OK, as promised, here it is. Send money...
Fork seal/oil changeNote: These instructions are for upside down forks only, but much of the information can be applied to conventional forks as well. This is also applicable to more than just the KX500, as the same steps work for most Yamaha?s, Kawasaki?s, and many other brands. I will not be using many technical terms, but rather calling the parts as they appear or are normally called by the novice just so things are easy to understand.
Tools: Closed end wrenches and sockets either metric or standard (the standard sizes are close enough to complete the task, as there are not any high torques required); Oil ? I use BelRay 5 weight; Tape Measure; CLEAN rags ? it?s going to get messy ? preferably blue disposable shop towels; hammer; hacksaw; small punch; can of spray carb cleaner (or 2); Optional ? ? inch impact and hex head socket that will fit into the bottom of your fork (this is actually the valve); I constructed a metal tray is 48?x 8? with 2? sides turned up at a 45 degree angle. The tray has a fitting in one corner to which I attach a tube to drain fluid into a jug. Of course, I have welded end caps on my tray to actually make it a tray that will hold fluid. This is useful for motor rebuilds, brake caliper rebuilds, carb work, fork/shock rebuilds, essentially anything that is going to release fluid gets done in this tray. Keeps the bench clean and dry.
1. First thing, wash your bike. The ports inside the fork are small, so no reason increasing risk of getting dirt inside the forks. If the forks are already off the bike, wash the forks.
2. If not already done, remove the forks. If removing the forks requires instructions, stop here, as you certainly do not have the skills to complete the rebuild. Run, do not walk, to your local motorcycle shop and beg them not to take to much advantage of you.
3. Remove the fork slider (the plastic guard over the bottom fork leg. Put the screws where you can find them again.
4. Here is where it begins to get tricky. To do this rebuild right, you really need to remove the valve from the bottom of the fork. This will accomplish two things: easy way to remove the oil and allows complete disassembly of the entire fork for cleaning. I will assume that everyone will remove the valve from this point forward. If not, simply skip the sections that deal with removal/installation of the valve and inner tube. (As a note, the fork seal and oil can be changed without removal of the valve, but getting the oil out can be a pain. Cleaning is also tough, as you can?t really do a good job. However, if you do not have access to an impact wrench, just focus on the sections that relate to changing the seal and adding oil. To get the oil out without removing the valve, just remove the top cap and spring and turn the fork upside down. Pull the small tube the cap screws to in and out to help get all oil out of the fork. It will just have to do. If you really want to be sure, after dumping the oil, turn the fork upside down on the bench overnight and let it drain.)
5. Here is where you need a ? drive impact wrench and hex head socket that fits into the valve in the bottom of the fork. Removing the valve takes impact speed and can not be done by hand. Go ahead and give it a try by hand?..see what I mean? Turn the fork upside down in front of you or place in your parts tray on its side. Insert the hex head socket into the bottom of the fork and activate the impact. The inside tube may turn, but the impact will turn the valve fast enough to spin it out. Place the valve on a clean rag and dump the oil in the tray or other receptacle like a coffee can.
6. Once the oil is down to a dribble, use a box end wrench or socket and remove the top cap from the top of the outer tube. This cap is not very tight, so should come out easily. I use a small impact on low setting to remove, but NEVER use an impact to reinstall. Best strategy is to just use hand tools.
7. You will notice that the cap is attached to the inside parts with the spring pushing on the bottom of the cap. Wiggle a wrench between the spring coils just below the cap and fit a wrench on the nut below the cap. This nut acts as a jam nut to ensure the cap does not screw off. Fit another wrench on the top of the cap and screw the cap off the inside tube. Put the parts in order of removal on a clean rag. Remove the cap, washer, and spring. The inside assembly will also come out, but be careful not to scratch the inside of the fork tubes.
8. There is a rod inside the tube. One some models, there is a part about 3 inches long that will need to be removed first and then another small tube about 12 inches long just below this little top piece. On other models, there is just a solid rod inside the large tube. In any event, remove the parts on the inside of the tube, paying attention to which way the little 3 inch top part goes in, as its not the same on both ends. If you screw it up, no problem, you still have another fork all assembled that you can check. Incidentally, this is the only part that will cause confusion when putting the fork back together, as you have now disassembled the inside parts as much as I believe necessary for cleaning.
9. To review, you should have the following parts on your bench: fork valve, fork cap, spring top washer (and maybe a spacer), spring, a small tube or rod (and maybe a little 3 inch top piece)that was inside the tube the cap screwed on), the inside fork assembly; and the original fork tubes still assembled but now empty. Move all but the outside fork tubes to the back of the bench and we?ll deal with changing the seal before we return to them.
