KDXRIDER.NET

Hello everyone. I'm new here. It's probably a bit premature to start this build thread, since I don't have the donor bike yet, but I'm excited about it and I'd like to get the kinks worked out before I start the build.

I'm new to dirt bike modification, but I've built enough rock crawlers to know my way around a grinder, welder, plasma cutter, etc. And this looks like a fun challenge, and it's a TON cheaper than building another rock crawler.

I currently ride a 2002 KDX 200 and I love it. But I love the idea of building a CR125 hybrid even more.

I'm currently looking for a donor roller cr125, then the madness will begin. So hit me up if you have any leads. I'm in Utah.

Well, I found my donor, a 2002 CR125. With all the great trails finally opening up, I probably won't start the hybrid build 'till the winter. I don't think i could stand a month of downtime on my bike.

Here's the KDX (ignore the dirty garage)



Here's the CR:

Wow, a whole two days to track down a donor CR! I'm considering a CR hybrid myself, so I'll be following this with great interest. Thanks for posting from the very beginning!

Thanks. I promise to take lots of pictures. I'm no expert on what needs to be done for the conversion, so it'll be a LONG thread with lots of questions and chit-chat (I apologize in advance). But I also promise to take LOTS of pictures with detailed explanations. I'm an instructional designer, so I'll try to make it understandable to an 8th grader. We'll see how that goes

I'm having a hard time tracking down a 17mm reamer. Any suggestions on where to get one? Is this the right type? http://cgi.ebay.com/2pc-17MM-17H8-Machi ... 962wt_1139

Also, since I can't send PMs for some reason, I'll ask it here. Just to triple-check, I want my swingarm bushings cut down to 47mm each, right?

More good news. My buddy has offered to let me ride his CR150F while I build this, so I can still ride mid-build.

nothing is set in stone when it comes to cutting, every bike is different. It should be close to what you have read though. just make some measurement of the kx and kdx swingarm, and kx and KDX engine, then do the math

I thought you didn't have to cut the swingarm on the CRs, just the bushings. Regardless, I'll be measuring 4 times and cutting once.

I found a buddy with an adjustable reamer (not ideal, but I'll take what I can get), a mill, a lathe, and a tig welder. Looks like I'll be starting this build this weekend. My aggressive goal is to get the KDX engine in the CR frame by the 4th of July.

The trick is to get the CR swingarm and the KDX motor on the bench. You know where the sprocket has to end up. With the bearings and bushings installed in the CR swingarm it will be pretty easy to measure what has to be done to the bushings. Most people doing CR hybrids have had to grind a bit on the CR swinarm to cleara part on the KDX motor. You'll see what's up when they are both on the bench.

A buddy of mine is doing a KX/KDX right now. I'm giving him a little help. We keep getting reminded that there is an order of operations:
Get two bikes you want to put together to make one better one.
Work out the swingarm issues
Work out the pipe, airbox, gas tank, and radiator issues
CUT MOTOR MOUNTS LAST. Motor mounts follow the best position of the motor.

I started motor mounts too early and had to do them again. I'm not saying my buddy did the same, but he could have...

Have fun

KarlP wrote:The trick is to get the CR swingarm and the KDX motor on the bench. You know where the sprocket has to end up.

How do I make sure the sprocket is in line? Hybridracing65 made it sound like you center the engine in the CR swingarm and it all turns out perfect. Not to mention that the KDX engine fits in the lower motor mounts of the CR.

Should I just make a mark on the CR swingarm where the CR sprocket is? Then just make sure the KDX sprocket lines up?

I'm probably over-thinking it. It'll probably make perfect sense when it's on the bench.

Whoa there!
http://kdxrider.net/forums/viewtopic.php?t=10307
The swing arm does not require any cutting according to this guy who used an 03(02-06 are the same).
What even cooler is that the bottom motor mounts lined up perfectly as well. This guys thread is pretty self explanatory.

yeah, that's the thread I've been referencing. It sounds like the swingarm is already wide enough, i just need to cut the CR bushings. Front motor mount will be a cinch since the swingarm and lower engine mount will position the motor for me. Sounds pretty simple.

I think most people are so used to seeing a KX build that they forget how different the CR build is.

I almost bought an 02 cr125 after reading that thread, lol. Very simple.

yeah, that thread is exactly why I chose a '02-'07 CR over a KX. Sounds like I could do it in a week or two. That's the goal at least. I should have the motor mounted by July 4th. Then it's tank, pipe, wiring, etc to get it all going. I'll be making this street legal too, since some of the best singletrack in the country is right up the road from me.

The fact that the KDX motor fits in between the ears of the CR lower engine mount is unimportant. The motor needs to be in the best position first for that to be a valuable coincidence.
I would not compromise on pipe fitment because I did not want to relocate a couple of mounting ears.

From experience - Pipe, carb and airbox, confirm tank fits and radiator will mount, THEN motor mounts

Chain alignment is crucial, and if it lines up, thats fine with me. Karl, if you read that thread, then you would have noticed that the build was almost a bolt on deal.

I got a ton done today, but not as much as I'd hoped.

I tore down the CR to the frame.

I tore down the KDX and got the engine out of it.

I trimmed the swingarm bushings

I sanded down the swingarm ever so slightly

Then I went to ream the case hole bigger, and I found out my adjustable ream only went down to 18mm. D'oh

If I had a 17mm reamer, I would have had the front motor mounts installed, and the engine bolted to the CR125 frame tonight. Oh well, it's not a race. Although it would be nice to spend the 4th putting the bike back together instead of waiting for a ream to ship to me. Any other ideas of what I could use besides a ream? It's drilled out to 5/8" right now.

I took about 50 pictures today. I'll go through them and upload a few of them tomorrow. I should be able to do a nice step-by-step when this is done.

I started out by tearing down the CR.




I was surprised that the CR pipe bolts on, and the KDX pipe is just a pressure fit with the spings.

And here are some pictures showing the flow of the CR radiator: