31 BMW 1983 R100RS Replace Fork Seals, Install Slider Dust Covers

When I bought the bike, the forks had both rubber fork gaiters and torn rubber fairing boots. But, I can’t turn the forks lock-to-lock as the gaiters interfere with the fairing boots. I think this is dangerous so I’m going to remove the gaiters and the fairing boots and install the black rubber cups on the fork sliders. I will wait for when I do the complete tear down of the bike to replace the fairing boots. I also replace the fork seals since I have to do all the work needed to get to them and I don’t know there condition.

Fairing Fork Tube Cup Ripped; Gaiters Prevent Moving Forks Lock-to-Lock

Fairing Fork Boots Ripped; Gaiters Prevent Moving Forks Lock-to-Lock

The virtue of using the gaiters is they protect the fork tubes from stones and gravel that can put dings in the tube and cause fork oil seal leaks. For now, the gaiters and the fairing boots will go.

Remove Front Wheel

I remove the disk brake calipers. There are four bolts, but only the top and bottom bolts secure the caliper to the fork.

Only Very Top and Bottom Bolts Secure Brake Caliper

Only Very Top and Bottom Bolts Secure Brake Caliper to Fork Lower

Brake Caliper Removed

Brake Caliper Removed

The calipers are retained but the brake line brackets and won’t fall down. I remove the axle nut and then remove the pinch bolts on each fork.

Removing Axle Nut

Removing Axle Nut

Remove Fork Pinch Bolt

Remove Fork Pinch Bolt

I pull the axle out from the left side facing the front of the bike exposing the bearing dust cover hat. There is a spacer on the right side as well as a bearing cover hat.

Right Side Bearing Cap

Right Side Bearing Cap

Left Axle Spacer

Left Side Axle Spacer

Then I remove the wheel from the calipers.

Wheel Removed and Calipers Hanging on Fork Brace Bracket

Wheel Removed and Calipers Hanging on Fork Brace Bracket

Remove Fork Brace and  Fender

I remove the bolts securing the fork brace. The caliper bracket goes under the rear nut on the inside of the fender, so I hold the caliper to prevent it dropping when I remove the rear nut.

Removing Fork Brace

Removing Fork Brace

Brake Line Bracket Mounts Behind Rear Fork Brace Nut

Brake Line Bracket Mounts Behind Rear Fork Brace Nut

Then I secure it to the exhaust header with some wire so there is no strain on the rubber brake line.

Securing Brake Caliper to Remove Tension on Rubbder Brake Line

Securing Brake Caliper to Remove Tension on Rubbder Brake Line

Then I remove the fender and brace from between the fork legs.

Sliding Fender and Fork Brace Out of Forks

Sliding Fender and Fork Brace Out of Forks

Remove Fork Gaiters

I remove the fork gaiters by loosening the metal band at the bottom. When I do, fork oil leaks out of the gaiters. The fork seals are leaking and the fork oil is the color of the Mississippi River in a spring flood. The oil definitely needs changing. I remove the metal band at the top. When I remove the fork sliders, I can get the gaiters off the forks.

Fork Missing Dust Cover Since Gaiters Won't Mount With Them

Fork Missing Dust Cover Since Gaiters Won’t Mount With Them

Fork Seals Leaking Fork Fluid The Color of the Mississippi River

Fork Seals Leaking Fork Fluid The Color of the Mississippi River

Remove Handlebars and Fork Springs

I need to remove the fork springs to take the tension off the fork sliders. To do that requires removing the handlebars that are secured with four bolts under the top triple clamp.

Removing Handlebar Bracket Nuts

Removing Handlebar Bracket Nuts

The handlebar clamp has a long in front and a short stud in the rear. The long stud has a metal cover that goes over a rubber bumper.

Handle Bar Bracket with Nuts and Washers

Handle Bar Bracket with Nuts and Washers

I move the handle bars toward the speedometer so I can access the fork top bolt at the top of the fork tube. I remove the plastic covers to expose the 36 mm Top Bolts. The Allen head bolt in the middle is used to fill the forks and does not need to be removed.

