The BMW Airhead Oiling System
sketches, descriptions; caps; thermostats;
oil breather system

© Copyright, 2012, R. Fleischer

oilsketch.htm
50B

This article is expected to be used together with article 50A.

This first sketch is of the EARLY Airhead oiling system, through about 1979; and, comes from the BMW Factory Service manual.  This is a photograph taken of a double page of the BMW Factory Service Manual.  All the airheads from the /5 have a similar system....but changes were made in 1980, those changes are shown much further down this page.

EARLY system, through about 1979:

Oil is also returned to the sump by the amount escaping from bearings clearances.

Later system (from approximately 1980):

 In '1980', BMW changed the oiling system internally in the engine casting.  BMW re-routed the oil so it now went directly from the filter to the front crankshaft bearing.  It passed by the camshaft flange, via an angled path to it, on its way there.  This change was incorporated at various VIN numbers....that is, it was phased into production.  NOTE:  because of that phase in, certain swapping of engine castings/components might require some modification (front main bearing cap, for instance), and the information is in a bulletin from BMW, which I have on fiche.  The phase in occurred as follows:

R65, phased in at 6381867
R80/7, phased in at 6126171
R100T, phased in at 6170415
R100S, phased in at 6165103
R100RS, phased in at 6185422
R100RT, phased in at 6196045

There is a oil pressure bypass valve located at the innermost end of the oil filter metal canister; same as prior models.  The purpose of this spring-loaded ball-check valve device is to allow oil, unfiltered, to pass into the engine from the pump and canister, if the filter somehow is blocked from oil flow.   This ball-check valve has VERY VERY rarely come loose, and you find parts in the canister area.  Somewhat more often, but still quite rarely, the spring has broken, and bits of it gets into the oiling system....very bad news, as considerable damage is possible.  If you have to replace the valve or otherwise repair it, clean the threads with a good evaporating spray solvent, and then apply BLUE (medium strength) Loctite or equivalent, in a SMALL AMOUNT to the threads.   DO NOT get any on the ball and where it seats.  There is no specification on how deep to install the slotted holding part, so you will have to just estimate it....do NOT screw it in way too far, you will change pressure characteristics.  

NOTE:   BMW had the crankcase identified when those changes were phased in.   The CLUTCH side of the engine casting has a triangle with an N in the center of it....this is cast-into the crankcase there.   This mark is the standard Alcan mark.

If you would like the above 1980+ oiling system as a .pdf file:   CLICK

Cap models, thermostats, oil flow, how the oil moves at the canister area, ETC:
 

The internal cap models are not equipped with a cooler.   They also do not have the later type of outer cover.  The oil flow inside the canister is rather similar to the later or thermostat or GS models.  The canister, whilst closed/sealed by the internal cap cover, has its oil from the oil pump going to the outside of the filter, and the central pipe is much shorter, therefore the oil flow passing through the filter goes directly into the shorter central pipe.   An in-depth discussion of the later versions, withOUT the cap-cover, is just below::

The thermostat, on models so equipped, seldom fails.  They have been known, RARELY, to stick.  This does not have any real effect on engine oil flow.  The thermostat is NOT simply an on-off valve.  The valve inside the thermostat determines what percentage of oil is routed to the cooler.   The thermostat is specified to begin opening at 80°C (176°F) and be fully open at 110°C (230°F).  GS models do not use the thermostatic plate, and thusly, without the thermostat, they use a sized hole to control the oil flow to the cooler.  That, in practice, seems adequate, although using a lot of rpm with very cold engine oil at startup, MIGHT be hard on the cooler soldered/brazed seams.  The GS cooler is supposed to be COVERED in really cold weather, to avoid OVERcooling the oil.   It is not clear to some folks exactly what the path of the oil is in the canister and cooler.  The high pressure oil output from the oil pump goes directly to the oil canister chamber, such that it is applied to the OUTSIDE of the filter.  The oil passes through the filter and then to the outer filter end, where sort-of slots in the metal filter cover allow oil to pass to the right.  The oil goes into the outer cover via a hole that is offset from the center hole.  The filter right end is semi-sealed to the cover by the square-sectioned smaller O-ring.  In the thermostat models, that outer cover hole is 8 mm in diameter.  On the GS models, early versions had the hole at 2 mm, but they should be drilled out, if you have that one, to 4 mm (5/32").  The oil flows into the cover plate and immediately out of the plate into the central pipe, which is a light fit into the cover, as the cover is installed during a filter change.  Thus, it is important, if checking the central pipe for tightness, that you do not make burrs on the pipe end.  The pipe must stick into the cover central hole.  The pipe normally sticks into that cover central hole about 3 mm.  The central pipe is the route for the oil to get to the engine oiling passageways.  If the filter should get clogged (highly unlikely), the oil goes into the engine via a spring loaded ball-valve, located at the far inner end of the canister.  That should be inspected with a flashlight at oil filter changes.  There have been instances of that ball check valve spring disintegrating....which could allow metal to go directly into the sensitive engine areas.  There is little if any filtering, if the ball check valve is not intact.   When the thermostat begins to heat up, and gets to about 176°F, it starts to open the passageways allowing SOME diversion of the oil that normally went from outer hole to inner hole....said diverted oil now goes to the oil cooler. 