10. With a small screwdriver, remove the dust cover. Here again, if you don?t know where the dust cover is located, you may be in over your head. Slide the dust cover up the fork tube and out of the way. Just under this dust cover you will see a small snap ring. Using a small screwdriver, pop out the snap ring and put on the bench with the other parts. Grab the bottom fork tube in one hand and the top fork tube in the other hand. Push the two tubes together about six inches and quickly pull apart. Since the seal is driven into the bottom of the top tube, the idea here is to drive the seal out the reverse direction it went in. Continue this in and out process until the tubes come apart.
11. Once the two tubes are apart, you will notice that the top tube is now completely empty. The bottom tube will have from top to bottom: a bushing that snaps into a groove, a bushing that fits over the fork tube, a washer that rests against the back of the seal, the seal, and finally the dust cover. Using a small screwdriver gently spread the top bushing and remove it from the fork leg. Remove the remaining parts and place them on a new clean rag for inspection later.
12. Inspect the bottom fork leg for any nicks or damage. If you find a nick, these can be removed with 600 or finer grit wet/dry sand paper using an up and down motion. A good rule is to start with fine paper and work towards the 600 grit. I have NEVER used anything more coarse than 600, as this has always been sufficient to remove any burs that could damage the seal.
13. Grab your can of spray carb cleaner and safety glasses and clean the dust cover. Dry thoroughly, check for damage (I?ve only replace one of these) and place on a clean rag. Wipe down both bushings and the washer and place on a clean rag.
14. Grab a new seal. Remove the spring on the back side of your old seal and add it to the back of the new seal so you have two springs. If you are able, do the same with the outside spring as well (newer models will not accept a spring on the outside of the seal, but older model will). I must say at this point that some folks don?t like this step, but in my experience, this creates a better seal and does not harm the fork in any way. I usually get more than two years between fork seal changes, and that?s with riding/racing every weekend in the rain, snow, heat, mud, water, sand, etc. I ALWAYS add a spring to the back at a minimum, and the front if possible. Place the new seal on the clean rag.
15. Hold the bottom fork tube over a can or your parts tray and spray carb cleaner into the tube. Let it run out the bottom, and try and get the carb cleaner all around the inside of the tube to wash out the old oil. Wade up a CLEAN rag and push it into the top of the tube. I use a dowel or something similar to push the rag to the bottom of the fork leg, and then push back to the top. The idea here is to clean any debris, old oil, and carb cleaner from inside the tube. Repeat this step a couple of times with a clean rag. Move to the bottom of the tube where the valve screws in and clean this area well. Start over with carb cleaner if you must, just get it clean.
16. It?s time to put all those bushings and seals back on the bottom fork leg. Go to the kitchen and acquire a plastic sandwich bag. Heck, grab two in case you screw up the first one. Cut the corner off the sandwich bag and place it on the top of the bottom fork tube. You want the bag long enough to hang below the groove on the top of this fork tube. Ok, I?ll wait until you cut the second bag to get it long enough??.
17. Using a little fork oil, coat the sealing edge of the dust cover. Slide the dust cover over the sandwich bag onto the top fork leg. See how smoothly it slides past that groove? Without the sandwich bag, you risk damaging the sealing surface as it passes over the square edge of the ridge. If you feel it hit the ridge, try placing your hand around the sandwich bag corners and holding downward pressure, expanding the seal as it passes over the ridge.
18. Coat the sealing surface of the oil seal and slide it over the sandwich bag onto the fork tube. Remove the bag and add the washer and two bushings (hopefully you paid attention as you removed the bushings, but if not, the small bushing goes on last to hold everything else in place. It?s worth noting here that you should inspect the inside of the bushings. If the coating is frayed, trim with a razorblade. Better yet, replace them, but I must say that I have never replaced a bushing, just cleaned them up a little. On older bikes, you?re probably going to need to think seriously about replacing the bushings, as the inside coating will be gone. There are several companies who sell these for low dollars. Once assembled, set the bottom fork leg aside.
19. Grab the top fork leg, spray carb cleaner down the inside, and push through clean rags all the way down. Don?t use anything that will scratch the inside of the fork tube. Repeat a couple of times, making sure that the seal pocket is clean, especially the snap ring groove.
20. Installing the seal into the top tube: Things are going to get a little tricky on this step as well. First, get another person to help you, anyone will do, even your kid. Second, you need to cut through one side of the old seal with the hacksaw. This will allow the seal to be twisted and put on the bottom fork leg to be used as a seal driver. I use a chop saw so I get a little extra space, so if you are using a hacksaw, you might have to twist the seal open and grind one edge. Either way, once the seal is cut, you must use a wire brush to remove any burs that might damage the new seal.
