- Remove Top Hat And Grease Seal
- Remove Inner Race, Center Pipe And Spacer, aka, The Wedding Band
- Remove Outer Bearing Races
- Set Wheel Bearing Preload
- Install Inner Bearing Races, Grease Seals & Top Hats
Before I install new stainless steel spokes and chrome plated brass spoke nipples, I replace the front wheel bearings. The rear wheel does not have wheel bearings. Instead it is mounted directly to the rear drive. Since the rear wheel does not have an axle, there is no need for wheel bearings.
I use the Cycle Works wheel and swing arm bearing tool to remove and install the front wheel bearings. Here’s a picture of the tool; “some assembly is required”. This is explained in the included instructions, and I’ll show you how it goes together.
You MUST heat the front wheel hub to 225-250 F before pulling or installing the outer bearing race or you will damage the aluminum bore in the hub.
I use a spring scale that measures in grams.
The Cycle Works wheel bearing preload tool is 113 mm, but it is too long for the axle on the R80ST front wheel. I use a 1 inch diameter piece of steel pipe about 3-1/8 inch (80 mm) long. I had a friend mill the ends so they are flat and parallel.
Bob Fleischer has a number of sections of content about wheels, hubs, top hats, bearings and how to adjust the preload on the tapered roller bearings used in the wheels.
- Bob Fleischer: WHEELS, Wheel Spacers, Seals + Hints
- Bob Fleischer: Airhead Wheel Bearing Clinic, BMWMOA National Rally, July 2005
- Bob Fleischer: Wheel Bearings; preload & servicing
Duane Auscherman also has a good page about wheel bearings.
- Duane Auscherman: BMW motorcycle wheel bearings, 1956 to late 70s
The graph Duane shows of the tapered roller bearing life vs. preload setting was instructive. I conclude that lower preload values affect bearing life less than too high a value. And, the miles available from a preloaded bearing are “large” compared to the typical mileage expected for a BMW motorcycle, except when the preload is too high.
Bob Fleischer points out that BMW’s recommendation of 21 – 42 inch-ounces of torque puts too high a value on the range. He recommends no more than 30 inch-ounces unless you have a side car attached. He is concerned with a bearing overheating if it has too much preload and that can lead to welding a bearing to the axle.
|07 11 9 985 005||TAPERED ROLLER BEARING – 40X17X14, Front||2|
|36 31 1 240 238||SHAFT SEAL – 22X40X7||2|
I got a wheel bearing adjusting kit from Cycle Works. The kit includes two “wedding bands”, in my kit they are 6.30 and 6.75 mm, with a number of shims that are 0.05 mm so I can adjust the roller bearing preload without investing in various size wedding bands.
This short video summarizes how I do this work.
VIDEO: 1983 BMW R80ST Replace Wheel Bearings & Set Pre-Load
Remove Top Hat And Grease Seal
The wheel bearings are the classic two piece roller bearings with an outer race and inner race. The bearings are lubricated with bearing grease. There is a “top hat” on each side that fit into the grease seals. The top hats on the 1983 R80ST are the same length, 13 mm.
I use a screwdriver to pop out the top hat and the grease seal.
Remove Inner Race, Center Pipe And Spacer, aka, The Wedding Band
I remove the inner bearing with my finger and pull out the center pipe. Next to the inner race on the other side inner of the wheel is a spacer, aka, the “wedding band”. It is used to set the pre-load on the wheel bearings.
The wedding band is 6.45 mm thick. BMW supplies them from 6.30 to 7.70 mm in 0.05 mm increments to set the preload on the wheel bearings.
Here are the wheel bearing parts with the exception of the outer races that I still have to remove in the order they go together.
Remove Outer Bearing Races
The front wheel is an aluminum alloy. There is no steel sleeve installed in the hub as was done on the later model snowflake cast rims. I verified that with a magnet which did not stick to the inside of the hub since it is aluminum, not steel.
Therefore I have to heat the hub to about 225-250 F before removing and installing the outer races to avoid damage to the aluminum hub.
If you don’t heat the hub to 225-250 F, you will damage it removing/installing the outer bearing races.
I use the Cycle Works tool to remove the wheel bearing outer races.
The following pictures show how to assemble the tool.
I insert the puller plate with the six Allen bolts surrounding the larger bolt with lock nut and the long Allen bolt into the hub so the edges of the six Allen bolts are below the bottom edge of the outer race.
Since the outer races are pretty deep inside the hub, I can’t use the large flat washer under the nut.
There is a shoulder with four ribs underneath the outer race that act to position the race inside the hub.
Set Wheel Bearing Preload
The wheel bearings are tapered roller bearings. For long bearing life, they need to be under axial load, or what is called preload. Preload is set by measuring the torque needed to spin the wheel bearings. The target torque is 20-30 INCH-Ounces. That’s a small value to measure. The tools for doing it are a spring scale that measures in grams, about eight feet of string, and an 80 mm long, 1 inch diameter metal tube.
Computing Range Of Bearing Preload Force
Torque is a measure of force applied at right angles to a lever arm. If you have 500 ounces of force and apply it at right angles to an arm that is 1 inch long, you will create a torque of 500 INCH-Ounces. If you shorten the arm to 1/2 inch, the torque is reduced to 1/2 as much, or 250 INCH-Ounces.
The complicated part is figuring out how to convert the torque setting BMW recommends to the force I can measure on the spring scale. To do this requires knowing the diameter of the sleeve and converting from ounces to grams. This is explained in Bob Fleischer’s material, shown above in the Resources section, that I summarize here.
- I measure the diameter of the sleeve, mine is 1.0 inches.
- I divide this by 2 to get the radius, or 0.50 inches.
