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Old 07-10-2013, 06:45 PM   #1
Sundog
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Default Fork rebuilding and upgrading - '04

I'm going to post some tips and general advice for the process of rebuilding '04 front forks. '06 forks are different. In my case, I also swapped out the springs for 0.85 kg Racetech linear springs ($115), 15 wt oil ($11, 1L), and added Racetech Gold Valve cartridge emulator valves ($170). Seals and bushings are $115.

The shop manual does not provide an interval for when the forks should have bushings, seals, and oil replaced. I did it at almost 50k miles, and it was time. The oil was dark and grimy, bushings were showing some wear, and the metal band inside the rubber oil seal was corroding. I didn't have any leaks or notice poor performance before the rebuild.

Skier did a similar write up in this thread:
http://honda599.com/forums/showthread.php?t=5672

Settings for cartridge emulator:
http://honda599.com/forums/showthread.php?t=7513

Discussion on emulators:
http://www.honda599.com/forums/showthread.php?t=9751

Another discussion on sag and spring preload:
http://honda599.com/forums/showthread.php?t=7027

Preload and preload adjusters:
http://www.honda599.com/forums/showthread.php?t=9618

Initial Settings:
Given a 2004 599, 160 lb rider weight, and "aggressive street riding" (debatable compared to some of you crazy types... quad), Racetech recommended 0.85 kg springs, 15 wt oil, Gold Valve emulators set to 2 turns of preload on the yellow (64 lb/in) valve spring, and 10 mm of fork spring preload to result in 25-35 mm of static sag. I ended up needing 22 mm of preload to get me to 29 mm of static sag. I used 2.5 turns of preload on the emulators. These settings work great for me so far. Not too harsh.

Static sag is the distance between the fork slider at full extension, and the fork slider at the normal riding weight with you in the normal riding position. Measuring this the right way is complicated. Go to the Racetech website for directions.

Fork spring preload is this:



Which you modify with spacers on top of the springs.

Tools and parts
First thing you need is a shop manual. I don't think anyone should attempt this without one, unless you've already rebuilt many motorcycle forks. Without step-by-step instructions, there are just too many ways you can put all the bits back together wrong. My writeup is just hints and tips, not the full set of instructions.

You also need a way to lift the front of the bike by the frame, not the forks. Obviously. Some people use straps and their garage rafters. I lack a garage, so I bought a front lift that inserts a peg into the triple tree stem:





You might also want a driver tool for reinstalling the oil seal, or you can make a crude one out of a split 2" PVC pipe, like I did below.

If you are installing Gold Valve emulators, you need to drill holes in your damping rod. A center punch helps get the drill started in the right place.

Having a long allen head that connects to a ratchet driver is useful to get to the screw at the bottom of the fork slider.

Here is the diagram from the shop manual:



And here is the microfiche from bikebandit.com:



For a full rebuild, you need (two of each):

Microfiche # / part name
#23 / 8mm copper washer, $2.34 x 2
#8 / fork slider bushing, $11.02 x 2
#18 / oil seal AND dust seal, $26.07 x 2
#9 / fork pipe bushing, $9.09 x 2
#13 / piston ring, $5.85 x 2
#25 / o-ring, $3.19 x 2

Note on the teflon bushings - the manual calls the outer portion "slider bushing" (microfiche part #8 ) and the inner portion that clips onto the fork pipe the "fork pipe bushing" (microfiche part #9). However, bikebandit.com called the microfiche part #8 the "bush, guide", and #9 the "bush, slider." Which is kind of the opposite naming. Plan to replace them both.

The manual says replace bushings if the teflon is worn so copper shows on 3/4 of surface. This seems ridiculous. In my opinion, if any copper is showing through, and you have the forks in pieces anyway, it makes sense to replace the bushings.

Here is what all these parts look like (I accidentally ordered an extra set of dust seals on the left):



Here are the new springs, the old springs, and the cartridge emulators:



Note the old springs are two-part linear - there is a region with the coils closely spaced, and a part with the coils far spaced. As the springs compress, the tighter coils will all bind at once, and the spring rate will suddenly increase, which is a simplified progressive spring.

Rebuilding
When you are pulling the fork tube out from the fork slider, just grab the slider and yank it out until it hits the stop. Each time it will slide out a little further. It took me maybe 50 pulls until it came loose, without using too much force.

This is what it looked like when the fork tube came out:



Notice the corroded metal inside the rubber oil seal. The slider bushing didn't look too bad (new on the left, old on the right):



However the fork pipe bushing was missing some teflon (although not bad enough to be replaced according to the manual's 1/4 teflon remaining rule)(old on the right):



Here is everything disassembled:



Drilling new holes in the damping rods:



Racetech included this aluminum tubing, which I cut to length to get the proper spring preload:



This aluminum spring collar goes in the same place as the new cartridge emulator, so at first I just swapped them. As it turned out, the recommended 10 mm preload gave me too much static sag (more preload = less sag), so I put spring collars back in on top of the springs, giving me about 22 mm of preload and just the right amount of sag.



The washers that Racetech provided to fit on either end of the preload spacer were too big to fit in the fork tube. I reused the old spacer washers instead.

Driving the oil seal back on is a pain in the ass. These are delicate. You can buy a $40 driver tool which is a heavy ring of metal, or you can buy a length of 2" PVC pipe, cut it in two, and hammer on it from the top to drive the seals in place:



It's difficult to discuss how the modifications improved the suspension. It's easy to fool yourself into feeling an improvement after all that work and money. I can feel a difference hitting bumps at high speeds, and I took it out on a dirt road with some 3" deep potholes and it was smoother than before - the front that is. Since the back is stock, that helps me judge the improvement, and it's obvious that the front soaks up bumps which the back slams into. However I would say it doesn't fundamentally change the feel of the suspension. I haven't ridden it hard on a twisty road yet, and that's where I would expect the biggest benefit in terms of composure.

