OILING
SYSTEM AND RELATED ITEMS
Oil usage; thermostat; cooler;
oil pressure bypass valve in the canister, etc.
©
copyright, 2012, R. Fleischer
oilingsystem.htm
50A
This article is expected to be used together with 50B and others!
Everything that
follows here is my personal belief, and a NON-leaking engine is
assumed.
OIL USAGE:
In my opinion a good running airhead....particularly the later
types with Nikasil....or earlier iron barrel ones in very good
condition...will have over 3000 average-Joe-rider miles per
quart. WELL over 5000 is NOT unusual with Nikasil
cylinders, sometimes even with the old iron cylinders; if
cylinders, rings, and valve guides are all excellent. With the Nikasil
cylinders, this can often be the situation for over 100,000
miles, even as valve guides wear out. Some
riders like to go above 6000 rpm (roughly) a LOT. They will
use oil up much faster. Riders in very hot desert
type weather conditions will generally use oil faster. Oil
usage goes up as valve guides and rings (also old iron cylinders)
wear.
I want to caution that the quality of the oil has a
LOT to do with 'oil burning', and moreso if one
has the early low capacity oil pan, especially on the larger
engines. The condition of the breather valve
and if the stock breather hoses are in place, may also affect
things a fair amount too. I actually worked on a
breather setup once in which the modified hose arrangement by the owner
had such a nice slip-stream effect that it literally tried to
suck oil out of the engine breather. Cheap oils almost
always have additive parts (of the oil compounding) that burn off
rapidly, and that is NOT a great idea....because sometimes it is
some valuable parts of the oil that disappear too fast.
Some fairly good changes in oil viscosity can occur, and there
are cheap wear protectants in most car oils which are NOT
designed for air-cooled flat tappet engines.
As the engine burns oil, it tends to leave some deposits,
coking/carbon, on the top of the piston, in the upper ring
grooves where the temperature is hotter than below, and on the
head. That raises compression ratio, but also leaves
nice places for some of that carbon to glow red, and cause
improper ignition. Use of poor oils can tend to promote problems in the
guides, and deposits on the stems. There are other niceties
that happen, including a situation with the carbon absorbing some
fuel mixture....but that, and some other things, are mostly....as
I call it....Nerdie-philes information. Because of all the
variables, I hesitate to give a maximum usage before any deep
investigation is recommended. Perhaps 2000 miles per quart
may be a point where some thinking should be done, and certainly
if maybe under 1000. If ring and barrel wear is the
cause, but compression is not too bad, and the valves are not
excessively old, I probably would just ride for awhile....but one
should not let wear go too far....penny wise, pound foolish.
On the older engines, with shallower pans, I suggest NOT filling
the level to the maximum mark.
Modern petroleum based oils (and, except for the temperature of
breakdown, synthetics too) are designed to work best in the range
of 110° C...130° C (230° F-266° F). Above 150° C
(302° F), oil breakdown increases
exponentially,
and by about 160° C (320° F), degradation is
quite
rapid. Petroleum oils will
cease to
lubricate with any effect, at about 170° C (338° F)...synthetics
at about 190 C (374° F).
For
practical purposes, petroleum oils are OK to about 240° F.
The temperature of the oil in the airhead oil pan is one
thing....it can be FAR higher in the cylinder head. The oil
needs to reach a reasonable temperature in the pan, for condensed
moisture to boil out (evaporate, if you will).
Thermostat, oil
path, cooler:
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 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; so see below on the proper hole size. 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. 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 gets 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 and functioning.
MORE: 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. This caution paragraph is repeated elsewhere's in this website, and you can get a better idea of the oiling system by going to: oilsketch.htm
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.
***
On
the GS models with oil cooler and the non-thermostat cover,
there is a factory bulletin on the early
covers. The bulletin says to
inspect the small hole in that cover, and if 2.0 mm, to
drill it to 5/32" (that is 4 mm) diameter. That is the
bypass port hole,
the function of which is to allow SOME oil to flow, even if
cold. Increasing the hole size reduces the amount of
oil passing through the cooler. Speculation is that
with the original smaller hole, some coolers ruptured with
starts in quite cold weather from the VERY high oil
pressure when the oil is very cold. That hole is a bit smaller
in diameter than the hole in the thermostatic type covers (which is, as
noted well above, about 8 mm)
The GS cover does not have a thermostat. It uses that
specific internal hole size to ALWAYS allow some oil to flow, and
as the oil thins from heating up, more oil flows. As noted
above, the EARLY GS covers had a too-small hole, and it needs
drilling....for the reasons outlined. The GS radiator must
be COVERED in quite cold weather to avoid OVER-cooling the oil.