- Bob Fleischer recommends a range of 20 – 35 INCH-ounces, but the upper end, 30-35 inch-ounce, is only applicable if you have a sidecar. Since this bike does not have a side car I use 20 – 30 INCH-ounces as the acceptable range of torque.
- My scale measures in grams so I convert ounces to grams. There are 28.35 grams in 1 ounce. I convert the lower and higher torque values of the range to INCH-grams by multiplying the values by 28.35: that gives a lower value 567 INCH-grams and an upper value to 850 INCH-grams.
- To compute the force on the pull scale, I divide the torque by the actual radius of the sleeve. The sleeve radius is 0.50 inches, therefore the spring force range is:
Lower: 567/0.50 = 1,134 grams; say 1,150 grams.
Upper: 850/0.50 = 1,700 grams.
- For simplicity, I’ll use a range of 1,150-1,700 grams of force.
How Bearing Preload Is Applied
Inside the wheel hub is a pipe. The wedding band typically goes on the left end of the pipe up against the left inner bearing race.
One inner race butts up against one end of the tube and the other inner race butts up against the wedding band on the other end of the tube.
By adjusting the thickness of the wedding band, you adjust how close together or far apart the two wheel bearing inner races are from the outer races. If the inner races are closer together, they fit tighter in the outer races and there is more force, or preload, on the rollers in the bearing. It they are farther apart, then the preload force on the rollers is less.
BMW sells a large variety of wedding bands in 0.05 mm (0.002 inches) increments of length. The shortest wedding band is 6.30 mm and the longest is 7.70 mm. That’s a lot of different wedding bands to cover the adjustment range. The front wheel has a 6.45 mm wedding band.
I use the Cycle Works wheel bearing preload adjustment kit. It comes with two different wedding band sizes, 6.30 and 6.75 mm, and a number of 0.05 mm shims. This is an affordable way to adjust wheel bearing preload.
Configure Axle & Bearings For Preload Measurement
The wheel bearings normally are packed with grease. However, to measure the bearing preload force, they have to be completely clean, dry and then lubricated with some light oil, not engine oil. My bearings are new, but I use carburetor cleaner to clean the inner race roller bearings and then apply 3-in-One oil to the rollers.
Here is the order of the front wheel bearing components that are installed in the hub when setting the bearing pre-load. I don’t install the grease seals or the top hats.
From left to right side of the wheel:
- Axle Nut,
- Thin Flat Washer (not the stock thick one),
- Inner Bearing Race;
- Wedding Band;
- Axle Spacer
- Inner Bearing Race
For the front wheel I use the 80 mm sleeve on the left side of the axle that has the threads and substitute the thin washer for the stock thick axle washer. The sleeve compresses the two inner races when the axle nut is tightened establishing the preload force. I also include the axle spacer that goes on the right side of the axle.
Since I am replacing the spokes, I don’t have the wheel assembled. So I mount the front wheel hub in rubber jaws in my vice and also use shop towels to cushion the hub to avoid scratching it. Of course you can mount the assembled wheel in the vice if you have removed the front tire and tube.
I insert the axle with the axle spacer and an inner bearing race from the right side of the hub.
Then I insert the pipe, the original 6.45 mm wedding band, and the inner bearing race on the left side of the hub.
Then I install the 80 mm sleeve, the thin flat washer and the axle nut centering the sleeve on the inner bearing race. Then I torque the nut to 25 Ft-Lbs using a screwdriver in the right side axle hole to keep the axle from turning.
Measure Preload On Front Wheel Bearings
To make the preload force measurement for the front wheel bearings, I wrap the eight feet of string evenly around the 80 mm sleeve. I attach the spring scale to the loop on the end of the string. Then I walk back from the wheel pulling at a steady rate and read the scale when it settles down to a steady reading.
The original 6.45 mm wedding hat made the bearings so tight I couldn’t turn the axle. So I tried the 6.75 mm band that is included in the wheel bearing shim kit from Cycle Works. That was too loose only requiring about 200 grams of force.
I went back to the original 6.45 mm wedding band and begin adding 0.05 mm shims from the Cycle Works shim kit. The shims go against the narrow side of the inner bearing and will butt up against the wedding band when I install the inner race. I check the force on the spring scale as I add each shim.
At three shims the force required was close to 2,000 grams and at four shims it was about 800 grams. So the preload I need is somewhere between three and four shims.
Since four shims makes the inner bearing races too far apart resulting in too low a pre-load, I fine tune the preload by reducing the thickness of the wedding band. I use 320 wet/dry paper and sand the faces of the 6.45 mm wedding band to reduce its thickness. I start out sanding each face 10 times in a figure-eight pattern. Then I install the wedding band with four shims and measure the preload force. I repeat this process until I get the preload within the range of 1,150-1,700 grams. After about 30 laps on each face, the preload force is 1,200-1,300 grams on the front wheel bearings. So I called that good.
Install Inner Bearing Races, Grease Seals & Top Hats
I pack the bearings with high pressure red grease. I have a large socket the fits over the grease seal so I can drive the seals into the hub if they won’t go in by hand.
The top hat fits into the grease seal so the brim of the hat is on the inside of the seal.
I pack the inner bearing races generously with Sta Lube, Sta-plex Extreme Pressure Premium red grease.
I use the large socket and tap the right side grease seal with top hat into the hub until it is even with the face of the hub.
I flip the hub over and I install the center pipe and the wedding band inside the hub. I stick the four shims into the grease on the narrow face of the left side inner race and install it into the hub. Next I install the grease seal with top hat. I marked the left side of the hub so when I install the wheel, that side of the hub will be on the left.