H Series with Kayaba SSS fork assembly from a Yamaha

[soup-n-sandwich]

Hi guys,
I'm in a bind right now trying to get some information about an H series KDX (before this used KDX is sold out from under me) and what it would take to swap out the conventional stock fork with front end from a YZ 250.
1) Would this work and if so what is involved?
2) Is the SSS KYB fork the same length as the stock fork or would the SSS have to be shortened?
3) Is the SSS fork just as usable in terms of installation modification as any of the KX fork conversions or are they a completely different animal?
4) I've been hearing a lot about the guy that was doing the fork swap conversion is retiring. Is this still the case and is there anyone else that has the skills and machines to do the fork swap?

Thanks guys
C

[doakley]

it's actually not that hard but you will need the forks and a matching triple clamp set. You press out the Yamaha stem from the lower triple clamp and press in your existing KDX stem. You'll probably have to shim the top triple clamp stem to make it fit correctly.
I used KYB forks from a KX250 and did not have to shorten the forks. I did have to raise the fork tubes in the triple clamps to get the geometry right. You may need bar risers to get the space to raise the forks.

[SS109]

Yup, what Doakley said.

The toughest part is that you might have to have the KDX stem knurled to fit the YZ lower triple clamp. Ron Black does that but, if he's not taking any more work, any competent machine shop should be able to do it rather cheaply. Also, Ron's top clamp spacer, while not mandatory, is a really nice piece to complete the swap.

Also, to do the swap you'll probably want the axle, wheel, and brake caliper to make it all bolt up without a fuss.

[soup-n-sandwich]

Yup, what Doakley said.

The toughest part is that you might have to have the KDX stem knurled to fit the YZ lower triple clamp. Ron Black does that but, if he's not taking any more work, any competent machine shop should be able to do it rather cheaply. Also, Ron's top clamp spacer, while not mandatory, is a really nice piece to complete the swap.

Also, to do the swap you'll probably want the axle, wheel, and brake caliper to make it all bolt up without a fuss.

Thanks very much guys. There is a lot to it when it coes to making a KDX on the same page with a "modern" bike. Since I'm going to race this bike I want to make the bike everything it can be. I'm going back and forth between the KDX and a YZ250 with the necessary mods to become a good offroad bike rather than an MX bike. Since the KDX220 must be raced in the 250 class it's at a disadvantage so I was looking for a 200 rather than a 220 for this reason. I love the KDX but need to address it's weak points. The suspension being the first on that priority list. Having the Kayaba SSS fork would be a major step in the right direction.

Do you guys know if the shock off the YZ would fit the KDX or should I be starting up another topic for that question?
C

[doakley]

If it were me, and I've been there, I would send the shock to Jeff Fredette and discuss with him. He does his own revalving to the rear shock and it is excellent (IMO).

[KDXGarage]

Check to see where the KDX steering stop is going to contact the YZ lower triple clamp. For example, an aluminum frame KX250F (2006) has the stops on the clamp differently than the lower clamp for the steel frame.

I would just rebuild / revalve the stock shock.

[SS109]

The stock KDX is pretty decent and especially so if a competent suspension guy revalves it for you. That said, the YZ shock will NOT fit. The one series of shock that will fit, as I have one on my own bike, is the '01-'06 Suzuki RM125 Showa shock with some mods but this mod isn't for everyone. Here's a link to this shock swap: Full Showa USD fork/RM125 shock conversion

UPDATED: I have changed this post to eliminate any confusion on the Showa shock swap and have included a link to all the info on this swap. I also split off the recent discussion of this swap also to that same link and starts at the last post on Page 5.

[ebulic19]

Hi guys,
I'm in a bind right now trying to get some information about an H series KDX (before this used KDX is sold out from under me) and what it would take to swap out the conventional stock fork with front end from a YZ 250.
1) Would this work and if so what is involved?
2) Is the SSS KYB fork the same length as the stock fork or would the SSS have to be shortened?
3) Is the SSS fork just as usable in terms of installation modification as any of the KX fork conversions or are they a completely different animal?
4) I've been hearing a lot about the guy that was doing the fork swap conversion is retiring. Is this still the case and is there anyone else that has the skills and machines to do the fork swap?

