This little FAQ is in relation to my 2009 SID Race but is probably applicable to other 2009/2010 and later SID models. Just make sure you check the oil quantities for your particular fork.
Step 1 - give it a good clean
It is possible to service the fork with it still on the bike, but its just easier to take it off. Getting the slightest amount of dirt or grit on the inside of the fork will drastically reduce its lifespan. For that reason I'd recommend removing it from the bike and giving it a thorough clean.
I use CT18 truckwash, a soft brush and lots of water to get all of the dirt, oil and grime off. Don't worry about getting water into places you don't want it, we're going to pull it all appart anyway.
Step 2 - let the air out
Before doing anything on your air fork, make sure all of the air pressure is let out. The SID has two air springs:
- positive air spring accessed on the top of the left fork crown; and
- the negative air spring accessed on the bottom of the left fork leg
Remove the relevant caps and let the air out of both of those air chambers. A small amount of oil may come out with the air. That is normal. The air spring cavities have a small (5ml normally) amount of 15W suspension fluid in them for lubrication.
Step 3 - remove the lowers
Invert the forks and using a long/deep 10mm socket, undo the retaining nut from around the negative air spring valve. Once you've backed the nut out level with the top of the air spring valve use a rubber mallet to give the 10mm socket a tap to free the air spring from the stanchion lowers.
Remove the rebound adjuster by pulling on it (it is held in place with an o-ring).
Then use a 5mm allen key to remove the rebound rod retaining bolt.
Grab the lowers by the brake arch and the uppers by the fork crown and separate them.
Step 4 - clean lowers
Clean the inside of the lowers using isopropyl alcohol and dry with a clean cloth.
Remove the foam wipers and wash in isopropyl alcohol.
Carefully clean the seals and inspect for damage.
Inspect the bushings for wear and/or damage.
Set the lowers aside for reassembly.
Step 5 - air spring service
Undo the positive air spring cap using a 24mm socket.
Remove the negative air spring rod by removing the circlip and then pulling the assembly from the bottom of the stanchion.
Give everything a good clean and inspect each of the o-rings to see if they are perished or damaged.
Re-assemble the air spring by giving everything a liberal coating with 15W fork oil. Put in 5ml of 15W fork oil into the positive air spring chamber before screwing the air cap back on.
Step 6 - damper service
Using a 1.5mm allen key undo the grub screw which retains the floodgate knob, remove the floodgate knob, compression adjuster knob and the oring underneath.
Undo the motion control damper using a 24mm socket and put it into a clean oil drain pan. Tip the oil out of the fork.
Remove the retaining circlip from the bottom of the stanchion and remove the rebound damper.
Once again, give everything a good clean and inspect o-rings, piston seals and rods for damage/wear.
Re-assemble with a liberal coating of 5W suspension fluid. After re-inserting the rebound damper, put 93ml of 5W fluid into the motion control chamber and re-install the motion control damper.
Step 7 - reinstall the lowers
Lay the lowers on you bench and prop up the open end slightly. Use a syringe to put 5ml of 15W fork oil into each leg. Because you've got them propped up on a slight angle the fork oil should not run out the top or the holes in the bottoms of the legs.
Soak the foam rings in fork oil and re-install. Give the seams a liberal coating of fork oil.
Insert the stanchions into the lowers and re-install the negative air spring retaining nut and the rebound piston retaining bolt. Put the rebound adjuster back into place.