Vintage BMW Motorcycle Owners




Knowledge Base




Snowbum's BMW Motorcycle Repair & Information Website

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Oil pans; oil pan gaskets; engine case threads
for the oil pan bolts; oil capacity; dipsticks;
oil pickups; windage, etc.

Copyright 2020, R. Fleischer


HINT #1: A high percentage of time when a pan gasket seems to be leaking, it is not the pan gasket, but the leak is from someplace else.  When the gasket does leak, it is usually due to over-tightening and/or improper tightening sequence ....or damaged sealing surfaces.  Leaks from the timing chest, head gasket, cylinder base area, and pushrod seals, etc. are often found to be the actual cause with careful inspection.

HINT #2:  If you do need to replace the pan gasket:
The early cork gaskets are no longer available and tended to leak anyway.  The presently available gaskets are a fiber material, and are much better.  They MAY have a side with writing on it, coated with a heat-activated glue.  That side is normally upwards; but the gasket only fits one way. Gaskets have been seen that do not conform.  Modern gaskets are dual-coated with heat-sensitive material.  None need any sort of sealant NORMALLY.  More info later herein.

HINT #3:  Stuck pans can usually be released by a wood or plastic mallet AFTER you HEAT a corner, >>>do not break fins. Do be sure you have removed all the bolts first!  I usually try to loosen a pan immediately after a ride, so the entire engine and, of course, the pan, are hot.  Do not pry with a screwdriver!

HINT #4:  Clean the pan and engine surfaces very thoroughly. You may need to use chemical cleaners to remove whatever glue, adhesives, etc., are there.   Use a fine file if you have to on the edges, on an angle, if any have metal nicks sticking up proud of the surface ...I have seen people use screwdrivers to get a stuck pan off, and gouge the metal, so clean that up if need-be.   If any deep gouges are found that are really bad, clean them and apply a two-part epoxy and when fully cured, file very carefully to be flat.   This is particularly important if any of the gouges are over 50% across the surface.  Re-said: If you have serious nicks, you can clean them up, fill them with high temperature epoxy, and after that stuff cures, file/scrape/sand, etc. ...until dead flat.  Use a mechanics flat rule, on edge, or other means to ensure flatness.  Flatness and having no nicks is critical.  You must not remove metal, gouging the metal, leave nicks, etc.  If you are tempted to use a rotary abrasive disc or sandwich disc, don't!   Do NOT use any rotary brush that has stiff bristles.   Acceptable, if you must, is the type of rotary brush that fits into your electric drill chuck, but only if it uses very fine and relatively soft bristles.  Yes, these bristles can be made of steel, that is OK. ......but the bristles must be fine (thin, soft).   About 0.006" diameter bristles, nothing larger.  Don't use excessive pressure.  These fine bristle brushes, used in an electric drill, with light pressure, will remove old glue, old RTV, etc., quite nicely ...without damaging the aluminum of the engine case nor the oil pan!...but only if you are VERY careful.  I usually use plastic scrapers and chemicals.

HINT #5:  I am not a believer in the aftermarket-available soft silicon rubber gaskets ...too many problems ...although sometimes they do work.   I do not use silicone pan gaskets ...nor any type of sealant, silicone or otherwise, on the pan gasket surfaces (that means engine and pan metal surfaces), unless absolutely necessary.  I make sure the pan is flat, nick-free, and I install a standard stock BMW pan gasket, lettering upwards, the way they fit.

HINT #6A:  There have been instances of annoying leaks from the pan bolt located below the oil canister area.  Use NON-hardening version of Permatex Form-A-Gasket on that bolt's threads and on the bolt washer.

HINT #6B:  Some have used a medium strength Loctite, such as the common blue stuff, on all the pan bolts.   I do not.   In my opinion, there is no need for a thread locker compound, except as otherwise noted in this article.  Keep in mine that once a Loctite or similar product is used, if that substance is not removed on the next pan bolt removal, it can be more difficult to know what the true torque is on the bolt.....AND....the waverly washer under each bolt is quite good enough to secure the bolt, if you use a proper torque wrench.  You certainly do not want to over-torque those can, too easily, pull the threads.   That is also part of the reason I have specific recommendations in this article on 'testing' your threads, before you remove the bolts (each time, actually), and I supply specific torque values.

