Are my forks rebuildable?

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Are my forks rebuildable?

Postby NCKDX » 11:36 am Jul 12 2018

This my first post so let me start by saying "hello" and "thank you" to all of the users here that have made this forum an amazing resource for someone like me new to the KDX.

Now to my question...I just bought a 2004 KDX 220 and am in the process of rebuilding it. I pulled the forks to replace the boots and quickly realized one of them was shot. No damping effect, oil pours out the top if you turn it upside down, and the top tube extends up significantly farther than the other one. Here are some images...you may have to click to see them.

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I'm a decent home mechanic but have never pulled forks apart before.

1) What's broken allowing the one side to hyper-extend?
2) Is it rebuildable?
3) Assuming yes, I'd rebuild and customize for my weight. Are Racetech gold valve cartridges worth the $? What do they do for you?
4) Should I consider a KX fork swap? I have so much to do on this bike that I really don't want to go down a rabbit hole and spend a lot of time with custom fitment, sourcing a bunch of parts, etc., but still have to ask.

In terms of riding style and terrain, I rode a KX80 as a young teenager and now at 42 am just getting back into riding again. I took a guided riding trip in Baja a few years ago on a CRF450…it was a handful but tons of fun. I'm 5'9" and 158 lbs w/o gear. Terrain is east coast woods trails and fire roads we maybe occasional rides in the NC mountains. I'm very comfortable on a bike but guess I'd consider myself an intermediate rider at best. I won't be riding all that often due to travel and family constraints.
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Re: Are my forks rebuildable?

Postby Jason » 11:50 am Jul 12 2018

Welcome to kdxrider.net. :bravo:

It definitely has something wrong. :shock: I would guess that the cartridge has come loose from the base valve (compression adjuster) assembly.

I would not spend the money on a KX conversion right now. Most used bike purchases have a few things wrong with them that need more attention.

Skip the Race Tech Gold Valves for now, too.
Thank you, Julien D for all your hard work!

PLEASE! Do not "dip" PWK Keihin carbs in Berryman's to clean them! It will damage the internal o-ring (jet block gasket).
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Are my forks rebuildable?

Postby Redhurricane » 12:10 pm Jul 12 2018

Personally I would not buy ANY parts until I had the forks apart to see what is going on- agree perhaps one base valve is broken or other issue to let extended length be different per fork. If you do find that they are intact and able to be rebuilt, I am a fan of RT gold valves and setup. They are not hard to do, and will come with complete instructions on how to assemble. If you can read, use a torque wrench and set of calipers, you can do the job. Might as well make sure you have the correct spring rate for your weight while you are in there, correct suspension setup will make a world of difference in how the bike handles.

Did you do your baja tour with Tim Morton (Bajabound) or someone else? We just got back from 8 days, 1500 miles Tecate to Cabo.
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Re: Are my forks rebuildable?

Postby NCKDX » 12:13 pm Jul 12 2018

Thanks Jason. So it sounds like you are saying proper springs, oil weight, and fork adjustments should be good enough for a guy like me just looking to have some fun in the woods? Regarding the RaceTech Gold valves, I don't mind spending the money if I already have the forks apart if I'm going to see an obvious improvement. But if it's just a minor improvement, I'd pass. I've heard the KDX forks are a weakness so want to get the bike set up right.
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Are my forks rebuildable?

Postby NCKDX » 12:44 pm Jul 12 2018

Redhurricane wrote:Personally I would not buy ANY parts until I had the forks apart to see what is going on- agree perhaps one base valve is broken or other issue to let extended length be different per fork. If you do find that they are intact and able to be rebuilt, I am a fan of RT gold valves and setup. They are not hard to do, and will come with complete instructions on how to assemble. If you can read, use a torque wrench and set of calipers, you can do the job. Might as well make sure you have the correct spring rate for your weight while you are in there, correct suspension setup will make a world of difference in how the bike handles.

