1993 KDX 250 REBUILD.....WITH SOME KX PARTS

[romanm]

WELL. UPDATE ON THE THREAD. THE KX FRAME I BOUGHT IS PRETTY TRASHED. ALMOST BEYOND WHAT I WOULD CALL SALVAGEABLE. UPON DISS-ASSEMBLY IT WAS VERY EVIDENT THIS THING HAS BEEN BEAT HARD AND PUT AWAY WET

THE NEW PLAN

KDX 250 FRAME----> I MIGHT WELD ON SOME LIGHT DUTY TUBE RAD GUARDS. THESE THINGS ARE HARD TO FIND NOW I BET....DON'T WANT THEM BREAKING. ALSO WELDING ON 4 TABS ON THE BOTTOM FOR A CUSTOM SKID PLATE THAT WILL COME AT A LATER DATE. PAINTING IT EITHER GREEN, BLACK, OR WHITE.

91 KX FRONT END-----> REBUILDING THE SHOCKS, AND SETTING THEM TO STOCK. I WEIGH 175LBS SO I'M HOPING THE 0.39 STOCK SPRINGS WILL BE FINE.

REAR SHOCK----> I HAVE BOTH THE 93 KDX AND THE 91 KX. IM GOING TO ASSUME THE KX IS BETTER HERE. IM ALSO GOING TO REBUILD IT, SET IT BACK TO STOCK AND STICK IT IN. NEW BEARINGS MORE THAN LIKELY.

REAR LINKAGE/SWING ARM----> KEEPING THE KDX ONE FOR THE KICKSTAND OPTION. SANDING AND POLISHING IT TOO. IT DIDN'T SEEM THAT I HAD ANY PLAY IN THE REAR PIVOTS AS WELL. I WAS RATHER SURPRISED WHEN I TOOK APART THE FRONT END AND NOTICED NICE CLEAN BEARINGS AND FRESH GREASE. HOPING THE REAR IS SIMILAR. I WILL BE ADDING ZERK FITTINGS HERE THOUGH FOR SERVICE INTERVALS.

PLASTICS---> NEW HEADLIGHT, STOCK SIDE PANELS, AND THE KX TAIL. EVERYTHING WILL BE WET-SANDED TO BRING IT BACK TO LIKE NEW CONDITION. NO STICKERS HERE EITHER.

MOTOR---->STILL UNDECIDED. I HAVE A KX JUG THAT'S SLEEVED. ITS THE CHEAPEST OPTION AS I HAVE A PISTON TO USE WITH IT. OR DO I SEND MY JUG OFF TO BE RE-COATED TO STOCK SIZE. OR DO I DO A 265 ERIC GORR JOB. I DON'T KNOW. DON'T EVENT KNOW IF I SHOULD REBUILD THE CRANK OR STICK THE STOCK ONE BACK IN AND SAVE A FEW HUNDRED.


EDIT
Found this thread
http://www.dirt rider.net/forums3/showthread.php?threadid=177398
This isnt going to be alot of work. Now Im on the hunt for a kx250 chassis
got a lead on a 91 and a 93.....93 is more complete so naturally I want that one....but we shall see

Frame
-I have a lead on a 99 kx 250 complete frame, front forks, front brake, and what the guy calls street plastics. It would still need the whole rear suspension. While Im looking for a deal....could I put my rear suspension and rear brakes off the kdx on it?

The Motor
- Well.....the pros of this motor are the low rpm torque, the light stator, and the wide spread tranny.

- Question is....If I get something with a motor, I might use that engine as the kdx one can only be punched out to 265cc....and if im dumping money, I might aswell go right up to 295cc...itll match the low rpm grunt of the kdx....and have really nice mid-top end powa!!!. Do it once....do it right.
The engine case will be polished, for that nice show quality look....as will every aluminum bit on the bike.....I like shiny stuff

The amount of fab work necessary will also play a role....that will alll be figured out as soon as a rolling chassis is found







It runs like a slut....does what it wants, when it wants. Im sick of it, so Im rebuilding it to solve some issues, and boost some power.

