Fork Swap

[Lutz]

Hey everybody,

I just picked up (actually I'm waiting for them to be delivered) a set of 1994 KX125 forks that I'm going to swap onto my 1995 KDX200. I don't have any questions at this point; instead, I want to make this thread a good reference for others when making such a swap in the future (and easy to find - see title: "Fork Swap").

I've got to thank everyone who has already posted on their projects, as they will make this project much easier for me. Hopefully, I'll have time to add the links to the other important posts on this subject in the future so that people can link directly off of this post to get important info with regards to the swap.

Here's my plan right now (I have direct access to a machine shop free of cost, except for certain materials):
1) I will probably knurl the lower clamp to fit the kdx stem if the parts won't press fit in their stock condition. I may even machine a new stem if it looks like the best route.
2) I will either modify the stock KX125 axle to fit the KDX200 wheel, or machine a new axle if too much meat would come off of the KX axle - I plan to do a bit of strength analysis on the parts as I go (otherwise, how will I be able to call myself an engineer?). I will use, modify, or create new spacers as necessary.
3) According to Buykawasaki.com, the brake will swap on without a hitch.

I'll update this thread as I get further into the process, and, hopefully, I'll have lots of digital pictures.

If anyone has any suggestions, please feel free to make them known. :thumb: I'm excited already!



As promised, here are links to other good threads on this topic. There are others, but these sum up most of the information available to date - try searching for 'fork swap' to find other threads.

Just finished KX fork install!!!

kx front end: Install KX hub or make spacer?

1996 KDX200 with KX forks & triple clamp

KDX to KX front end conversion - Complete!

KX125 Forks on 98 KDX 200

USD fork Report for KDX.

Brake Line Routing KX forks on KDX

 

[skipro3]

If you machine a new stem, use steel and not aluminum like the KX. The smaller diameter of the KDX stem would be too weak in aluminum. That's why when Kawasaki went from a steel stem in the KX to an aluminum stem, they had to increase the diameter. Since you will have the stem off, why not add a zerk fitting to the steering frame? I wrapped the stem in a piece of foam pipe insulation to help take up some of the space so I didn't use up too much grease. If my suggestions don't add to the way you want your thread to go, PM me and I will edit it. Your idea of an all inclusive point of reference will help many here, I believe.
Jerry

 

[FLBusa]

If you machine a new stem, use steel and not aluminum like the KX. The smaller diameter of the KDX stem would be too weak in aluminum. That's why when Kawasaki went from a steel stem in the KX to an aluminum stem, they had to increase the diameter.

Err... That's not entirely true.

The difference between the KX and KDX steering stems is on the order of .050" and that's only on the last 2" of the stem. While there is moderate compression load on the stem most of the forces are on the bearings and triple trees. The remainder of the load is on the steel neck of the frame. You can most certainly make a new neck out of aluminum and have it just as strong as the KX stem. All you would need to do is reduce the inside bore by .050" to obtain the same wall thickness as the KX stem. IMO the reason the KDX stem is made from steel is stricktly cost. It costs more to make a light weight aluminum stem.

Lutz...

I did some checking and it turns out the a '95 KX125 uses the same lower bearing as your KDX does. KOYO 32006JRRS 55mm x 30mm x 17mm. The stems should press right in. As far as your brake goes... The parts diagrams on the buykawaski site spec the same caliper for both bikes but beware... mine was not the same caliper that was in the diagram. Mine has two thick fins cast into the bottom of the caliper and as a result I could not use a KX250 brake line. Instead I used a KX500 line that routes similar to the '95 KX125. One last thing... if you haven't checked and greased your steering head bearings on a regular basis... be prepared to buy some new ones. My bottom bearing was toast. :eek:

 

[skipro3]

Sorry if my source for stem material is not correct. It came from Kawasaki when I contacted them about my fabricating an aluminum stem for the KDX out of the 1996 KX stem I had. They told me that removing that much material from the KX stem would weaken it too much. I took that to mean that a stem machined from aluminum stock would also be too weak using the dimensions of the steel stem. Maybe it's not the stem diameter but the thread diameter portion that would be the issue? Would the anodizing on the aluminum stem also contribute to the strengh of the stem?

 

[FLBusa]

Sorry if my source for stem material is not correct. It came from Kawasaki when I contacted them about my fabricating an aluminum stem for the KDX out of the 1996 KX stem I had. They told me that removing that much material from the KX stem would weaken it too much. I took that to mean that a stem machined from aluminum stock would also be too weak using the dimensions of the steel stem. Maybe it's not the stem diameter but the thread diameter portion that would be the issue? Would the anodizing on the aluminum stem also contribute to the strengh of the stem?