Did you do your baja tour with Tim Morton (Bajabound) or someone else? We just got back from 8 days, 1500 miles Tecate to Cabo.


So what are the advantages of the gold valves?

And yeah, looks like the next step is to pull the fork apart. But maybe I need to actually rebuild some other things first (final batch of parts is coming next week) to keep things straight in my garage.

Oh and the Baja trip was with Chris Haines Co., 5 day trip. Total blast!
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Re: Are my forks rebuildable?

Postby Jason » 01:10 pm Jul 12 2018

I wouldn't spend any money until you figure out what is wrong with the forks. It looks really bad to me. Having parts bounce around is not a good thing.
Thank you, Julien D for all your hard work!

PLEASE! Do not "dip" PWK Keihin carbs in Berryman's to clean them! It will damage the internal o-ring (jet block gasket).
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Are my forks rebuildable?

Postby Redhurricane » 01:46 pm Jul 12 2018

NCKDX wrote:So what are the advantages of the gold valves?

And yeah, looks like the next step is to pull the fork apart. But maybe I need to actually rebuild some other things first (final batch of parts is coming next week) to keep things straight in my garage.

Oh and the Baja trip was with Chris Haines Co., 5 day trip. Total blast!


Chris is a great guy. On the gold valve topic-

The valve itself is not much different than a stock valve, other than having higher flowing ports. The magic is in the shim stack, and how it is built to work based on your weight, riding ability, etc. The price of the gold valve gets you the valve, assortment of shims, and a key to setup using Race tech's software to build the stack the way you want it based on their knowledge and expertise. Any suspension shop can do something similar, using the stock valve, but unless you are fluent in shim stack setup the common guy does not have resources available to build from.

I've used gold valves on a handful of bikes, in forks and shocks. every one was a vast improvement. Even the emulators for damping rod forks do wonders for old technology. Suspension is modification #1 on every bike I buy.
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Re: Are my forks rebuildable?

Postby bufftester » 04:37 pm Jul 12 2018

I'd agree with disassembling first and assessing the issue. The KDX fork is a simple mechanism and is easily rebuildable. +1 on springing for your weight (both front and rear) and new seals/bushings/oil once you find out what is mechanically wrong. I'd save the money on the Gold valves and put it towards springs and other things (like a new piston on the 220). You can research shim stack mod here for the DIY version of the RT valve setup, though if you're just getting back into riding the stock forks will be adequate. Congrats onthe new bike and welcome to the group.
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Are my forks rebuildable?

Postby Jason » 07:11 pm Jul 12 2018

Redhurricane wrote:
NCKDX wrote:So what are the advantages of the gold valves?

And yeah, looks like the next step is to pull the fork apart. But maybe I need to actually rebuild some other things first (final batch of parts is coming next week) to keep things straight in my garage.

Oh and the Baja trip was with Chris Haines Co., 5 day trip. Total blast!


Chris is a great guy. On the gold valve topic-

The valve itself is not much different than a stock valve, other than having higher flowing ports. The magic is in the shim stack, and how it is built to work based on your weight, riding ability, etc. The price of the gold valve gets you the valve, assortment of shims, and a key to setup using Race tech's software to build the stack the way you want it based on their knowledge and expertise. Any suspension shop can do something similar, using the stock valve, but unless you are fluent in shim stack setup the common guy does not have resources available to build from.

I've used gold valves on a handful of bikes, in forks and shocks. every one was a vast improvement. Even the emulators for damping rod forks do wonders for old technology. Suspension is modification #1 on every bike I buy.


The KDX forks' base valve is NOT one that anyone is going to use to get any good tuning from. It is a "reverse bend" style.

Buy a service manual and take them apart. Don't spend a penny until after you check them out.
Thank you, Julien D for all your hard work!

PLEASE! Do not "dip" PWK Keihin carbs in Berryman's to clean them! It will damage the internal o-ring (jet block gasket).
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Re: Are my forks rebuildable?

