Replacing fork seals (great time to install an Ohlin front shock too...)

So it's happened again, oil's weeping out of one or both of your forks.  An expensive fix at the dealer, but a fairly easy one for you to do with some basic tools and a purchase from your local Home Depot's plumbing department.  Here's what you'll need:

• Set of new fork seals (BMW)
• Hydraulic jack (see pic)
• 4"x4" piece of wood and 2"x2" piece of wood ( 2x4 or 1x4)
• 1-1/2" x 12" galvanized nipple (see pic.  Get it at Home Depot and refer to the same bar code.)
• Various sized zip ties
• Tools: 17 and 24mm hex socket; 3, 4, 5 Allen wrenches; 6, and 8mm hex bits (Allen bit with 3/8" drive); torque wrench (that measures 21Nm thru 105 Nm); 3, 6, and 10" drive extensions; rubber mallet; large flathead screwdriver; small jeweler's screwdriver.

Now, the actions you must take to get to the components.  You do not need to take the side covers off the bike.  You must do the following to replace either or both of the forks' seals.

• Put the bike on the center stand on a flat, level, and smooth surface (like a concrete garage floor, for example)
• Remove the rear wheel, front fender and mudguard, and black ABS belly pan.
• Remove both front brake calipers' mounting bolts.  Remove calipers from disks; if this seems impossible, relax.  Pull the caliper directly away from the wheel axle (towards the rear of the bike), ensure the curve of the outside of the caliper conforms to the curve of the wheel, and gently pull the caliper out (towards you as you are facing it).  Use zip ties to prevent calipers from dangling with their weight on the brake lines.
• Referring to the following diagram, remove axle nut (#7) and loosen pinch bolts (#2 and 6).
• Put the piece of wood on the lifting part of the hydraulic jack, position the hydraulic jack so that the piece of wood is directly under the oil filter cover, and actuate the jack until the front wheel is off the ground.
• Pull the front axle out and remove the wheel.  Put items #3 and #5 (diagram) back on the wheel and put the axle back through.  Set the wheel aside.

At this point you will remove the fork whose seal you want to change.  The following directions refer solely to the side you are dealing with.  The 'slider' is the fat part of the fork and the 'fork tube' is the shiny tube that slides in and out of the slider.

• Referring to the following picture, loosen pinch bolts (#2 and 3) at the handlebar.
• Referring to the following picture and using a 3mm Allen wrench, remove the small bolt (left arrow in the picture) on the side of the fork you are removing.  This will liberate the brake line assembly for that side and it is imperative that use use a zip tie to prevent the weight of the caliper from jerking the whole thing downward.
• Referring to the following picture, remove the two fork bridge bolts (indicated by arrows).  These have been installed with Loctite and are hard to get out.  Best way to get to them is from above; take your ratchet wrench, put the 10" and 6" extensions on end-to-end and the 6mm hex bit, and remove them.  Before you remove the second bolt, hold the fork tube in your hand so it doesn't sag when the bolt is removed.
• Holding the slider in one hand, grab the fork tube under the handlebar and twist it while pulling downward.  The fork tube will come out and you can then take the whole thing out the bottom.

Now you have to remove the old seals and seat the new ones.  Refer to this picture throughout.

• Holding the fork tube firmly, remove the fork cap (#1) using your 24mm socket.
• Gingerly pull out the fork tube, ensuring the dripping oil stream goes into the slider.  Wipe the tube down and lay it on a towel so that it does not get scratched  and so that oil remaining on the inside doesn't get on everything.  Put the fork cap back on and screw it in by hand as far as you can.
• Holding the slider firmly and keeping it vertical (it's full of oil), use the screwdriver to remove the dust seal (#21) by prying it off.  To ensure you do not dent the edge of the slider, put a thick bunch of cloth under the screwdriver shaft as you pry the seal off.  Discard the seal.
• Using the small screwdriver, remove the spring clip (#20) and set it aside.
• Using the small screwdriver and cloth pad, pry out the fork seal (#19).  Take your time; you can savage the seal all you want since you won't be reusing it, but take care not to damage the lip of the slider.
• Wipe the inside of the cavity.  Take the new fork seal and look at it from the side; it's tapered slightly.  Carefully put the seal wider side down, and ease it in as far as possible using your fingers.  It is imperative that is be pushed in evenly.  If you can seat it fully by hand this means you probably put it in upside down and you must remove it and turn it over.  The pressure you'll need to apply to seat it is critical to forming a tight seal against the fork tube.
• Carefully insert the fork tube into the new seal and push it down until you feel the resistance of the trapped air; unscrew the cap slightly so that you can slide the fork tube down until only about 8" are sticking out.  Carefully slip the 12" length of pipe over the fork tube and rest the bottom of the pipe against the seal.
• You need four hands at this point (your friend or SO doesn't need any significant strength and you only need them for a couple of minutes).  Your assistant should hold the slider upright against the floor.
• Place the 2"x2" piece of wood on the top of the pipe and tap it gently with the rubber mallet several times.  You want the seal to seat straight down so make sure you tap the piece of wood straight down.  Once you feel the seal is not seating further, remove the 12" pipe and check whether the seal is down enough to expose the groove that the spring clip (#20) fits into.  If so, you are done with seating the seal; if not, put the pipe back on and tap the piece of wood a little harder.
• Reinstall the spring clip.
• Slide the new dust seal over the top of the fork tube and seat it in the top of the slider by hand.  It's tight but you'll do it as long as you gradually seat it evenly all around.
• Unscrew the fork tube cap (#1), pull the fork tube out slowly until you expose a small hole on its side just over the dust seal, screw the fork tube cap, and push the fork tube back in until you feel compressed air resistance.
• Wipe the fork tube off and push it into the slider several times.  You may get a little oil coming out but after several strokes the tube should be dry.  If it keeps weeping oil, you may have installed the fork seal upside down or damaged it if you were careless when seating it.  You'll need to try and remove the seal without damaging it, or try a new seal.

Reassembly.  Basically, just do the removal steps backwards.  When reinstalling the wheel, make sure you follow the note on which nuts to tighten when.  Torque figures are as follows.

• Fork bridge bolts: 21Nm
• Handlebar pinch bolts: 21Nm
• Axle nut: 30Nm
• Pinch bolts: 20Nm
• Rear wheel bolts: 105Nm

You're done.  Check that everything's tight, wipe down the fork tubes one more time and take it for a ride.

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