The best reference is of course the shop manual. Here's my simplified version.
1. Remove the cotter pin on the back of the pivot bolt for the rear brake lever, then remove the lever.
2. Remove the three 8mm bolts that secure the black cover. Clean off the gunk that's probably accumulated under the cover and around the perimeter so there's nothing to fall inside your engine once it's open.
3. Remove the 8mm bolts that secure the clutch cover. Then pry off the cover using a fat screwdriver levered behind the little tab at 3 o'clock. Set aside the cover where it won't get contaminated with grit. Now you can see the clutch assembly.
4. Remove the 10mm silver nut and washer in the centre of the clutch. Note that the clutch actuating rod it's threaded onto spins freely. You may need to hold it in place with a Phillips screwdriver to loosen the nut.
5. Remove the five bolts that cover the clutch springs using either a Phillips screwdriver or 10mm socket.
6. Remove the clutch basket cover and check the outer flange for uneven or excessive wear. It should be shiny and fairly smooth.
7. Slide off the friction plates (7) and metal disks (6), and inspect them for any obvious damage, contamination, or wear. The OEM friction plates use a standard cork wear material.
8. Using calipers, measure the thickness of the each friction plate across the cork at four locations 90º around the circle. They are fine if 2.90 - 3.10 mm thick. They should be replaced if 2.80 mm or thinner. Happily, all of mine were in the range of 2.95 - 3.10 mm. If you choose to install new cork-based friction plates, be sure to first soak them in clean engine oil before installing them. The cork needs to be saturated with oil or you risk damaging the plates.
9. Check the metal friction plates for wear or warping. These are unlikely to wear significantly before the cork plates, and it's unlikely you need to replace them. However, the manual recommends checking to see if they are warped by laying them on a reference flat surface. If you can slide a 0.1 mm feeler gauge under a raised area, the plate should be replaced. Since I don't have a reference flat, I just stacked the metal disks together and looked for gaps between them while rotating the disks 90 degrees against each other. No gaps, so probably fine.
10. Check the length of the clutch springs. The spec is 41.20 mm and they should be replaced if 39.14 mm or less. All of mine were in spec.
11. Now you can put stuff back together, simply reversing the steps above. When you install the clutch springs, first wind them finger tight in a star pattern, then tighten to 8 N-m using a torque wrench.
12. Install the washer and nut finger-tight onto the centre actuator rod. You may need to use a Phillips screwdriver to keep the rod from spinning. Adjusting the rod (which governs the clutch actuation point on the lever) is simple: turn it clockwise until you feel resistance, then back it off about 1/16 of a turn. Hold it in place with the screwdriver then tighten the nut against it with a 10 mm box wrench. Test it by actuating the clutch lever. If you've tightened the rod too much, the clutch won't fully let out as needed to give the maximum friction provided by the springs. But if you leave the rod too loose, the clutch won't pull in until partway through the lever travel or won't pull in at all. It just takes a few minutes of playing with it to see the adjustment range. Once you're satisfied, tighten the nut to 8 N-m. Beware that using a socket on a torque wrench may mess up your adjustment unless you can somehow use a screwdriver to keep the rod from turning. In the end I just tightened the nut with the box wrench. 8 N-m is not a lot of force -- go easy!
13. Install the clutch cover and finger-tighten tighten the bolts in a criss-cross pattern. Then tighten them to 10 N-m, also in a cross-cross pattern. A few of my bolts were corroded so first I wire-brushed them and then gave them a shot of Rock-and-Roll ceramic anti-sieze.
14. Install the black plastic cover and tighten the bolts to 10 N-m.
15. Lube and install the brake lever.
So that's it! Fortunately I don't have to replace my clutch friction plates or springs. I called my local Yamaha dealer for pricing (C$) on OEM parts:
- Steel plates (x6), $13.99 each
- Cork friction plates (x7), $16.99 each
- Springs (x5), $4.99 each
Aftermarket options were hard to find in Canada. I couldn't find an EBC friction plate kit for the WRR, but there were some options from Barrett and one other company that I can't recall at Canada's Motorcycle. Opinions on various forums range from use the OEM, to good results with EBC, to don't use carbon fibre (gums up your oil), to good results with Kevlar (although it may be too grabby for trail use).
I also looked at pimping my ride with a Rekluse clutch but they don't make one for the WRR. If they did, it would likely be in the $1000 range by the time I landed it in Canada.