Thanks guys
C

How did this end up for you? Did you have to get new steering stem bearings in the conversion?

[soup-n-sandwich]

Hello Ebulic19,
Well a few thing have changed. So I have a 48mm Kayaba SSS fork off of a Kawa KX450 instead of the Yamaha. The steering stem has been pressed out of the OEM KDX bottom clamp and refitted to the triple clamps of the KX450. I have new stem bearings also but haven't pressed them on yet. I'm working on the rebuild of the engine now and will send the fork and shock to get worked on as the fork for the KX450 is a tad too long compared to the KDX fork. I'm talking about the distance between the center of the axle and the top of the fork. Overall the KDX fork is actually longer but that doesn't really matter as it's not the critical measurement. The suspension needs a revalve too so it's all going to Factory Connection in NH. A while ago I posted lots of pictures showing the weights of every component I took off of the KDX as I broke everything down. Funny thing is that the KDX fork and clamps where 5 pounds heavier than the much larger 48mm units off of the KX450!

The progress has been slow but this is only because I'm working on the shop to make the rest of this project much easier. Adding a spray booth/welding area with a 3200CFM blower that will suck the paint off the walls. I'm almost done with this and then I can resume on the rest of the complete rebuild, but I'll keep everybody posted as progress is made.

[brademan76]

Lots of different triple options for using 48mm SSS/AOS forks on KDX without swapping over the stem. The key is the adapter bearing and triples with appropriate length stem. Lots of discussion here:
viewtopic.php?t=26420

[ebulic19]

Hello Ebulic19,
Well a few thing have changed. So I have a 48mm Kayaba SSS fork off of a Kawa KX450 instead of the Yamaha. The steering stem has been pressed out of the OEM KDX bottom clamp and refitted to the triple clamps of the KX450. I have new stem bearings also but haven't pressed them on yet. I'm working on the rebuild of the engine now and will send the fork and shock to get worked on as the fork for the KX450 is a tad too long compared to the KDX fork. I'm talking about the distance between the center of the axle and the top of the fork. Overall the KDX fork is actually longer but that doesn't really matter as it's not the critical measurement. The suspension needs a revalve too so it's all going to Factory Connection in NH. A while ago I posted lots of pictures showing the weights of every component I took off of the KDX as I broke everything down. Funny thing is that the KDX fork and clamps where 5 pounds heavier than the much larger 48mm units off of the KX450!

The progress has been slow but this is only because I'm working on the shop to make the rest of this project much easier. Adding a spray booth/welding area with a 3200CFM blower that will suck the paint off the walls. I'm almost done with this and then I can resume on the rest of the complete rebuild, but I'll keep everybody posted as progress is made.

Thanks for updating. I am eying up a set of KYB SSS off of a 2016 YZ250F, along with complete triples, front wheel w/axle, and the complete brake front brake system for $400. Does that sound like a fair price? I have not a clue what the part-out market is like.

The KDX fork is much longer top to bottom of lugs just based on how low they hang underneath the axle i'd presume, correct?

Enjoy the shop! Thanks again for reaching back. I am trying to do as much DD as possible before purchasing anything.

[soup-n-sandwich]

Hello Ebulic19,
Well a few thing have changed. So I have a 48mm Kayaba SSS fork off of a Kawa KX450 instead of the Yamaha. The steering stem has been pressed out of the OEM KDX bottom clamp and refitted to the triple clamps of the KX450. I have new stem bearings also but haven't pressed them on yet. I'm working on the rebuild of the engine now and will send the fork and shock to get worked on as the fork for the KX450 is a tad too long compared to the KDX fork. I'm talking about the distance between the center of the axle and the top of the fork. Overall the KDX fork is actually longer but that doesn't really matter as it's not the critical measurement. The suspension needs a revalve too so it's all going to Factory Connection in NH. A while ago I posted lots of pictures showing the weights of every component I took off of the KDX as I broke everything down. Funny thing is that the KDX fork and clamps where 5 pounds heavier than the much larger 48mm units off of the KX450!