The advantage of the GS plate is that it is simple, and takes up
less room in the canister area.
***The
frame on the GS models is high, and the thermostat unit
would NOT FIT those frames. Take a look at
a GS sometime.
For information in great detail about the oil
filter canister, oil cooler system, etc., refer to this website
elsewhere's, especially
OIL.HTM;
and, also the Technical Tips section at the Airheads Beemer Club
website:
http://www.airheads.org
Note: a sketch, with
notes, on the oiling system passageways, etc., is at:
oilsketch.htm
Those notes contain information on many things
dealing with the oiling system...and some changes made by BMW.
MORE:
The BMW airhead uses a wet sump oiling system. That is, there is
a container, called the sump, which you might call the oil pan,
that holds most of the oil, and plumbing/piping is arranged so
that an oil pump draws oil from the sump to the oil pump for
pressurized delivery elsewhere's in the engine. The type of pump
design that BMW uses is called an "Eaton"...which uses
a sort-of trochoid arrangement. The pump is very long lived,
extremely powerful, and is capable of an enormous volume,
hundreds of gallons per hour at high rpm. It is best not to
remove the oil pump parts unless you have a reason to. I
do, however, remove the outer pump plate and take a few
measurements, and replace the oil seal, anytime the flywheel
(clutch carrier in later models) is removed. In the pump
area there is an index mark to line up and the vane has one inner
edge chamfered, which goes on first. You MUST replace the O-ring
if the plate is removed.
I use a wee drop of Loctite BLUE
on each clean and dry screw and female thread.
Oil is lifted (sucked?) from the sump into the fixed non-movable
pickup, and that pickup, which dips well down into the sump, has
a coarse metal screen. There was a difference in the design of
the early pickup and the late one. The early model had a
small gasket on each side of an adapter that is on the top of the
oil screen unit; later models had the engine casting changed so
only one gasket is needed, and there is no adapter. Be sure
the bolts are tight and Loctited (blue), if you have the pan off
for any reason.
BMW has had at least three sizes of oil
pan. And....various oil pickups; dipsticks;....etc.
I have some of my own information in my Engine Internals article,
that is a bit different, particularly on the dipsticks. So,
see that article too. Instead of listing all
the variations of pans, pickups,... and putting photos here,
etc., Anton Largiader has done just about all of that already
(but, see my engine internals article for the rest), and here is
the hyperlink:
http://www.largiader.com/tech/oilpan/
In a rare instance of quite hot oil and
very abrupt braking, the system may loose pressure for a moment,
turning on the OIL lamp. Should you ever have your pan off,
that is a good time to gaze up and inspect a cam lobe, marvel at
the engine design robustness, understand what a tunnel-engine
means. At that time, clean the screen, and be sure
no
cracks are seen in any part of the pickup
and
casting!!...and that the two bolts are treated with a drop
each of Blue Loctite, and the bolts tight. If the spacer is
plastic, replace it with the later metal version. I use a
very
thin amount of Permatex
non-hardening
sealant on the pickup junction gasket(s). No sealant is needed,
and in fact NONE should be used for the pan gasket, and the pan
bolts must
not be overly tightened,
which will warp the gasket and cause leaks. 5 or 6 foot
pounds plenty on the pan bolts. You can check them
after a few rides.
The oil pump is located at the rear of the engine, to the right
of the crankshaft, behind a 4 bolt (or screw) cover plate. The
center drive of the pump, which is the rear end of the camshaft,
is different on early and late models. That plate has an
O-ring, and if you should have your flywheel (called a clutch
carrier on the later models) out for such as a new main seal (and
flywheel O-ring on some models), then you should remove the
cover, install a new O-ring,
oil it,
and
immediately replace the cover
assembly. As noted above, I use blue Loctite on the clean
threads. Two types of O-rings have been used. The original was
black, and a later type which is a few thousandths of an inch
thicker, is
red. Two types of plates
were used, one for taper head phillips screws, and one for bolts.
Allen bolts have also been used. The sort-of trochoid 4 lobed
vane is attached directly to the rear of your camshaft. That vane
rotates inside of a 5 lobe rotating ring, and it may be hard to
visualize how it works even if you have the cover off and are
looking at it....until the engine rotates, and all seems clear to
you (one hopes!).
The oil goes from the sump to the oil pump to the oil filter
canister, where the oil is presented to the OUTSIDE of the oil
filter, under very high pressure. The passageway (galley) from
the pump to the oil filter canister area is plugged at the left
side of the engine by allen plugs or screwdriver slot plugs,
and are best left alone. One such plug is quite
visible, the other is rearward and inward a bit (around the
corner, so to speak). That is, you will see one on your
engine below the oil pressure lamp switch...horizontal with the
left pushrod tubes. Another is a bit to the rear, 90° around the
corner, near where the transmission mates to the engine casting.
