KX-DX cookbook part 1

Discussion for swapping a KDX motor in a MX frame...
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ebeck
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KX-DX cookbook part 1

Post by ebeck »

The reason someone wants to do this swap is varied and personal. Rather than make a case for it I’ll tell you why I'll just tell you how. My story is in other posts. I'll approach this from the perspective of a person having a KDX and wanting more from it.

One note, I set out to use parts that looked quite bad to see a bigger transformation. In this manner, others with worn out bikes do not get discouraged. You can take worn out or dirty parts mismatched parts and convert them into a great bike.

If one has a KDX and wants to do a fork swap I contend that this is not that far off. The biggest expense is the Motor and the forks/Wheel. The second most expensive bit is the rear shock. The rest is nickel and dime. Frames can be had for <$100 all day. I paid $25 for a swing arm and $30 for a tank. Plastics chain and what not you probably want to redo anyhow. You need:
-Frame
-Swing arm
-Linkage
-Air box
-Forks
-Front wheel
-Rear Wheel
-Tank
-Plastics
-Brakes
-Seat
-Shock
-Radiators
-Chain

If you use a KX rear wheel it will be 19” instead of 18”. You can always buy an 18 rim and lace it up. There is a possibility that the KDX rim will work with the KX hubs but that is for someone else to look ito. I used Talons ad Excel rims. I used an 18" rear myself

Your KDX parts can be resold as well making you as much or damn close to what you laid out actually for the KX parts. The KDX parts tend to be cheaper but these days the KX parts are getting really cheap. Some parts are the same cost regardless of bike like radiators by the way.

The recipe is simple. Get the missing parts and sell your KDX parts. Make new motor mounts, drill the cases for the swing arm pin, modify the swing arm, wire it up, extend the pipe head tube (weld or spacer), sell your old parts and go ride a much better bike for little to no cost.

If you can deal with the down time, and you have a good KDX, I suspect the whole deal will net out about $500 including some new goodies like bars and what not. If you start rebuilding everything and adding all new bearings and bushings which I recommend the cost goes up but honestly, if your KDX is a few years old it probably need that anyhow so it is a push.

The key is to bide your time and not hop on the first part you see. 99-02 bikes get parted almost every week. Also, when in doubt about a part use http://www.buykawasaki.com/ to cross reference parts. Sometimes the part numbers change but the mounting hardware is the same so the newer parts will fit as well.

I started with nothing and bought every part on eBay by the way. On mine I rebuilt everything. Suspension, bearings, bushings, seals, races, motor (top and bottom) etc. I figure most looking to do a fork swap also need to rebuild the forks and probably need their suspension bushings redone and maybe even swap the shock. You probably want killer clamps and new bars and controls too. If so this is even closer than you think.

The first question is what year to use? As of 2007, the 99-02 are really good candidates. Here is why. Most that have them when they break are opting to buy new bikes. This means that the bikes do not sell for a lot so they part them. In turn those parts are not getting bought for top dollar because many bikes are not getting fixed.

An 03+ frame works really well to. It used a rear head stay not a front head stay. Pre 95 KDX motors used rear head stay and 95+ motors used front and rear head stay. The 99-02 KX125 used front head stay only and the 03+ used rear head stay. So if you have an older motor and want to do an 03+ swap you will need a new head. If you have a 95+ motor you will need to cut off the front or rear head stay depending on the year of the 125 used. If you use an 03+, you'll have to modify the rear head stay sine I believe it is off ceneter. I never did it but I can think of at least 2 ways to do it. Make an offset bracket or cut and weld the rear mout point on the frame. Then fab brackets to conect the cylinder head stay to the new bracket.

While I will focus on 99-02, the basic steps are the same regardless of year.

I know many want to see one so here it is and then I’ll explain how to get there. You can see how the pipe looks from the top too. Pretty good actually.

I used an 01 KX125 with 99 KX250 suspension to better match my weight at 190 pounds.
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victor
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KX 250 forks

Post by victor »

Ebeck
i have a question on the KX250 forks, did you have to replace the tripple trees on the 2001 kx125 or did you just replace the forks? does the wheel and axle still work or did you have to change all that out also?

thanks
sixstringsteve
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KX-DX cookbook part 1

Post by sixstringsteve »

ebeck wrote: An 03+ frame works really well to. It used a rear head stay not a front head stay. Pre 95 KDX motors used rear head stay and 95+ motors used front and rear head stay. The 99-02 KX125 used front head stay only and the 03+ used rear head stay. So if you have an older motor and want to do an 03+ swap you will need a new head. If you have a 95+ motor you will need to cut off the front or rear head stay depending on the year of the 125 used.
Is this a typo? Don't you mean to say "if you have an older motor and want to do a '99-02 swap, you'll need a new head"?
prityboy69
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Re: KX-DX cookbook part 1

Post by prityboy69 »

That is so sexy and so clean. Did you have to change all the motor mounts or did you have one or two to use as a start point? Also you said you did need to bore out the swinger bolt hole in the motor?
MX KFX471R, 87 250R with 421Banshee motor (Drag Bike), RM80 (son's bike), CR80 (son's bike), E-Ton Viper 50 ( little girls MX quad), PW50 ( little girl's trail bike), 03 Tonycart shifter cart with KTM250SX engine (The Beast)
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G22inSC
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Re: KX-DX cookbook part 1

Post by G22inSC »

May not get any response on a 7 year old post, especially since ebeck hasn't been on here in 4 years. Good luck.
'05 Kaw KDX200 ('00 KX125 forks / '02 RM125 Showa "K2" shock)
'14 Yam YZ125(x) (oldest boy's)
'22 Yam YZ125X (youngest boy's)
'17 Yam YZ85 (soon to be FOR SALE)
'10 Honda Recon (wife's)
'08 Kaw KX65 (Sold)
'07 KTM 50SX Sr. (Sold)
'09 Yam PW50 (retired)
'97 Kaw KX250 (Sold)

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2005 KDX200 Bike Profile
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Tedh98
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Re: KX-DX cookbook part 1

Post by Tedh98 »

prityboy69 wrote:Did you have to change all the motor mounts or did you have one or two to use as a start point? Also you said you did need to bore out the swinger bolt hole in the motor?
There are a lot of variations from build to build. I had to redo all 4 mounts. I have seen a few where the stock lower mounts were kept but had the holes elongated to fit. The most important thing is to position the engine correctly and see where you end up with the mounts. You shouldnt try to re-use anything and hope it is close enough.

You could get bushings made to keep the KDX 15mm swingarm bolt but I think that would be more work and expense compared to reaming the cases out to accept the KX 17mm swingarm bolt.
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bufftester
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Re: KX-DX cookbook part 1

Post by bufftester »

+1 on what Ted said. I had to redo all 4 of my mounts. I could have slotted the lower rears and probably got away with it, but since I had to cut and weld new front ones I just did all 4. As for reaming the case, not worth the effort to try and keep the KDX bolt. The odds that you'd build a hybrid and later put the motor back in the KDX frame are awfully low...otherwise you wouldn't be building a hybrid!
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