The progress has been slow but this is only because I'm working on the shop to make the rest of this project much easier. Adding a spray booth/welding area with a 3200CFM blower that will suck the paint off the walls. I'm almost done with this and then I can resume on the rest of the complete rebuild, but I'll keep everybody posted as progress is made.

Thanks for updating. I am eying up a set of KYB SSS off of a 2016 YZ250F, along with complete triples, front wheel w/axle, and the complete brake front brake system for $400. Does that sound like a fair price? I have not a clue what the part-out market is like.

The KDX fork is much longer top to bottom of lugs just based on how low they hang underneath the axle i'd presume, correct?

Enjoy the shop! Thanks again for reaching back. I am trying to do as much DD as possible before purchasing anything.

Oh yea that's a good price for all of that. I did the same thing, wheel, brake, axle from the KX450. The KX250F and the KX450F use a different set of clamps and different fork legs. The 250F is 47mm and the 450F is 48mm. ALso in certain years of those bikes the 250F is a Showa fork and the 450F used a Kayba unit. You might find the same with the Yamaha but not sure.

Yes the KDX fork overall length is much longer than the inverted fork design. However it's the length from the center of the axle to the top of the leg that matters. BUT the inverted Kayaba fork that I have is longer than the KDX fork when measuring the center of the axle to the top of the leg. So this has to be addressed internally otherwise you would have to slid the fork up in the clamps. Factory Connection is very much aware of this and will make the necessary mods when re-valving the fork for me.

[ebulic19]

Hello Ebulic19,
Well a few thing have changed. So I have a 48mm Kayaba SSS fork off of a Kawa KX450 instead of the Yamaha. The steering stem has been pressed out of the OEM KDX bottom clamp and refitted to the triple clamps of the KX450. I have new stem bearings also but haven't pressed them on yet. I'm working on the rebuild of the engine now and will send the fork and shock to get worked on as the fork for the KX450 is a tad too long compared to the KDX fork. I'm talking about the distance between the center of the axle and the top of the fork. Overall the KDX fork is actually longer but that doesn't really matter as it's not the critical measurement. The suspension needs a revalve too so it's all going to Factory Connection in NH. A while ago I posted lots of pictures showing the weights of every component I took off of the KDX as I broke everything down. Funny thing is that the KDX fork and clamps where 5 pounds heavier than the much larger 48mm units off of the KX450!

The progress has been slow but this is only because I'm working on the shop to make the rest of this project much easier. Adding a spray booth/welding area with a 3200CFM blower that will suck the paint off the walls. I'm almost done with this and then I can resume on the rest of the complete rebuild, but I'll keep everybody posted as progress is made.

Thanks for updating. I am eying up a set of KYB SSS off of a 2016 YZ250F, along with complete triples, front wheel w/axle, and the complete brake front brake system for $400. Does that sound like a fair price? I have not a clue what the part-out market is like.

The KDX fork is much longer top to bottom of lugs just based on how low they hang underneath the axle i'd presume, correct?

Enjoy the shop! Thanks again for reaching back. I am trying to do as much DD as possible before purchasing anything.

Oh yea that's a good price for all of that. I did the same thing, wheel, brake, axle from the KX450. The KX250F and the KX450F use a different set of clamps and different fork legs. The 250F is 47mm and the 450F is 48mm. ALso in certain years of those bikes the 250F is a Showa fork and the 450F used a Kayba unit. You might find the same with the Yamaha but not sure.

Yes the KDX fork overall length is much longer than the inverted fork design. However it's the length from the center of the axle to the top of the leg that matters. BUT the inverted Kayaba fork that I have is longer than the KDX fork when measuring the center of the axle to the top of the leg. So this has to be addressed internally otherwise you would have to slid the fork up in the clamps. Factory Connection is very much aware of this and will make the necessary mods when re-valving the fork for me.

That makes sense, what ID/OD stem bearings did you end up with? Are you thinking you can use the OEM KDX bearing for the bottom triple clamp?