Last compression gave 130psi cold at WOT. It uses some gearbox oil too.

So I cracked it open.....and this is what I have on my hands. Im assuming stock everything as it was a bitch to take apart. Anyways without further waiting. One thing I Would liek some advice on is the bottom of my jug.....is this thing cracked? or is it supposed to be like this? let me know.

ALL MY PHOTOS ARE HERE.....I ONLY PUT A FEW ON THIS SITE
http://s1231.photobucket.com/albums/ee512/roman169/

[Mr. Wibbens]

looks rusty

[romanm]

Nah, Its not. Just really oily I think.

Does a 91 kx250 cylinder jug bolt in? I have a lead on a 91 kx250 parts bike for cheap....I would like to use if mine is cracked.....which it looks to be. ANY INSIGHT?

Thnaks

[Fletch]

I think it's a casting flaw just by the way it rounds in. I would send it in for a replate with a wiseco and make sure your powervalve is a1. Are you doing crank work? Check for a crack in the upper center of the main exhaust port. Hareline.

[romanm]

So. Ordered the flywheel puller last week. I will be splitting the cases sometime this week.

I still need to decide the following.

1. Replate....or Sleeve
2. Is my jug cracked? IS it worth fixing or should I order a new one?
3. 250cc.....265cc......295cc........310cc.....Should I get some port work done?
4. Who am I going to send my jug/head out too....Eric gorr.....Kustom Kraft. Any advice?



Im now shopping around for a rolling KX Chassis. I thought about doing a full rebuild on this one...but the shocks are crappier, the frame heavier....the swingarm shorter....I might aswell get a better chassis right?
The only thing that would stop me would be if I could get blue plates for the bike.....but thats easier said than done in ontario.

[Fletch]

1. I have used cv tech aab outside montreal for my jug. It costs 350 after tax and shipping and they did a fantastic job on my 89 200. Actually it was a swap out for one they had on the shelf so it only took 2 days. This was a replate btw. Nice chamfering around the ports and a good clean job. I recommend them absolutely if you want to replate in Canada.
Go with a replate for sure and a wiseco. Strong and transfers heat better.
2. I don't think your jug is cracked but when you send it in for a replate the techs at cv will tell you if you ask them and give detailed instructions on where to look.
3. I'd stay with a 250. Have heard very good things about that motor...
4. Already answered that but some here recommend Millenium and Langcourt.

A canadian kx 125 chassis may be tricky to find but a worthy swap if you are inclined. I've heard not so nice things about the handling of the 250 but fantastic things about the motor. A kx chassis may be more expensive in Canada as compared to the US but still a worthy swap if you wait for the right donor.....

If you do the hybrid, I'd leave the motor alone (after rebuild of course) as the weight difference will really wake that sob up!

[romanm]

Ya so far for replating vs sleeving argu,ments I have the follwoing. If you know more, please list

Sleeving
-Slightly cheaper initially
-Potentially cheaper in the longrun being able to overbore at a local machine shop


Replate
-Lighter
-Better heat transfer
-Slightly more expesnive
-better heat transfer


I would like to get a bit of port work done right away though, thats why im learning towards eric gorr or kustom kraft. I figure since Im doing the whole motor right the first time, I might aswell uncork some power too. Nice thing with eric gore is he will send it back to me with the power valves all set up and what not.

If port work is a bit of money, then ill do it myself. Ive taken a few fluid dynamics courses, so I think I could extract 2-3 hp no problem myself just by cleaning up the castings and maybe using some jb-weld to fill in some spots where there would be a negative pressure. The casting work looks pretty brutal, so i dont see why just doing some cleanup work wouldnt gain me 2-3 hp on the top-end

CHASSIS
I do want to do with a kx chassis. Ive read that the kx is like a 40-50lb drop, which is pretty good......plus better chassis/suspension dynamics to boot is great. This will be primarly a woods bike....I like racing, but I stick to 4 wheels and lapping days for that.
I thoguht the kx250 is more or less a bolt in affair. I would like to have this thing set up by the summer, so welding new brackets and what not is out of the question for this project. Im assuming the kx125 would require rewelding. If you know of a write-up where this was done, ill have a look at it and see if its within my scope of work.