HINT #7:  I suggest the pan gasket work be done at the same time you do a regular oil change, with or without an oil filter, A/R.  It's a good time to inspect the oil pickup mounting, etc.

HINT #8:  Do NOT!! use a big torque wrench like used for swing arm locknuts or for the cylinder stud nuts, on the pan bolts.  Be sure you do not confuse foot-pounds, inch-pounds, Nm, etc.

HINT #9:  Read #13 in the next section.


1.  At the next oil change, drain the hot oil.  If the drain plug is frozen and cannot be removed, try heating it and CAREFULLY using a Vice-Grip pliers.  If no luck, find a Torx bit that is just a bit bigger than the hex hole. Hammer it into place and then unscrew. A hot pan can help here. AVOID any type of screw extractor, they are hard, brittle, and will cause a considerable problem if they break in the drain plug.

2.  Check that all of the 14 bolts can be tightened to 78 INCH POUNDS  (absolute maximum, in my opinion, is 85 for this test); if any are stripped, fix with Helicoils after pan is removed.  If your FEEL is truly OK, using a SMALL offset 10 mm box end wrench (4 inch length?); or ...better ...a SMALL square drive wrench with a 10 mm socket on a torque wrench, try tightening the 14 pan bolts for the test.  Best really is to use an inch-pound torque wrench.   If any of the bolts have bad threads, note which ones, mark the case (felt tip pen or pencil, or make sketch?), so you can fix them after the pan is off.   You don't want to replace the pan gasket and then find you have bad threads at any of the 14 threaded holes.

3.  Put a large and soft towel or other item on the floor, as the pan may fly off the engine. The pan may have been put on with a sealant, which is wrong!   The pan may be difficult to remove.  Occasionally even a pan that does not have sealant applied will prove difficult to remove.  Check that every pan bolt is removed!  There are 14, so count them.    Heat a corner area of the pan if not already hot from riding.    Use a block of wood and a substantial hammer & give the well-placed piece of wood a substantial whack from the hammer.  Do not bust fins, ...remember, I said 'well-placed'.     Do not allow the pan to fly across the area & be damaged.  I usually have an assistant, wearing gloves (pan will be, or should be, hot!) assistant should grab the pan so it cannot fly.  Do not use a screwdriver to try to pry the pan off, because YOU WILL leave nicks and depressions that are difficult to seal against leaks.

4.  With the pan removed, VERY thoroughly clean everything.  Some gasket remover products work pretty well.  I suggest you be VERY careful about using sharp tools, including safety razor blades and rotary brushes, in cleaning off any old gasket and sealant residues.  Do a preliminary inspection for the oil pickup, bolts for the pickup parts, etc.  Inspect for cracks in the casting the pickup mounts to. To remove the old gasket, if need-be, use a sharp blade on a very flat angle (nearly flat to the surface) to remove any old sealant or other substance found.   Use a strong commercial gasket remover if you wish.    The crankcase surface absolutely must not have any old gasket material and no nicks that have metal proud of the surface nor below the surface that could cause leaks.  Clean the area very well!  Final cleaning of the crankcase surface should be with a good solvent that does not leave residue.  I am particularly fond of acetone or MEK for this.

It is critical that you do not nick the pan and engine mounting surfaces.  Any projected nicks you find should be dressed flat.  You may find a nick that needs filling, you can use one of the metal epoxies for that (clean surfaces excellently first using a fast drying solvent), then after epoxy overnight curing, make it dead-flat.  Take your time to do it correctly.     If you have gouges and nicks that are serious, repair them.  Metal-containing epoxy will work OK!

