Fork Oil / Fork Spring Change
First, it is important to know that a backyard mechanic can easily perform these tasks. However it is also easy to damage the fork and cause expensive repair work. Please do not perform this task unless you have reasonable mechanical skill and can accept responsibility for your own actions. Be sure you have the service manual for your country/year handy for torque specifications and reference of oil levels, as the OIL LEVELS VARY depending on exact model!!! Non USA models especially need to check the manual for oil height levels!!!
You need several tools to perform these tasks.
14 and 17mm wrench. 24mm long socket. An allen head socket set. Something to measurethats at least 120mm long. Small screwdriver. Front axle removal tool. Oil pan, rags, latex gloves are shop must-haves. And a Front End bike stand, like the one on Micapeak.
I recommend a quality fork oil. Silkolene RSF Race 10W, PJ1 Type3 Race, and BelRay appear to be excellent choices. Honda also has a premium blend as well as Torco and Motul. Any of these types will be premium options. 10W is preferred, but 7.5W or 15W can also be experimented with as suspension preferences tend to vary. By all means try a lighter weight oil if you think the front end is harsh and cannot remove the harshness through clicker adjustment. By aware that the longer the fork oil is used, the thicker it becomes (from particles in suspension, no pun intended). This fact alone leads to a harsher ride.
Ok, youve got the oil, tools, stand, and an afternoon.
Remove the two side fairing pieces, the two front-end black inner panels, and horns. Front fender needs to come off as well.
Now the actual fork removal and flush/refill process:
1.) Raise front end.
2.) Remove brake calipers from fork and rotor area.
3.) Remove front wheel. First, loosen pinch bolt, then axle and slide out wheel. Keep spacers arranged left to right for correct reassembly. Note, a special tool needed for the front axle.
4.) Loosen top triple clamp bolts, but do not remove.
5.) Remove handlebar bolts and let the bars relax downward. Use towels to product tank, triple clamp, and fairing from handlebar components.
6.) Turn fork preload adjusters to full soft (out to 5 rings) A. 17mm wrench is needed.
7.) Slightly loosen the top fork caps as these will be tough to loosen if the fork is removed. Two turns should be enough with a 24mm long socket.
8.) Loosen the lower triple clamps bolts on one side while supporting that fork. The fork will slide down easily. If they do not slide out for some reason, gently pry the clamps open while supporting the fork. 2 people might be handy here, but not needed unless its stubborn. Mine slid right out.
9.) Repeat step 6 on other side
10.) OK the forks are off the bike. Clean the black brake dust with tire cleaner/water. Its a great time to remove brake pads and clean them, brake pistons, and the pad pin. Pad pins should be replaced often, especially if they are grooved.
11.) Hold fork upright and twist fork cap off. It will slightly pop up but is still attached.
12.) Fully extend the fork by holding the cap/rebound adjuster. Push down the tube to expose the entire top assemby, then hold the 14mm nut below the cap firmly while loosening the cap by the *17mm preload adjuster* The fork cap will unscrew. Once fork cap is removed from the rod, remove the nut, and long spacer as well as the thinner internal roed (damping rod) and clean/set aside.
13.) Use a magnetic pickup to remove the washer inside the fork. (optional step, you can just dump the oil now and fish out the large steel washer)
14.) Remove fork spring, compress fork several times, ending with a firm push down (it will slowly sink down the last few mm's) and measure oil height. 100mm from the top of fork leg should be used for US models. This is an optional step, were measuring for reference. If they are drastically off, this could explain a handling problem or seal leak if you have one.
15.) Turn fork upside down into oil pan and pump the fork leg several times to remove all oil. Find a hook and rope to hang them upside down to drain for a few minutes.
16.) Service manual won't tell you this, and the shops won't do this, but I refilled, pumped the forks, and again drained to flush the forks. The original oil at 8K miles/13 months was very dark with some metallic flakes. The flushed fluid came out darker than it went in, so I think this is an important step and only costs a few more $ for oil. I hung the forks upside down from a rope and drained overnight after flushing, but 20-30 mins should be sufficient.
17.) Refill oil to appx. 100mm from top of fork tube at full compression. Compress/decompress fork leg several times to distribute the oil in the dampening stacks. When the hissing stops, the air is removed. Recompress fork, press it down hard at the bottom part of the stroke it will slowly creep to the bottom. Measure oil height and adjust back to 100mm. You could experiment with different heights using caution and common sense, but I wouldnt go past 90mm (except for some other models, which may be 79mm stock!!!). Again, refer to your service manual for country/model year variances!
18.) Reinstall spring (new spring if so purchased) then the washer. Put on long spacer, nut, screw on fork cap by hand until it bottoms (be sure the nut is not interfering) Unscrew 10-20degrees and tighten nut down.
Since you've got this far, go ahead and do the steering bearings as it will only take another 30 or 40 minutes, maybe more if you take your time and clean everything thoroughly. Mine needed cleaning and regreasing badly. A few balls were caked in crud and were replaced the following year.
19.) Forks are ready to reinstall. Align top of fork cap with edge of triple clamp. Tighten lower clamp, then tighten the cap, then the top triple clamps.
Remember to readjust the preload! Oh, also clean the inside of the triple clamps and fork legs (chromed portion) with Brake Cleaner before reinstalling!.
20.) Install wheel/axle, brake calipers, fender. Tighten axle while compressing the fork (two people needed). Once axle is tight, tighten the pinch bolt. Tighten calipers and fender.
21.) Reinstall horns and fairing, then take her for a test ride! Youll be rewarded by plusher suspension and longer life of fork components :O
No torque settings have been given here as I cannot possibly know if differences exist between models. Please refer to your official Yamaha service manual for these figures.