KDXRIDER.NET

well im doing it! i just bought a 99 kx 250 full bike minus the engine i have date set to bring the bikes to a buddies machine shop next friday the 26th of april. my other bike is a 95 kdx 200. i have checked out some other builds on here and im wondering what the exact measurements are that u use to shave off on the inside of the kx swing arm? and how much to cut off the caps? i will have the swing arm bolt to spec out for drilling out the rear of the kdx engine. i do believe some have taken off 9mm to each side of the swing arm and others have different measurements side to side. i just need the proper and exact measurements to do a proper job. thanks for the help

Most folks use a 125. I'm not sure anyone will have the exact measurements for a kx250. You'll have to figure out how to set the motor in the frame, and then line the swingarm up so that the front and rear sprockets are in exact alignment. That will determine if and how much the swingarm needs to be cut.

I have a 2000 KX 250 swing arm and a 2001 KX 125 swing arm and they are the same except that the 250 swing arm is about 2 inches longer, but the engine side casting is identical. So the swing arm cuts should be the same. Like J said, most use a 125 frame so most of the frame mounting will be up to you to determine.

How much different is the 125 and 250 frame? I really dont want to run into pipe issues

Please if any one out there in kdx land has ever done the kx 250 swap please get back to me

This was on an '04, but the 250 cradle was substantially larger than the 125. With as close as the pipe is on the 125 frame, there is no way the pipe will fit the 250 frame without cutting and then welding an extension.

I would assume the situation would be the same with your year frame since the 250 is just a physically larger engine.

Are the plastics and tank seat and sub frame the same between the 125 and 250?

They were for the year of bike I was working with, not sure about other years though.

A parts lookup will tell you for sure.

I imagine it is too late in the day for this to be any help.....

All you really need to do is take the 250 swingarm and your KDX motor to the shop and they can get the two of them together. The chain will have left marks in the slider on the swingarm. Don't forget the swingarm bolt!

sounds to me like the biggest issue will be mounting the pipe
i cant remember for the life of me where or who but i know that i saw a build on this site where someone placed a KDX engine into a frame with exhaust clearance issues (might have been a suzuki frame?)
if i remember correctly they cut the neck off a stock pipe to make an extension which they then press fitted into an aftermarket pipe and they were golden

The problem with modifying a pipe is that the first foot or so is the most important part of the pipe. Adding to the pipe at the inlet is going to drop the power curve of the pipe a lot. Somewhere on the web there is a write up of what dents in a pipe have the most impact on performance and the first (I think) 8" are the most important. The Fredett torque ring is only about 1/4" and it makes a noticeable difference.