5.  Bad threads are best fixed by installing Helicoils.  You will want a M6 x 1.0 thread Helicoil kit.  I suggest you use kit number 5403-6, which has all you need except a drill and tap guide.  The inserts are 12 mm in length, perfect for the application here.  You will need a 1/4" drill bit, unless whatever kit you purchase comes with the drill bit.  YOU MUST drill and tap at 90 degrees to the surface.  USE A DRILL GUIDE AND a TAP GUIDE.   If you drill and tap on an angle the results are often 'It always leaks...'.  Check the threaded holes in the engine case ...any been drilled through into the oil area and Helicoiled ...or?   Is the bottom engine area FLAT? ...not been dinged by someone? ...looks good around the threaded holes?  Are any Helicoils (or?) BELOW the surface ...they ALL should be!   Are the internal Helicoil tangs, used when installing the Helicoil, removed?  They should be!

6.  Look upwards with a strong light and slowly and carefully inspect the oil pickup parts look OK & their bolts tight.   Inspect the pickup, tube, & casting area, for cracks ...some have been seen on extended pickup models.  Early models with the "plastic" adaptor may loosen over the years ...update with the aluminum version.   If it needs it, remove the metal screen and clean it.  If the two bolts for the pickup are even slightly loose, remove, clean with solvent, use new gasket(s) and apply Loctite BLUE to the threads before tightening evenly!  If you absolutely insist on reusing the gaskets, and they look OK ...that is, not torn, you can install them with a thin, but thorough, coating of non-hardening Permatex form-a-gasket (type #2).  It is preferable to install new gaskets.  The reason to install fresh gasket(s) is that the gasket will not go back onto the assembly in EXACTLY the same position, and you might even have it reversed or upside down, as they fit both ways.  These things mean that the raised area and non-raised areas no longer match-up, and you can get air sucking-in at that point; and, oil leaking (or air sucking).   Using an old gasket is generally a bad idea, unless it is mandatory in some field situation.   You do not want loose bolts because they will eventually loosen enough so that the engine will get less and less oil circulating, and if the pickup parts get loose enough, or fly apart, it is near certain that you will have a massively expensive repair job, as the entire lower end, including the crankshaft, will likely fail.

7. Check the pan for actual flatness. Use #1 eyeball with the pan on a piece of glass or other surface plate, and a strong light ...or a feeler gauge or both/all.   Any sanding of pan surfaces must be done on a flat surface, such as an old piece of window glass or a real Surface Plate.  I use even pressure, and figure-eights, varying my hands position, etc.   Do not use spot sanding as you are unlikely to gain a really flat surface.  Spot sanding may be needed if you have repaired a bad gouge, and I always do it by hand, not with motorized tools.  You can use a lamp or flashlight at the pan-to-flat-plate surface to see any problems ...or, as I do, with a very thin feeler gauge (.002" happens to be the one I use). More details on sanding, etc., later in this article.    If necessary, place the pan on a flat piece of glass or machine-shop flat plate, with a large piece of upside-down sandpaper, perhaps grit 320.  Do careful figure eights, with evenly spread hands pressure.   If you are good at it, use a long flat mill file carefully covering adjacent and cross-surfaces ...otherwise do the eights.  Do just enough to be sure the pan is flat, smooth, and there are no dinged edges that have protruding bits, etc.  Don't round the pan edges, flatten unevenly, etc.   It is not necessary to try to flatten the pan to remove every irregularity, but you want it quite good.

8.  After the pan is known to be flat and without serious nicks (do not nick with your scraping tools!), and all old gasket material is removed from engine and pan surfaces, and the engine surface appears good, and all surfaces cleaned (I use acetone on a rag), I install conventionally, without any sealant.

9.  Do not use any sealant on the gasket surfaces!  Gasket writing will usually be upwards.  There is a heat activated glue on that surface if the pan gasket was made properly (some are reportedly not).  Some reportedly have no such glue on either side.  Some have markings on the wrong side. Some have heat-released glue/sealant on both sides.  Don't worry, the gasket only fits ALL the holes in one direction.  Note that if the pan and/or the case is truly in bad-enough condition to warrant a sealant, you may use such as #2 Permatex Form-a-Gasket or some appropriate RTV. 