If anyone has done a kdx250 swap into a kx chassis, please chime in. Any specific chassis I should look for? I did find a 91 kx250 for 250 bucks, but it was missing a few odds and ends here (all electrical). I also have a lead on a complete 93 chassis for 500 with blown motor....but the guy wont return calls.

[SS109]

If you go with Eric Gorr you can get a 265cc kit, replated, porting, all ready to bolt on for $550. That is what I plan to do with mine. If you don't want to go that route, just get it replated. Sleeves can cause all sorts of problems such as port mismatch, poor thermal conductivity, and it can potentially move after installation.

Chassis. For as close a bolt in swap as possible you will need a '90-'91 KX250. Anything other than those two years and you might need to do some fabrication. Not sure on whether you will need to ream the case for the KX swingarm bolt so keep that in mind as well. Don't even think about a KX125. That would require some reworking of the cradle and mounts.

[romanm]

So this isnt really a direct swap on a newer chassis? I would prefer to go as most up-to date as possible. I can do a bit of machining/grinding if required (have free access to a machine shop). I would like to stay away from welding new mounts though on this project.

Side thought. The gears from my engine...would they fit a 93-01 kx250 engine? Becuase depending on what kind of parts bike I get, I wonder if it wouldnt make more sense to just swap over to the wide ratio tranny, and punch out the newer motor to 295 and get it proted for more low-mid power. After all....there is no replacement for discplacement.

[SS109]

Anything newer and you might have to weld on new mounts. I can't honestly say how much different the mounts are from the '90-'91 bikes to the newer models.

As for the trans swap, yes, it can, and has, been done. TT member no1clyde did and posted up a great write up on it. Here is the thread: http://www.thumper talk.com/topic/902713-91-94-kdx-trans-into-a-01-kx/

Just copy and paste into your browser and remove the space between "thumper" and "talk".

[romanm]

So I should most likely pick up this 1991 bike then eh?
How much lighter is the 91 kx frame vs mine?
Any things to look out for?
Are the newew frames significantly improved? Would I need to do anythign to the suspension or just rebuild it and put new oil in? I weigh 180lbs

I also read you have done the kdx 250 into a kx frame swap. Do you have a thread somewhere, or can you please tell me more about it?

EDIT....incase someone else wants to do this.....I found this thread...space between dirt and rider needs to be removed
http://www.dirt rider.net/forums3/showthread.php?threadid=177398

I can pick one up (91 incomplete roller) for 200 bucks. It is however missing the transmission gears, rads, electrical pieces amongst other things. He says all the plastics are there though, shocks, wheels and tires

How much do you think I can sell a 91 KX250 jug. It has a sleeve already, so it would just need to get bored to the next size to be good as new

[Fletch]

SS and romanm what's the big deal about welding new mounts on a 125 chassis? It's just grinder work then line it up and find a buddy with a welder.

Is the 91 kx chassis that much better than the kdx? I would think for all the work about to go into a 91 you would be better off finding a 03 125 with a blown motor, or even a good one that you can sell for 5-600 bucks.....
Just playing devils advocate...

[romanm]

your doing a damn good job convincing me! lol

find me a cheap chassis and i might just do it. I read that the kx125 and 250 chassis is the same.....is this true? minus the engine mounts ofcourse

Finding a cheap chassis is whats going to be the hard part here.

[SS109]

SS and romanm what's the big deal about welding new mounts on a 125 chassis? It's just grinder work then line it up and find a buddy with a welder.

The KX125 and KX250 (given the same year) are essentail the same except for the one important area for a swap.

Fletch, a KX125 would not need just mounts. It would need the cradle removed and either reworked or a new one constructed. Then, of course, you would have to add the new mounts. Remember, we are talking about the KDX250 and not a KDX200 or 220. The 250 engine is quite a bit larger as it is based on the KX250 engine and not the KX125 engine like the 200/220. Plus, making an exhaust to work would be a real pain in the butt not to mention the air box. Personally, I wouldn't waste my time when there are perfectly good KX250 chassis out there.

