Motor swap in KX

[chris82785]

I've got a 97 kx 125....the motor is toasted as the crank is tweaked, hitting the cases when you try to turn it over - haven't torn it down, but I know it's going to be $$ to fix it. Truthfully though, I've out grown the 125. So, I've been researching if I can put a 250 motor in the frame. All the parts diagrams for the frame match my frame with the kx 250's frame from 95 to present on kawasaki's web site.

Can anyone confirm whether or not a kx 250 motor will "bolt" in to the frame...my main concern is the swing arm/case clearances...

 

[YZ165]

So you have a 250 motor laying around collecting dust?

 

[MXSparx]

So you have a 250 motor laying around collecting dust?

Isnt that what they are designed for????


My bad that was just plain non productive on my part. But mines all dusty :think:

 

[chris82785]

So you have a 250 motor laying around collecting dust?

Actually, no, but I can get my hands on some for a decent price....

The whole thing is, if I can put a 250 motor in the bike as opposed to spend the cash on a 125 rebuild, I'd rather do that....

 

[YZ165]

Anything is possible, but I think you're wasting your time. Fix the problems with the tiddler motor, then sell the bike and buy a 250. There's more to the swap than just fitting the motor. You'll need the right CDI, carb, airbox boot, exhaust, upper motor mounts,bla, bla...the list goes on and on...YZ165

 

[chris82785]

you're not giving me any real info...I know that i need the car, CDI and electronics, exhaust, and airbox for the 250. The frame is the same, so they *should* bolt up. I've got access to all that for a decent price.

So, I guess I'll ask this question then....any idea on how much it's going to be for an entire rebuild for a 125 motor? Along with cases I'd assume as they're probably marred from the crank

 

[holeshot]

you're not giving me any real info...I know that i need the car, CDI and electronics, exhaust, and airbox for the 250. The frame is the same, so they *should* bolt up. I've got access to all that for a decent price.

The frame's engine cradle is not even remotely the same between the 125 and 250 (even though the rest of he frame is close). This is true of any of the modern 125/250's. All you have to do is go down to the local dealer and compare frames.....

With some exceptional fabrication skills and time, it would be possible, but certainly not worth it. :whoa:

 

[dante]

Actually, no, but I can get my hands on some for a decent price....

The whole thing is, if I can put a 250 motor in the bike as opposed to spend the cash on a 125 rebuild, I'd rather do that....

were are you getting all the donor 250 parts :|

 

[83MX80]

personally i think all these guy's are a bunch of morons and dont know how much parts actually cost... trust me i know what parts cost... i just spent 300.00 canadian for 2 parts for my KDX. the kickstart shaft was 200.00 canadian by the time i got it here, and the idle gear was another 100.00 CDN. i've only ridden this kdx MAYBE 2 months. and i bought it last summer. i rode like 200 feet and snapped off 3 1/2 teeth on the idle gear... so needless to say the KDX is up for sale and FIXED.

im guessing but it will cost you at least 1000 bux to fix your kx125. not worth the time and money, and if you can get the 250 parts for less than that then ya go for it.



but first, take the engine apart, make a list of ALL the parts you need to repair the 125 and then price out all parts and see what the total cost is. then see what you can get the 250 parts for and go from there.

 

[Okiewan]

personally i think all these guy's are a bunch of morons and dont know how much parts actually cost...

First of all, "personally I" is redundant.

Second... who are "all these guys"?

 

[Rich Rohrich]

personally i think all these guy's are a bunch of morons

The classic words of an internet lunkhead. :whoa:

 

[dante]

First of all, "personally I" is redundant.

Second... who are "all these guys"?

Okie, are you hooked on phonics? :laugh:

 

[Okiewan]

Personally, me myself?
Nah.

 

[YZ165]

personally i think all these guy's are a bunch of morons and dont know how much parts actually cost...

Are you talking to me?

 

[chris82785]

The frame's engine cradle is not even remotely the same between the 125 and 250 (even though the rest of he frame is close). This is true of any of the modern 125/250's. All you have to do is go down to the local dealer and compare frames.....

If the frames are "different", then why does kawasaki specify the same part number between the 125 and 250? The frame I have is a 97' 125, the engine I'll have is a 98. Even if the 98 doesn't pan out, if you watch **** there are tons of motors that go through there.

Here, let me show you - first the image of the 97 125 frame from kawasaki - note the part number

The second, an image of a 2005 kx 250 frame....also notice the part number....

point fact, it may have changes to it, but the cradle looks very similar

Here's the 97 kx 250's frame....notice it's identical to the 125's frame

These images lead me to believe that a 250 motor will fit in the 125 frame. Minor things such as the upper mounts would be easy to fab if there's some reason it doesn't fit. However, as stated before, my main concern is the rear portion of the cases that fits between the swing arm

*Those images are directly from kawasaki's site....couldn't link the page*

 

[chris82785]

im guessing but it will cost you at least 1000 bux to fix your kx125. not worth the time and money, and if you can get the 250 parts for less than that then ya go for it.

but first, take the engine apart, make a list of ALL the parts you need to repair the 125 and then price out all parts and see what the total cost is. then see what you can get the 250 parts for and go from there.

Bingo. The motor is going to cost upwards of a grand to fix. The crank is tweeked - that's 250 right there. Might as well do a rod, piston/rings while your in there, along with the lower end bearings, and probably tranny work. Not to mention the case is probalby going to need replacement, that's 450. I'm in the process of disassembly right now, need to find a case splitter.....

 

[MXSparx]

Not sure about the fit youre looking for, but there is a slight flaw in what you are listing as identical items. The frame in 97 and 98 are not the same. The numbers you are looking at are reference numbers not part numbers. The refernce number is the same because it asigned to an item ie frame? If you look in the part number column you will see they are clearly different numbers.
Again, I dont know if it will work or not but just wanted to point this out.

 

[MXSparx]

98 kx 250 k5
ref # 32160A ...........part # 32160-1513-CC
----------------------------------------------------------
97 kx 125 k4
ref # 32160A ...........part # 32160-1457-CC

 

[YZ165]

Not sure about the fit youre looking for, but there is a slight flaw in what you are listing as identical items. The frame in 97 and 98 are not the same. The numbers you are looking at are reference numbers not part numbers. The refernce number is the same because it asigned to an item ie frame? If you look in the part number column you will see they are clearly different numbers.
Again, I dont know if it will work or not but just wanted to point this out.

:rotfl:

 

[holeshot]

Images shmimages..

Here's a couple of the KX250

http://www.kawasaki.ca/motocross/images/2006_indexpage/Large_2006KX250_c.jpg
http://www.kawasaki.ca/motocross/KX250/images/05_KX250.jpg

Here's a couple of the KX125

http://www.kawasaki.ca/motocross/images/2006_indexpage/Large_2006KX125_c.jpg
http://www.kawasaki.ca/motocross/KX125/images/05_KX125.jpg


Note that the 125 engine cradle is completely different from the 250. Makes sense, doesn't it? Different engines, different engine cradle -duuuuuh.

This is also true for RM's, YZ's, CR's and other makes going waaaaaay back....

 

[dales298]

Pictures may be worth a thousand words, but its the measurements that tell the tale.

Dale

 

[ecy063]

KX swaps

The only way to find out is to try. Back in the '80s my friend did the same swap to his kx 125. That bike was so fast! It's to bad it caught fire after about one week. I recently installed '02 suspension on my '94 kx250. Wasn't sure what kind of problems I would run into. It did cost me a few hundred more than i planned. Two month later I'm lovin it. Love this site.