H Series with Kayaba SSS fork assembly from a Yamaha

Questions and comments about converting to beefier forks..
Post Reply
soup-n-sandwich
Member
Posts: 20
Joined: 03:08 pm Feb 09 2020
Country: United States

H Series with Kayaba SSS fork assembly from a Yamaha

Post by 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
User avatar
doakley
Gold Member
Gold Member
Posts: 1220
Joined: 02:58 pm Mar 10 2016
Country:

Re: H Series with Kayaba SSS fork assembly from a Yamaha

Post by 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.
User avatar
SS109
KDXRider.net
KDXRider.net
Posts: 5184
Joined: 05:11 am Aug 23 2009
Country: USA
Location: Tucson, AZ, USA
Contact:

Re: H Series with Kayaba SSS fork assembly from a Yamaha

Post by 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.
AZ State Parks OHV Ambassador - Trail Riders of Southern AZ
'11 GasGas EC250R
Current KDX: '98 KDX220
Old KDX: '90 KDX200 -White/Blue
My Youtube Channel: WildAzzRacing
soup-n-sandwich
Member
Posts: 20
Joined: 03:08 pm Feb 09 2020
Country: United States

Re: H Series with Kayaba SSS fork assembly from a Yamaha

Post by soup-n-sandwich »

SS109 wrote: 02:16 pm Jul 30 2022 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
User avatar
doakley
Gold Member
Gold Member
Posts: 1220
Joined: 02:58 pm Mar 10 2016
Country:

Re: H Series with Kayaba SSS fork assembly from a Yamaha

Post by 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).
User avatar
KDXGarage
KDXRider.net
KDXRider.net
Posts: 13665
Joined: 06:45 am Nov 01 2004
Country: United States of America
Location: AL, USA
Contact:

Re: H Series with Kayaba SSS fork assembly from a Yamaha

Post by 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.
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128
User avatar
SS109
KDXRider.net
KDXRider.net
Posts: 5184
Joined: 05:11 am Aug 23 2009
Country: USA
Location: Tucson, AZ, USA
Contact:

Re: H Series with Kayaba SSS fork assembly from a Yamaha

Post by 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.
AZ State Parks OHV Ambassador - Trail Riders of Southern AZ
'11 GasGas EC250R
Current KDX: '98 KDX220
Old KDX: '90 KDX200 -White/Blue
My Youtube Channel: WildAzzRacing
Post Reply