Question about 2003 KX250 fork Upgrade

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3/7/2018 10:49 PM

Not sure if I should have posted this in the tech help or if bike builds is appropriate if it's not I apologize but I'm really hoping someone can give me a quick answer to my question as I'm going to be starting on a 2003 KX250 that I picked up its really low hour and in great shape the forks really aren't that bad as the old style KYB open bath forks, of course theyre no match for I the KYB SSS Yamaha YZ Forks and i would LOVE TO upgrade to a set of KYB SSS forks.

My question is if I can accomplish this with the stock clamps on the 2003 KX250 the reason I asked that is because the 2003 KX has the same Forks that came on the 2004 Yamaha YZ's the older style open bath 48 mm Forks.
I remember reading that on the 04 YZ you could use the stock clamps to mount up the KYB SSS Forks without making any other modifications except maybe wheel spacers.
The 2003 KX250 and 125 have the same larger diameter upper tube for the forks as the 04 YZ's.
I have a good feeling the 2006-up KYB SSS Forks will fit perfectly on my KX250 without changing the triple clamps. Might be some slight wheel spacer mods/swap to figure out but don't really think it'll be THAT difficult.
Id REALLY like to stick with the OEM wheels too they are those cool looking did shoulderless rims that came on the KX125/250 for a couple years and I really like them....any input would be greatly appreciated!! Thanks

3/8/2018 2:05 PM

If you know someone with an 06 up YZ try it out. If you are going to commit I would go with the 08 up forks they shortened something in the internals that helped those forks a bunch. I would see the difference in how big the axle hole is compared to your stock kawi axle or you can go the more expensive route and get a suspension shop to do the lower lug swap.

3/8/2018 4:20 PM

JohnnyT_983 wrote:

If you know someone with an 06 up YZ try it out. If you are going to commit I would go with the 08 up forks they shortened something in the internals that helped those forks a bunch. I would see the difference in how big the axle hole is compared to your stock kawi axle or you can go the more expensive route and get a suspension shop to do the lower lug swap.

I WISH I knew somebody with an 06-up YZ125/250 or YZ250f/450f Bec I would've already attempted it.....I don't know anything about a part of the fork internals that was shortened but I do know that there was an overall width change where the spacing between the forks was widened utilizing new triple clamps around the 2008 year model and larger width wheel spacers, something that using my stock Kawi clamps won't affect. A couple years ago I got to demo both the 2015 YZ125 and YZ250 2-strokes and the forks were so butter straight out of the gate on the demo bikes!! I had been riding a 2003 YZ250 with RG3 suspension and bone stock those forks blew mine away and I was instantly faster AND found myself doing things on the track with absolutely no holding back because I had confidence in my front end although I didn't care for the aluminum chassis as compared to my steel frame.

Being 6'3 by default I ride over the front of the bike so almost all my confidence in my bike comes from the front end and the forks.

I'm on the hunt for a set and regarding your "shortened" comment I know the YZ250f forks were/are 1/2" shorter, is that what you meant? I was really hoping someone might have done the swap already, hopefully someone meticulous that can explain any road blocks they ran into but so far I may end up being the guinea piggy here ...hopefully not. What's funny is that the 48mm kyb forks that came on my 2003 kx250 and all KX's from 03 thru 05 these are the EXACT SAME forks that Yamaha ran on all their 2004 big bikes and I know that swap to the KYB SSS forks is cut and dry you can use the stock clamps for the swap on the 2004 YZ/YZf's ...now logic dictates that since the swap is that simple on the 04 Yamahas that I should be able to do exactly the same on my KX250 in which my only concern would be front wheel spacers and linening up the front wheel keeping my shoulderless Kawasaki OEM wheel....I'm 99.99999% sure that since the same forks were used on the Yamaha and the Kawi that the front axle should be the same diameteter.

But there's always that chance and I'm really hoping someone will chime in and confirm or denymy thoughts based on the research I've done this far.....I know a lot of people have put the KYB KX450 2006-2011 forks on on the KX125/250 from 03-up and those forks are absolutely Identical to the to the Yamaha KYB SSS version except Yamaha has some proprietary valving spec exclusive to them but that's an internal difference that has nothing to do with dimensions or the ability to mount them up....I really want to keep my stock clamps in play here due to the flex characteristics Kawasaki built into the clamps to work in unison with the bike. I found this out the hard way when I put a set of those beautiful RG3 Clamps they were making out if billet aluminium and I hated the way the bike felt afterwards but they were noticeably more rigid and it threw off the feel of the bike.

Sorry for the long winded post I hope people still read it as I tried to be 100% clear as to why I'm trying to go this rather unique route. If I can pull it off this bike will go from awesome to incredible!!

3/9/2018 1:12 PM

Fair enough. I did the 09 kx250f form conversion on on of my 06 KX250s and regretted the conversion once it was done. And with the conversion I retained my stock KX axle and spacers, given This isn’t what your looking for I will still talk about it. I’m not sure on the earlier gen Sss stuff but I know the showa twin chambers had to have a kx250f stem and clamps then I added some to the original fork stop.

Now I’ve got a buddy with a newer yz450f and I have an 07 kx250 currently that I could try the conversion (at least pushing the forks in) to let you know if that part is going to work for you.

I know the axle diameter on his 450 is bigger than that on my kx250 but hey I’ll give it a go. Give me about a week and I should have it tested out.

If it’s of no help I won’t bother but hey it’s something.

3/10/2018 8:59 AM

JohnnyT_983 wrote:

Fair enough. I did the 09 kx250f form conversion on on of my 06 KX250s and regretted the conversion once it was done. And with the conversion I retained my stock KX axle and spacers, given This isn’t what your looking for I will still talk about it. I’m not sure on the earlier gen Sss stuff but I know the showa twin chambers had to have a kx250f stem and clamps then I added some to the original fork stop.

Now I’ve got a buddy with a newer yz450f and I have an 07 kx250 currently that I could try the conversion (at least pushing the forks in) to let you know if that part is going to work for you.

I know the axle diameter on his 450 is bigger than that on my kx250 but hey I’ll give it a go. Give me about a week and I should have it tested out.

If it’s of no help I won’t bother but hey it’s something.

JohnnyT ....that would be AWESOME if you were able to do that!!! I'm pretty sure the axles should be the same diameter but this is the only way to find out.

I want to retain my stock clamps and wheel if possible ...the clamps Bec they're designed from the factory to flex with the chassis and the front wheel would be more for aesthetics

Please let me know if you're able to try this I would so appreciate it

3/10/2018 4:19 PM

Measure your hub width wise, distance between fork tubes outer edges, axle diameter, outer diameters on the upper fork tube, and try to get a somewhat accurate measurement of how far the brake rotor is from the edge of the fork lug.

I will take those same measurements on my YZ tomorrow and we can cross reference them and see what needs to change.

I think I’ve read about the swap before and it requires some doing I think. Maybe you’ll need a Yamaha front wheel.

If you're not mixing gas, you're not haulin ass.

3/10/2018 9:59 PM