10.  I hold the pan and gasket to the engine flatly, then finger-in all of the 14 bolts (with waverly washers).  Sometimes I hold a 10 mm socket in my fingers and go finger tight while using the socket (no handle).   Then I tighten evenly, in a criss-cross-pattern (very important), and for the first go-around, I use a quite low torque, just by feel.  I'd guess at maybe 10 INCHpounds or so; never have measured it.  I might use the socket and a 4" or so stubby square drive tool; or a box-end wrench.

Actual real torqueing is next.  I use a small 10 mm box wrench or 3/8 drive socket and short ('stubby') handle ratchet.  I usually do it by feel, and I guess I do it to around 6 foot-pounds ...but I have seldom measured it (but I do, occasionally ... and if your feel is not good, do use a proper torque wrench). Use of a torque wrench is always recommended by me.  DO NOT go for full torque immediately.  Do the tightening in STAGES, in a cross-pattern. That is VERY IMPORTANT!  Do one amount of tightening using a cross pattern, then when all 14 bolts are at that tightness, increase the torque slightly and start the criss-cross-pattern tightening again.  The idea is to completely avoid 'bunching up' the gasket.  Continue until final tightness is reached.

BMW has shown various specifications for the pan mounting bolts.  Some literature shows 8.7 FOOTpounds (don't!!!); some 6.5-8.0 (don't!!!).  Use MY figures:   For the final torque, between 65 inch-pounds minimum to 74 inch-pounds maximum.

Over-tightening or failure to do tightening in several stages, cross-patterning ...will OFTEN cause LEAKS!

11.  Install a fresh drain plug crush washer, and refill the crankcase.....DO NOT FORGET TO INSTALL OIL!!!  ...yes, folks HAVE done that!  I prefer the old-fashioned fold-over crush washer for the drain bolt, rather than the later solid aluminum washer BMW now sells..

12.  After a few heat-cool riding cycles, touch up the torque on the bolts again; again in a cross-pattern.  Again, it should be 65 inch-pounds minimum to maximum 74 inch-pounds. DO NOT EVER use a 75 ftlb torque wrench for this low INCHpound setting.

13.  If you find any leaks at any pan bolt, you can remove the bolt & apply some common NON-permanent sealant at the bolt threads & under the bolt head and washer.  I use Permatex NON-hardening Form-A-Gasket #2.  This is what I have mentioned before.  Do not use #1, it is much too hard & permanent.  Any decent non-permanent sealant will probably be OK.  The most common threads leaking problem (but can be at other areas) is at the pan bolt hole below the oil filter canister area.  I make it a habit to use a flashlight and/or stiff solid wire to investigate those holes, before I button-up the pan and gasket.  Through-holes are always suspect for leaks.

Note:  if someone has previously used a sealant at the bolts, you may have to use a tap to clean it from the threads.

Torque Wrench Conversion Factors:

While there are articles on this website with full information about torque readings, wrenches, conversions, values, etc. are some conversion factors.

Use an inch-ounce torque wrench if that is what you have.  Do convert properly if you need to convert.  Common torque wrenches with maximum's of 75 or 100 foot-pounds are not accurate enough at the low settings needed for the pan bolts...NEVER use them for this pan bolts job.
Foot-pounds multiplied by 1.356 is Nm.
Nm multiplied by 141.6 is inch-ounces; divide that by 16 if you want inch-pounds.
Nm multiplied by 0.7376 is foot-pounds.

IF...and only IF ... you have oil leaks that you have been unable to fix by replacing a pan gasket and after paying careful attention to the surfaces, including checking for old gasket, nicks, flatness, particular leaking bolts, and sources for leaks besides the pan area...etc.:

Apply Permatex NON-HARDENING version of Form-a-Gasket onto CLEAN, NON-OILY surfaces.  Use a very thin coating, coat 100% all the surfaces.  I use my fingertip to apply.  Some use RTV, but I do not.

If the leaks are at the pan bolts, and especially if the bolts that are below the oil canister area, COAT bolt threads & washer with the same Permatex goop, before installing them.

