While I am sure that some will probably provide the fork specs, I'll give you the process to figure it out for yourself, just in case.
There are potential 5 critical factors in swapping forks:
1. The diameter of the fork where the top tripple clamp mounts.
2. The diameter of the fork where the bottom tripple clamp mounts.
3. The axle configuration (assuming you will not use the front wheel from the new forks being installed, in which case this is not relevant)
4. The inside diameter of the top head bearing
5. The inside diameter of the bottom head bearing.
In order to determine in the new forks will work in your old tripple clamps, you simply need to measure (using a micrometer) the diameter of the forks where the top and bottom tripple clamps mount. If they are teh same diameter, the swap is easy. If you will use your current front wheel, you will also need to compare the axle configuration to ensure it is the same. If it is not, you will need to use a front wheel that is made for the new forks.
If the fork diameters are different at the tripple clamp mounting points, you have two possible solutions. If the difference is very small, you can have your tripple clamps machined (not the best option). It the difference is too much, you will need to use the tripple clamps that were originally installed on the new forks. This is where the head measurements come into play. If the steering stem is the same on both the old and new bottom tripple clamp, your done. However, if the steering stem is larger or smaller, you will need to swap the stems. The stems are held in place with a snap ring. Simple remove the bottom snap ring, press the stems out, and press the old stem into the new bottom tripple clamp.
Now for the hard part.
If a stem swap was necessary, the new top tripple clamp stem hole will either be too large or too small. If it is too small, take it to the local machine shop, and for about $10 bucks, the will open it up to the correct size. I the stem hole is too large, you will need to make a spacer, as you do not want any play. If the difference in diameter is great, the machine shop can make a spacer. If the difference is small, you can make your own spacer by measuring (using a micrometer) the stem and hole to determine the total difference. Divide by 2, and you will have the thickness of shim stock you will need to buy. drop the measurement by a 1/1000 to all for ease of installation. Cut a strip of shim stock, and using a large socket, form it into a circle. After setting the top tripple clamp in place, tap in the shim stock circle that is now your spacer.
Sounds kind of complicated but it works. I used to swap my KX500 forks for KX250 units, as I felt like the 250 units were easier to tune, and performed better. However, on my '02, the forks are good enough that I did not do the swap.
Hopefully, the new forks will slide into the old tripple clamps, but I will bet you there is a difference in diameter.
Good Luck
Rick
