OILING SYSTEM AND RELATED ITEMS...
This article is expected to be used together with #49 through #51D.
Everything that follows here is my personal belief, and a NON-leaking engine is assumed.
Cooler = oil cooling finned radiator
OIL USAGE, OIL DETERIORATION:
Thermostat, Oil Path, Outer Cover, Ball Check Valve, Oil Cooler, GS, Lamp, ETC!:
The thermostat, on models so equipped, seldom fails. They have been known, QUITE 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. If starting ANY Airhead engine at 40°F or below (engine temperature), do NOT use excessive RPM during startup and initial running. The oil pressure in the oil filter area can be so high as to collapse the oil filter element, until the oil warms up a bit.
Exactly what is the path of the oil? The oil in the oil pan is 'sucked-up' through a very coarse strainer, and then goes to the oil pump. The high pressure oil output from the oil pump goes to the oil filter canister chamber & is applied to the OUTSIDE of the filter. In the early model, like the /5, the oil goes through the filter, and then into the engine via a short pipe, the filter chamber right end having a metal cap cover with a large single bolt in the cap. The flat plate covering the filter access hole requires a paper gasket.
In all the models withOUT that internal metal cap cover, 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 longer than the /5 no-cooler type, and 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. Cooler equipped models have a modified outer cover, to divert oil to the cooler.
On all Airheads, if the filter should get clogged in some fashion and oil not get into the central pipe in proper fashion, the pressure increases in the oil filter chamber. A spring loaded ball-valve, located at the far inner end of the canister will open, allowing some oil to flow into the engine. The ball check valve 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.
The ball-check valve has VERY rarely come loose, and when it does, SOMETIMES you find parts in the canister area. Somewhat more often, but rarely, the spring has broken, and bits of it gets into the oiling system ...this can be bad, as considerable damage is possible. If you have to replace the valve or otherwise repair it, clean the male and female 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 Loctite on the ball and where it seats. Once in place, I suggest you immediately oil the ball/spring, to avoid the possibility of Loctite having gotten to the ball and carrier. 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:http://bmwmotorcycletech.info/oilsketch.htm
When the thermostat begins to heat up, and reaches ~176°F, it starts to open the passageways allowing SOME diversion of the oil that normally went from the cover plate outer hole to inner hole, and the diverted oil now goes to the oil cooler.
On the GS models with oil cooler (the GS has a NON-thermostat outer 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 smaller in diameter than the hole in the thermostatic type covers (which is ~ 8 mm). The GS cover uses that specific internal hole size to ALWAYS allow some oil to flow to the cooler (radiator), and as the oil thins from heating up, more oil flows. The GS radiator SHOULD 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, and since the frame on the GS models is higher, 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:
Note: a sketch, with notes, on the oiling system passageways, etc., is at:http://bmwmotorcycletech.info/oilsketch.htm
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 very briefly.
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. DO install a later cover with bolts, and a fresh O-ring, as the later cover O-ring groove has a changed dimension & stops leaking problems. Allen bolts have also been used. The sort-of-trochoid 4 lobed oil pump 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 is rotated, while you watch the pump.
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 warning lamp switch is NOT located in the 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 rather a lot with oil temperature, type, and grade. The 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 ~ 75 psi. At very low rpm & with hot oil, there is minimal lubrication. The chain wears little. The upper sprocket wears, the one on the crankshaft. It is common to call repairs here a timing chain job, but usually the sprocket and guide/tensioner are the worn parts ...but all worn parts in that area are replaced normally when needed. There is an article on this website on that....http://bmwmotorcycletech.info/timingchain.htm. Because of the need for chain, guide, & sprockets oiling, it is NOT a good idea to idle the engine too slowly. Under 800 rpm is BAD, and 900-1050 is OK. I tune all Airheads so hot engine idle is 1025 RPM. Carburetors work better and are easier to adjust at that RPM.
Be sure there is a metal shim against the canister edge, unless your canister HAS a lip ...and even then a shim MIGHT be needed! Read that article! Failure to do things correctly 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; EVERYTHING you need or might want to know is in that linked article!!! NOTE that MANY BMW dealership shops do NOT understand Airheads! Do NOT unnecessarily 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/failed oil filter has stopped oil from reaching the engine oil galley. 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 through the filter and then 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: http://bmwmotorcycletech.info/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!
1. An outlet 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 through that area.
Things get complicated from the crankshaft main bearing area. There are SEVERAL routes for the oil from the bearing holder area:
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. The main bearing is a press-fit, but if the pin, which is supposed to be pressed-in and staked, comes out (substantial 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 usually 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 oil consumption by utilizing reduced breather output. Later models have a drain-back hole in the bottom of the breather valve area, which additionally reduces oil consumption out the breather valve. My article on the system has sketches.
EXTERNAL oil filter conversions:
External oil filter conversions HAVE been done. A 'kit' to do this was sold commercially by Suburban Machinery. There was a major article in Airmail in November 1997 by OAK on that specific conversion, his misgivings, the company's reply. There are probably some Airheads around still running those external filters. That type had hoses from the oil filter cover plate area, to a remote mounted spin-on filter. A conversion has also been done by individuals in somewhat similar ways, not from Suburban Machinery. You might even run across a previously-owned setup, and be interested in it. I recommend you do not install a Suburban Machinery type setup.
The only other commercial type I know of is this one:
For other oiling system things, such as information on pan gaskets,,,,ETC ...see sub-section articles under Articles 60.
If you happen to have the flywheel or clutch carrier removed, be sure to check the oil pump cover. If it has the single slot or phillips screws, I suggest you update to the later cover and later bolts. The O-ring sealing is better, as is the changes to the cover to enable use of bolts. You will need a new O-ring for that new cover.
© Copyright, 2012, R. Fleischer
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