Solvent-wash the area so it is clean and dry. Go for a 10 mile ride. Blow a bit of talcum powder onto the areas. No leaks?  GOOD!   Now, with engine still hot, check the torques, and then again when the bike is cooled. Do not exceed the torque values I listed. Torque in a pattern only.

Pan and pickup differences (and some other stuff):

The oil pans were not the same over the years of Airhead production (1970-1995), and some aftermarket ones were also available, supposedly to improve cooling, which they really do not do much of ...just a small amount.

Early pans were flat.  In 1976 the pan was lowered a bit, it was a bit deeper, which gave more room for crankcase pressure and reduced oil consumption from oil mist through the breather due to the extra air space. The engine breather area (on top, near the starter motor) was also modified a bit later was still the round disc at that time, but added in 1978 was a tiny hole in the bottom of the oil condensation chamber in front of the breather drain oil back into the engine.  That teeny hole MUST be clean and clear, if not, you will use oil more rapidly.   When the pan was lowered half an inch or so in 1976, BMW had to add a 2 bolt spacer in the oil strainer pickup tube.  In the /6 era, the spacer was phenolic (bolts tended to loosen on those), then later aluminum.  Two paper gaskets are used when the spacer is used.  I prefer to use a tiny amount of evenly spread sealant like Form-A-Gasket non-hardening #2 on both sides of the paper gaskets, using my fingertip ...remember, THINLY ...and Loctite BLUE on the threads of both bolts.  The spacer surfaces need to be flat and nick-free, and the two bolts need to be evenly tightened back and forth.  Some folks have used red Loctite, and I am OK with that.

You can't use the one piece cast pickup on the early pans; that part is used only with the 1981+ pans.  The one-piece casting versions eliminated the need for the spacer and the extra gaskets.

In 1981, BMW made the pan a fair amount deeper, adding more oil capacity, and a slosh baffle in the pan construction, so the engine would not, supposedly, momentarily run out of oil on very hard braking.     Also in 1981, the pickup became a cast aluminum item, no longer was a sheet metal steel pressing, and was changed slightly on size.

There were 3 types of oil pickup assembly bolts used, all M6, but of various lengths depending on the bike's oil pickup items.  There may have been 4 types, not sure, I seem to remember one of the bolts had two head styles had more taper under the head.  My memory might be faulty in this matter.  This is hardly anything critical ...the bolt must simply be long enough to fit the items properly and capable of tightening properly.

Mystic, Roadster, G/S, and GS models use a shallower pan.  The pans have threaded holes for mounting a bash plate.  These shallow pans will also replace the original NLA /5 pans. The GS pans were slightly deeper from 1991; and GS pans have a rear wall drain.  There were special pans for the GS in, I think, 1988 ...with a large capacity.

1970-1975 center-stands do not work with deep oil pans, unless you modify or change, the center-stand.

There is confusion with what dipstick to use, see below.

I am NOT in favor of non-BMW (aftermarket) 'oil cooling' extension pan items, that give a larger oil capacity and have tubes in them running for and aft.   Rare, but they have been known to give serious problems.   They don't add much cooling, contrary to advertising claims.

Anton Largiader has a considerable amount of information with photos of pans and dipsticks.  He also covers some aftermarket pans at the end of his article.

Dipsticks ....and ....the confusion over measuring them:

BMW has used two 'styles' of dipsticks on the Airheads.  The early style had a silvery metal top, and had a metal crush-ring type of gasket (which was not tightened so tight as to crush it! ...just snug).  The later style has a black top, which stays cooler to the touch, and uses a rubber O-ring in a groove in the top. It also is not to be more than snug.

One way to identify a dipstick is by the top style and by the measured distance from the bottom flat area of the top part, to the minimum and maximum marks.  However, many (including myself, early-on), did such measurements from the underside of the threaded area.  For all of us, this makes those measurements ~3/8" shorter than from where we should measure from.   Why the "should" ??   Well ... it does not account for the possibility of the threaded portion possibly being different, & as that threaded portion is not important, it needs to only be enough for the dipstick to properly tighten to the engine case. Thus, there has been confusion, between numerous parties, as to dipstick dimensions, because folks, including me, back then, did not measure from the sealing surface, which is the only truly proper point.  In my later measurements, see below, I did it properly.

