Difference between 1989 and 2000 motor for SF conversion

[jcm3]

I found a 1999 KX250 with an '89 motor in it on Craigslist and am considering it.  I know that I'd probably need to do a lot of work to it, but want to swap out the 89 motor with my 2000 motor since it was just completely rebuilt by Tom Morgan.

I've done a bunch of searches, but am not getting hits probably due to not using the right words.  

Does anyone know how the engines are different externally, and what would be required to swap out my 2000 motor in that SF bike?  Should I skip this one, or is it a bolt in, or maybe something in between?  

Thanks for any info!  I'm hoping to make a choice before he sells it.

[jcm3]

Seems like I'm finding some hits that the motors should be the same.  Found an old post from Motorrad to back up a post that I found on Thumpertalk.

From what I'm reading, it should be an easy engine swap unless there is something that I don't know about.

http://www.kxriders.com/forums/index.php/topic,10807.0.html
http://www.thumpertalk.com/topic/1052060-kx500-engines/ 

I'd love to do this!

[sandblaster]

I've never tried but I'm sure you could do it.
In fact, I'd look at using the KX125 chassis if I had the opportunity.

[jcm3]

I've never tried but I'm sure you could do it.
In fact, I'd look at using the KX125 chassis if I had the opportunity.

This one should be fairly easy, since it's already been done.     I'd just want to swap out his motor for mine.

[sintax]

I've never tried but I'm sure you could do it.
In fact, I'd look at using the KX125 chassis if I had the opportunity.

I tried this, it does not work.

The frame cradle is much much too small.

I tried using a 2004 KX125 rolling chassis for my first attempt at a hybrid. That being said sure you COULD make it work, its only metal after all. But its not a simple affair as using a 250 2stroke frame.

[motopunk]

I've never tried but I'm sure you could do it.
In fact, I'd look at using the KX125 chassis if I had the opportunity.

I tried this, it does not work.

The frame cradle is much much too small.

I tried using a 2004 KX125 rolling chassis for my first attempt at a hybrid. That being said sure you COULD make it work, its only metal after all. But its not a simple affair as using a 250 2stroke frame.

   ... 250 and 500 always used the same framerails.... 125motor is much smaller and also the frame rails are made for the smaller engine...  you could bring a 125 in a 250/500 chassis,  but not the bigger engine in the 125 frame , without cutting and modifying the frame rails...  big diference between 125 and 500 except the motors were ever the frame rails since 1990... all other parts are 99% the same

[Kwackerman]

jcm3,

Hey again - I just left you a note on your other thread. 

I owned a 89 KX 500 and I currently own a 1990 model.  From 1989 - 2004 (last year of the K5) all the motors are the same.

The only changes, other than "Bold New Graphics" after 89 came in 1994, when they changed the triple trees to accommodate the newer KX250 forks, and changed the brake caliper mount on the swing arm to accommodate the newer KX 250 rear caliper.

Other than those few changes, everything else on those bikes were exactly same for all those years.

Howie

[jcm3]

jcm3,

Hey again - I just left you a note on your other thread. 

I owned a 89 KX 500 and I currently own a 1990 model.  From 1989 - 2004 (last year of the K5) all the motors are the same.

The only changes, other than "Bold New Graphics" after 89 came in 1994, when they changed the triple trees to accommodate the newer KX250 forks, and changed the brake caliper mount on the swing arm to accommodate the newer KX 250 rear caliper.

Other than those few changes, everything else on those bikes were exactly same for all those years.

Howie

Thanks for your input, sir.