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KDX/KX info

Joined
Dec 25, 2003
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#1
Back in the mid eighties I fitted a KDX 200 engine to a kx125 rolling chasis. I would like to do this again as it works out to be a cheap competive bike. What I would like to know what engines fit what frames? I know you can fit any engine to a frame if you want. What I really want ti know is the width of the swing arm pivot on the KX's and which ones fit the KDX engines. I would prefer to use a 99 on KX chasis and a later model KDX engine.
Marty
 
Joined
Feb 1, 2001
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#2
I still got my 94 with an 89 motor and am thinking of doing the same thing. Since Jeff Fredette built this one I would probably call him again. I tried a Gas Gas in 2002 and a WR250 in 2003 the Gas Gas was unreliable and the wr is still too heavy
 

Svock

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Nov 28, 2001
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#3
Hello,

I have a 1996 KDX 200 engine fitted into a 1996 KX 125 frame.  This required "machining" the KX swingarm to fit the wider KDX engine.  The word machining is in quotes because I simply ground each side of the swingarm untill it fit.  Also, the pivot bolt for the swingarm is a larger diameter on the KX than the KDX engine.  This requires you to drill out the cases of the KDX engine.  This is not as bad as it seems....Just go slow.  I smoked a $35 bit in the process.  Besides these modifications, you must also fab and weld new motor mounts, including the bottom, front, and upper aluminum mounts.  The KX 125 frame does not have the mounts for the rear headstay mount.  While it is possible to fab a mount onto the KX frame if you feel the need, note that you will have to build a custom gas tank.  On my bike I simply "machined" the head stay off the head.  I now have only the front head stay.  This has posed no problems whatsoever.  It is also notable that the pipe mounts do not line up, and must be relocated.  The countershaft sproket line up very niceley with the rear sprocket, and I have had no abnormal wear problems or de-railment.  Aside from this, the wiring is different length, and the Ignition is located in different locations on each bike.  The regulator and ignition are both mounted inside the airbox of my KX 200.  No splicing was required.  Also, I must say, that after a few simple clicker adjustments, this is THE BEST BIKE I HAVE EVER RODE!!!! I LOVE THIS BIKE!!!  Email me with any more questions.  I would be glad to help a future KX 200 rider ;)

Svock
 
Last edited:
Joined
Sep 11, 2000
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#4
Hey vtcoh or anybody out their. Will a kdx motor fit into a 99 KX250 chasis. I rode a friends new KDX today and wish I had one. I have a 13oz flywheel weight and steel clutch plates and still think the KDX's motor is far better for woods riding. Now I am thinking of selling my motor and installing a KDX motor and revalving my suspension to try to make it plush like KDX.
Any help would be appreciated.
Thanks
 

Svock

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Joined
Nov 28, 2001
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#5
It will work.  Key word is "work."  It will take some "work" to do it.  Basically it is NOT a simple bolt in mod.  It requires fabricating new motor mounts as well as modifying the KDX engine and your KX Swingarm.  It WILL work though.  It comes out as a GREAT BIKE!! GO FOR IT!

 

Svock