Later dipsticks have an identifying letter, such as A, B, or C, molded into the finger-turning area. This is identified in Anton's article photo, a link to his website article is well below.

HINT:  When removing or replacing the dipstick, avoid bending the left carburetor throttle cable.

This first table of measurements applies only to stock dipsticks, and are from bottom flat area (at lower end of threads).  The 1982 R100RS and the 1983-4 bikes really should be identical.  I have figured out why differences were reported to me.  Not being taken into account was that the proper measuring point is the underside of the dipstick where the gasket or O-ring fits. The threaded area end base should not be used for measuring, as it possibly could vary (although I have not studied that).  The important distance is from the engine case flat top opening area for the dipstick.  That is the same as the original metal dipstick plus its metal gasket; and, for the black plastic head dipstick of later models, it is the same as the effective flat area the rubber O-ring fits into.  I tried to prove that this was the problem, and so I measured the dipstick from a stock 1995 R100RT, measurements were from the sealing lip area.  This dipstick has a molded-in "A" on the handle.

From sealing area to tip is 11-13/16".  This is not an important measurement.
From sealing area to the MIN mark is 11-5/8".
From sealing area to the MAX mark is 10-3/4".
The threaded area, for the curious, was 3/8"....but was not used in the measurements.

Year and model

to tip

 to min. mark 

to max. mark


1975 R60/6, R90/6   11-5/16" 11-3/16" 10-5/16" Note where measured from
1979 R100RT, 1982 R100RS 10-15/16"       10-3/4"         9-3/4" "
1983, 1984 R100RT    11-3/8"     11-1/4"     10-3/8" measurements done by Snowbum; see notes above table.

This second table of measurements applies only to stock dipsticks, and are from bottom of the sealing lip:

For these three dipsticks, the information came from John Falconer from a posting he did on the Airheads LIST on 09/06/2003 (corrected from mm to cm).  Measurements are from the sealing lip to the indicated mark.

1)  Dipstick from an early /5 (metal cap, no markings) :   25.7 cm to full, 28.3 cm to low.
2)  Dipstick from an early '80s R65 (plastic cap with molded in "A") :  27.2 cm to full, 29.3 cm to low.
3)  Dipstick from a '92 R100GS (plastic cap with molded in "C") :  26.6 cm to full, 28.4 cm to low. 

See:  Note that Anton Largiader's site measurement is from the underside of the threaded area, & not the underside of the lip which would be the ~equivalent to the crankcase dipstick area. Because of that, the measurements by Anton, should have 3/8" (9.5 mm) added, for the measurement to the sealing surface, that Anton did not show.   If you do this, then Anton's figures and mine are the same.

Engine oil quantities:
There is sometimes confusion about how much oil an engine takes during an oil change.   Your owner's booklet has the figures, and should be accurate for the stock oil pan.   Here are guidelines, for stock oil pans:

Without oil coolers, up to 1980:   2.25 liters.
With oil coolers to 1980:  2.50 liters.
From 1981 through end of production in 1995, without cooler:  2.50 liters.
From 1981 through end of production in 1995,  with cooler:  2.75 liters.
R80GS to 1990:  2.25 liters.
GS from 1991:  2.50 liters.

To fill the engine from the MIN to the MAX mark on the dipstick will take nearly a full liter (~ a quart U.S.), except that after 1980 it was a bit less ...about .85 Liter or .9 quart, approximately.

Unless leaving on a long tour, I suggest you have the oil level at ~1/3 quart lower than the maximum line on the dipstick, this is to reduce oil consumption.

This section was originally prompted by a lengthy thread on the Airheads List in mid-February, 2014.  I have edited my original reply, and put it in this section.

1.  Review Anton's website article:

2.  My own work, my own measurements, has proven that a deeper oil pan does give a FEW degrees of extra cooling. That is not very important, although slightly helpful if cruising at quite high speeds for long distances, as every degree lengthens oil life (esp. dino), especially once the oil is above roughly 230F, and oil temperature also has an effect on consumption.

