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Fork seal replacement

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79K views 27 replies 17 participants last post by  fishinking86  
#1 · (Edited)
First, this set of guide lines is written around conventional forks. Upside down forks will be different and require you to get a "real" seal driver.

The instruction also assume some basic knowledge and tools. A means of supporting the front of the bike is a given...using a rear stand for stability is recommended.

As with any job, get yourself a clean place to work, lay out a towel or some rags to lay parts out on.

Before removing the fork tube from the bike, you want to break the cap loose (blue in the picture), don’t remove it, just break it loose. Also back off the spring preload all the way (silver in the picture) and turn the rebound dampening screw all the way in to the last click (brass screw head), do not “tighten” it.
 

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#2 ·
Take the front wheel and fender off.

Loosen the pinch bolts on the triple clamps and the clip-on.

With the fork out of the bike, you can begin disassembly. Unscrew the fork cap completely by turning the [blue] outer portion.
 

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#3 · (Edited)
To remove the fork cap from the damping rod you need to loosen the jamb nut, then unscrew the fork cap from the rod. I remove the nut from the damping rod for work later in the process. Also remove the small rod in the center of the damping rod…this is the push rod for the rebound damping adjustment. After you let go, the damping rod will slide down into the tube, and that’s OK for now.

Remove the upper washer and spring spacer. Now you can dump the oil into a suitable container…..you’ll want to pump the tube a few times and stroke the damping rod as well. The lower washer and spring will also fall out at this time. Just lay these parts out in order. The oil is likely to smell burnt and also will look a very milky grey. The grey is aluminum worn off the fork leg and teflon from the bushings that is now floating in the fluid….your new oil will look dirty in just a few hundred miles too, so don’t let this scare you.

Note the spring in this case has a tapered end, which rests on the top of the cartridge.

If you wish, now is a good time to flush the fork out. I use 5w30 engine oil because its cheap….pour enough in there to cover the cartridge….stroke the fork tube and the damping rod a few times, dump it out….repeat, let drain upside down.

Now, carefully pry off the dust seal. I do this on the inboard side of the fork so that if I nick the paint it won’t be seen.

Next, remove the retaining ring for the seal….don’t make any new scratches in the fork tube.
 

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#4 ·
Now we need to remove the cartridge….its held in place with a screw in the bottom of the fork. You’ll likely need to remove the axle pinch bolts. A 10mm Allen is needed in this case. If you have an air impact, this screw will come out easy. If you have hand tools you’ll need a cartridge holder. In the case of these KYB forks a piece of ¾” square steel tubing works…I had just a short piece in the scrap bin and welded it on the end of a piece of metal conduit….otherwise you can get a couple feet of this at your local hardware store.

Remove the screw and copper crush washer from the bottom of the fork. More oil will leak onto your bench. You should really replace the copper washer…I’ve gotten away with reusing them if you carefully clean all the parts and surfaces. Take the cartridge out and let it dribble oil all over your work bench…standing it up in a bucket or jug to drain is fine.

Now you’ll see that the tube slides out further. You want to slide the tube out firmly in a repetitive motion against the hard stop to break the seal loose and begin working it out. You don’t need to go nuts…but do need to do this firmly. I don’t do it in the bench vise…I hold the leg in one hand and the tube in the other. To get the seal to break loose takes considerable force…after you’ll feel/see the seal start to move, and you can reduce your effort so that you keep control of the tube and don’t make a huge mess when the seal comes out.
 

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#5 · (Edited)
When the seal comes out, the upper/outer bushing from the lower fork leg and a washer will come with it….and the lower/inner busing will be on the fork tube. In these forks there is a cup around the bottom of the cartridge and its probably still inside – so don’t loose this…we’ll put it in at the same time with the cartridge at reassembly.

Remove the seal and washer. Most all the manufacturers recommend you replace the bushings during this process. If the teflon coating is in good shape, I’d reuse them. Anything with ~12K street miles and some mixed track time is probably just fine. The Teflon is over copper, so if the dull grey is mostly gone and copper showing dominantly, replace them.