It's all dependant on wall thickness (if you have a hollow stem) and the type aluminum that you use. I'm sure that the KX stem has been engineered very near it's limit. Let's face it... the MX world is very competetive and every gram of weight that can be saved is. It makes perfect sense that they would not recommend reducing the stem diameter.

On the other hand... If you are fabricating your own stem from scratch. You can replace the mass that you removed from the outside of the stem to the inside bore by making it smaller. If you weren't concerned with weight you could make the stem from a solid aluminum bar.

My guess is that the KX stem is made from 6061-T6 a very good strong alloy with a yeild of 40,000psi and an ultimate of 45,000psi. You can just as easily obtain some 7075-T6 which has a yeild of 75,000psi and an ultimate of 85,000psi.

Just to give you an idea of just how strong aluminum is...

ASTM A-36 Steel has a yeild of around 36,000psi and an utimate of 58,000psi.

 

[skipro3]

Thanks for clearing that up for me,FLBusa :ugg:
I rely on the intelligence of others like you to keep me out of trouble, but only once I realize I had better listen to guys like you who do indeed seem to know what they are talking about. I was only parroting what I was told without understanding the whys. So I'm going to have to take your word on it and start thinking about what you said means. Not knowing steel from smeel, I'm wondering why chains aren't made from aluminum if there are alloys out there that tough. Is the steel a different kind than the A-36 you mentioned?
Sorry Lutz, that this took a turn away from fork swap but perhaps this will help folks think about what it is they are changing before they do something that might leave them broke somewheres or worse, hurt.

 

[FLBusa]

Skipro3...

I think what you did is exactly what anyone who is researching the Fork Swap mod should do. Asking questions is how you get the answers you need to make an informed and intellegent decision. Me... I'm just trying to give back something for all the great info that you and others here have contributed. :thumb: Without it... I wouldn't even have considered doing the mod.

In addition I don't think that our discussion has taken anything away from Lutz's post. Fabricating a new stem is really the most professional way to go about doing the mod. IMO making spacers is kind of the easy way out, albeit the most cost effective.

For those interested, this is what I needed to fabricate to do the swap on my bike.

Bike: 2000 KDX200

Forks: 2000 KX250

Spacer:
One 1.50" OD x .950" ID x .156" Thk.
Mat'l: Aluminum

Spacer to raise the top triple tree to the correct height. Spacer can go either on top of or below the triple tree.

Sleeve/Bushing:
One .980" OD x .925" ID x .785" High.
Mat'l: Stainless Steel (I used Aluminum but the wall is very thin and a tougher metal is more desirable)
This sleeve goes into the top triple tree to make up the difference between the smaller diameter KDX stem and the larger diameter KX stem.

Brake Line:
The KDX line is too short... I used a 2003 KX500 line. I routed it (starting from the caliper) Up over the caliper, then down under the axle, then back up into the factory pinch clamp at the front of the fork. The line then runs up along the fork guard and through the two guides.

 

[skipro3]

:thumb:

 

[Lutz]

Hey everybody,

I've added some links in my first post to some of the most complete threads on this topic.

FLBusa and skipro3,
Thanks for being active on this thread; I think you've covered some issues that haven't been much discussed previously.

As far as materials go, it is true that the strongest of aluminums rival some steels for strength, but the best steels are stronger. However, there are a myriad of other issues to be considered - such as what happens under fatigue (repeated loading and unloading), corrosion, etc. Within any given family of materials alone, there is such a wide range of mechanical and chemical properties that generalizations are generally not safe.

There is really a lot of engineering that should go into changing the material of any given part - long story short, for most people that might do this mod, it is probably best to use the stock KDX stem with spacers.

Even though I am a Mechanical Engineer (well...almost - I don't actually get the paper that says so until May) I don't feel comfortable just saying that by modifying wall thickness, I can use aluminum for the stem. Yes, a new stem could be made out of aluminum, but without even knowing the what grade of aluminum the first design was, it is a bit of a crapshoot to make a new part with the same strength. Sure, I could just use the strongest alloy available, and hope to err on the side of safety, but that's not a wise way to do things. I do plan to modify the KX axle or make a new axle (and maybe stem) for my swap, but you can bet that I'm going to be doing a lot of homework to make sure it's going to be safe. I'll post what I figure out when I get it figured - just be warned not to take anything I say as gospel.

 

[tedkxkdx]

Lutz, You asked for it and here is the kdx brake line on a kx fork. Pictures in the document are all about the clamp for the line to the fork guard. Notice there is no fork sliders anymore. Using the clamp and the sliders won't work together.

 

[Lutz]

tedkxkdx,

Thanks a lot! Like they say, a picture is worth a thousand words. That will make my work a lot easier.

