2003-1990 KX-DX Hybrid Build

[dfeckel]

I just thought I'd chime in with the very beginning of my KX-DX hybrid build. Don't get too worked up looking for freuent updates, though--this will take me all winter.

What we have here is a 2003 KX 125 that the owner believed spun a crank bearing on its last ride. It showed up on CL last week, and what do you know, it was literally five minutes from my house. After a couple offers/counter offers, I got it for $880.





I was kind of hoping to get it for closer to $600, but it's complete, so I can hopefully sell the motor for a few bucks. It has lots of compression, it just won't start and makes a few weird noises when kicking. My seven-year-old son is just itching to take the motor apart, so maybe we'll take it apart to see what's wrong with it before I sell it.

The bike's pretty clean. Everything is straight, good-ish tires, the plastic is usable underneath all the stickers, lots of pad on the brakes with firm lever and pedal. Pretty much all good. The only gig I could come up with is there's a lot of stiction in the forks--they don't compress very easily when pusing down on the bars. But that's it. I'm likely going to send the forks and shock out for a woods revalve, anyway.

Tomorrow I'm looking at the donor KDX, a white 1990 in need of a top end for the exhorbitant fee of $375

[Indawoods]

Nice... good choice on the motor and donor body....

Those should work together like peas and carrots!

[skythrasher]

I wonder if it could be as simple as a sheared woodruff key on the flywheel? Wouldn't that be something?

[dfeckel]

It just might be something simple like that. It seems to me that a spun bearing in the bottom end might still run, or at least start to run or cough or kick back or something. And it has loads of compression, still. Once i dig into it, I'll let you know.

Anyhoo, here's the second half of the upcoming frankenbike.







You ever feel like a thief?

I did, after I grabbed this 1990 KDX 200, mostly complete, for $380. I wasn't sure what I would find when I drove to look at it, but it was pretty much all there (minus side panels, kickstand, odo, headlight bulb/socket and miscelaneous fasteners). It was advertised as a runner needing a top end, so I tried to start it in the guy's yard. Long story short, I have so far kicked this bike a total of eight times, and it has started EVERY TIME. It runs up through the gears just fine, the clutch feels good, finds neutral easily, idles great. I really haven't ridden many KDXs, but it felt like it had great low-to-mid. I didn't run it to the top end (destroyed driveline, hundred-year-old, dry-rotted back knobby, loose head bearings, and I didn't want to terrorize the neighborhood too much). But I think I got a seriously good deal on this. Almost makes me sorry to steal its motor. Almost!

[Indawoods]

Those are great bikes as is.... your going to have something special....

[m0rie]

You got a steal on both those bikes!

[KarlP]

This looks like the start of a succesful build.
It sure is nice having as much of both bikes as possible when starting. You never know what gizmo from A or B will work better on C

[dfeckel]

I was thinking about cutting off the KDX's lower and front engine mounts and welding them onto the KX frame, rather than fabbing up new ones. Is there any reason to not do this?

[KarlP]

There is no reason to believe they'll be the right size and shape. It is most likely that they are not going to be.

Hey, spend NEXT winter putting the KX motor in the KDX frame

(NOT my idea, see post in general forum section)

[Tedh98]

It doesn't take that long to make new engine mounts. I used some light weight cardboard as a template. You can get very close to the right shape with just scissors, leaving just a minimal amount of grinding/filing of the actual mount.

[dfeckel]

You mean I can't just use scissors on the KDX's mounts once I remove them? I guess it will be a lot easier just to fab them. Lots easier to cut cardboard than grind metal. Also, by not cutting off the KDX mounts, I can at least TRY to sell it on eBay. Maybe someone with a looped-out pretzeled subframe will want a cheap replacement...

[KarlP]

Yeah, I wouldn't start with motor mounts anyway.
See bulabula90's current troubles for why.