Postby doakley » 04:51 am Jul 13 2018

I wouldn't spend a dime on parts until I had the forks apart. Even then I would only rebuild the forks as stock. Springs and gold valves are expensive. IMO money is better put towards a set of KX 125/250 forks. I've done both and the difference is enormous. Money spent on anything other than a stock rebuild kit is being tossed down that rabbit hole on stock forks IMO.

Where are you in eastern NC? I'm in Southport.
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Are my forks rebuildable?

Postby Redhurricane » 05:34 pm Jul 13 2018

Jason wrote:The KDX forks' base valve is NOT one that anyone is going to use to get any good tuning from. It is a "reverse bend" style.

Buy a service manual and take them apart. Don't spend a penny until after you check them out.


Or you can replace the base valve with an entire shim kit here for $139 and get newer technology, no modifications to triple clamps, numerous other modifications to get KX forks to work on a KDX.

http://www.racingsuspensionproducts.com ... vekit.html

To each their own, just offered another option for the original poster who weighs 158# without gear. stock spring rate is likely just fine for him as well, but sag settings will tell the truth of the matter.

EDIT by JASON: Please do not get kdxrider.net involved in any copyright issues with illegal manuals, links and sales.
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Re: Are my forks rebuildable?

Postby NCKDX » 01:32 pm Jul 21 2018

Good news! I tore the forks apart and other than the cost of a rebuild kit, it looks like I'm only going to be out $7 for a mangled spring washer. The rod apparently came unscrewed from the top cap (threads were pretty clean) and somehow the spring pushed the top washer through the spring spacer. It was a bear to get the spring out, but I did. The only other damage is the rod is ever so slightly bent about 7" down from the top.

So my plan is to rebuild the forks, do the shim mod, and get the proper springs for my weight (158 lbs w/o gear). I have a few questions…

1) What springs do I have? I don't know the history on the bike (2004 KDX 220) so am not sure if I have stock springs. The fork springs measure 470mm. Does that sound stock? And while there are Racetech stickers on the forks, the valve stack has not been opened up (maybe the PO just likes stickers, IDK).

And the rear spring is blue, which I think is the stock color. Any way to tell if it's stock?

2) Per RaceTech's site, I want 0.37 kg/mm front and 4.6 rear. Stock is 0.35 kg/mm and 5.0. Given that the next size up on the spring is 0.42, I'm thinking stock front springs is the way to go. Agreed?

3) And for the rear, is the change from 5.0 to 4.6 a big enough deal to do? I want the bike to be balanced so am fine doing so if it will make a difference.

4) RaceTech states 130mm oil level, but my Cyclepedia manual specs 85-89mm. I've also seen some members here talk about using 100mm. Which is right?

Oh and doakley, I'm near Charlotte so will probably be riding out at Carolina Adventure World (and hoping to find a place to ride in the mtns too).

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Re: Are my forks rebuildable?

Postby bufftester » 08:20 pm Jul 21 2018

Rebuild the bushings seals, new oil, and ride it with the springs you have and see what you think. IIWM i'd save the money from springs and gold valves and spend it on good riding gear and then go ride. The stock suspension will certainly get you through a couple riding seasons before it limits you. Or use the money to buy the SO a nice gift, thus earning you more riding time lol.
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Re: Are my forks rebuildable?

Postby SS109 » 09:00 pm Jul 21 2018

NCKDX wrote:1) What springs do I have? I don't know the history on the bike (2004 KDX 220) so am not sure if I have stock springs. The fork springs measure 470mm. Does that sound stock? And while there are Racetech stickers on the forks, the valve stack has not been opened up (maybe the PO just likes stickers, IDK).

And the rear spring is blue, which I think is the stock color. Any way to tell if it's stock?

No way to know what springs you have unless you can find numbers on them you can cross-reference or put them on a spring tester.