Fork Top Nut and Plastic Cover

Fork Top Bolt and Plastic Cover

Remove Fork Cap Bolts-All You Need is a Bigger Hammer

And then, the fun begins. I start with the flat wrench in the tool kit and wack it with a hammer. Nothing. So I use a 2 Lb maul and again, nothing, except I dent the flat wrench and bend it.

Next, I use the 36 mm socket that I have with a ground off end so the tapered part of the socket is removed. The cap bolt is thin and the socket has to fully engage all the flats or the socket will round off the cap bolt. I use a 1 foot breaker bar and lean on it. Nothing. I use the two pound maul on the breaker bar. Nothing.

Okay, I need more leverage. I get a floor jack handle that is about 3 feet long and put it on the breaker bar. Nothing, except I start moving the bike around, but the cap bolt won’t budge.

3 1/2 Foot Cheater Bar - FAIL

3-1/2 Foot Cheater Bar – FAIL

Okay. This bolt is very stuck. I heat the top of the fork tube with a heat gun. If someone used locktite, the heat gun should melt it. Then, while it is still hot, I put Kroil on the cap bolt a couple of times and let it sit overnight. As the fork tube and cap bolt cool, the Kroil gets be sucked down into the threads. This should help loosen the bolt if there is rust in the threads.  Before going to bed, I send an email to the Micapeak Airheads forum asking for advice.

Kroil Soaking Into Cap Bolt

Kroil Soaking Into Top Bolt

In the morning, I try the 3 1/2 foot cheater with the 36 mm socket again. Nothing. The Airheads forum advice was GET A BIGGER HAMMER, and one of the bigger hammers is an air impact wrench.

Okay, I don’t have an air impact wrench, so now is the time to add that to my tools. I get a Husky 300 Ft-Lb model from Home Depot, set the air pressure on my compressor to 90 psi, chuck up the 36 mm socket and let it rip. Nothing. I run the wrench until the pressure in the tank drops below 90 psi and stop to let the compressor fill the tank to 120 psi. After three times of doing this,the top bolt still refuses to budge. Grrrrr.

I go back to Home Depot and return the impact wrench (“It’s not what I need.”) and buy an 800 Ft-Lb model. I run the tank down until the compressor comes on and wait for it to recharge to 120 psi and apply the impact wrench a second time. Oh Hallelujah … It comes loose. 🙂  The top bolt faces are not deformed much, but I’m going to replace them anyway. The threads may be weakened and it’s a good idea to have clean faces on the nut so the socket will fit tightly next time.

Impact Driver (800 Ft-Ibs) Finally Got The Cap Bolts Loose

Impact Driver (800 Ft-Ibs) Finally Got The Top Bolts Loose

I suspect someone put an impact wrench on these top bolts to secure them which is not necessary. I snug them to 55 Ft-Lbs and they have never come loose.

I remove the forks springs and get another surprise. Instead of one spring in each tube, there are two springs and a threaded rod with a spacer in the middle. And there is a PVC spacer in the top to increase the pre-load.

Fork Spring Components

Fork Spring Components

Fork Spring Assembly

Fork Spring Assembly

The Airhead forum says this is an aftermarket performance option. The shorter top spring compresses last effectively stiffening the spring when it compresses a lot. However, there was very little spring pressure on the top bolt so I suspect these springs are sacked. When I do the rebuild, I’ll replace these aftermarket springs with the stock ones.

Remove Fork Sliders

The bottom of the sliders have two Allen head screws; the small one drains the fork oil and the larger one secures the damper rod to the fork slider.

Bottom of Fork; Drain Bolt (Small Allen Head) and Damper Rod Bolt in Middle

Bottom of Fork; Drain Bolt (Small Allen Head) and Damper Rod Bolt in Middle

The problem with the damper rod Allen bolt is the damper rod wants to turn when you turn the Allen bolt. You can put the springs back in the fork and the axle into the forks and push up on the axle with a jack stand to put pressure on the damper rod so there is enough resistance that you can remove the Allen bolt. Or, you can use an impact wrench to try and get the Allen bolt loose. I have a small battery powered one and it worked with no problem.

