Kdx250 fork swap

Questions and comments about converting to beefier forks..
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Stevey30
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Kdx250 fork swap

Post by Stevey30 »

May have aquired a 92 or 93 kdx250. I want to upgrade the forks, will a late 90’s or early 2000 kx250 bolt on, or do you have to do a srem swap like on the 200 and 220 models?
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Re: Kdx250 fork swap

Post by KDXGarage »

Welcome back to kdxrider.net.

Would you care for some help in identifying which exact bike you have bought? Can you post a VIN and engine number?

If it is a 1991 - 1994 USA KDX250, then you could buy some 1991 - 1995 KX125 / 1991 - 1995 KX250 / 1991 - 1996 KX500 forks and front wheel (maybe brake system, too). You can keep the stock triple clamps. If you want to do the KX clamps, then any KX500 will do and KX125 / KX250 / KX250F / KX450F newer than 1991 (1992 and newer) will require a stem swap.

DO NOT try to add on a 1992 - 1995 KX125 / KX250 upper clamp. The offset is different.

The deal on the stem swap is the upper bearing is a lot bigger due to the steering tube of the frame being larger on top.
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Stevey30
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Kdx250 fork swap

Post by Stevey30 »

Thanks for all the info Jason, i am trying to meet with the guy today to buy it. I believe its a 92 or 93 model, will know more soon. I guess if all goes well i will do a fork swap like i am doing to my KDX200.
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Re: Kdx250 fork swap

Post by KDXGarage »

You're welcome.

Put the KDX250 forks on the 1996. :mrgreen:

http://www.kdxgarage.com/vininformation.html (my personal site)

M = 1991
N = 1992
P = 1993
R = 1994
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Re: Kdx250 fork swap

Post by Stevey30 »

I bought a complete 2002 KX250 front end for my 96, can’t wait to get it done
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Chuck78
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Kdx250 fork swap

Post by Chuck78 »

Thanks for posting up all that information, Jason.

My buddy had two bad crashes last weekend, the second one was in a nasty rocky section, and I noticed his fork was leaking immediately after when we loaded it in the truck. The chrome tube got gouged, so we'll be shopping for another set of forks.

Either need another KDX250D fork tube, or upgrade to the KLX300R or the list of non-stem swap candidates.
Thanks for the info, just what I was looking for!

I think I might look into some of those neoprene slip-on covers that I read about for mine, as I need to preserve the KX forks through all the many crashes they are likely to endure on my KDX swap!



EDIT: For ease of successful search results for others, I'll add this info I've compiled including from the post below and not make another post to dredge up an old post to the top, as it's a very thorough listing of what forks can be swapped WITHOUT a stem swap:


Reviving an old thread for info consolidation, but here's what I've learned.

KLX300R forks are the easiest swap, as they are valved similar to the stock KDX fork for woods, but improved valving, are the correct height without mods, and come with a decent spring rate for a lightweight woods rider at .37 or .38kg/mm. KDX wheel is a direct fit into these forks without any axle adapters. These are still the same cartridges and tube diameter as the stock KDX forks at 43mm, but they are significantly less flexy than the KDX forks due to being inverted. These are lacking the full external adjustment that the KX forks have, unfortunately, but come valved pretty decently stock, so these are absolutely the easiest upgrade with almost no hassles whatsoever.

1988+ KX500 use the same steering stem length and bearing sizes as the KDX (all KDX models 1986+).
1988 are conventional 43mm cartridge forks
1989 are a 1-year-only 46mm conventional cartridge fork (sounds like a great fork to revalve for woods riding)
1990-1996 are 43mm inverted cartridge forks. I believe some of the later years there have a mid valve (93-95 KX125/250 43mm forks do).
1997-2004 are 46mm KYB inverted cartridge forks with mid valves. slightly softer valving vs the otherwise virtually identical 96-97 KX125/250 motocross forks, as there was no longer an Open Class for the 500cc 2-strokes and the bikes were tuned more for aggressive recreational riding vs well groomed MX track racing. 96-97 KX125 stock springs are .38kg rate for those riders running the KX500 forks or triples, needing a lighter spring than the stock KX500 .40kg spring. 98 125/250 forks may be the same but there was one year with a different sized top clamping area on the tubes/triples, 98 or 99 perhaps. 98-99 KX125/250 all had progressive rate springs stock, which are frowned upon. KX500 had same straight rate springs all years of the 46mm inverted forks, 97-04. KX wheel swap or KDX custom machined axle spares are needed due to different axle diameters.