21. Put the top fork tube upside down on the bench. Slide the bottom tube top bushing into the top fork tube in reverse order of removal (since you just took it apart, this should be pretty easy to figure out). Once you get to the second bushing, things are going to get tight. Allow the second bushing to drop into the pocket with the washer on top. Ask your friend to hold the bottom fork tube high enough so it does not drop down into your way. This will allow you to work with both hands installing the seal and bottom bushing. Once you start this step, you will see what I mean here.
22. The easiest way to approach this next step is to gently tap on the washer over the bushing in an alternating pattern (12-3-6-9 on a clock face) from 12 to 6 to 3 to 9 to 12 (etc) to tap the bushing in place. NEVER tap on the bushing itself, as you will disfigure the bushing. By taping the bushing in first you reduce the resistance while driving the seal in place.
23. Once you hear the bushing hit bottom (change in tone), push the seal into place. Twist and install the old seal just as it was remove with the open end facing the new seal. Push the old seal on top of the new seal as far into the pocket as possible and begin to tap in an alternating pattern until the seal is all the way in place. You may need the help of the punch as you near the bottom, but be very careful not to damage the seal. Install the snap ring and tap the dust cover in place. Whew, you?re done. Thank your friend, because his/her arms are going to hurt by now. For smaller helpers, let them stand on the bench and hold the fork tube from waist level, as it is much easier on the arms. Put this assembly aside for now.
24. Clean all of the remaining parts with carb cleaner and wipe clean. You can also use air to help blow excess liquid from smaller parts like the valve (wear safety glasses when working with cleaners. You only get one set of eyes). Make sure you spray through the ports in the valve to ensure they are clear.
25. Collapse the two fork tube as if you had just hit a huge ditch and leave them that way. Insert the inside fork assembly in reverse order of disassembly. Install the hex head socket into the valve and push the valve into the bottom tube. Hand screw into place several turns to make sure the valve is started in the threads properly. Screw this step up and you won?t be happy. Once you are sure the valve is threaded properly, attach the impact and spin until tight.
26. Stand the fork in proper orientation on the bench with the tubes still collapsed. (At this point I should note that you need to find a screwdriver or other clean small tool that is 3 7/8 to 4 inches long. No more, no less. You will use this to check oil height). On newer forks, there is a washer at the bottom of the inside fork assembly that is below the spring when installed. You will need to angle this washer to allow oil to easily flow into the bottom fork tube. It will flatten out when you install the spring. Begin to pour oil into the fork tube until it is close to the top. Grab the center tube that the cap screws on and pull up. You will feel resistance at first, and then none. Continue to add oil and pull this rod up and down until you have resistance all the way to the top of the stroke. This will tell you all the air is out.
27. Now comes the hard part of setting oil height. I use a special little pump and tube that allows me to just pump all the excess oil out to a predetermined height. Since you don?t have a pump, you?ll have to use the screwdriver you measured in the last step. First install the little tube inside the tube the cap screws on. If your fork has the little extra 3 inch piece, leave it out for now, as it will come out and fall into the oil. Bad thing...
28. The trick to setting the oil height with a screwdriver is to guess at your oil height by adding and dumping small amounts of oil until the tip of your screwdriver just touches the top of the oil. It?s a pain, but I used this method for five years before someone gave me the fancy pump in exchange for doing their suspension work one time. I have gotten a lot of tools this way (I do the work and get to keep the tools), so think about it next time your friend needs a seal changed. The pumps are only about $40, so cheaper than letting a shop do the work. I also built an oil level tool using a large syringe (farm supply stores have these), a small length of clear plastic hose, and a piece of straight wire. Tape the wire to the end of the hose and bend a 120 degree angle in the wire at 4 inches. Hang the wire over the edge of the fork tube and viola; you too have an oil removal tool. The syringe is one use only, as the oil ruins the rubber plunger, but for $.79, not a lot invested. You can also use hydraulic brake pressure bleeders.
29. Once the oil level is set between 3 7/8 to 4 inches, you need to install the spring. Pull the tube the cap screws on all the way to the top of the stroke. Slide the spring over tube keeping the tube as high as possible. Insert a small box end wrench between the spring coils low on the spring and over the tube. Begin to turn the spring until the open end wrench contact the bottom stop on the tube, and keep turning. This will compress your spring against the bottom stop on the tube allowing you to expose the threads on top of the tube. Slip on the top spring washer and screw on the cap until hand tight. Unscrew the spring to release the tension on the wrench and remove the wrench. Insert a wrench of proper size between the spring coils just below the cap and hold the jam nut. Place a wrench or socket on top of the cap and tighten the jam nut against the cap. Pull the outer tube up to the cap and screw the cap in place. BE CAREFUL, as you do not want to strip the threads. The cap will only turn hard when you hit the O-ring. Tighten with hand tools and reinstall the fork on the bike.