Very high oil pressure can be in this galley at engine start-up,
particularly if the oil is cold. The oil passes
through the oil filter element into the other engine oil galleys
(cast-in piping).
NOTE: The oil pressure switch is NOT at this part of the left side galley I mentioned above. Rather, that switch is located in a different part of the oiling system...MUCH farther down the line, actually in the galley that supplies the rear main bearing. The pressure in the switch area is about 14.5-29 psi at 800-1000 rpm; and about 60-74 psi at 4000 rpm. These are official figures, and will vary with oil temperature, type, and grade. That switch has threads of 12 x 1.5 mm. NOTE that very early airheads had a 3/8 NPT thread. ...also note that the later switch is the same as mid-seventies 2002 BMW car sender.
NOTE: The timing chain is oiled from the
output of the pressure relief valve, which opens around 75
psi.
At very low rpm, the oiling is minimal. The
wear is not the chain, actually it wears little, but the upper sprocket, the one
on the crankshaft. It is common to call a sloppy chain
worn-out, but usually the sprocket is the worn part....but all
worn parts in that area are replaced normally when needed.
There is an article on this website on that......
timingchain.htm
Because of the
need for chain, guide, and sprocket oiling, it is NOT a good idea
to idle the engine too slowly. Under 800 rpm is BAD, and 900-1050
is the rpm I prefer, for ALL Airheads.
***There have been a
LOT of changes to the
oil filter area over the years. A considerable amount of
confusion has existed, and continues to arise.
DO NOT EVER GUESS at what you THINK should be fitted...see
the various Airmail and Airheads.org articles published, and I
have all you need on this this
website at
oil.htm, and remember that
Haynes
and Clymer's, with all their sketches, are WRONG in some details
(BMW TOO!)!!! Do
NOT
use a thick or even any outer gasket on the engine oil filter
cover on the models
after the /6...these are any models NOT having
the INNER one-bolt filter cover. There are exceptions, read
that
oil.htm article! The early
models with the inner cover are basically foolproof. DON'T
BE A FOOL, be SURE you TOTALLY understand how and what and why on
the later canister setup, whether you have an oil cooler or
not!!!
Be sure that there is a metal shim being used, against the canister edge, unless your canister HAS a lip..and even then it MIGHT be needed!!! Read that article!!! Failure to do things right can cause $$$$ damage. If the oil light ever comes on at IDLE, you MAY have done damage already!...except, perhaps, under severe braking. maybe.
There is that mentioned one bolt inner cover on
early models and there are several types of outer covers,
thermostat and non-thermostat covers, GS covers, metal canister
shim, two basic types of internal pipes, many changes in O-rings
and oil filter designs, use and non-use of a paper cover gasket,
ETC. Do something wrong here and you will soon have a much
reduced bank account. This is NOT the time to pose questions to
ME...do your homework if you have concerns. NOTE that
some BMW shops do NOT understand airheads!!!!.....do
NOT necessarily trust your BMW dealership mechanics to do a oil
filter change properly. You must KNOW that they have
considerable airhead experience!!!, and you can ASK about the
finer details...about those shims and O-rings! I suggest
you do it yourself.
The engine is lubricated by oil coming from the oil
filter/canister. If the filter is blocked, a bypass valve at the
inner wall of the canister will allow the engine to continue to
receive oil. In a VERY rare instance a collapsed and thus
failed oil filter has stopped oil from reaching the engine.
This may have been a poor aftermarket filter (??). It is MY
belief that the HINGED, BMW-SOLD filters are the BEST, and
STRONGEST. The outlet for the canister is the
central pipe. In the non-cooler equipped bikes, the
oil flows from the outside of the filter into the short center
pipe, thence to the engine. In the cooler equipped models,
the center pipe is longer, and the pathway more convoluted, a
look at the outer flange cover will show you the
pathway.
From the oil filter canister, oil goes to the CAMSHAFT front
flange. There is a passageway here that is about 2.5 mm for
lubrication. Oil then travels upwards to the crankshaft front
main bearing area.
For an oiling sketch with
NOTES!:
oilsketch.htm
That sketch/page has a lot more information on it, be SURE to see
that page!...it includes a breather area photo you WILL want to
see!
Things get complicated from that crankshaft main bearing area.
There are SEVERAL routes for the oil from the bearing holder
area:
1. There is an outlet that goes to the TOP two LEFT cylinder
studs.