 OIL PAN:  The oil pan has been changed a few times over the years.  First to deepen it half an inch to give additional room for crankcase blowby and normal operational pressures; then for more capacity (and the drain moved to the rear).  All are interchangeable on fit, as they all have 14 bolts in the same place.  The later one is better.  There is an article on this website that has information on dipsticks and fitting the pan gasket, which must NOT have sealant applied.  The cork gaskets of the old days are NLA.    Do NOT over-torque the bolts (I don't go over about 6 footpounds, and actually do it by FEEL), and tighten them quite evenly all around.   Recheck tightness after a few rides.  Do NOT over-tighten!  Whenever the pan is off, check the bolts for the oil strainer pickup.  Check the pickup parts, especially the earlier pickup connection area, for cracking.  

   MORE:   In 1977 BMW enlarged the oil pan capacity.   In 1981 BMW made changes to the oil pan AND the pickup.  There had been a few instances of the all-steel pickup tube assembly cracking, which often meant sucking air, not oil.  BMW went to a dual-piece pickup and aluminum adapter with 2 bolts, etc.   Use Loctite BLUE on those clean and dried threads when assembling (and fresh gaskets too!).   The enlarged (again!) pan now had a baffle in it.  The purpose of the baffle was to eliminate oil starvation at the oil pickup screen during very hard braking, especially if going downhill.   The parts are available and are a popular conversion.  Anton Largiader's website has a lot more information on the situation.

Breather system:  

The sketches are unclear about the layout of the breather system.  The above factory sketches for are both of the /7 era, so the sketches show the original round-disc type, but do show,  and NOT clearly, the oil condensation return hole #22.

The breather system varies from the early models to the later model, but the basics are the same. Engines FROM 1978 had the tiny drain-back return bore hole, item 22, being a 1.5 mm bore where much of the breather vapors condense and are returned to the crankcase.  Item 22 is called the "Return Bore in Settling Chamber" whilst the somewhat harder to understand item 21 is the actual settling chamber.  Item 20 is the breather valve.  Shown in the sketches at the top of this article are the earlier spring loaded (and adjustable to two positions for the smaller versus larger engines) round disc type.  The disc type tends to get chipped edges and also sometimes makes noises, often called a Turkey Gobbler.  The original disc can be made up from something like printed circuit board material, if one wanted to.  The later reed type can be installed in earlier disc type engines.  There is really nothing wrong with using the disc type, although they sometimes makes noises.  I actually prefer the earlier disc types.

Another thing that is hardly known, is that for a few months in the 1978 production cycle, the breather system fed both carburetors.  This is, of course, for the clam shell air cleaner models (the rectangular models came with the breather feeding both carburetors).  Use of the 1978 parts will help performance a wee bit, especially for racing.

In detail:
The crankcase breather is located in the starter motor area, in two sections, to the starter's right. Oil and moisture fumes are drawn into one or both carburetors depending on year and model, and burned during combustion. The early model breather looks like a round disc with a small spring and a holding clip on the shaft. There are two grooves in that shaft, the top groove is used for the R50/5, R60/5, R60/6 and R75/6, and the bottom groove is for the R75/5, R90/6 and R90S. This early type of breather valve has been known to make honking noises (the later ones which are reed valves can also make some noises, but usually they are quiet) and can be removed and the later style installed.  There is nothing wrong with the operation and design of a good early disc type breather valve.  It is arguable if the later reed type works better, but it IS quieter and does NOT seem to ever wear out.  You can make a new round disc from approximately 1/16" thick fiberglass electronics printed circuit board material.   The diameter needs to be about 1.06"; and the center hole about 0.22".