As an update, I just finished pressing the KDX stem into the KX clamp. The press fit was very good - it took about 5 tons of pressure to do, no spacers necessary. Believe it or not, it took around 15 tons or more to press the KDX stem out of the KDX clamp! Next week, I'll make the spacers needed to complete the triple clamp setup, then I'll move on to making the new axle to fit the KDX wheel to the KX forks.

 

[cyclebradd88]

I have the components to do my swap. :yeehaw: The KDX stem measured out the same as the KX250 stem. So the stem should press right into the new bottom clamp. My only question relates to the Top clamp mounting onto the KDX stem.

FLBUSA said "Sleeve/Bushing:
One .980" OD x .925" ID x .785" High.
Mat'l: Stainless Steel (I used Aluminum but the wall is very thin and a tougher metal is more desirable)
This sleeve goes into the top triple tree to make up the difference between the smaller diameter KDX stem and the larger diameter KX stem."

My Top Clamps (both of them) have a tapered hole to mate with the straight shafts. Does the bushing need to be split? Everyone that has undertaken this swap and published the results is to be commended. Thanks on advance for your responses! :thumb:

 

[Lutz]

I ended up just using 0.030" worth of shim stock to make the KX125 top clamp fit the KDX stem. However, the stems and top clamps are not tapered - I got that impression of the top clamps had tapered holes at first too, but that's not actually the case. I've got both setups sitting here with me and I checked them out again to be sure.

If you think about it, making these holes/shafts tapered would be counter-productive. The clamp has to sit right on top of the bearing adjustment nut, which in turn must move up and down from bike to bike to make up for part tolerances. If there was a taper, the clamp would only get tight if it bottomed on the taper, and would get increasingly loose as the top clamp moves up on the stem.

Anyway, IF there is any taper, it isn't significant, so a straight walled spacer will work, as will a bit of shim stock. Good luck with your swap. If you have a KX wheel, it should be very easy to do. I'm starting to wish I had a KX wheel - if I did, my project would be basically done now.

 

[cyclebradd88]

Where do you find shim stock? Some kind of specialty store?

 

[Lutz]

Where do you find shim stock? Some kind of specialty store?

The machine shop at my school had it in stock, but I believe you can get it at hobby shops, and probably at good hardware stores.

 

[Lutz]

More brake info.

As I believe FLBusa stated previously, the brake caliper from my KDX has two fins below where the brakeline attaches, making a KX brake line not work.

However, I noticed in a picture that the '97 KLX300 uses the same brake caliper as the KDX (with the two fins). The KLX brake line also routes similarly to the KX line, but there is one major difference: the KLX line uses a steel portion between the caliper and the rubber line.

So there is another brakeline option for those doing this conversion and using the stock KDX caliper: the '97 (maybe all years) KLX300. Note that there would be two pieces to buy for such a setup: the rubber line AND the steel line.

 

[FLBusa]

Where do you find shim stock? Some kind of specialty store?

You can get shim stock at W. W. Grainger's

http://www.grainger.com/

 

[FLBusa]

As I believe FLBusa stated previously, the brake caliper from my KDX has two fins below where the brakeline attaches, making a KX brake line not work.

Lutz...

There are three differnet routings for KX brake lines. :thumb:

1) There's the "Under the caliper" routing.
2) The "over the caliper and under the axle" routing.
3) And... The new "Inside the wheel, connected to the fork guard" routing.

I used a 2002-2004 KX500 brake line (routing #2) and it worked perfectly. :)

I especially liked this routing because the line doesn't hang out in the rear and is less likely to snag on a branch in tight trails.
:aj:

 

[skipro3]

Where do you find shim stock? Some kind of specialty store?

Another source is anywhere that sells model train stuff. I got several sheets of brass in various thicknessess (gauges). If you can't find any, let me know and I will send you some. A little goes a long way! :thumb:

 

[Lutz]

Steering Stops

New topic: what have you all done about the steering stops?

I know this subject has come up before, and that some of you haven't needed to change the steering stops, but...

My setup (94 KX125 on a 95 KDX remember) will clearly need to be changed. When I first got the KX clamps, I stuck the KX lower clamp/stem into the KDX frame and rotated it to see if there would be clearance problems - there will be, since the KX lower clamp will rotate well beyond frame tube.

I think I may fit a wider piece of steel to the bottom of the KDX frame stop. The plan would be to machine a notch into the new stop so that it fits snugly onto the old stop, and would provide a way to transfer the lateral forces into the the factory stop. This would also require minimal welding (in turn avoiding problems with weakening/embrittlement or distortion of the frame). In this case, I may even use JB weld to hold the new stop in place.

I'm getting a little long winded here, so I'll wait for some more feedback from you all.

 

[FLBusa]

I think I may fit a wider piece of steel to the bottom of the KDX frame stop. The plan would be to machine a notch into the new stop so that it fits snugly onto the old stop, and would provide a way to transfer the lateral forces into the the factory stop. This would also require minimal welding (in turn avoiding problems with weakening/embrittlement or distortion of the frame). In this case, I may even use JB weld to hold the new stop in place.