Last edited by Sundog; 07-10-2013 at 06:50 PM.
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Old 07-10-2013, 08:47 PM   #2
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Default Re: Fork rebuilding and upgrading - '04

Did you up the weight of the fork oil?
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Old 07-11-2013, 05:04 AM   #3
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Default Re: Fork rebuilding and upgrading - '04

Don't judge me, FireBreather.
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Old 07-11-2013, 08:07 AM   #4
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Default Re: Fork rebuilding and upgrading - '04

WOW, thanks for that. I just replaced my fork oil with 15w. The ride definitely stiffened up. I feel every bump in the road. I may go back to 10w. But thats me.

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Old 07-11-2013, 10:13 PM   #5
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Default Re: Fork rebuilding and upgrading - '04

Excellent work, Sundog.

The main reason for going for cartridge emulators is to make the hard bumps softer. The stock damping rod has the "Three Stooges" problem of a lot of fluid trying to get through the small holes in the damping rod. As I've heard many times before, it almost hydraulically locks with that much pressure, hence the jolting.

The emulators have their own spring, valves and holes in them. Drilling out the damping rod removes it from the equation: the emulators handle compression and rebound damping. Compression damping is determined by the spring stiffness and the preload of the spring: a stiff spring will be harsher than a lighter one, and more preload required more force to open the emulator valve. Rebound damping is handled by the holes in the emulator. That's a non-adjustable part of it. More accurately, rebound damping can be modified by drilling new holes for less and soldering existing holes shut for more.

The emulators are a compromise versus using a real cartridge fork, but a reasonable one. The next step up would be acquiring CBR F3 forks and swapping them in, but you have to track down a set of them, rebuild them, respring them and you're into it an easy $500. Emulators and springs are half that.

My Triumph has cartridge emulators in the front and every time I ride the 599 I am reminded that front fork upgrades are on the top of my want list.
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Old 07-13-2013, 07:21 PM   #6
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Default Re: Fork rebuilding and upgrading - '04

Thanks for the quick emulator lesson, that agrees with my understanding of how they work. I have the compression value spring set at a low preload (2.5 turns of the preload screw, with the suggested adjustment range being 2 for street and 4 for track). It's nice to know I could firm up the feel of the front under compression if I feel like it.

I went from 50mm static sag before the rebuild to about 30 mm static sag. That means I'm now 2 cm higher in the front than before - or more accurately - I was riding 2 cm lower than recommended sag values before.

But I miss the quick turn in.

So I'm going to raise the forks in the triple tree at least 1 cm to get some of that back.

I've always had some problems with the front getting the shakes when I took my arms off, now I have a better idea why that was happening.
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Old 07-14-2013, 12:25 AM   #7
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Default Re: Fork rebuilding and upgrading - '04

Solid write up Sundog, thanks for posting.
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Old 07-14-2013, 10:46 AM   #8
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Default Re: Fork rebuilding and upgrading - '04

Another possible cause for head shake when you take your hands off the bars is steering head bearings. I've had headshake with hands off the grips, especially at low speeds, for a long time now. Got a set of All Balls steering bearings in the other week and everything is excellent again, no head shake!
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Old 03-02-2014, 05:51 AM   #9
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Default Re: Fork rebuilding and upgrading - '04

Hi, I have a hornet 600 04 model, i 'll buy tha matris FH203KE http://www.ebay.com/itm/Kit-Molle-Fo...a7292d&vxp=mtr, also new bushing slides etc,
Why you
drill new holes in the damping rode :/
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Old 03-02-2014, 06:26 AM   #10
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Default Re: Fork rebuilding and upgrading - '04

I don't know if the Matris hardware works the same way, but for the Racetech Gold Valve Emulators you need to drill holes in the damping rod because adding the emulator restricts flow, so the damping rod needs to be opened up to make up for that. The difference is that the emulator restricts flow in an adjustable manner, and the amount of restriction in either direction (rebound vs. compression) is controlled separately.

Most importantly, you do it because the instructions say to do it.
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Old 03-02-2014, 06:53 AM   #11
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Default Re: Fork rebuilding and upgrading - '04

I did a little research on the linked Matris kit:

http://www.matrisdampers.com/catalog/category/13.html

"4. Flow regulator, dedicated for the different front forks"

I'm not sure what the "flow regulator" does, and a quick search indicates other people confused about this as well.

If the flow regulator restricts flow, it seems like you would need to drill holes in your damping rod. Maybe it only restricts compression flow, increasing compression damping but not rebound damping?

My wild guess is that there is no modification of the damping rod, and you just end up with greater damping due to the regulator.
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Old 03-02-2014, 12:03 PM   #12
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Default Re: Fork rebuilding and upgrading - '04

I see many people with this kit and they don't do nothing else
neither the instructions say something
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Old 04-12-2014, 09:41 AM   #13
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Default Re: Fork rebuilding and upgrading - '04

So I have already install my matris fork kit, of course I feel like a new bike, but I have a question, the springs that send me are 9.5nm, I' m a rider about 65kg - 140lb is that the wright spring rate? Also I don' t know how to adjust the preload, I have it yet in the zero point

Last edited by igatos; 04-12-2014 at 09:44 AM.
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Old 07-21-2017, 01:00 PM   #14
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Default Re: Fork rebuilding and upgrading - '04

I recently salvaged these off my first 599 and put them into my second, and now cratered NYC streets are only half as nerve-wracking as they were with the stock forks.
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