The engine casting base area of each of those two TOP studs, has
a small hole. Oil travels from that hole outwards along the
cylinder studs to the valve gear, and on its return from the
cylinder head flows down the pushrod tubes to the sump,
lubricating the cam and lifter during its passage.
2. A similar pair of stud oil hole outlets lubricates the RIGHT
cylinder valve gear, and back to the sump in the same manner.
3. Another outlet goes to the oil pressure switch and the
crankshaft rear bearing. Pressure at the switch is likely to be
towards 30 psi at idle, and over twice that at high rpm.
4. Yet another outlet goes to the pressure relief valve, which
opens at about 75 psi. That oil relief valve is located in the
chain compartment at the front of the engine, it is a simple
spring loaded plunger. Since this point is WAY down
the oiling system from the pump...and oil has traveled through a
lot of smallish passageways, it is notable that the pressure at
the left side oil galley, the direct pump output, discussed
previously, can be very much higher, especially with cold
oil.
5. The crankshaft itself has a bore, and fed from the same area,
lubricating the rod big ends. Since the cylinders on a BMW
airhead are NOT directly opposite, these are separate.
6. The little ends (piston rod ends) are splash lubricated.
7. Oil from the valve rockers area flows back via the
pushrod tubes, and that lubricates the camshaft surfaces, etc.
All the oil eventually travels via bearing clearance flow and
valve gear flow, ETC., back to the oil sump, and the process
begins anew.
If your motorcycle has an oil cooler, some oil can be routed from
the oil filter canister area to that cooler. That system uses a
longer canister central tube and a special outer plate and
o-rings, etc., to ensure that oil can flow to the cooler. A
thermostat (or restrictive hole sizes) may be used in that outer
cover.
***NOTE: on models before the approximate 1981 introduction of
the electronic ignition models, oil routing was somewhat
different to the front bearing, but this is of no real
consequence. The exact serial numbers, dates, models, of the
changeover is not known by me...I think it was phased into
production so as to use up all the old parts/castings.
On the LEFT side of all Airhead engines, below the starter cavity, to the left of the dipstick, is a small HOLE. That hole is the drain for the starter cavity. If a breather hose fails, oil may come out of that hole.
In the 1985/1986 and later models a system of two electric solenoids, and a few other things, and a fuel tank modification, was standard on airheads shipped to the U.S. The purpose was several, one was to positively shut off the fuel, petcock or not, another was to route fumes from the fuel tank (perhaps the bike was in the sun, especially if parked?) into the crankcase, where the fumes would be sucked into the carburetors upon the engine starting. A vent pipe led into the crankcase, and that pipe was on the left side of the starter cavity (inside the cavity area). MANY folks have removed the solenoids, one or both, and may have removed the flapper valve in the fuel tank that prevented a full load of fuel. When that is done, venting to the tank is a must. The vertical pipe going into the crankcase MUST BE PLUGGED, because otherwise a LOT of oil CAN be dumped rearward into the clutch....and some will undoubtedly come out that left side HOLE.
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.
As mentioned much earlier herein, oil capacity depends on model and pan fitted. Pan changes have been made for extra air volume for reduced breather output.
The Suburban
Machinery remote oil filter kit:
I am not in favor of
this product. See AIRMAIL, November 1997, for a
rather full discussion, pro and con.
For other oiling system things, such as information on pan gaskets,,,,ETC...see sub-section articles under Articles #60
Revisions:
04-18-2003: add .htm title; add oil deterioration
temperature information.
06-21-2003: clarify oiling system internal flow and
direction details; expand upon details of oiling system pressure
08-31-2003: add hyperlink to oilsketch.htm
09-06-2003: expand #4
09-21-2003: minor
09-26-2003: add top of page Oil Usage section
05-22-2004: Edit entire article for more clarity, minor
hints, more hyperlinks
08-24-2004: add oil switch threads information
10-10-2004: hyperlink re: breather
11-14-2004: add Suburban Machinery remote oil filter kit
notation.
07-05-2005: add slightly more information on breather oil
return hole, and re-arrange order of how I said it, slightly.
12-18-2006: add photo of late style breather valve
11-21-2007: Add Anton's website link on oil pans and
dipsticks
01-24-2008: Incorporate breather information from soon to
disappear engineinternals.htm
02-03-2008: Remove engineinternals.htm hyperlink
04-28-2008: add thermostat information
01-03-2009: add information to clarify how the oil canister functions,
with the covers
10/17/2009: a few words referring again to the oilsketch,
regarding the oil drainback hole
07/27/2010: Update here and there. Add breather disc
dimensions.
02/24/2011: completely revised...with 50B
© Copyright, 2012, R. Fleischer