99' KX / 03' KDX Hybrid build......

HRDROKN · Post by **HRDROKN** » 01:39 am Aug 13 2010

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...

HRDROKN · Post by **HRDROKN** » 02:10 am Aug 13 2010

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 are local.

Another thing I noticed is that the KTM has a much steeper fork angle compared with the KX? I would think that (the KX) would not be so good for tight single tracks?

HRDROKN · Post by **HRDROKN** » 05:26 pm Aug 14 2010

As of this morning the KX motor is out....

HRDROKN · Post by **HRDROKN** » 05:30 pm Aug 14 2010

And now the KDX.....

HRDROKN · Post by **HRDROKN** » 05:35 pm Aug 14 2010

After getting a first hand look at whats 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 measurments and 9mm on each side is sufficient....

HRDROKN · Post by **HRDROKN** » 05:42 pm Aug 14 2010

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. And I would imagine it don't cut easy... probably hardened!

last pic for the day.....

frankenschwinn · Post by **frankenschwinn** » 08:15 am Aug 15 2010

I used a cutoff wheel on my 4" angle grinder to cut the bushings. Worked like a charm.

HRDROKN · Post by **HRDROKN** » 10:15 am Aug 15 2010

Ya.... I'm going to hit them with a carborundum wheel. I'm going to hit the case with a 41/64" and then a 21/32" which will be a tight 17mm and see how the fit is at that point. If she is too tight I will grab a ream from work.

HRDROKN · Post by **HRDROKN** » 07:48 pm Aug 20 2010

So I got some more work done today. Drilled the cases by 64ths to 21/32's then used a 17mm ream to finish....

HRDROKN · Post by **HRDROKN** » 07:56 pm Aug 20 2010

Figured out a good way to hold the bushings while cutting.... I used the swingarm bolt in the vise!

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.

HRDROKN · Post by **HRDROKN** » 08:03 pm Aug 20 2010

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 new ones....

HRDROKN · Post by **HRDROKN** » 02:00 am Aug 21 2010

Interesting...

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 fit....

With forward rotation, the pipe just misses the down tube.... a little dent in the pipe should provide desired clearance...

When you rotate the moto forward you lose the lower mount position...

And I have a solution....

HRDROKN · Post by **HRDROKN** » 02:19 am Aug 21 2010

Rear headstay needs to go.... this is how we do it old school!

I will clean it up before I send it off to RB... along with the carb.

Tedh98 · Post by **Tedh98** » 08:25 am Aug 21 2010

You may be doing it but just haven't mentioned it, but how is the c/s lining up with the swingarm pivot bolt?

That is the 1st thing I focus on and in my mind, the most important relationship of fitting the engine. Everything else can be modified to fit.

Post by **scheckaet** » 09:09 am Aug 21 2010

Tedh98 wrote:You may be doing it but just haven't mentioned it, but how is the c/s lining up with the swingarm pivot bolt?

That is the 1st thing I focus on and in my mind, the most important relationship of fitting the engine. Everything else can be modified to fit.

You are absolutely right, was gonna say the same thing. If you put it forward too much (or not enough) you may have issue with your sprocket alignment, chain getting too tight when shock is fully compressed. I'd spot weld then install everything with wheel+ tire, swing arm and chain to see how the chain behaves when the shock is totally compressed.

HRDROKN · Post by **HRDROKN** » 09:56 am Aug 21 2010

I will put the swingarm back on and double check....

HRDROKN · Post by **HRDROKN** » 08:51 pm Aug 21 2010

Well I put the swingarm, wheel and chain on.... moved the motor around and I can't really tell much difference.

So I guess I will keep the motor rotated forward and work on some new lower mounts...

Tedh98 · Post by **Tedh98** » 06:01 am Aug 22 2010

It could be a camera angle thing, but the engine looks like it is tilted too far forward to me. The sprocket looks low and it doesn't look like you could even slide a bolt through the future lower mount without it hitting the frame.

HRDROKN · Post by **HRDROKN** » 11:24 am Aug 22 2010

Tedh98 wrote:It could be a camera angle thing, but the engine looks like it is tilted too far forward to me. The sprocket looks low and it doesn't look like you could even slide a bolt through the future lower mount without it hitting the frame.

You are correct! Taking all the pieces into account, pipe, fuel tank, carb and airbox... I found that the further the motor was forward, the better potential fit of the components. The problem with that position is the lower motor mount, but I have a solution for this, just waiting for UPS to deliver the materials.

Any other reason to avoid this direction?

HRDROKN · Post by **HRDROKN** » 01:59 pm Aug 23 2010

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.

KDXRIDER.NET

KDXRIDER.NET

99' KX / 03' KDX Hybrid build......

99' KX / 03' KDX Hybrid build......