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I found an '84 KDX that a guy is parting out on Craigslist not to far from me. To me, it seems as though the majority of the guys that have done the hybrid swaps have used the newer KDX series engines. Any input on the '84 engine/trans?

I currently run an '01 KX 125. I picked it up for free last spring and rebuilt it and ran a few hare scrambles. I really liked the chassis and how it handled in the woods but always wanted a bit more low end power, more than what would have come from a fly wheel weight.

My main question is, would it be feasible to start this project with the '84 KDX and '01 KX? Any input would be greatly appreciated. Thanks!

Anything is possible swap wise with enough fabrication skills. You certainly can make the '84 motor fit into the '01 chassis, but it will require much more work than most people put into these hybrids. The reason is the '84 has a side exiting exhaust port designed to work with the '84 frame, which has a single front down tube. The '01 chassis is made to work with a center-exiting exhaust port, so it has a much shorter front down tube which splits into two, forming the engine cradle. The '84 will want to put its exhaust right through one of those engine cradle loops. You would need to remanufacture a new left hand engine cradle with a fancy bend in it to clear the '84's exhaust. Is it doable? Certainly, but not without some serious fabbing skills. Most of us ham-handed hybrid builders (like me specifically), go for the 89-later motors because the swap is so easy. No remaking engine cradles, no major pipe mods needed.

I have often wondered about the best chassis for an air-cooled KDX swap, and I think the best bet would be a steel-framed modern 4 stroke, like the early KX/RMZ 250f (when they shared everything), the steel framed YZ 250f, or even the Husky 4 strokes. These bikes have long single front downtubes that split into the cradle way down low, and would likely provide the needed exhaust clearance for an air-cooled KDX motor. Even so, I think one would have to do a lot of pipe mods to get it to work with a modern chassis.

Thanks for the input. That's exactly what I was looking for.

tyson501 wrote:Thanks for the input. That's exactly what I was looking for.

If you go to http://www.off-road.com there is a project that old super hunky did like what you are wanting to do.
I would not have done it like him but i think you have an interesting project.
For ease of build i would recomend steal as it can be done with a simple lo cost mig and some skill!

I'm doing a kx500 frame with 84 motor. The 500 frame has 2 down tubes like u mention I was able to cut the two pipes to work with each other and clear everything. I had to cut 3/16 off each side of the engine case to clear the linkage. And a newer kdx220 carb boot lined the intake back up. Slid right in
Should b a big improvement over the 84 frame and susp and brakes and the money ill have into it I can let anybody ride it. There is something cool about an air cooled 200 2 stroke. I would really like to build a yz125/blaster200 hybrid.

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