3.  The tubes-type of aftermarket oil pans provide only a very little more for oil cooling, although 'common sense' would seem to say otherwise. The over-all effect of cooling tubes and a larger oil pan is somewhat effective, but very considerably more-so is just a stock BMW oil cooler setup.   Even the stock oil cooler setup is not wildly efficient at oil cooling; but, it is enough.  Keep in mind that over-cooling the oil is not a good idea, and that is why BMW said to cover the oil cooler on the GS models (which have no oil thermostat for the cooler) in cold weather.

4.  'Windage' has two meanings, in common usage, regarding oil pans and engines:

(a) There can be enough of a sudden fore-aft movement of oil upon acceleration ....and deceleration under hard braking, ...that can cause the oil pickup screen to momentarily run out of oil and suck air.  There is also a movement of oil to the left, or right, when leaning the bike in a turn or otherwise, and this reverses, in the same turn from centripetal forces. Note the photos in Anton's article, showing the early side baffles, and the much later cast-in forward baffle. These baffles help control the possible uncovering of the oil pickup from inertia, during sudden movement of the motorcycle.    These things are called windage.

(b) The other meaning of 'windage', the churning of the oil in the oil pan and in the air above it. The crankshaft is a prime producer of such churning, but also having a large effect is the rod and piston movement, and even the camshaft.  The effects are very complex due to the cam rotating at half crankshaft speed and the reciprocating rod motion.  The result is a huge amount of swirling & mixed-up vortexes of air it WIND! ...inside the crankcase area.  This "wind" is simply huge; very fast rotating too, but rotation is not entirely at crank speed, and it varies with distance from the crank and various friction effects of items in the vicinity. That makes it hard to control. This rotating and otherwise complex motion of oil, oil-laden air, etc. is enough to scoop up from the oil pan oil surface, and somewhat below the surface of the oil ...and the crankshaft need not dip into the oil for this (if it did, that would be bad for several reasons).  The oil is whipped into a frothing spinning every-which-way cloud.  If that cloud of oil was smooth and even, it would be easier to control, but that is not so, and not only is it rotating and spiraling, but you have the pistons moving in together and out together. The pistons movement creates a varying pressure, even slight vacuum is possible during a portion of the cycle, in the crankcase.  Poor quality oil may froth worse, and cause all sorts of oiling problems.   This whirling air/oil has frictional effects, and uses up horsepower, and creates heat, and there are some other effects.  Can you imagine this swirling rotating mass of oily cloud that is also being moved about by piston and piston rod movement?

5.  There is a breather valve to help control, moderate, and release, excessive pressure from the crankcase.  The breather system must be quite carefully designed, to avoid releasing much oil-laden air. That is usually done by multiple sharp turns in long passageways, pressure sensitive valves, drain-back holes, etc. Sometimes baffles are built into the crankcase, or there are bolted-in items that surround some parts, and sometimes there are various types of baffles built into the oil pan; and even sloped pans have been used.  Another system that was popularly used, particularly in English motorcycles, but also in some  American motorcycles, is a remote oil tank, which is usually just called a Dry Sump method.   It also usually enables more ground clearance.  More on the dry sump later herein.

6.  As with many things, distances have a big effect.  In the case of the rotating crankshaft and associated parts as affecting the oil in the pan, the effects are a mathematically squared function, so lowering the oil level a rather modest amount has a considerable effect. There are volume and irregular surfaces effects, and some other things, that would make this response much longer, that I will avoid here.

7.  There are substantial reasons for some engine designs to have the oil reservoir in a separate tank, and not located in an oil pan. This is called the Dry Sump system; a misnomer, since the sump is not dry. It can be done for enabling the engine to sit lower for various reasons, ....and it can also be done for reducing, very considerably, "windage losses", and often dry-sumping is done for both reasons, and more.