Dewalt Impact Driver Used to Remove Damper Rod Allan Bolt

Dewalt Impact Driver Used to Remove Damper Rod Allen Bolt

When I remove the large Allen bolt, the slider comes off the fork and a spacer fell out from one fork. Later, when I was cleaning out the forks sliders in the parts washer, the other spacer came out. They can get stuck in gunk at the bottom of the slider.

Fork Lowers Off Damper Rod and Draining

Fork Lowers Off Damper Rod and Draining

Fork Slider Allan Bolts and One Spacer

Fork Slider Allen Bolts and One Spacer From Bottom of One Fork Slider

The button on the bottom of the fork slider can contact the spacer to prevent the fork slider from impacting the lower fairing.

Fork Damper Rod Buttons

Fork Damper Rod Buttons

Replace Fork Seals

I clean out the inside of the fork sliders and find the other spacer.  There is a fair amount of gunk in the bottom of the sliders. To remove the fork seals, I put a slider in the vice using rubber jaws and clamp the tube by the axle hole at the bottom.

Fork Sliider Mounted at Axle Hole in Vice with Rubber Jaws

Fork Sliider Mounted at Axle Hole in Vice with Rubber Jaws

I use a seal remover tool and carefully hook the seal in the middle where the groove and steel spring are located.

Fork Seal Removal Tool

Fork Seal Removal Tool

Fork Seal Removal Tool in Groove of Seal, Not Against the Tube

Fork Seal Removal Tool in Groove of Seal, Not Against the Tube

It often helps to heat the top of the slider with a heat gun before removing the seal. I didn’t do that this time since the seals came loose easily. I inspected the seating surface the seal goes into for any nicks or deep gouges. One tube is clean, but one has a couple nicks in it from previous seal removal.

No Nicks in Fork Tube Seal Land

No Nicks in Fork Tube Seal Land

Some Gouges from Previous Fork Seal Removal

Some Gouges from Previous Fork Seal Removal

I use some 220 wet/dry grit to remove the sharp edge of the nicks and smooth them out. I follow with 1000 wet/dry grit to smooth out the surface.

Remove Fairing Rubber Boots and Fork Gaiters

The old ones had a bit of adhesive applied. It helps keep them in place as the fork tubes are turned. I cleaned the old adhesive off the fairing.

Fairing Boot Had Adhesive to Keep the Boot in Place

Fairing Boot Had Adhesive to Keep the Boot in Place

Hole for Fork Tube With Old Adhesive

Hole for Fork Tube With Old Adhesive

They were pretty shot.

Old Fairing Rubber Boot

Old Fairing Rubber Boot

Gaiters Were Not Used on the RS Forks, But Do Protect Fork Tubes From Dings and Nicks

Gaiters Were Not Used on the RS Forks, But Do Protect Fork Tubes From Dings and Nicks

The fork gaiters are the 11 rib version instead of the 13 rib version originally used on the /5 and /6 series. I loosen the hose clamps at the top and they slide right off. They are in good shape and I’ll hang onto them. I may opt to use them without the fairing boots as they do protect the fork sliders from nicks and dings from sand and rocks.

The fork tubes are in good shape with no nicks I can feel. There is a slight bit of wear at the bottom of the tubes.

Minor Fork Tube Wear

Minor Fork Tube Wear

Install New Fork Seals

The new seals can be installed into the fork lowers using a 36 mm socket as a driver.

New Fork Seals and 36 mm Socket To Drive Them In

New Fork Seals and 36 mm Socket To Drive Them In

Use 36 mm Socket to Drive Fork Seal Keeping it Square With Lip

Use 36 mm Socket to Drive Fork Seal Keeping it Square With Lip

I hold the lowers in my vice using rubber jaws. I lightly oil the outside edge of the seal, center it on the hole and drive it straight in with a rubber mallet on the 36 mm socket. Be careful to keep the seal straight as you drive it in. I use some mild taps of the mallet to get it started and to ensure it’s straight. If it cocks, I can easily remove it and try again. If I drive it in crooked, it will permanently damage the seal and I’ll have to get a new one. Although I didn’t do it this time, I have also heated the lip that holds the seal with a heat gun and then driven the seal. Sometimes the fit is very tight and some heat makes driving the seal easier.

