KXF /KX250

[Reddy]

I'll apologise before I start - I couldnt find a KX250AF forum

I own a 2007 RM139, and have looked at puttnig the engine into an RMZ chassis. That was until at the weekend I was offered a blown up 2007 KXF250 bike for little to no money!
I have also found a KX250 engine, with electrics and carb for decent money, so this is going to be my project this winter.

Does anyone have any advise on where to start?
After reading other threads it looks like the exhaust is the most awkward part of the project. Anyone know of a good exhaust to start with?

Thanks in advance

This is a good place for your post, don't worry about it.
Admin.

[don46]

I don't think the pipe will be an issue on a 250/250f conversion, in my opinion the airboot will be the most difficult issue, that is depending on the year of motor, there could be headstay issues as well. nothing that can't be overcome. I may do the same project this winter if I have time, have most of the components already just short time.

[Reddy]

Right ok, the engine i've got doesnt come with an exhaust, so i'll just try and get a standard one.

The engine is 2004, i'm gonna start by getting the swinging arm bolt and then take it from there.

I'll try and take pictures on the way and keep you all updated.

[Reddy]

Picked up my donor chassis this morning.
Engine should be with me by Friday - have a good weekend then to start the work.

[Reddy]

Right i stripped the KXf down to the bare basics yesterday so once my engine arrives I can drill it and try to get it centred.

[AJ]

reddy
- i have built them (KX250AF)
(i need to get some finished photos up)

The key things youll have to address are:
countershaft alignment..both vertvcal and horizontal.

moving the yoke "Y" area of the frame up to clear a 2 stroke exhaust.

engine mounts

headstay and a headstay mount of some design.

the pipe and exhaust ,,but those are fairly easy to modify from a stock KX250 stuff.

radiator clearence of the Y area ,and the several hose barbs  relocation 

and a few incidentals like a cdi and coil bracket etc.

**********


none of it is too hard to do, if you are a faricator,
and have a welder , mill  or lathe and  stuff you need

working out the rads..
is likely the largest challenge

[Dutch-K5 Fan]

reddy
- i have built them (KX250AF)
(i need to get some finished photos up)

The key things youll have to address are:
countershaft alignment..both vertvcal and horizontal.

moving the yoke "Y" area of the frame up to clear a 2 stroke exhaust.

engine mounts

headstay and a headstay mount of some design.

the pipe and exhaust ,,but those are fairly easy to modify from a stock KX250 stuff.

radiator clearence of the Y area ,and the several hose barbs  relocation 

and a few incidentals like a cdi and coil bracket etc.

**********


none of it is too hard to do, if you are a faricator,
and have a welder , mill  or lathe and  stuff you need

working out the rads..
is likely the largest challenge

With  "radiator clearence of the Y area" you mean placing them more to the out side???
Gone look tomorrow again with mine, looks like it's pritty tight around the Y section
for radiator and exhaust to fit both.


Dutchie

[Reddy]

Thanks for the advice, unfortunately i am not a fabricator! But will have a go at most things.

My plan is get the engine mounted through the swinging arm, and then get someone to sort the frame out.

THen the rest will be up to me! I'm looking forward to the challenge though.

Any more info and pics would be great.

[Dutch-K5 Fan]

Thanks for the advice, unfortunately i am not a fabricator! But will have a go at most things.

My plan is get the engine mounted through the swinging arm, and then get someone to sort the frame out.

THen the rest will be up to me! I'm looking forward to the challenge though.

It's the same for me Reddy, only I will do the frame a much my self for what I can.
It's funny that we are doing the same at the same time, only 250 vs 500.

 Dutch

[Reddy]

Yeah I'm trying to do as much of it myself as well.

Whats even funnier was my plan this winter was to put my RM139 engine into a RMZ frame! never mind, means I can keep that now

Still waiting on my engine will update with pics when I get it mounted.

[Dutch-K5 Fan]

I was planning to buy a 09 rmz450 or 09 kxf450.
Now it's the kx500af

Dutch

[Reddy]

Received the engine today, the swinging arm hole is already 17mm and will bolt stright in.

Will post some pics once I get the engine fitted and mounted from the top engine mounting.

I'm excited, and its not for xmas

[Reddy]

I've had a few good days on the build, have made the spacers for between the engine and swinging arm.
Also cut the frame to clear the exhaust, in doing do I managed to save the y piece, clean it up and am basing that on the rebuild.
As it finished today I had the engine braced in situ where I want it to sit, also I have the exhaust clamped so I know that is in the right position.
There are still a few problems to solve:-

• Left hand radiator is too long
• Water pump is vey close to frame and need to check it will clear
• spark plug is going to be very close to bottom of the tank

[Reddy]

Image of Y piece after removing the 2 old engine mount holes



First fitting to check if the Y piece will clear the engine (it didnt and we had to cut it 1" below right have rad mount)

[Reddy]

Fitting the Y piece


Final Fitting, all looks good, even clamped the exhaust in situ




Picture from the rear - chain alignment and exhaust position perfect