8.  Excessive windage causes more than just problems with the breather and oil loss, it also causes considerable horsepower loss from frictional effects.   There are various types of friction happenings with an oil cloud.  Just one is that the oil at the surface of the crankshaft parts is moving at a different speed than the oil a bit away from the crank surfaces. That in itself is power-robbing  friction, much more than you may imagine.  Think of it as multiple friction layers.  The oil flow also piles-up at various places on the crankshaft, and thus creates friction, which additionally robs the engine of output power, and can even cause unbalancing of the crankshaft, if not compensated-for.  Besides oil piling up here and there, the oil is not regular and smooth at the crankshaft surfaces, and so there is even more friction, with multiple layers.  The frothing swirling oil also causes, directly and indirectly, an increase in temperature.  Frothy oil does not pump and distribute nicely.  The oil pump finds it difficult to deal with frothy oil, which is full of air bubbles, which compress, and the oil pump does not like compressible air. Put simply, lubrication can be much less. The pump was designed to suck up & distribute oil as a liquid, not an aerated froth.  An aerated froth is compressible, and just that alone reduces volume in circulation, quite considerably actually; and the cooling provided by the oil, let alone the lubrication, will suffer. Quality oils contain anti-frothing additives, but there are limits to their effectiveness.

9.  Lowering the oil level in the pan may have a good effect, if done within reason.   It is 'common knowledge' that if you fill to the max fill line on an Airheads dipstick, you will 'burn off' (dumped through the breather mostly unless engine wear is enough) ~1/3 quart much faster than the rest of the oil. There are multiple reasons for this, including the mentioned things; but also there are changes in the oil itself over time/miles.  Note that the size of the engine (especially piston diameter) determines crankcase pressures, and that the early Airheads with a round breather disc had two positions possible on a breather post clip, and so were adjustable for the engine size.  The adjustment controlled the pressure of the spring above the breather disc, and the lower clip setting was used with the larger engines which had more air movement with pistons movements.  As the engine becomes more and more worn, crankcase pressures tend to rise, increasing oil usage.  This also happens from worn valve guides, where the engine oil mist is drawn into the combustion chamber.

10.  Poor quality oil contributes to faster use.

11.  There is a quite small condensed oil return hole in the breather area on later models ...which should be checked for being open and not obstructed.  Photos/sketches:  which will clear up confusion over where that hole is located.

02/26/2005:  Minor.
08/13/2006:  Emphasis on the glue and writing upwards.
11/21/2007:  Was article 79.  Minor changes in emphasis also.
01/15/2008:  Move page position on Tech Index Page during re-organization of site; edit the article for clarity during this process; add Pan Differences from the Engine Internals article.  MAJOR changes to this article.
07/07/2008:  Add Anton's website link to pickups heading.
01/22/2010:  Cleanup, clarify some details.
03/19/2010:  Edit for clarity; include the LIST stuff.
02/24/2011:  Changed to 50C.
03/23/2011:  Remove oil pan information from 50B, move here; revise this article for more clarity and hyperlinks.
04/05/2011:  Minor clarifications.
10/18/2011:  Another "C" anomalie?...make note.
10/18/2011:  Correct the discrepancies on the dipstick measurements, noting WHERE they are measured from.
10/12/2012:  Add QR code; add language button; update Google Ad-Sense code; clean up article, incorporate a table, etc.
2013:           Remove language button, as the javascript caused problems.
02/13/2014:  Add Windage section.
09/23/2014:  Clean up.
12/22/2015:  Add part number for temperature dipstick.
03/11/2016:  Update metacodes; format, layout, colors, fonts, re-arrange order of things; eliminate many redundancies, Step-by-Step improved.
09/30/2016:  Repeat, mostly, of 03/11/2016 work, s/b final fixes.
11/09/2016:  Improve clarity on the Helicoil fix in item 5.
04/08/2017:  Add to HINT 5.
03/19/2018:  Reduce html, font changes, color changes.  Improve layout including tables.  Improve explanations. 
11/26/2018: and again on 01/01/2019:  minor corrections for syntax, spelling, etc.
12/26/2021:  Check that the updates done about a year or two ago were incorporated and put on Internet.

Copyright 2020, R. Fleischer

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Last check/edit: Sunday, December 26, 2021