Install Felt Into Fork Dust Cap

I bought new fork dust caps that were fitted to the fork lowers on the RS. They have a felt ring that goes inside a groove located at the top of the cap.

Winding Felt Wiper Into Groove of Fork Dust Cap Boot

Winding Felt Wiper Into Groove of Fork Dust Cap

Fitting Felt Wiper Into Fork Slider Boot Until Angled Ends Meet

Fitting Felt Wiper Into Fork Dust Cap Until Angled Ends Meet

The felt is long and needs to be pushed into the groove with my thumbs and slide around the groove until the angled ends meet up. Do not cut the felt to fit as it needs to be very tight in the groove to act as a wiper on the fork tube to keep grit and dirt from getting into the seal. DO NOT OIL IT. This will retain grit and dirt and hasten fork seal failure.

Felt Wiper Installed in Fork Dust Boot

Felt Wiper Installed in Fork Dust Cap

Felt Location At Top of Fork Dust Cap

Felt Location At Top of Fork Dust Cap

I slide the dust caps onto the fork tubes before I mount the lower sliders on the tubes.

Fork Dust Caps on Fork Tubes

Fork Dust Caps on Fork Tubes

Assemble Fork Sliders On Fork Tubes

Fork Slider Bolts, New Washers and Spacers

Fork Slider Bolts, New Washers and Spacers

The sliders attach to the damper rods with large Allen bolts. There is a spacer that goes at the bottom of the fork slider that acts as stop when the forks are compressed.I drop the slider into the fork lower.

Spacer Goes In the Bottom of the Fork Slider

Spacer Goes In the Bottom of the Fork Slider

Axle Installed Loosly in Fork Lowers

Axle Installed Loosely in Fork Lowers

I carefully slide the lowers onto the tubes being careful to easy the fork seals onto the fork tubes so the edge of the tube doesn’t damage the lip of the fork seal. I use a little bit of oil on the lip of the fork seals to make them easy to slide onto the fork tubes. Then I insert the axle through both fork lowers to keep them aligned.I add the fork springs into the top of the fork tubes. There is a spacer that goes on the top of the springs.

Installing Fork Springs and Top Spacer

Installing Fork Springs and Top Spacer

Fork Spring Top Spacer

Fork Spring Top Spacer

Fork Spring Top Space Installed

Fork Spring Top Space Installed

PVC Spacer for Spring Pre-load

PVC Spacer for Spring Pre-load

I insert the PVC spacer that was used to add pre-load to the springs.

PVC Spacer Installed

PVC Spacer Installed

Fork Tube Top Bolt with Washer

Fork Tube Top Bolt with Washer

I screw in the new top bolt and washer. I replaced the top bolt just to be safe since the old ones had been tightened much too tight and it may have damaged the threads. I only screw in one top bolt on one fork tube at this point.With the top bolts installed, I screw in the large Allen bolt with a new washer at the bottom of the fork slider into the damper rod. Since this rod can rotate, I push up on the axle with my knee and then tighten the Allen bolt to 25 Ft-Lb. The spring pressure keeps the damper rod from turning. Then I remove the top bolt on that fork tube and put into the other fork tube and tighten the large Allen bolt on the other tube. I screw in the fork drain screws with new washers.

Fork Drain Bolts with New Washers

Fork Drain Bolts with New Washers

Using Handlebar when Torquing Fork Tube Top Bolt on Opposite Side

Using Old Handlebar when Torquing Fork Tube Top Bolt on Opposite Side

I install the handlebar clamps and an old handlebar into one of the clamps. I use this as I torque the top bolt down to 55 Ft-lbs so I don’t have the forks against the stops. This can distort the fork clamps and cause the forks to get out of alignment. I torque the top bolt on the opposite side of the handlebar. I brace the handlebar against my side as I apply the torque to the top bolt so the wheel doesn’t rotate against the stop.Then I put the handlebar into the other clamp and torque the remaining top bolt into the fork tube. I slide the fork dust caps down onto the fork lowers.