NOTE that some of these types of noises are often confused with noises in the rear crankshaft SEAL (turkey gobbler noises, honking noises).  The breather system appears to be simple, yet is more complex than one might think, with settling chamber and using very faint vacuum at the carburetor intake to allow it to function properly.  The breather system also has potential problems.  If the round disc is at all damaged, especially if cracked or chipped at the edges, it will cause high oil consumption.  Just barely forward of that disc is a small hole that was first introduced in the 1978 models, and this hole is often not seen with a quick glance. It MUST be clear!! That hole allows condensed oil to return to the crankcase.    If the small hole mentioned is not clear, oil consumption will be rather high.  DO poke a wire, or?, into that hole during inspecting the breather.   The actual system involves not just this disc valve, or reed valve area, but the outlet area forward and to right of the starter motor.
 

This is the 1978 and later, engine cutaway, showing the drain-back return hole mentioned above

UPDATING the breather valve to the later reed type (not really needed, you can make a round disc, as noted two paragraphs above):

To update the valve you must remove all parts except the post, and then fashion a way to pry up the post, without leaving bits to fall into the tiny hole (assuming you have a 1978+).   You can fashion a puller for the valve using socket and screw or??  The new valve consists of only three pieces, which include a membrane (reed) and a screw.  Install so that the cap fits properly.   Depending on the model, you may find the screw needs to point to the right foot peg, perhaps at about 5:00, tapping the assembly using an appropriate size of socket that clears the top reed stop plate.  Use RED Loctite on the screw threads.   Another way of saying this is that the open end of the reed faces the left handgrip....about a 10:00-11:00 positioning.  Be sure your cap, etc., fits properly, and the reed is oriented correctly, before fully installing, as there are differences over the years in what the area and cap looks like.

 If upgrading to the reed valve on a clam shell air cleaner housing model Airhead, you may want to upgrade the cap, using cap 11-15-1-335-756; hose 11-15-1-338-215; and gasket 11-15-1-338-431.  The actual breather valve assembly is 11-11-1-335-712.   The early R65 can use these too.   These other parts are only really needed for these bikes of the clamshell variety (and earliest rectangular models???)....where the venting is directly to the airbox, with no intermediate junction.

NOTE!!....use of the reed breather is a MUST!...if you are racing and using very high RPM....this is particularly so if you installed the racing camshaft, the so-called "336".

The pressure sensor switch area might have 14.5-29 psi (1-2 Bars) at about 800-1000 rpm, and perhaps 60-74 psi (up to roughly 5 Bars) at 4000+ rpm.   This all varies considerably with temperature of the oil, viscosity of the oil, and condition of the various parts of the engine.  The switch threads are reportedly 12 x 1.5 mm. Early /5 threads were PIPE threads.  NOT so the later threads!!

   

    Note:  A RARE event, but has been seen now and then, is an engine with the front main bearing having rotated, which cuts off oil to the rocker arms, and lowers oil pressure.  You will usually find a steel pin, of about 4 mm diameter, about 11 mm long, in the oil pan.  Whilst the main bearing is a press-fit, if the pin, which is supposed to be pressed-in and staked, comes out (big oil pressure is there, helping to push out the pin), then the bearing MIGHT rotate.  The pin is 11-11-1-253-184.   This is a SERIOUS event, and requires the entire front of the engine to be disassembled.

Revisions:
09/21/2003:  add information on phase in identification numbers and the Alcan mark.
08/24/2004:  add switch thread information
07/05/2005:  Revise for clarity of years and models, etc., the breather information.  
12/21/2006:  Completely revise, with much clearer and very much larger sketch, edit the text for clarity, and add a table for the 25 sketch items.
02/03/2008:  Remove engineinternals.htm hyperlinks.
04/28/2008:  add thermostat information
05/08/2008:  minor clarifications and editing AND add the 1980+ oiling sketch.
01/03/2009:  add information to clarify how oil moves in the canister area
10/17/2009:  add photo of settling chamber hole in a cutaway casting view
11/24/2009:  add .pdf of the 1980+ system
03/18/2010:  straighten out wording on the thermostat function in the CHART section
02/24/2011:  Combine with the reed valve photo, and edit entire breather system area
03/23/2011:  Remove oil pan information from title

© Copyright, 2012, R. Fleischer

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