NCKDX wrote:2) Per RaceTech's site, I want 0.37 kg/mm front and 4.6 rear. Stock is 0.35 kg/mm and 5.0. Given that the next size up on the spring is 0.42, I'm thinking stock front springs is the way to go. Agreed?

Sounds soft to me but I always have ran .40-.41's up front and I weigh 140lbs. However, they will be plush and will probably work fine as long as you aren't doing high speed stuff or jumps.

NCKDX wrote:3) And for the rear, is the change from 5.0 to 4.6 a big enough deal to do? I want the bike to be balanced so am fine doing so if it will make a difference.

Yes, that is a serious change in spring. The 4.6 will balance much better, allow you to get the proper sag, and keep the geometry of your bike intact.

NCKDX wrote:4) RaceTech states 130mm oil level, but my Cyclepedia manual specs 85-89mm. I've also seen some members here talk about using 100mm. Which is right?

Oil height is subjective. Every rider will like it a bit different as it changes the way the fork behaves. I would start out at the minimum and, if it blows through the suspension travel too fast, add 5cc to each leg and try again until you get it where you like it. If you reach max level and still blowing through the suspension you either need heavier weight oil, heavier spring, and/or different valving.
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Re: Are my forks rebuildable?

Postby NCKDX » 10:31 pm Jul 21 2018

SS109 wrote:
NCKDX wrote:1) What springs do I have? I don't know the history on the bike (2004 KDX 220) so am not sure if I have stock springs. The fork springs measure 470mm. Does that sound stock? And while there are Racetech stickers on the forks, the valve stack has not been opened up (maybe the PO just likes stickers, IDK).

And the rear spring is blue, which I think is the stock color. Any way to tell if it's stock?

No way to know what springs you have unless you can find numbers on them you can cross-reference or put them on a spring tester.

NCKDX wrote:2) Per RaceTech's site, I want 0.37 kg/mm front and 4.6 rear. Stock is 0.35 kg/mm and 5.0. Given that the next size up on the spring is 0.42, I'm thinking stock front springs is the way to go. Agreed?

Sounds soft to me but I always have ran .40-.41's up front and I weigh 140lbs. However, they will be plush and will probably work fine as long as you aren't doing high speed stuff or jumps.

NCKDX wrote:3) And for the rear, is the change from 5.0 to 4.6 a big enough deal to do? I want the bike to be balanced so am fine doing so if it will make a difference.

Yes, that is a serious change in spring. The 4.6 will balance much better, allow you to get the proper sag, and keep the geometry of your bike intact.

NCKDX wrote:4) RaceTech states 130mm oil level, but my Cyclepedia manual specs 85-89mm. I've also seen some members here talk about using 100mm. Which is right?

Oil height is subjective. Every rider will like it a bit different as it changes the way the fork behaves. I would start out at the minimum and, if it blows through the suspension travel too fast, add 5cc to each leg and try again until you get it where you like it. If you reach max level and still blowing through the suspension you either need heavier weight oil, heavier spring, and/or different valving.


Thanks SS09. Do you think I'd be better off with the stock 5.0 rear spring and to go with a heavier front spring to balance it out (instead of going lighter with the rear)?
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Re: Are my forks rebuildable?

Postby Jason » 11:22 pm Jul 21 2018

It's late
I am getting old
I am typing on a telephone

Can you please define, ever so slightly bent cartridge rod?

I can't imagine the cartridge top containing the rod bushing appreciating that. :shock:

158 pounds with no gear.. 173 all geard up? 5.0 should be close. DO NOT buy a spring until after you triple check your sag numbers, race and static.

What does the manual say spring length is?

Maybe someone else has their forks apart and you can compare coil numbers and spring coil diameter .

Look on eBay for Honda XR400R stock springs. Maybe someone has some. 1996 - 1997 are 0.38 and 1998 - 2004 are 0.40.

