KDX Hybrid by HRDROKN .pdf
Nom original: KDX_Hybrid_by_HRDROKN.pdfTitre: Hey GuysAuteur: Simon Job
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I just wanted to share with you all my 99' KX125 / 03' KDX220 build. This build is in progress
and comments are welcome!
I had picked up a fairly clean 2003 KDX 220R a few months back for $900. I had been riding
this bike comparing it to my 300exc... if there is such a thing. There are a few things I like
about the KDX and many things I like about the KTM! The KDX is easy to ride... the KTM can
be a handful and I feel it the next day, but she handles so much better at speed. So rather
than my original plan of a KX fork conversion etc. I picked up a 99' KX125 for the best of
both worlds? Of course that is only what I have read...
Started stripping down the KX chassis early this morning and noticed that my lower motor
mounts are of the double variety? Thought I read that that was different in the 99' compared
to the 00'-02' frames.
Not a big deal by any means... wonder if it was a change that some of the later production
frames received in that year?
Also ordered up a 18" wheel and spokes to mate up with the KX hub.
I think I will take the forks and shock up to Dicks Racing for a rebuild/re-valve, since they
As of this morning the KX motor is out....
And now the KDX.....
After getting a first hand look at what’s needed, I see that the actual cut on the swing arm
is the least critical of the operation... you can do this with a hacksaw and file!
Did all the measurements and 9mm on each side is sufficient....
The greatest concern and area to get correct is the swing arm bushing. It has to be fairly
darn close, as it will set the overall compressed length.
Drilled the cases by 64ths to 21/32's then used a 17mm ream to finish....
Figured out a good way to hold the bushings while cutting.... I used the swingarm bolt in the
I then used a flapper wheel to clean the cut, then hit the bushings on a carborundum disc
and then a course stone to the target dimension.
With all the swingarm mods out of the way, it was time to see how she was going to line up
in the chassis...
And would the lower mounts line up..... it was close! So I will cut the lowers out and fab
Ive been playing with motor location as it compares to the pipe, airbox and fuel tank....
looks like things fit better the more you rotate the motor forward.
The boot on the airbox is too long and it seems as though the KDX boot would be a better
With forward rotation, the pipe just misses the down tube.... a little dent in the pipe should
provide desired clearance...
When you rotate the motor forward you lose the lower mount position...
And I have a solution....
Needed to remove the rear headstay to fit the tank in place.... this is how we do it old
I will clean it up before I send it off to RB... along with the carb.
With the motor rotated further forward as the goal... I put the swingarm, wheel and chain
on.... moved the motor around and I can't really tell much difference in regards to pressure
on the chain guide, at least no more/no less than taking a tooth off the front sprocket
So I guess I will keep the motor rotated forward and work on some new lower mounts...
After trying several different ways of configuring the airbox, I think the best solution is to
use the stock KDX box... it requires one of two modifications to fit correctly.
First and the best solution is to cut the stock KX airbox mounting tabs off and re-weld them
to match up with the KDX mounts. You can see it in the pics. EDIT: This is not the best way
to go as those tabs are used for the fender also! So the second way is the best!
Second, modify the stock KDX box and utilize the KX airbox mounts on the sub frame as is...
I went this route as I'm not set up to weld aluminum. After cutting the KDX box for
clearance I will fab some aluminum plate to cover the holes and provide for mounting.
Finished off the KDX airbox mount.....
I set it up with shock in place before taking all the suspension to Dick's. Hard to see from
this pic, but there is at least .125" all the way around.
Here is the fender without the bolts in.... but they line up and the KX fender fits the
contour of the box perfectly!
Got after the lower mount tonight, so this is what I came up with...
Finished up with the front mount...
Pipe is sitting all the way in the head and looks like a small dent in the pipe to clear the
downtube..... Hmmmm, just thinking that I don't have the exhaust gasket in there yet and
that should give me some more clearance? Bottom line with the motor rotated further
forward there is no need for a headpipe extension.
Picked up my suspension from Dick's Racing yesterday....
Sent the carb and head off to Ron Black today...
And now getting the frame ready for powder!
Just got my head and carb back from Ron Black.....
Truly a nice guy and does one heck of a job on his machine work! I noticed that the carb I
sent had a slight off-center bore and when it returned Ron had not only bored the carb, but
corrected the factory machine work in centering the bore! In speaking with Ron it was
apparent that he is all about a first class job!
Finished up the frame, welded the case saver hoops from the KDX frame and now she's
sitting at the powder coaters for a nice coat of silver....
So with the frame gone.... it's time to get some other things ready. I decided that I would
go to a 18" rear and settled on some black Excel's with ProWheel stainless spokes on stock
Picked up the frame from the powder coater today and was able to get a little assembly
done before work. The down side (besides work) was that in my rush to get the frame to
powder (before taking off to Disneyland), I completely forgot about the sub-frame.
I was able to get all the swingarm, linkage and shock bearings/seals replaced today along
with getting the motor in place...
I got a little more work done...
Front wheel laced up...