KDX250 1991-1994 triples are a direct bolt in, as are their inverted forks, but the valving is a little bit odd on these, look into this further for yourself. These triples will clamp onto certain years of KX forks however.
These forks all supposedly share the same upper and lower clamping diameters:
1991 - 1994 USA KDX250
1991 - 1995 KX125
1991 - 1995 KX250
1991 - 1996 KX500
(and I am assuming KLX300R as well, see below, triples could likely be the same or nearly identical to the 1990's KDX250)

KLX300R triples apparently will clamp directly to 1993-1995 KX125/KX250 forks to bolt directly into a KDX if using the KX front wheel. As with all other KX, YZ, etc Motorcross forks, they need revalved for woods riding in order to still get traction in the rougher sections. These are also taller, but bar risers / fat bar adapters will allow you to slide these up considerably in the KLX triples. Apparently I read that you can also use KLX330 (300? 230?) springs which are similar but shorter, and some spacers in the cartridge, to lower the fork internally.

Lastly, there are a few early years of KX125/250 triples which WILL bolt directly into the KDX frames, so the forks/triples and matching KX wheel will be a direct bolt on, but as with the rest, they will need internally lowered or else bar risers / fat bar adapters added to be able to slide the fork tubes up in the triples to lower back to stock KDX height and stock intended steering geometry.
1988 KX125/250 is a conventional cardtridge 43mm fork
1989 KX125/250 is a conventional cardtridge 46mm fork
1990 KX125/250 is an inverted/upside-down 41mm cardtridge fork
1991 KX125/250 is an inverted/upside-down 43mm cardtridge fork
the 125 came stock with .37kg springs all years 88-91. The 250 stock had .38kg and .39kg (91) springs those years). The KX500 years/sizes/types are the same as the 125/250 88-91.

On KX front wheels,
88-92 (& even earlier, basically all disc brake fork models) use a 17mm axle with 6203 bearings (17mm id x 40mm od x 12mm wide)
KX500 is the same but through 1993 also.
93+ KX125/250 & 1994+ KX500 use a 20mm axle with 6904 wheel bearings (20mm id x 37mm od x 9mm width). Some models as late as 2019 use this exact bearing part number https://www.partzilla.com/product/kawasaki/92045-1284
The KDX models use a 15mm axle with 6202 front wheel bearings (15mm x 35mm x 11mm)

Most other swaps of other KX forks will most likely require the KDX steering stem to be heated and pressed out of the KDX triple clamp and fit to the donor triple, as bearings are not available in the sizes needed. Other model forks will likely require the same, but I'm sure there are some that do have the required conversion bearing sizes available to make their triples a more direct fit.


Steering stops will likely have to be modified on many of these, but that is an easier detail to overcome, so I'm not looking into that part of the fitment.
KDXGarage wrote: 05:28 am Aug 10 2018
Unless there is something I am missing, then the following are just a direct bolt-in swap on bearings and triple clamps:

1986 - 2006 KDX200
1997 - 2005 KDX220R
1991 - 1994 KDX250
1993 - 1996 KLX250
1997 - 2007 KLX300R
1993 - 1996 KLX650
1986? - 1991 KX125 (could be earlier)
1986? - 1991 KX250 (could be earlier)
1986? - 2004 KX500 (could be earlier)

Somebody correct me if I am wrong. Also, be sure to check steering stop engagement.

1992 + KX125 / KX250 / KX250F/ KX450F / KLX450R all have the larger top bearing.

I don't know about KLX offset, but KDX250 triple clamp offset is the same as 1991 KX125 / 1991 KX250 / 1991 - 1993 KX500. 1992 - 1995 KX125 / KX250 / 1994 - 1996 KX500 is a little smaller offset.



Here's some KYB 46mm open chamber fork tips on disassembly, seal replacement, access to valving on both the base valve and the mid valve / rebound. This is the same basic fork as the 97-04 KX500, 96-98 or 99 KX125/250, and probably very similar to the 1995 mid valve 43mm KYB KX125/250 forks.

https://www.thumpertalk.com/forums/topi ... bly-guide/
Last edited by Chuck78 on 04:08 pm Aug 11 2022, edited 7 times in total.
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Re: Kdx250 fork swap

Post by KDXGarage »

Dang. I hope he heals soon.

As for the bike, that tube may indeed be toast.

Unless there is something I am missing, then the following are just a direct bolt-in swap on bearings and triple clamps:

1986 - 2006 KDX200
1997 - 2005 KDX220R
1991 - 1994 KDX250
1993 - 1996 KLX250
1997 - 2007 KLX300R
1993 - 1996 KLX650
1986? - 1991 KX125 (could be earlier)
1986? - 1991 KX250 (could be earlier)
1986? - 2004 KX500 (could be earlier)

Somebody correct me if I am wrong. Also, be sure to check steering stop engagement.

1992 + KX125 / KX250 / KX250F/ KX450F / KLX450R all have the larger top bearing.

Neoprene covers = mud and grit holders, in my book.
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