[dfeckel]

Yeah, I've been reading all the hybrid build threads to glean as much info as possible. I plan on having EVERYTHING that will mount up to the bike right at hand when I design the mounts. I just ordered the KDX Pro Circuit Platinum 2 pipe and their KX 250 "Environmentally Friendly" spark arrestor (complete with little picture of a pine tree on it). I'll get the swingarm and rear mount modified just to get the motor initially located. Then I'll play with rotating it forward and backward to get the optimum fit with the pipe and airbox and fuel tank. Hopefully I can get everything to fit without modding the pipe or airbox--maybe even the tank if I'm lucky.

I also want to have the big tank on hand when making the mounts. Is there an opinion as to whether the IMS or the Clarke 3.1 gallon tank works any better than the other? I did notice the Clarke is $50 cheaper.

[BobbyZ]

I must say I'm a little jealous,I've been wanting to build this same bike for a while.You beat me to the 125 I was going to buy too I'm Rob and I live down in Cape May So I'm guessing I'm not all that far from you so if your looking to get rid of the bones left from the 90 kdx let me know as I have one with a bent frame I'd be interested as I'm going to rehab one bike and swap the parts from my other to make a kx kdx after the holidays as my budget allows.

P.S. Since you beat me to the kx there is also a sick set of low hour 05-06 irrc kxf 250 forks just listed on ebay that I am pretty sure will go into the kx trees.I'd grab them but I cant do anything budget wise till after the holidays

[Julien D]

Both sweet bikes. Should be an excellent build!

any chance you want to let go of those blue shrouds?

[dfeckel]

I promised a bunch of stuff from the KDX to a friend of mine, but he's mainly interested in the suspension and brakes. I need to check with him before I get rid of the frame or shrouds.

Also, I'm probably going to cut the engine protector loops from the KDX frame and add them to the KX. BobbyZ, if my buddy doesn't want the frame (he probably won't), then maybe we could work out a deal where you cut the loops off your bent frame and give them to me, and you can have my unbent KDX frame with the loops intact.

juliend, my buddy has a green KDX, so he likely won't want the shrouds, either. I have an e-mail in to him and I'll know this weekend. If he doesn't want them, you have dibs.

[dfeckel]

I've done a bit of disassembly to get the motor out of the Kdx, and I found a couple of things. First, the bike has been running without an air filter for who knows how long. The airbox had its lid, and the filter cage was dutifully fastened in place, but no filter. No wonder the kid said it needed a top end!

Next, I found the tranny drain plug threads are stripped. The plug was held in mainly with RTV. Hmm... Helicoil?

Third, I was a little dismayed at how much play the new-looking countershaft sprocket had on the trans output shaft. Plus, I could see a bit of wear on the shaft, too. I noticed in the forums that lots of folks have lots of play in the countershaft sprocket and there doesn't seem to be much concern about it. Should I be concerned?

These things are adding up to what looks like a complete rebuild. I was sort of hoping to not split the cases, but with the history of filterless running, I'm not sure how well I trust the bearings in the bottom end. Also, I've never placed a helicoil before--is there any reason to split the cases just for the helicoil, or is that somehing that can be done without splitting the cases? Also also, should I think about replacing the tranny output shaft because of the sprocket play?

I've never split cases, and the last thing I need is to buy a bunch of new, specialized tools. How much is a basic bottom-end rebuild at a dealer?

[dfeckel]

The frame and plastics are available. My buddy just wants the shock, front end with triples and wheel, and brakes. I don't seem to be able to PM anyone on the site, so juliend and BobbyZ, you can e-mail me at dfeckel@yahoo.com to make arrangements.

[Indawoods]

http://kdxrider.net/forums/faq.php#33

[KarlP]

Dfeckel-
I think I would not worry about the motor too much at this point. If it runs at the moment, that is good enough for now.
I'd get the air filter sorted out and go ahead with the build, knowing that you are going to have to go all the way through the motor.

This is only my opinion, of course.

when I did mine, I used a motor that came on a bike that I had picked up with a blown crank. After I got the motor/airbox/electric/exhaust/motormounts/radiators all set I sent the motor out for a complete lower end rebuild. I took care of the top end. I spent WAY more on that motor than I expected, but oh well. While the motor was gone I worked on suspension, controls and so on.