Now, I would inspect the fork tube for any nicks or dings that may have damaged your seal in the first place....the smallest nick can do it. If you have plain old chrome form tubes you can polish them with 600 grit sandpaper. Relax…Chrome is HARD stuff, you’ll barely leave a mark. Use a wet sanding approach, and wrap the sandpaper around the tube and SPIN the tube in your hand working your way up and down the area where the seal rides, repeatedly dipping the sandpaper in water…don’t stroke up and down...we want to make a very shallow angle cross hatch pattern. Any more significant dings you can rub on them with your thumb in small circles, and severe nicks you can sand down progressively…320-400-600. Wrap the paper tightly around a file and stroke over them in a rolling motion. Rinse the tube off, wipe off with an oily rag to remove any debris. Edit: Look for/address any nicks from the sealing area to the top that may damage our seal during installation.

Before we go further, we need to make another tool….a seal driver. For these 46mm zx6r forks, a piece of 2” thick wall PVC works great….your local hardware store should have 3 or 4 foot pieces of this for a few bucks. I used my miter saw to cut the ends square if they are not already. Then with fine tooth wood saw I cut the end to have 8 “fingers” about 3 inches long so than it can flex down to size for this application. I put an end cap on it for easier pounding as we’ll need to do later. Don’t forget to clean off the extra plastic shavings from our sawing. Sadly, this will only work for coventional forks. If you have upside down/inverted forks you’ll need a real driver for your application.
 

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#6 ·
Now its time for reassembly.

Slide the tube into the lower leg. I position the split line in the bushing to be facing inboard/outboard…rather than to the front or rear…but its not a big deal. Then, get the upper/outer bushing. Again, I position the slit to the inboard/outboard side. Put the heavy washer on top of the bushing, give things a wiggle so it starts in the bore and pound down with our seal driver we made….if you replaced the bushings, you can use the old one on top of the new one, and use a punch and hammer or the heavy washer and seal driver….just don’t nick up your freshly polished tubes. Make sure you put the heavy washer in before moving on to the next step.

Next install the new seal over the end of the tube. Orient the seal so the tapered end is going into the leg first.

I wipe a little moly or lithium grease on the seal lips first (the seal and the wiper). Now, don’t just jamb the seal over the end of the tube, you can damage them and be doing this all over. I start one side, the press it against the tube and tip the opposite side down. I’ve also put a piece of saran wrap over the end of the tube of forks with a sharp edge...these ZX6r forks were not

Next, drive the seal home with our driver. If you don’t get it far enough you won’t be able to reinstall the retaining ring. Install the retaining ring. Then install the wiper (unless you have really low miles and age, replace these too). Give the wiper a firm push, then tap around the edge with your mallet until it’s seated.
 

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#7 · (Edited)
Now we need to install the cartridge. I stand the cartridge upside down on my holder, set the bottom cap on it, then lower the fork assembly over it. You’ll be able to see the bottom of the cartridge if you look in the hole on the bottom of the fork leg to see if its fully in place. Then I put the assembly into my bench vise and install the bottom screw….don’t forget the copper washer on the screw. Torque this per the manual. At this time I put a long zip tie on the end of the damping rod to make it easier to grab for the remainder of the assembly process since I never bothered to make a bleeding tool.

Now, position the fork upright in the vise. Its time to add oil. Fill the fork until the cartridge is covered by a inch or two of oil….it will likely be a little over half a quart per leg for modern sport bikes. Stroke the tube fully till you don’t hear air bubbles woshing around. Next lift the damping rod using our zip tie and push it back in a few times until you don’t hear air bubbles…you need to keep the fluid above the cartridge while doing this. Oil level is checked with the damping rod full compressed, the rebound rod removed, the tube full compressed and no spring.

To measure oil level you can eye ball it with a ruler or use the ruler as a dip stick. Or you can make an oil level gauge….a small syringe from the pharmacy and some clear vinyl tubing. I placed marks on the tube at 110, 120, 130 140 150 mm. Then I zip-tie this tube to the rebound rod we removed earlier to hold it straight…you could get a small piece of metal tubing at your local hardware store.