For the record, IMO, there is nothing wrong with doing some welding. If I felt that way I wouldn't have picked up the '06 KX250f chassis to install a 2t engine into! (new frame rails, engine mounts, and main downtube/Y section mods)

So I should most likely pick up this 1991 bike then eh?
How much lighter is the 91 kx frame vs mine?
Any things to look out for?
Are the newew frames significantly improved? Would I need to do anythign to the suspension or just rebuild it and put new oil in? I weigh 180lbs

I can pick one up (91 incomplete roller) for 200 bucks. It is however missing the transmission gears, rads, electrical pieces amongst other things. He says all the plastics are there though, shocks, wheels and tires

Me, I would find something newer ('96 up) and make the necessary mods. The improvements on newer bikes are worth it IMO but not necessary to ride hard and fast. Every weekend I ride against a KTM200xcw, KTM250xcw, KTM 300XC, Husqvarna TE310, Suzuki RM250, and a Honda 450x or 450f depending on which one he brings. I can keep up with any of them on my KDX250 except for the kid on the RM. All of them except the RM are brand new or a year old. Remember, it is the rider and not the bike that makes you fast. Destry Abbot could probably smoke any of us riding on a little KX100 just because he is that good!

The '91 KX250 chassis would be a very noticeable improvement over the KDX250 chassis in handling, ergos, and weight reduction. For $200 I don't know how you can go wrong unless everything on the bike is worn out and needs to be replaced. You don't need the trans from it, your radiators might bolt up just fine or with a little bit of modification, and you will use all the electrical items from your KDX anyways. If the suspension, frame, plastics, and wheels are all in good shape then you have the perfect roller chassis to do a swap.

I also read you have done the kdx 250 into a kx frame swap. Do you have a thread somewhere, or can you please tell me more about it?

I picked an '06 KX250f chassis to swap my KDX250 engine into but I have not even begun to start on it. I'm trying to get my '90 KDX200 done first and then I'll tackle the first ever KDX250af conversion! The thread I started for it is here: http://kdxrider.net/forums/viewtopic.php?t=11257 My '90 KDX200 build is here: http://kdxrider.net/forums/viewtopic.php?t=10130

BTW, have you checked out the KDX-MX Hybrid subforum here on KDXrider? If not, there are tons of threads on conversions and possible conversions that have been discussed there. You might find some info that will help with making a decision. Here is a link to that subforum: http://kdxrider.net/forums/viewforum.php?f=111

[Fletch]

Hey SS thanks for the clarification. Can't wait to see the af swap.

[romanm]

Frame

I have a lead on a 99 kx 250 complete frame, front forks, front brake, and what the guy calls street plastics for 250. It would still need the whole rear suspension...seat...handlebars. While Im looking for deals on the rear setup....could I put my rear suspension and rear brakes off the kdx on it?

[SS109]

....could I put my rear suspension and rear brakes off the kdx on it?

No. They are completely different.

[rbates9]

Frame

I have a lead on a 99 kx 250 complete frame, front forks, front brake, and what the guy calls street plastics for 250. It would still need the whole rear suspension...seat...handlebars. While Im looking for deals on the rear setup....could I put my rear suspension and rear brakes off the kdx on it?

I have most if not all of the rear suspension for a 00 KX 250 I'm looking to part with if you go that route. Let me know.

[romanm]

Well you see.....

I would also be looking for a seat, reaer supesnion brake and tire. Do you have these. if so....how much are you looking to get for them? Driving into canada anytime soon??? I can see shipping being a bit of a bitch

[rbates9]

Cheap. I do not have the seat. It was broken so I got rid of it. Check to see how much it would be to ship from 12816 and we can go from there. The rear wheel I do have and might be willing to part with but your KDX wheel will work fine with the KX wheel spacers. I do have the brakes, shock, axle, swing arm bolt, and linkage. The wheel would probably cost the most to ship anyway.