I'm getting a little long winded here, so I'll wait for some more feedback from you all.

I don't think that you'll have any weakening/embrittlement problems with welding any additional components onto the frame if you decide to weld an additional part to the stop as long as you impart to much heat and use the proper filler rod. IMO... the steering stop is "NOT" a stressed member. By that I mean that it's not comming in contact with nor bearing any forces while you're riding apart from the occational low speed turn around or when it's resting on the kickstand. You may want to look in the other direction instead. You could drill and tap a hole in each of the risers on the lower triple tree and screw in a SHCS or BHCS. The head of the screw is probably enough to fill the gap. A little LockTite Red and you won't have to worry about anything comming loose.

 

[Lutz]

I like the idea about using screws in the lower clamp, but...

One thing I failed to mention in the last post is that the top side on one of the risers on the lower KX clamp has been sheared clean off at the riser/frame stop contact point (must have been a hard crash :ohmy: ). There is still most of the riser there, just not from the contact point up. Incidentally, the contact point is the same between the KX and KDX, even after the swap.

Anyway, the point is, there isn't enough material to tap a hole into (at least on the side that is broken). The other point is, in a crash, there can be quite a bit of stress on the steering stop components - and I have been known to crash on occasion :joke: .

Yeah, I'm really not worried about weakening the metal of the frame by welding - my real concern would be distorting the portion of the frame where the lower steering stem bearing rides. However, like you said, without excessive heat, that isn't likely.

I'll keep everyone updated on what I decide - it should be easier to figure out when I actually have everything assembled in front of me. Everything should be going together this weekend, assuming that I get my axle finished tomorrow. So hopefully, I'll have a buildup conclusion and a ride report by next week.

 

[FLBusa]

Lutz...

Yeah... My stops lined right up and I didn't have to make any mod's albiet I had anticipated that I would have to.

I'm interested in what you did to get the wheel spacing to work with the KX forks. I assume that you have to fabricate some spacers. Are you using the old ODO hub on the right side?

 

[Lutz]

It's Done!

Well, I got everything done over the weekend, everything worked out well. Here's a quick summary of what I did.

To use KDX wheel with KX forks:
I made a new axle and axle nut to the KX axle dimensions except with a smaller diameter to fit the KDX wheel bearings. No new spacers were needed; I reused the stock KDX wheel spacer and odometer drive. If anything, the KDX wheel with its stock spacers is slightly wider than the KX wheel with its spacers (though I haven't had a KX wheel to measure). Some other minor differences between my new axle and the KX axle are that mine is solid, whereas the KX axle is hollow, and I cut the hex on the axle nut to a smaller dimension than the OD of the axle nut (the hex is larger than the OD on the KX axle nut).

Steering Stops:
Without new steering stops, the upper clamps would hit the tank, and the fork tubes were much too close to hitting the frame (meaning zero clearance to the naked eye). So I welded a piece of 3/8 inch thick steel to the bottom of the stop on the frame (slightly wider than the original stop). I have some fine tuning to do on the the stop - meaning I have to grind the stop to a slightly smaller dimension to get as much steering lock as possible without interference.

A note of caution!!!! If you are welding anything on the bike, make sure not to ground through any bearings, and unplug all of your electronics. Bad things can happen if you don't.

Brakes:
I used all of the original KDX parts from the lever to the pads. I routed the brake line per tedkxkdx's method: the original line clamp was mounted to the lower fork guard.

I'll post some pictures and dimensions when I get a chance - but that might be a while.

 

[Lutz]

Ride Review

After getting everything bolted together, I had a chance to do a little riding. As of right now, the results are mostly good, though I haven't actually done any real trailriding yet - mostly just jumping and a few small whoops.

As I was rolling the bike out of the shop, I noticed there is definitely A LOT more stiction in the KX forks than the KDX forks. When everything was first assembled, I could push the front end down two or three inches and it would stay there until I pulled up on the bars. This may be because the forks need a rebuild, or because the forks had been lying horizontally for who knows how long, or because there may have been some misalignment somewhere - I'll figure it all out somewhere down the road.

Anyway, I didn't notice the stiction after I started riding. Off any jump, big or small, the improvement was amazing. The KDX forks used to blow through the travel extremely fast, then rebound so fast that the front end would almost jump off the ground. The KX forks on the other hand just soak up the landing. The suspension has never felt so good on my bike. My friend who was watching me said he'd never seen the bike work like that, and that the front and rear looked like they were acting as one shock. And this is without ever even turning the clickers.

Next time I go home for the weekend, I'll do more riding and have more of a report on how it works on the trails in real riding conditions, but for now, I am totally satisfied with the swap.