KDX250/KX125 hybrid????

[kiwi kdx]

hey guys im new here (been on canadian daves for a few years)

i have a 91 KDX250, and have fully rebiult it, buti have nothing left to do to it, so im looking for a new challange, its either bore it out to 300cc with a gas gas EC piston or a KX125 roller transplant as im still not happy with my suspension and a 101kg bike is still a little heavy for my 75kg.

then i decided if i can do the transplant first i can still bore it out later
(300cc in a 125 MX frame, i must not be rite in the head!!)

i have seen heaps of 200 and 220 transplants, but has anyone done a 250???

here is my donor......

and here is a link to my rbuild if your intereted:

http://www.dirtrider.net/forums3/showth ... al+warning

[Julien D]

I've wondered about this myself. I think the 250 motor would make a great powerplant for a conversion. I think you're treading in untested waters though, so some measurements and test fits would likely be required.

[SVandal]

Posted the same over at CD-JKDX's.

I'm interested to see how the hybrid goes. If you need dimensions for a cr125 frame I can give some rough measurements. Good luck.

[zz3gmc]

The lower cradle for a 125 frame is much different, smaller, and will need to be replaced with the cradle from a 250. You would be better off swapping it into a KX250 chassis.

[Julien D]

The lower cradle for a 125 frame is much different, smaller, and will need to be replaced with the cradle from a 250. You would be better off swapping it into a KX250 chassis.

What makes you say this? Any experience? You do know the KDX200 engine fits into the kx125 without too much work, yes? The KDX250 frame is quite similar to the E series KDX200 frames. Additionally, I have recently seen a KX250 engine in a kx125 frame, and there was no cutting of engine cradles involved there either.

I'm not saying one way or another, but I highly doubt you'd need to cut the engine cradle off and swap it over. That'd just be silly....

[zz3gmc]

Actually, I have quite a bit of Kawasaki experience, Ive been on them for about 25 years. The frames may look similar in that they are both perimeter frames but thats about where any similarity ends. Yes, I do know that the 200/220 engine fits the 125 frame. I may build one and is one of the reasons I joined this site. The 250 engine cases are very different from the 200. Look for a side shot of a 125 and a KDX250 and you will see the difference that I speak of. I have a 96 KX125 in my shop as well as a 03,04, and 07 KX250. Also have a 96 KDX200 and a 04 KX250/500 hybrid im building.
Heres a side shot of a KDX250SR
http://www.joopdekokmotoren.nl/images/kawasa23.jpg
Heres a 96 KX 125
http://www.santacruzsuspension.com/images/kx125_96.jpg

[Julien D]

Nice of you to take the time to link pictures and all. I still fail to see the point. Look at an 89 kdx200, and a newer cr125. Yup, COMPLETELY different, yet the engine swap is not too difficult.

Look at KX250 vs. kx125. Smaller engine cradle, different engine cases, yet the swap is still possible without much frame reworking, other than mounts.

Look at an 89 kdx200 vs a newer kx125, yup again. COMPLETELY different, but yep, you guessed it, engine swap HAS been done.

I find it hard to believe that a KX250 engine will fit, while a KDX250 engine will not. The lower cases are similar between these two engines.

It's nice to know you have experience with kawi's, but if you have not actually tried to fit a kdx250 engine in a 125 frame, you do not have the experience required to make a blanket statement like this:

The lower cradle for a 125 frame is much different, smaller, and will need to be replaced with the cradle from a 250.

So have you??

Dont' get me wrong, I'm not trying to say this 100% will work, I'm just saying it's not so easy to discount the idea just because the kx125 engine cradle is smaller, and different. Hell, I have even seen a cr500 engine crammed into an old xr80 frame.

[zz3gmc]

Anything is possible, I never said it couldnt be done. Its just that it would be much easier and less time consuming to put the KDX250 engine into a KX250 frame. No, I havent tried putting a KDX250 engine into a KX125 frame. I would just put it into the 250 chassis. Other than the cradle, the 125 and 250 chassis are pretty much identical. My 02 KX500 engine actually fits into my 04 KX250 chassis with less work than it would take to install a 200 into a KX125 chassis. Ive seen a KX500 in a KX80 frame.
Also, the 200 is loosely based off of the 125. The cases are physically similar in size and shape. So it stands to reason that the 200 engine would fit a KX 125 chassis w/o too much effort. The same reasoning could be applied to putting the 200 into a CR125 chassis. Being a 125, the CR125 is dimensionally similar to the KX125,KDX200 bottom end or pretty much any other 125 for that matter. On a 125 frame, the bottom tubes start to angle upwards towards the front down tube. On a 250 frame, the bottom tubes stay pretty flat, because of the size of the 250 cases. What I see happening when trying to install the 250 into a 125, is that the engine would hit the frame rails or would have to be angled upwards. You would then have pipe fitment issues, airbox issues etc. If someone has the welding and fabrication skills, then have at it. I just think it would be much easier to stick it into a KX250 frame.

[Julien D]

Agreed, there's is plenty of chance of running into trouble. Might work, might not. I'd sure like to see someone try it!

Yes, you are completely right about the 200 fitting the 125 and the reasoning why. I was more impressed and influenced by seeing a kx250 powerplant in a kx125. There's a thread over at TT with some pictures, if you can stand to spend any time over there ;). Looks pretty friggen nice.