KX250 Chassis With 500 Motor

[BigGreenMachine]

Hey guys, what would it take to put a KX500 motor in a KX250 chassis? Does it fit at all? Can you use the airbox and not have to mod the tank?

[don46]

I Can't speak for all years of 250, but, the 99-02 is quite easy to do. My avatra is a 05 250f chassis, its a pain in the a$$. The 250 conversion will require the swingarm to be narrowed about 8mm on each side, the swingarm motor mount to be drilled to 17mm, the head stay cut off the back of the motor and a new one fabricated on the front of the head, the 250 fron motor mount will be removed and repositioned, the bottom mount will fit, The pipe has to be modified, some guys are using a CR500 pipe and denting it around the water manifold and kick starter. The air box works as is, either use a short ceramic plug or warm the gas tank a bit and push up the bottom to gain clearance for the plug. This makes an awesome bike that handles night and day better than the stocker, the 250 has better suspension than the k5 and is much narrower.

[MadKaw]

got me hurtin on that one...got the stuff, but scared of the mods.

[KXcam22]

Don,
  I take it that you mean the 99-02  2-stroke 250 is the easiest frame to convert to 500 power.  Can you give me a rough list of things that you had to mod. Thanks. Cam.

[don46]

You are correct, 99-02 250 2t. Front motor mount needs to be re-positioned, swing arm spacers and the actual swingarm need to be narrowed to accomodate the k5 motor. bottom motor mount should be OK, motor needs to have the swingarm bolt mount drilled to 17mm, pipe needs to be modified to fit the 250 chassis, head stay cut off and new one fabricated.  Pretty much what I'd said in my first post. I bought all the parts off ebay for 600-700 bucks and then rebuilt everything.  I can take some pictures and show you the mod to the swingarm. It is truly an easy swap if you have a modest amount of mechanical ability, at most 1 weekend. I would say the pipe is the most time consuming part.

[doordie]

Here do you have some pic?s!

[don46]

Here do you have some pic?s!

If your asking me for pic's, look up a couple of replies. Is your first picture of a KDX chassis? In the states, when the KX250 went perimeter they also went upside down forks.

[MadKaw]

don46 could you post some pics of the swingarm mod and some close ups of the head stay and front motor mount?

[BigGreenMachine]

Anyone know about the earlier KX like a 96 or thereabouts?

[BigGreenMachine]

What about the 05 KX250? I've found one for $200 almost complete.

[hillclimber147]

I did a 97 KX250 conversion. If I had to do it again I'd look for a 2003 or newer 125 or 250. Personally for me steel is easier to work with than aluminum, and the 03 and newer KX's have the head mount to the rear like the 500. I don't know if the tank clears but if it does the head mount would be much easier to build.

[don46]

I would stay away from a 03, it`s a one shot wonder, different than the 02 and different than an 04-07.

[BigGreenMachine]

  Picked up an 01 and will be doing the swap as soon as it arrives. Thanks guys, will post my progress here.

[MadKaw]

 :-oHave fun with it Big Green

[don46]

don46 could you post some pics of the swingarm mod and some close ups of the head stay and front motor mount?

OK so I finally have pictures to post

The width of the aluminum part of the swingarm is 49.7 mm s, The spacers are cut down to 45.2 mm, stock is 53.9.

I have more pictures of the motor mount and the head stay if you want to see them.