Harold Bawlzangya Racing

Installing KX450F front end

After having several eBay searches set-up for many months, I finally got a decent price on the entire front end from an ’07 KX450F.

(click picture to enlarge)

In reading up about putting TC forks on a non-TC equipped bike, I had read that the 4-stroke forks were longer than what is/was typically found on a 2-stroke.  Once the boxes arrived and I was able to unpack the forks, a quick measurement confirmed these KXF forks were longer than the KX forks.  I wasn’t sure if the increase was due to larger travel, longer lower tube, longer upper tube or a combination of them all.

My first step was finding out a way to compare the two sets of forks to identify where the differences in length were coming from.  To do this, I kept the KX front end on and  pulled the front wheel off and put the axle back in.  I would then rest a ruler on the top of the axle.

(click picture to enlarge)

I then stuck a magnet to the head tube as a reference point.

(click picture to enlarge)

I then measured from the top of the axle to the magnet to get a reference number.  With the KX forks at their stock height, my reference measurement was 755 m

(click picture to enlarge)

Now with that number, I unbolted everything related to the KX front end and installed the KXF front end.  I initially had the fork caps nearly flush with the top of the triples.  That measurement wasn’t even close to my 755 mm target.  With sliding the forks as high up as I could, I was still several mm’s off.  The problem wasn’t with the forks hitting the bars, I still had some room there.

(click picture to enlarge)

The problem was with the lower mounting area.  The forks have a smooth machined area where the lower triple clamps.

(click picture to enlarge)

It is a little hard to tell from this picture, but the bottom triple is at the very end of that smooth machined area.

(click picture to enlarge)

Sliding the forks any higher would put the lower triple clamp on the non-machined surface.  It probably wouldn’t hurt anything, but it didn’t seem like the correct thing to do.

I had to decide how I wanted to shorten the forks – cut internal components or use spacers.  Since spacers would be reverseable, I tried going that route first.  After contacting two large suspension shops and one smaller suspension company and not having any luck, it looked like cutting components was my only option.  But shortening the cartridge rod was only one part of it.  I would either have to find shorter springs or have the spring seat adjusted for stock length springs.

This is where I got really lucky on this project.  I had a set of aftermarket Diverse .44 springs from my KX forks.  One of the major online suspension companies listed the KXF springs as being 43.6mm x 472mm.  That site listed the KX springs as being 43.5mm x 461mm.  My Diverse springs were 450mm in length (Diverse supplies a 10mm spacer to make up the difference).  I was willing to take a chance that the difference between 43.6mm and 43.5mm wouldn’t impact the functioning of the forks, so it looked like I found a set of shorter and lighter springs for the KXF front end.

When I pulled the stock .47 KXF springs out, I measured them to be 468mm in length, not 472mm.  With the Diverse springs being 450mm, the amount I would be shortening the forks would be 18mm (468mm-450mm).

The first was to cut down the cartridge rod.  In order to do that, I’d need to remove the piston holder.  Once again I machined a high tech tool for the job.

(click picture to enlarge)

(click picture to enlarge)

With the piston holder removed, I could then start cutting down the rod and threading it.  The OD of the rod was a little large for the die.  I think I could have forced the die, especially if I used a lot of lubricant.  But reducing the OD of the rod first seemed to be the right thing to do.  I set-up the table saw to just skim some aluminum off the rod.

(click picture to enlarge)

With the OD of the rod reduced slightly, I could work on cutting new threads.  An M12 x 1.25 die is needed.

(click picture to enlarge)

(click picture to enlarge)

The most critical step in the whole process was cutting the rod down to the right length.  After triple checking the measurements, I set-up the fence as a stop so I could cut both rods the same length.  I also made sure I had the die on the rod so I could clean the threads after the cut.

(click picture to enlarge)

Here is the rod after the cut.

(click picture to enlarge)

The last step is making the recessed area at the very end.  Not as pretty looking as the factory machined relief, but not bad for a table saw.

(click picture to enlarge)

Original vs modified rod

(click picture to enlarge)

The only other item that needed to be cut was the rebound rod.  Again, just triple checked the measurements and then cut both rods on the table saw.

After cleaning the forks and putting them back together, it was time to get them back on the bike.  Doing the same procedure of measuring from the top of the axle to the magnet reference, I set the forks at 755mm.

(click picture to enlarge)

Now I’ve got enough room for adjustment.

(click picture to enlarge)

(click picture to enlarge)

In this picture, I’m still using the KX front wheel and caliper.  Those parts appear to be interchangeable between the KXF and KX.

(click picture to enlarge)

Finally all of the KXF components bolted in place.

(click picture to enlarge)

(click picture to enlarge)

I left the stock valving in place, I just wanted to get to the point where the forks were installed while maintaining the correct geometry.  Details of a woods revalve on this TC forks will follow . . .

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s