As part of this work, I check the depth of the oil filter canister and shim the oil filter canister for the correct compression of the “$2,000 O-ring”, so called because if it doesn’t seal, the engine doesn’t get oil and a new engine was about $2,000 back in 1983.

Resources

These are good references on the oil system, oil cooler, filters and filter covers BMW has used on the airhead motorcycles.

• Anton Largiader –> The White O-Ring
• Anton Largiader –> BMW Airhead Oil Filters
• Robert Fleischer –> Oil & Filter Change Procedures
• Robert Fleischer –> The BMW Airhead Oiling System (has an oil flow diagram)

I use Oak Okleshen’s method for determining the number of shims to use, as described later.

Tools

This bike has the thermostatic controlled oil cooler. There is a special bolt (part# 11 42 1 335 394) that is screwed into the thermostat housing to open the oil cooler control valve to let oil fill the oil cooler. Since I drained the oil cooler, I use the tool when I crank the engine to pressure up the oil circuit so oil will fill the cooler. This is a precaution to prevent damage to the oil cooler if it should suddenly get pressurized while there is air in the oil cooler passages.

NOTE:
As Bob Fleischer points out in his articles, some of these bolts are too long and some don’t have the end rounded enough to avoid damage to the thermostat valve when you install it. The above bolt is correct.

I use a depth gauge and vernier caliper to make measurements of the oil filter canister depth.

And because I have grown to not “trust but verify”, I use a micrometer to confirm the shim and white o-ring thickness.

Parts

I install a new hinged filter, white o-ring, black square o-ring and the shims needed to ensure the white o-ring is compressed enough to seal the oil canister and the filter cover. The filter kit from Euro MotoElectrics includes the hinged filter, one shim, an oil filter cover gasket, the white and black o-rings and an oil drain plug gasket. Based on my measurements of the depth of the oil filter canister I do not need the gasket.

Video

Here is a short video summary of how I do this work.

VIDEO: 1983 BMW R100RS Shim Oil Filter Canister, Install Oil Cooler & Filter

Oil Cooler Operation

The oil filter cover contains a thermostat activated valve to allow more oil to flow through the cooler as the temperature goes up. The cover connects to hoses that go to the oil cooler which are secured by banjo bolts with a copper washer on each face of the bolt.

The oil filter is hinged and has a black grommet on one end. The grommet goes inside the filter canister against the back of the canister. The filter cover is installed with shims (at least one) that fits over the lip of the filter canister with a white o-ring on top of the shims against the cover

There is square profile black o-ring that fits in a groove in the filter cover to seal the center pipe that sends oil to the engine. The cover is secured to the engine block with three bolts with wave washers. I replace the stock hex-head bolts with Allen bolts since they are easier to remove in the tight quarters around the filter cover when I need to change the filter.

NOTE:
In the following paragraph, I use “left” and “right” from the perspective of facing the front of the bike rather than the traditional perspective of when you are sitting on the bike.

As shown in the picture below, there are two holes in the filter cover. The large center hole connects with the center pipe inside the filter canister that feeds filtered oil into the engine.  The smaller off-center hole connects to the right oil cooler hose (the one closest to the engine) to send oil to the cooler. The two holes in the cover are connected so if the thermostat is closed almost all the oil will go directly to the engine. As the oil temperature rises, more oil goes through the off-center hole to the cooler and returns via the left oil line (the one farthest from the engine) mixing the cooler oil returning from the cooler with the oil going into the center of the cover to the engine.

Measure Oil Canister Depth

I used both a depth micrometer and a depth gauge with vernier caliper to take measurements of the depth of the oil canister from the top of the engine block. I was curious how close the measurements are using these different methods. I found they agreed within 0.1 mm (0.004 inches), which for this purpose means the less costly depth gauge with vernier caliper is accurate enough.

I took four measurements at 12:00, 3:00, 6:00 and 9:00 around the circumference of the canister and averaged them to compute the depth of the canister. To take the measurements I put the depth gauge flush on the engine block and extend the rod until it touches the lip of the canister. I lock the rod with the set screw then transfer the length of the rod to the vernier caliper for an accurate measurement.

I take a “trust but verify” approach to the shims and white o-ring since sealing the oil filter cover and canister are critical to ensuring oil flow to the engine. I measure the thickness of the shims to confirm they are nominally 0.3 mm thick and the white o-ring to confirm it is nominally 4 mm thick.

Oak Okelshen’s Formula for White O-ring Compression

Oak Okelshen wrote an article in the Airhead newsletter, Airmail, on how to compute the compression of the white o-ring when using shims and the optional paper gasket. Mike Valenti sent me this information in a private Email.

