Looks like a KX/KDX hybrid in my future...

CMcCarthy

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#1
Well, I have this friend-of-a-friend with a 2000 KX 125 that has mortally wounded the motor. I think I can get it for around $800. It's a typical motocross bike, with a few little goodies but nothing special.

I've seen several KDX motors on Ebay lately and they all seem to go for $350ish. I think this is going to be a cool project, and one that I've wanted to undertake for quite some time.

My main questions for those who have experience in this swap are:

1) What did you do about the rear wheel? I'd like to go to an 18 incher for woods use.

2) What pipe did you use? hacked up KX pipe, or hacked up KDX pipe?

Any words of advice, or "gotchas" to look out for?
 

CMcCarthy

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#4
fender92883 said:
In case you haven't seen it, take a look here. It might help a little. http://justkdx.dirtrider.net/kxkdx.html

It looks like it's a little complicated to get the motor to bolt on, but it's definitely possible. Good luck with the project!
I've looked over that page MANY times. The only problem with it is that it offers absolutely no useful info on the swap. I guess Jeff didn't want to share any trade secrets. Oh well, I'll figure something out.
 

Fred T

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#5
YOu could ship the rolling chassis to jeff and have him bolt the engine and pipe up for you. He would do it right for you and it may cost you less that tril and erroy on your part. Just a thought.
 
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#6
Another Classic case of somebody stealing Jeffs idea and not paying the man his dues, but go ahead. I would try and do it myself too.

Ben
 

CMcCarthy

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#7
Stealing his idea? Uuuuuhhh... ok

Listen, I have the bike, I can get a motor, and I can weld. does that mean I owe Jeff a licensing fee or something? Here, does this make you happy...

THANK YOU JEFF FREDETTE FOR INVENTING THE KX/KDX HYBRID. I'M SORRY YOU DIDN'T PATENT IT SO I COULD PAY YOU A FEE BEFORE I BUILD MINE.

I swear, it's not like I'm offering the service of building them for others. I just want to build mine.
 
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#8
Charles,

Do an advanced search in the KDX forum for "kx frame kdx" and look what pops up. Try some different permutations too. I've read several different threads on building this and one guy offering suggestions because he built a couple.

As for swapping motors/drivetrains, how many people have owned/seen an old Ford/Dodge/Chevy/whatever with a newer V8 in it? Then there's the old Brit cafe racers - Tritons (Triumph in a Norton frame), Norvins (Vincent in a Norton frame), etc. My point is that no one "owns" the engine swapping idea because somebody did the first one long ago.

Now Mr. Fredette could say that he could build it better or faster because he's already put the development time in. :-)

Best,
Greg
 
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#9
the KDX rear wheel off of any 95 or newer KDX well bolt right onto a 99-2002 kx125/250.....so you can go that route, or you can also get a KDX rear rim, or an excel rear rim, and excel or white bros, or even the stock KDX spokes and lace a wheel up to the KX hub.
 
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#10
"His Idea" Get a grip that has been going on here since the early 80's try a PE175 in a RM125 Z chassis ?? I did a KX/KDX back in the 80's too. Its not his idea at all, he just has the brains and the chance to do it. One fella on here a has a later model KX said he had to machine the cases to fit and bore out the cases to take the KX rear engine mount bolt. A bit of work but still a cheap bike once done if you can do it yourself.
Marty
 

CMcCarthy

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#11
As I understand it, you're better off massaging the frame tubes and rear swingarm then machining the cases, but I could do either I guess. I suppose the first thing is to strip the 125 motor out and slide the 200 up in there, then see what hits.

By the way, I'd like to say thanks to the folks providing useful info here. If I pull this off, I'll owe you all a brewski.
 

TVRider

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#12
I asked Jeff about this mod about a year ago and he flat out said he wasn't doing it anymore. It was too much work and not worth the effort and money. When I asked about doing it myself, he said no problem if you have a milling machine!
 
#13
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BucKat

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#14
Well,,, I guess I'll pipe in here.
I have a project on the go now and have been in contact with Jeff via e-mail a fair amount. He does not and will not do the mod work for you but will answer any questions you may have.
Dyno port is the way to go and I believe the FMF pipes may fit..I'll update on that soon.

Ok,, I too have a 2000 KX125 and I'm installing a 96KDX200 motor. I'm using a 94 KX125 airbox as it bolts up to the carb quite nicely. The newer airboxs reqiuire a ring to take up the gap at the bell end of the carb as the air box duct is larger in dia.
For some reason,,,my KX came with an 18" rim.....and new tire to boot...heheee.
I have decided to mod the swing arm itself and not the engine case itself. Most of the work can be done at home with little machining required. The engie need not be taken apart either.

I have been documenting my progress on my web page.. I've just started it sooooo please be patient. .I'm a family man and hold down a full time job so........... you get the point.
Keep in mind,,,,I'm no web head either so you may find the site a bit dull. I'll work on that aspect.
You may have to cut and paste the link into your browser or the link may just work..Sometimes it's stuborn so keep trying.
Enjoy please give feedback as to what type of info you'd like to see on the site.:clue:
Cheers

My orginal post
http://www.dirtrider.net/forums3/showthread.php?t=88953&highlight=buckat
Buc
http://mywebpage.netscape.com/Buckatana12/page1.html
 
Last edited:

Duneman

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#15
I say go for it, I put my PC kdx engine in a 2002 cr rolling chassis and it is the best bike I have ever had, it took me some time and money, but I smile the whole time I'm riding.