot nicer with spot on shock valving and proper spring rates for rider and riding condition .

I think this is what you were clearly trying to say.


An expereranced rider cant have one with out the other. before kids It was standard procedure when getting a new bike to pull the suspension and send it out for revalve and springs.

the sad part is I know what youre saying and what needs to be done, but what I am talking about is shade tree suspension tuning, thats not a good or a recomeded way but very affordable.

my buddy is 220 lbs with a properly valved suspension and I am 175 with a properly valved suspension and when we switch bikes the ride report tells like goldie locks and the three bears.

but then again it doesn't really make you any faster or slower just helps you from meeting the ground so often. I would prefer to ride a what some would consider soft suspension in the woods, I prefer more of a enduro type trails than high speed open trails. If it was not for the under hang on the oem forks I would have kept them because the action was good. the oem forks I had were re valved and sprung with .40 springs, I disassembled the cv shim stack and revalved the KX forks in the same format. The only difference was .43 springs in the KX forks and of course more adjustability of the forks. I have very little experience riding bikes with USD forks and have 20+ years of riding with conventional forks.

USD forks provide a broader range of adjustability and compensate for a wider range of terrain and rider preference than stock KDX. Stock forks are adequate for what they were designed for, up to a point. The high speed compression and low speed compression of newer USD forks are widely tunable as well as the rebound having good adjustability. With proper shim stacks and/or CV lift one can zero in on a set-up that will be good on both slow poke trails and GNCC type riding. Throw in sand riding and whoops and there is even a bigger task for the suspension. In short, once the valving is very close, the clickers can compensate for the rest. This is why I stated I would not use spring rate to adjust but rather valving/clickers. I wish you all could ride mine in the woods and in the whoops. The forks are super plush on the slow rocks and roots (first 3” of travel = LSC) and can still eat all the whoops (forks don’t shoot through the first 3” of travel = HSC). The HSC and LSC are incredible and I didn’t have to sacrifice one for the other, that’s the beauty of great valving and allowing the different circuits to do their job. The Showa on the rear helped immensely on the whoops but not noticeable in the slow stuff.

What is your shim config Brad?