Spreadsheet Calculations For Number Of Shims

This is the spreadsheet I made to help determine how many shims I need. Based on my measurements, the canister on this bike is deeper than BMW’s specifications. According to Bob Fleischer’s information, this is not uncommon and is one reason you should measure your canister depth before deciding on the number of shims you need.

NOTE:
Bob’s material states that the filter canister depth can change over time so it’s a good idea to check the depth every time you replace the oil filter and keep a record of the canister depth. I believe mine receded about 0.2 mm since I got this bike which is almost the thickness of a shim.

This section is where I measure the depth of the canister at the four locations shown.

This section is where I enter the values for Oak’s formula and the nominal measurements I got for the shim and white o-ring thickness. I do not use a cover gasket since my canister is recessed more than BMW’s specified range for the canister depth.

This section computes the compression of the white o-ring as the number of shims increases. I want the o-ring compression to be between 10-25% of the original 4 mm thickness of the white o-ring (0.4 – 1.0 mm).

I decide to install three shims as my canister is recessed more that the BMW specification which compresses the white o-ring about 21%.

Clean Up And Mount Oil Cooler

The oil cooler mounts with a bracket to a frame tube under the steering head. I remove the bracket from the cooler and clean and polish it.

I removed the hoses on the oil cooler and cleaned up the fittings and the hoses and inspect the hoses for any cuts, nicks or signs of deterioration. Mine appear serviceable.

I attach the bracket to the top of the oil cooler so the cooler is facing in the correct direction. The sloped edge of the tab on the cooler the bolt goes through faces to the front of the bike. I temporarily attach the cleaned up oil cooler bracket to the frame tube under the steering head so I can adjust it when I install the oil cooler hoses to the thermostat-oil filter cover to eliminate any kinks or strain on the hoses.

Install Oil Filter and Thermostat-Oil Filter Cover

I install the black square rubber gasket in the groove on the inside of the filter cover.

The hinged oil filter has a rubber grommet on one end that goes inside the filter canister against the back of the canister.

I need three shims to compress the white o-ring enough to seal the canister and cover. The shims fit over the edge of the canister.

NOTE:
I took these pictures before I installed the filter, but you should install the filter and then the shims.

The white o-ring goes on top of the shims. However, it’s easier to install it on the ridge on the inside of the filter cover which keeps it in place.

I attach the cover with the three Allen bolts and wave washers.

After I install the cover, I attach the banjo fittings on the end of the oil cooler hoses. I make sure the hose fittings on the bottom of the cooler are loose so the banjo fittings can rotate so the faces of the fittings will be flush with the mating surface on the thermostat-oil filter cover.

I attach each banjo fitting with a banjo bolt. I put a copper washer on the bolt head and a second washer between the banjo fitting and the mating surface of the thermostat-oil filter cover making a sandwich with the washers acting as bread and the banjo fitting as the filling. The banjo bolts are torqued to 13 FT-Lbs. Since this is a low value, I use my INCH-Lb wrench set to 156 INCH-Lbs. It’s a good idea to wait 24 hours and torque the banjo bolts again to the proper torque as they can loosen as the copper washers compress.

WARNING:
If you over torque the banjo bolts you can shear them off, so always use a torque wrench. And use a socket wrench on them, not a crescent wrench.

I tighten the hose fittings on the bottom of the oil cooler. I move the cooler so it’s centered on the frame tube and the hoses are not kinked and then tighten the two bolts that secure the oil cooler bracket to the frame tube. I also make sure the hoses are not touching each other so they won’t rub together. When I install the fairing I may have to adjust the hose routing to be sure the hoses don’t touch the fairing panels either.

Filling The Oil Cooler Safely

Since the oil cooler has been drained, it’s filled with air. Should the thermostat valve open suddenly, it could over pressurize the cooler. And when the cooler fills, the oil level will drop in the oil pan. So I use a special bolt to force the thermostat valve open in preparation for my first engine start.

There is a bolt on the bottom of the thermostat-oil filter cover that I remove. The special bolt is 23 mm long and I thread it into the hole and snug it up.

To prime the oil cooler and all the oil passages in the engine, I remove the spark plugs and disconnect the GREEN–Blue coil power wire so the engine won’t start and optical-electronic ignition is not damaged. I remove the valve covers and crank the engine until the oil pressure light goes out and I see oil dribbling out of the top rocker assembly pillow blocks on top of the heads. The rocker pillow blocks are last in line in the oil system so when oil comes out of them it indicates all the oil passages are clear and the oil cooler has filled with oil. Then I check the oil level in the oil pan, add more oil as necessary, install the valve covers, remove the special thermostat bolt and install the original bolt, and attach the GREEN–Blue coil power wire to the right lower coil terminal before attempting the first engine start.

Revisions

2020-08-01  Cautions about oil cooler filler bolt, banjo bolt torque and routing hoses & cover gasket.
2024-01-26  Correct some minor typos.