KX Guru Racing

10-1-15 UPDATE.
You can use 06-15 KX450F front forks if you use the 97-04 KX500 triple tree..
You can bolt them right up from at least 1988-04 KX500 frames.
I have not tried the front wheel or front brake yet to see what is usable...
A customer of mine did try the front wheel and brake from his KX500 and says it all works but that you need some different spacer lengths.
I don't have the length's but I will soon.

Below is some info on using the KX450F triples on the KX500.
Yes, it can be done with a custom made steering stem from Emig racing.

I will be writing this over time so don't be in a hurry
First off, will the triple clamps bolt right up?
Nope...
Let's take a look at why not..
What I am using for this demonstration is a 94 KX500 frame and a 07 KX250F triple clamp.

Thanks for looking into this swap Sandblaster! I have a few comments that may help someone who is considering this swap.

The first thing I found when I began researching this swap is that the KX500 and 07 KX250F share the same lower steering head bearing.
This allows the 250F triples to slide into the KX500 frame, and everything is taken care of as far as the LOWER bearing goes.

The LOWER bearing (All Balls Racing, Part #99-3519-5) dimensions for both bikes are:
30mm I.D.
55mm O.D.
17mm Height


The UPPER steering head bearings are different between the two bikes.

The KX500 UPPER bearing (All Balls Racing, Part #32205-5) dimensions are:
25mm I.D.
52mm O.D.
19mm Height

The KX250F UPPER bearing (All Balls Racing, Part #99-3513-5) dimensions are:
28mm I.D.
52mm O.D.
16mm Height

As you can see, both the KX250F, and the KX500 use the same O.D. on the upper bearing. This is good! That means that the UPPER bearing pocket in both frames has the same O.D.

However, the two bikes use a different I.D (25mm vs. 28mm) on the UPPER bearing because the 250F uses a steering stem with a 3mm larger diameter.

The solution is to use the 2007 KX250F UPPER bearing and race in the UPPER location of the KX500 steering head.

This should work because the KX 250F UPPER bearing (All Balls Racing, Part #99-3513-5) has the 28mm I.D. to fit the top of the 250F stem, and a 52mm O.D. to fit the UPPER bearing pocket on the KX500 frame.


Also, the two bikes use a different bearing height or thickness (19mm vs. 16mm) on the UPPER bearing because the 250F uses a shorter, or thinner UPPER bearing.
To solve this problem, we install a spacer or large washer into the KX500 UPPER steering head bearing pocket PRIOR TO installing the KX250F upper bearing. This spacer or washer must have a thickness of 3mm (19mm KX500 bearing - 16mm KX250F bearing = 3mm spacer needed), a 28mm I.D. , and a 52mm O.D.

Following the previously described procedure SHOULD allow the KX250F triple clamps to be bolted into the KX500 frame without the need to have a new stem pressed into the KX250F triple clamps. Then we can continue to address the issue regarding differences in the steering stop locations between the two bikes, as Sandblaster has so beautifully done in his pictorial posts above.

Excellent info and totally accurate.
Thanks!

And now, for my next question!

If the 250F triples are actually installed IN the 500 frame, will the steering stops need to be changed to ensure that the fork legs don't hit the radiators or tank?

It looks like I need to order a set of the KX 250F UPPER steering head bearings (All Balls Racing, Part #99-3513-5) and a set of clamps and find my answer!

We can do better then that.
Wait till you see what I come up with tomorrow

You asked for it.
What we have here is a 94 KX500 frame mounted up with a front end from a 07 KX250F.
We already discussed the need for a different steering stem.
Here is the front end mounted up.
The next pics show the front end turned all the way to the right.
As you can see, the forks touch the gas tank and just barely miss the right radiator... Not good....

The next pic shows the front end turned all the way to the left.
As you can see the forks hit the gas tank and the radiator.
Bummer right???
Not really.
It will take very little to fix this problem.
Something as simple a bolt welded to the bottom of the steel stop on the frame will easily fix this issue.

With the bolt sitting there and the forks turned all the way to the left you can see that there is plenty of room...
Not shown in the pics is the steering turned all the way to the right, there is also plenty of room.
In fact, there is room for a narrower bolt head, block of steel, or if you wanted to get really fancy you could use a block that is tapped all the way through and you could install a bolt in either end that you could adjust exactly at what point the stops worked.

Looking good Sandblaster! Thanks for mocking this up.

So you think it will take a stem swap into the 250F triples? My research shows that using the KX250F upper steering head bearing with a spacer below it should work fine.