|WP Inverted Fork Oil Change - by Steven Iveson
[Additional comments by Jerry Riedel]
Having just changed the oil in the forks from my Daytona I might be able to lend some insight. These instructions are for the models with the inverted, WP forks. Yes there is an allen bolt at the bottom of the fork leg behind the axle. No, that isn't the way to remove the oil. A small amount of oil will dribble out (3-4 cc's). Remember, each fork leg contains 400 cc of oil. You must disassemble the top of the fork.
[Some items you will/might need: large vise mounted on a workbench, old clip-on or similar to hold the fork leg while loosening/tightening the fork cap, piece of leather (old glove works good), pan to catch dripping oil, gallon plastic jug, funnel, newspaper, protractor, rags, wooden cradle to support the bottom of the motor and a cinder block. You may want to buy a couple of the copper washers that go on the bottom bolt on the forks. I reused mine, but they probably won't be reusable next time. If your fork seals are leaking, now is a good time to change them.]
[I used the protractor to measure the angle of the clip-ons with respect to the top triple clamp so I could easily get them back at the same angle on re-assembly.]
[I built a wooden cradle (photo available) to go under the oil pan.
When it sits on the cinder block, it is just the right height to be able to pull the forks out of the bottom triple clamp. Whatever method you use, you do not want to find out that you can't pull the fork leg out because the bike is not sitting high enough.]
[Since you have the bike blocked up with the forks free to turn, this
is a great time to check the steering head bearings. While in front of the bike, grab the forks and try to move them fore and aft. If you have any play, you can adjust now or before you put the wheel back on. If you have never greased the steering head bearings, now might be the time. The shop manual covers how to adjust, but does not explicitly describe disassembly required to grease or replace the bearings.]
First, completely back off both the rebound and compression damping to "0". Now unscrew the top fork cap. When the cap is off you should be able to slide the top (outer fork leg all the way to "bottomed" position). What you will see is the cartridge assembly, spring, preload spacers and a pair of half retainer "shims" holding it all together.
[If there is any gunk accumulated on the fork slider just above the cast end at the bottom of the slider, clean it off before disassembly to prevent it from getting into the fork seal.]
[After removing the cap, I secured the fork slider in a vise by wrapping an old leather glove around the brake caliper mounting bracket, similar to how it is shown in the shop manual, with drip pan below. The shop manual says to incline the fork leg at 45 degrees, but this doesn't work as well as mounting it vertically. If you can't break the cap loose, wrap the leather glove around the top of the fork leg and secure it in the vise.]
You have to compress the spring in order to continue with the disassembly. A short distance down from the top of the cartridge (3-5 inches) you'll see a small hole in the side of the cartridge. Find an
allen wrench that will fit securely in the hole. Place the allen wrench in the hole and then twist the fork spring in the appropriate direction so that it "rides" down the allen and compresses. You don't have to compress it far, maybe an inch or so. The spring and everything will be covered with fishy smelling fork oil so keep some rags handy.
With the fork compressed you can easily remove the retainers, metal washer and the plastic preload spacers. You can now relax the fork spring by twisting it in the opposite direction from when you compressed it.
Remove the fork spring (more dripping, fishy fork oil).
Now take the fork assembly with the cartridge in place and carefully invert it over an oil pan. This will drain about 80% of the oil. Be careful with the sliders: they will move back and forth freely- it gets kind of awkward.
[I dumped the old oil into used an old plastic jug with a funnel, since
I take the oil to the recycler.]
NOW you can remove the bolt at the bottom of the fork leg. This allen bolt (relatively high torque) holds the cartridge in place. More fishy oil to deal with. Remove the cartridge, place over oil container and invert and compress and uncompress the cartridge piston. This will remove the rest of the oil.
I left all the oil containing components inverted, hanging over the oil pan overnight so that all the old crap would dribble out. I also took a clean rag (or paper towel) and wiped out-off all the components.
[The shop manual shows disassembly of the damper units, but this looks like more trouble than it is worth.]
For reassembly, re-attach the cartridges with the allen at the bottom of the fork. Make sure that the retaining washer (that the bottom of the fork spring rests upon) is seated properly (it's located about half way down the cartridge assembly). Now I used my ratio-rite to add 400cc of WP fork oil. At this point you need to (slowly at first) extend and retract the cartridge piston. This will fill the cartridge with oil.
You will hear gurgling noises while this is occurring. One of my cartridges filled in a minute or so, the other took me much longer. You'll know you're getting it right when the piston becomes harder to push and pull and the gurgling stops. I think that it's vitally important to get this right.
[I used Bel-Ray 5wt fork oil. On the compression leg damper, I couldn't get it to fill until I turned the brass adjustment screw in a few clicks. On the rebound damper, all I had to do was let it sit and I could hear gurgling, and almost all of the air purged just sitting in the oil. You will know that all the air has been purged when the resistance is smooth and consistent over the full range of travel, in both directions. While the compression damper also has some noticeable resistance in the rebound direction, the rebound damper doesn't seem to have much resistance in the compression direction. If you play with the adjustment screws at this point, you should be able to notice the effect of making adjustments while working it by hand.]
Now slide the fork spring back over the cartridge, place the allen wrench in the hole at the top of the cartridge. Twist the spring to compress it and reinstall (in the proper order) the pre-load spacers, metal washer and the retaining plates (washers, whatever you want to call them) release the spring tension, screw on the top cap and you are finished.
[This is a little tougher than it sounds. The damper wants to telescope down so that it is almost flush with the fork tube. After you put the spring in, you have to somehow pull the damper up so that you can fit the spacers and retainer. I used a thin piece of wood with a notch cut in the end that fit the "waist" of the brass adjustment screw to walk the damper up the spring in the same way that the allen wrench is used to compress it.
Just for kicks, I tested the leg assemblies before putting them back on the bike by putting the bottom of the slider on a piece of carpet on the floor and pushing down on the leg.]
I'm no master mechanic, but I was able to do both forks in about 3 hours total time.
If you doubt any of these instructions, seek out a shop manual (Carl Allison's site for example) or find a qualified mechanic. This worked for me, but your results may vary. Proceed at your own risk :) If anyone has found an easier way to do this, please let me know.
[Inserted text by Jerry Riedel