Black Fork Dust Caps Installed on Fork Sliders

Black Fork Dust Caps Installed on Fork Sliders

Fill Forks with Fork Oil

Fork Oil, Measuring Cup and Syringe

Fork Oil, Measuring Cup and Syringe

I use 7.5 wt fork oil. I’ll see how this works for damping. There is 5 wt for less damping and 10 wt for more damping, but a friend uses the 7.5 wt in his R100RS, so that’s what I’ll start with.

I measure 225 cc of oil and then suck it into a large syringe so it will be easy to add to the filler hole in the top nut.

Filling Syringe with Fork Oil

Filling Syringe with Fork Oil

Using Syringe to Fill Fork Tube with Fork Oil

Using Syringe to Fill Fork Tube with Fork Oil

When I fill both tubes, I screw in the Allen bolt into the top of the fork top bolts.

Tighten Filler Bolt in Fork Tube Top Bolt

Tighten Filler Bolt in Fork Tube Top Bolt

Then I install the dust cap on top of the top bolt.

Plastic Dust Cap on Top of Fork Tube Top Nut

Plastic Dust Cap on Top of Fork Tube Top Bolt

Install Handlebars

The handlebar mounts at the front fit through a large rubber mount that holds the instrument cluster bracket. It is covered by a metal cap, a wave washer and the nut. But, the rear mount uses just a flat washer, wave washer and nut. The picture below shows the two metal caps, one goes on the front mount of each handlebar bracket.

Handlebar Mount Hardware

Handlebar Mount Hardware

Grease on Underside of Metal Cover Helps Keep It in Place

Grease on Underside of Metal Cover Helps Keep It in Place

Getting the metal cap in place with the wave washer and nut can be hard. I use a little axle grease on the underside of the metal cap so it will stick to the rubber bumper while I thread the wave washer and nut onto the front stud.

The handlebars need to be centered so that the rubber dash that attaches to the bars will fit. I install the bar mounts and tighten up the nuts enough to hold the bars while I adjust them left-to-right so they are centered on the handlebars.

Center the Handlebar Under the Dash

Center the Handlebar Under the Dash

Mount the Fork Brace-Fender, Wheel and Brake Calipers

I removed the fork brace and fender as a unit, so I carefully insert the brace between the lower fork tubes.

Fork Brace with Fender Placed Inside Forks

Fork Brace with Fender Placed Inside Forks

I check that the brackets on the brace are parallel to the inside mounting surface of the fork lowers. If there is any difference front to back or a larger gap on one side than the other, then when I tighten up the bolts holding the fork brace it will bend the forks and increase stiction. This brace is true and doesn’t need to be shimmed.

The rear fork brace bolt also holds the brake hose bracket. The bracket mounts on the inside of the brace with the locking nut securing it.

Brake Line Hanger Bracket Goes Inside Fender on Fork Brace Rear Bolt

Brake Line Hanger Bracket Goes Inside Fender on Fork Brace Rear Bolt

I insert the bolts with the flat washer on the outside and torque the fork brace bolts to 16 Ft-Lbs.

Fork Brace Bolt, Washer, Nut

Fork Brace Bolt, Washer, Nut

Fork Brace Bolt with Wave Washer

Fork Brace Bolt with Wave Washer

I install the bearing caps on the wheel bearings. I mount the wheel and axle with the spacer on the right side as I face the front of the bike.

Wheel Right Bearing Cap

Right Side Wheel Bearing Cap

Left Side Axle Showing Spacer

Left Side Axle Spacer Goes On Top of Left Wheel Bearing Cap

The axle should slide smoothly through the fork lowers. If there is resistance, there maybe a burr on the edge of one of the holes in the fork lower. Remove the burr with a file so the axle will slide smoothly. I tighten the axle nut finger tight and leave the pinch bolts loose. I’ll tighten them after I get the brake calipers mounted.

The brake calipers have two bolts that mount into threaded holes in the fork lower. The brake pads don’t want to slide over the edge of the rotor, so I use a very large blade screw driver and gently pry the pads open a bit more so the caliper will slide over the rotor.