[soup-n-sandwich]

Hey, I used Tusk bearing kit for the stem. They are suppose to be an exact match to the OEM ones but honestly I haven't yet got to that yet. I'm about to tear into the engine. You see this build is not just a ground up restoration but a tribute bike for not only the KDX model but also Jeff Fredette. So it's not easy to rebuild a KDX in general because a lot of the parts aren't available but it's even more difficult to make one that doesn't have a spec of lime green on it, custom parts to improve the stock stuff and a color theme that doesn't exist unless I make it. So the progress has been slow. The other side is if I'm going to go this far with it I wanted to improve all of the weak links of the bike. Suspension is one of those, hydro-clutch and likely an electric start. I really don't feel that the e-start is necessary for bike in general as you can start this bike with your hand but when it come to competition where the race requires a dead engine start I think anyone that had to use a kick starter in that circumstance is at a disadvantage. I think it's wrong and quite stupid to have a dead engine start in any race because now the racers outcome depends on them starting their bike quicker than anyone else??? What the hell does that have to do with skill and consistency? Really Stupid. The bike should be running and the hands on the helmet would be the right way to do Hare Scrambles and enduros. If you need me to measure the stem bearings let me know man.

[Chopperpilot]

This may be just me, but after running two different USD forks (93KX and then 2003YZ250) that were both longer than the KDX forks....... I don't really see the big deal of getting the forks 'shorter'. I see this same idea in mountain bike circles as well. I have yet to have regrettable handling characteristics on a mountain bike or dirt bike with running a longer than stock front end. I've found I like it better. Running the adapter bearing you can get off of amazon makes most of these swaps much easier. For stops on the YZ front end, I ended up buying 2 extra fuel tank rubber snubbers for the frame and epoxied them in a spot on the outside of the frame that the fork tubes will run into before the triples hit the gas tank.

[billie_morini]

Soup said, "You see this build is not just a ground up restoration but a tribute bike for not only the KDX model but also Jeff Fredette."

I LIKE that!

[billie_morini]

Chopper said: "Running the adapter bearing you can get off of amazon makes most of these swaps much easier."

What is an adapter bearing? Will someone provide a hyperlink, please?

[Chuck78]

It's a bearing that is of different dimensions than stock but is the same on the frame side outer bearing race diameter, but matches the fork swap's steering stem on the bearings inside diameter, and is the same or similar enough height as the stock KDX bearings.

Generally all those lower bearings are going to be the stock KDX size for most fork swaps, however the top bearings are going to be the one that has to be different since the KDX uses a 25 mm or 26 mm inside diameter bearing to match the stem and everything else uses 28 mm or 30 mm inside diameter.

The particular size of the upper conversion bearing necessary is not a common industry standard off the shelf size. You can get a Japanese NTN bearing or an all balls bearing for the Honda triple clamp upper steering stem position but it is slightly shorter height than stock so you will need a spacer under the race in the frame at least as far as my preference goes, versus setting the race down in the frame and putting spacers on top of the steering stem inner race.
30x47x12 is the bearing size for the Honda CR and CRF steering stems in the KDX frame, and then removing the Honda lower bearing as it's not quite the right size either, and installing a stock KDX bearing on the bottom of the Honda triple clamp steering stem.

When using a KX/KX-F or Yamaha YZ250, YZ250F, YZ450, WR250, WR400/426/450 fork and triple clamp, their steering stem upper diameter is 28 mm. There is no industry standard bearing size that fits the required dimensions, but now due to this being something that is desired for for conversions, on Amazon eBay and AliExpress you can buy a special conversion bearing in a non-standard size of 28x47x12 as well as 28x47x15, and using the stock KDX lower bearing or a replacement for it since you don't really reuse them after removing a used one. The 15 mm tall height is preferred but on the 30 mm steering stem bearing, those only come in a 12 mm tall height so as I said a spacer is required to make up the rest of the distance since the frame bearing pocket is 15 mm tall.

[KDXGarage]

billie, around 15 - 20 years ago, the concern was that 1992 and newer KX125, KX250, KX250F, KX450F (2008 KLX450R) came with a larger diameter upper bearing and larger ID head tube on the frame. The newer bearing is too large to fit down in the various KDX / KLX250R / KLX300R / KLX650 / KLX650R/ 1991 on back to whenever KX125 - KX250. Also, KX500 2004 on back to whenever.