A problem with the stock springs is they ate 1. BUTTER SOFT and 2. Have massive preload, lime 28 or 38 mm I think. Put three or four mm of modern preload on them and watch them collapse and stink bug.

Measure OD on shock spring. KDX stock is smaller than aftermarket. RT from around 2005 or so is bright blue.

Otherwise OEM Kawasaki. A few KX were blue, but not as small OD and length as KDX
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PLEASE! Do not "dip" PWK Keihin carbs in Berryman's to clean them! It will damage the internal o-ring (jet block gasket).
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Re: Are my forks rebuildable?

Postby NCKDX » 03:40 pm Jul 22 2018

I made a fork spring test rig and came out at 0.36 kg/mm for the front forks, which is pretty darn closed to the 0.35 that is spec'ed as stock. Based on the condition of the rest of the bike (wheel and suspension bearings are toast, probably original) and the blue rear spring with no numbers on it, I'm assuming that is stock too. FWIW, the rear spring diameter is 0.443" / 11.25mm.

Regarding the slightly bent damper rod, it was out about 0.9mm (measured with a thickness guage) in the middle. I was able to bend it back straight with my hands and a rubber mallet as a fulcrum.

I can't measure sag as the bike is completely torn apart, and if I'm going to replace springs (front or rear) I'd prefer to do it now for the same reason. The RaceTech calculator asks for weight WITHOUT gear, so I put 158 lbs in to come up with the recommended 0.37 front and 4.6 rear kg/mm spring rates. Am I missing something there? If I enter full weight with gear estimated at 173 lbs, Racetech calls for 0.39 front and 4.9 rear.

I'm open to advice to the contrary, but right now I think the best course of action is to go with stiffer front springs. I didn't see any Xr400 springs for sale on ebay, but thanks for the suggestion Jason.

1) Should I just get some 0.42 RaceTech fork springs (I didn't see anything softer)? Or is there another source for something closer to 0.39-0.40?

2) How do you set preload? I understand this is done by adjusting spacer length, but what do you use for spacers and how exactly do you dial it in? TIA!

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Re: Are my forks rebuildable?

Postby Jason » 05:40 pm Jul 22 2018

Years ago, I used a broom handle and some workout weights to determine spring rates. I took the average of 1- 2 inches and 2 - 3 inches. Don't use 0 -1.

I think the RT chart is off sometimes. You might need a 4.8, but since springs are not real cheap, for me, I would check sag on the probably stock 5.0 spring before buying another one.

https://www.ebay.com/itm/Race-Tech-Fork ... =R40&rt=nc

There are some 42's, but I think 40 would be about right. I don't know if they still make them, but Eibach 996 in .41 would be an option, also. They also made .39.

PVC pipe cut to length for spacers. Do you have a tube clamp for a vise? Hold the inner fork tube up high on the tube, in the vise. Let the bottom down. Put in all the spacers, spring, washers, etc. Measure from the top of the fork tube to the underside of the fork cap (tightened down onto the top of the rod). That is your amount of preload. 3 mm or 4mm or so is good.

I wish that Eiback and Race Tech still made their full line of springs for our KDX's. We used to have odd rates from Eibach and even from RT. :oops:
Thank you, Julien D for all your hard work!

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Re: Are my forks rebuildable?

Postby NCKDX » 08:24 pm Jul 23 2018

I ordered some OEM XR400 0.40 kg/mm fork springs (part # 51401-KCY-761). I couldn't find any of the 0.38 springs for the XR400 (part # 51401-KCY-671); I assume they've been discontinued. Once I'm finished the rebuild I'll set sag and ride before considering a rear spring. Thanks for all the help.
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Re: Are my forks rebuildable?

Postby Jason » 11:05 pm Jul 23 2018

I didn't even consider buying them new. I see they were not an arm and a leg. Good job!

:bravo:
Thank you, Julien D for all your hard work!

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