So, I noticed my fork seals were leaking. How could I tell? Hmm...
This is a pretty simple operation, but I knew nothing about it before I tried it. So this one is dedicated to weekend warrior garage mechanics who are also inept like me.
- BMW 31 42 7 692 145 - Dust seal ($32.22USD each)
- BMW 31 42 7 692 147 - Oil seal ($25.08USD each)
- SFK KIT45M - Oil & dust seal (~$33USD each, sold together)
The stock seals are NOKs. Mine lasted more than 20,000 miles. I think the replacement interval is ~18,000 miles.
The seal sizes I listed below are correct for my bike, which is a 2009. It appears that the forks on 2013+ models may be different (43mm WPs instead of the 45mm Marzocchis).
I opted for SFK seals from Dual Sport Armory. The size of the stock seals is 45 x 58 x 14. Stamped on the inside of the dust seal are the measurements 45 x 58.4 x 4.0 x 14. The SFK kit has the same dimensions, save what I guess is the overall height (11mm for SFK versus 14 for the NOK). The lip insertion depth appears to be the same on both seals (~4mm).
- BMW 31 42 7 692 149 - Upper bushing ($32.02USD each)
- BMW 31 42 7 692 150 - Lower bushing ($22.88USD each)
My bushings didn't look worn, and they are on the expensive side so I just reused them.
- E12 torx (brake caliper bolts)
- T30 torx (fender bolts)
- T45 torx (triple tree pinch bolts)
- 8mm allen (damper bolt; possibly not stock? I have Bitubos)
- 13mm open-end wrench
- XXmm wrench or socket (fork top cap, depends on what kind of suspension you have)
- Flathead screwdriver (upper bushing and snap ring)
- Fork seal driver or similar homemade tool (PVC pipe, etc)
- Fork seal "bullet" or a bunch of soft tape
1) Unbolt your ABS sensor (if applicable), and remove the front wheel.
2) Unbolt the brake calipers (2 e-torx bolts) and zip tie them to the frame to keep weight off the hoses.
3) Unbolt the fender (2 torx bolts on the fork legs plus 1 bolt near the brake calipers on each side) and pull it off of the fork legs. Zip tie it to the frame if needed or make sure the weight is supported by the calipers.
4) Loosen ONLY the top triple clamp bolts (2 torx bolts). Use whatever size necessary on your top cap to pop it loose, but don't completely unscrew it.
5) Loosen the bottom triple clamp bolts and slide the fork tube out of the bottom.
6) Unscrew the top cap and slide the stanchion down to reveal the spring.
7) Drain the fork oil. You can optionally remove the fork spring by pushing the spring down, putting a 13mm open end wrench on the nut, and using your top cap wrench or socket to break the top cap loose from the damper rod. Then pull the spring off along with the plastic washer. (You'll have to do this at some point in order to pump the damper to get rid of the old oil and make sure it's purged of air when you refill the forks).
8) Use an impact wrench to unbolt the damper unit from the bottom of the fork leg (8mm allen bolt in my case, I can't remember if this is the stock bolt or not). Pull the damper unit out and lay it aside somewhere clean.
9) CAREFULLY use a screwdriver or pick to pull the dust seal off. This should come out pretty easily, if you have manly fingernails you can probably use those as well. Make sure you don't slip and scratch your fork tubes!
10) Once the dust seal is off, look under the upper stanchion. There is a lock ring with a couple of indentations where you can pry it out with a flat blade screwdriver or pick. Again be careful of your fork tubes, this should also come out pretty easily.
11) Once the lock ring is out, you need to unseat the oil ring. The easiest way I found on youtube to do this is to pull the upper and lower fork tubes apart like a slide hammer. It will take a few whacks but the oil ring should pop out along with a flat washer, the lower bushing and the upper bushing all on the lower fork tube.
12) Use a flat blade screwdriver to spread the upper bushing apart and slide it off the top of the fork leg. It is set into a small indentation, so it may take a little convincing. Still don't scratch anything!
13) Slide the rest of the pieces off, making a note of the order and orientation of everything. (I think the bushings and the washer are bi-directional, but obviously the seals are not!)
14) Clean up the fork tubes and bushings, if you plan to reuse them.
1) Slide the fork seal bullet over the top of the lower fork leg. The goal is to cover up the sharp edge of the indentation where the upper bushing sits. Use tape if you don't feel like spending a few buck for the fancy plastic thingy.
2) Slide the dust seal onto the fork leg. Make sure the metal ring is facing down
towards the ground.
3) Slide the snap ring onto the fork leg.
4) Slide the oil seal onto the fork leg. On the inside of the seal there is a double ridge, make sure this is on the upper
side of the fork leg, i.e. on the side closest to the handlebars. I put a dab of oil on the inside of both seals before I put them on to help lubricate them, not sure if it's entirely necessary but I figured it couldn't hurt.
This is a really bad picture of the correct orientation, but you can also sort of tell by the indents on the inside of the outer ring.
5) Pull the bullet off, or remove the tape. The rest of the parts won't fit over it. Slide the washer on.
6) Slide the lower bushing on.
7) Slide the upper bushing on, and make sure it is seated into its groove.
8) Slide the upper fork tube over the lower fork tube. Use the seal driver to individually seat the lower bushing. You should be able to hear when it bottoms out.
I actually put the washer between the driver and the bushing in order to drive it in since the tool I have has a gap that the bushing fits into perfectly, making it not fully seat.
9) Use the seal driver to seat the oil seal. If the oil seal is properly seated you should be able to see the groove that the lock ring goes into.
10) Reinsert the lock ring. I had to use my flat blade to get it all the way in because my fingers were too fat.
For reference, the bottom of the ring is in the groove but the top isn't quite seated.
11) Slide the dust seal in. You should be able to do this by hand.
12) Put the damper back in, refill it with oil. Pump the damper until the oil height doesn't change. Set your oil height, reinstall the spring, and button it up with the fork cap.
13) Put everything back together on the bike in reverse order. Tada!