Brake Caliper Bolt and Wave Washer

Brake Caliper Bolt and Wave Washer

The wave washer goes under the bolt head.

Brake Caliper Bolt Detail

Brake Caliper Bolt Detail

Mount Left Side Caliper with Two Bolts

Mount Left Side Caliper with Two Bolts

I check that the front brakes work. I have to pump the front brake lever a couple times to get the pads back into position.

I take the bike off the center stand and bounce the front forks several times while holding the front brake and put the bike back on the center stand. This should remove any minor tweaks in the forks and ensure the forks sliders will be smooth. Then I torque the axle nut to 25 Ft-Lbs. I torque the axle pinch bolts to 10 Ft-Lbs.

I mount the dash and then secure the steering damper knob with the center screw.

All Done

All Done

8 thoughts on “31 BMW 1983 R100RS Replace Fork Seals, Install Slider Dust Covers

  1. Pingback: 1983 R100RS Rebuild: Replace Fork Seals, Install Slider Dust Covers | Motorcycles & Other Musings

  2. Brook, thank you for taking the time to describe and show your step by step process for servicing and replacing front forks. You have answered many questions which were gap for me just using my Clymer manual. One Question: I notice you jack the bike up via contact with the oil pan cover. Any concerns with this as a jacking point? I have an 81 R100RS and would like to jack it the same way.

    Regards,

    Bruce B.

    • Hi Bruce,

      Thank you for stopping by and I’m pleased this material was helpful on your project.

      I use a 1 x 6 board under the oil pan so the force is spread across the entire cover. Since it’s wood, the ribs on the bottom of the cover sink into the wood so they don’t get stressed. I’ve had no problems doing this so far on the past four bikes I’ve rebuilt.

      Best.
      Brook.

  3. Hi Brook!

    I’m a big follower of your blog. It’s very interesting and informative. I currently own a BMW R100RS from the 500Series (1984) that rides like a dream. One of the rubber bits from the right fork is currently falling when I ride. I was wondering what kind of glue would you recommend to stick it to the fairing?

    many thanks in advanced!

    best,

    Jordi

    • Hi Jordi,

      Thank you for the kind words about the site.

      If I understand your question correctly, the rubber boot that fits into the bottom of the R100RS fairing that the fork tube goes through won’t stay in place in the mounting hole in the fairing. It’s possible that silicone seal (clear) would keep the groove in the rubber tight against the edge of the hole. I haven’t had to resolve that problem yet, so I don’t have direct experience with this.

      I hope this is helpful.

      Best.
      Brook.

  4. Hi Brook,

    I really appreciate all the effort that you went to in documenting this procedure for the rest of us. Your amazing attention to detail makes this somewhat complex repair so much easier to follow.

    I’m just about ready to begin this work on an 82′ R100RS and had a quick question before I started. I’m assuming the fork sliders will not have enough clearance to be removed from the fork tubes with the bike on the center stand – correct? If that’s correct, then would it make sense to hang the my bike off the end of my Handy motorcycle lift to gain that clearance needed, vs. jacking the bike up on the oil pan?

    Also, given the trouble you had with the 36mm fork cap bolts, I bought the Husky 800 ft-lb air impact wrench that you recommended – hopefully I won’t need it:-) Does it make more sense to loosen these bolts prior to putting the bike up on the lift – given that the bike is a bit more stable on the ground?

    Again thanks for all your help and I look forward to hearing back from you.

    Regards,

    Scott

    • Hi Scott,

      It’s gratifying to hear this material has been helpful to you.

      I think you can get enough clearance if you put a 2×4 under the center stand to raise the front wheel.

      I’ve only needed that much fore once so far, so I’m hoping yours come free with little fuss.

      Best.
      Brook.

  5. Hi Brook,

    Thanks for the quick response and helpful information.

    I’m in the process of restoring both a 1981 R100RT and 1982 R100RS and have a consulting question for you. If you would let me know via email the best way to reach you, I would really appreciate it.

    Thanks,

    Scott

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