25mm is 1 inch roughly (25.4 for those that like to be exact)….so 100mm is 4 inches. With that in mind overfill the fork a little from the spec. In the case of the 2001 zx6r fork here, the OEM is 116 mm down using 10W. Hold the syringe tube at the level required by the manual (or aftermarket instructions) and suck the extra out and put it back in the container to use on the next fork. Do this until you suck just air…might take a few times if you got carried away on filling.

Now, install the spring (tapered end down in this case), the washer, spring spacer, washer, and the nut on the end of the damping rod. The manual will call for a length of thread to be exposed above the nut on the damping rod. The damping rod will try to fall down and you are hopefully appreciating the zip tie I told you to put on earlier.
 

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#8 · (Edited)
Reinsert the rebound adjustment rod. Start the fork cap on the damping rod and with the nut now on, cut off the zip tie and push the shaft to the side and let the nut rest on the top washer. Spin the fork cap on with your fingers until it stops (I hope you remembered to turn your rebound adjustment in all the way like I told you earlier. Set the jamb nut against it. Torque per the manual.

Press the cap down and turn to install it….if you didn’t back the spring preload off like I told you earlier, it will take more effort to compress the spring. We’ll torque the cap to spec after its back in the bike.

Slip the fork back into the bike, set the ride height where you had it….if your bike came with clip-ons mounted over the triple clamp it will look like the picture.

Tighten the pinch bolts to spec, and make sure to tighten the fork cap to spec.

Re-assemble your bike and go for a ride…I hope this write up helped you out.
 

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#13 ·
seems like a huge pain in the ass! unfortunately, i think i have a busted seal on the SV650 i just picked up. i might give it a shot. if i jack it up, i can always take it to the stealership...
 
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J
#15 ·
great tutorial, I really appreciate it. I have my 99 zx6r forks apart right now. here's my question:

my manual refers to an "inner tube guide bushing" (very thin and wide) and "outer tube guide bushing" (narrower and thicker). are both of these teflon coated copper? The outer tube guide bushing is showing all copper, so I will replace it, but the inner one is a dark color. Is it possible that the copper is worn off as well? I can see copper on the edges but not on the contact surface.

The bike has 24,000 mi on it. Any advice?


I can take pics if it would help.
 
J
#18 ·
Its cool, thanks for replying. If I am correct, the outer guide bushing is coated on the inside only, and the inner guide bushing is coated on the outside only. the inner looks fine, I'll take the outer off tomorrow and look at it. If it looks ok I'm not gonna waste time waiting for the bushings. I've been partying out of town with some friends, so these things have been apart for like 2 weeks, I need to get them together asap.


What do you think?
 
C
#19 · (Edited)
HELLO! That was an awesome write up. I have a question about the fork seal driver. Is it really worth 65 bucks for a 41mm fork seal driver? Or can I use something else to set the seal? Is there a creative cheaper way to set the seal for inverted forks? I used PVC pipe to set the seals on my GS500 but I don't really know the difference between inverted and standard forks. Thanks guys.

Oh and anyone has any ideas, I will post a write up (with pics) on how to do a fork seal replacement for inverted forks using their idea. Thanks guys.
 
G
#23 ·
WOW! I cannot thank you enough! I bought myself a 2000 ninja zx6r around september 2007. The left fork seal has always deposited a slight oily residue, but never much until i had the bike strapped down for a 7 hour trip to bike week. I was always nervous about trying it myself. After studying this post and reading a few times I completed this job with ease. Very excellent and thanks again!
 
#26 ·
yes. they're legit.

thats all i use at my shop.

they replace the dust cap and main seal. theres a special washer sandwiched in between the cap and seal thats required tho.. they say if you don't install that, they'll leak and warranty is void.
ithe warranty is dependant on if you're a competent mechanic and if you fill out the shit and send it in.
 
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