An essay on lubricating oils for BMW motorcycles, engine oils

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Applicable to Airheads, K-bikes, and most engines.
Understanding how oils REALLY work/operate/function.
What things you should consider in selecting oils; how often to change them, etc.    

Copyright 2014, R. Fleischer



PRELIMINARY/BASICS: Additives are put into base stock oils to help form better 'thin oil films', so the oil is not pounded-out by impact forces. Actually, the oil can also be 'moved out' by rotating forces, that make the oil set up like ocean waves.  Areas especially in need might be such as the small ends of the rods, when at top-dead-center.     Very LITTLE engine wear is from dynamic friction...that is, from rotating, or constantly shearing movements.   MOST wear is from transient loads, such as at the cam lobes; with moderate wear on other areas during COLD STARTUP.    Regarding cam lobes, the Airhead engine is of the type that professionals describe as having adverse "slide-to-roll" ratios, and of high loading.  These types of engines are common to those of "flat-type" cam/rocker/follower systems, such as on the old VW Beetle, the Porsche 356, early Corvette's, even the Ford Pinto. Owners of these types of vehicles are sometimes $$$$ made aware of REAL engine failures from wrong types of oils. In particular camshaft and lifter wear.   Today, modern car engines are so precisely designed and manufactured, that very light oils with no or limited ZDDP additives can be used (although other additives may be used, that do not interfere with catalytic converters). NOT SO with MANY early engines. 

Much has been said about synthetic oils, and mostly it is about how much better they are than petroleum oils.  While based on quite a few facts, many things said are misleading.  Especially misleading is that oil change intervals may be increased GREATLY.  While relatively true (doubling, or a bit more perhaps in some situations) for the lubricating qualities, it is NOT necessarily true as far as the additives for swelling the seals (without which the seals would shrink and leak); and it is very much not necessarily true for the ability of the particular oil to deal with acids that accumulate in the oil. Fuels contain sulfurs which react with moisture from combustion, condensation, etc., to form acids.  Petroleum oils, as opposed to most full synthetic oils, also contain sulfurs.  Very short trips, particularly in cold weather, let moisture accumulate in the oil.  Lots of cold weather starts and low miles per start, all lead to oil contamination and degradation. 

To be fair here, most modern seals are neoprene or silicon types, hardly needing specialized swellers.  For Airheads, one of the important protective additives is some form of ZDDP for flat tappet (flat cam follower) type of operation.

There are a lot of additives in oils.  Some protect against absorbed moisture and MANY other potential problems.  SOME additives 'burn off' rather too easily, leaving the oil without enough.  Additives are used for many functions.   Just how often to change oils, based on time and mileage, depends CONSIDERABLY on how the engine is operated, the type of oil, etc.  

Use of premium oils is sometimes warranted, sometimes not.   In the over-all expense of operating a vehicle, oil is almost always a very miniscule cost; thus, use of a better oil, that protects better, is something that will pay off....particularly if the owner intends to keep the vehicle a long time.

There are a LOT of specialized tests done on oils, that are not generally talked about, besides between lubrication engineers. 
While I mention, in this long oil essay article, how some oils 'burn off' some of their oil rather quickly, I don't get into it deeply.   But, it can affect your wallet....compared to oils that don't seem to hardly burn much....all in the SAME engine, same circumstances of use, etc.   Just one of these tests is called the NOACK.  That test is supposed to simulate what happens at the extreme temperatures oils are exposed to in all engines, at very specific places.  Most of the time, when engine oil temperatures are talked about, it means the oil temperature in oil tanks (dry sump engines) or oil pans.  But, you probably know that oil that is circulating in the HEAD is exposed to much higher temperatures around the valve guide, and other areas of the valve, particularly, of course, at the exhaust valve area.  But, think about the CYLINDER AND PISTON AREAS.  The cylinder walls ARE lubricated, in EXTREMELY thin oil layer amounts....fraction of a drop, perhaps, over the whole cylinder.  That oil comes in contact with the VERY hot top piston ring(s).  Thus, the NOACK test is done at 250C (yes, Centigrade).  That is 482F  !!!     All engine lubricating oils will 'evaporate' or 'burned', or otherwise changed, by such temperatures.
Unless your engine is using a very tiny amount of oil per oil change period, your actual oil cost might be higher with some oils that 'burn off' quickly...if you have to add oil. 
This is just one tiny example of 'oil talk'.

The balance of this article delves fairly deeply into lubricating oils for vehicles, how they do their job, recommendations, hints, etc.

ZDDP (and ZDTP):

ZDDP (zinc dialkyl-dithiophosphate) is a common anti-wear additive for use in mineral-based oils.  ZDTP is approximately the equivalent (zinc di-thiophosphate), which is normally used in synthetic oils.  Both are usually just said to be ZDDP in common usage.  Both have been used as an anti-wear ingredient in engine oil for many decades. The zinc and phosphorus ingredients are most effective when they are used together. ZDDP and ZDTP are some of the many additives that are put into conventional motor oil to improve lubrication qualities.


Many premium motorcycle oils are produced with large percentages of synthetic components, and may well have quality additives that will last longer than the commonly accepted (and often WRONG!) 3,000 mile change intervals.   It depends CONSIDERABLY on the 'quality' and amount of additives, and particularly how the motorcycle is ridden....such as very short 3 mile trips in high humidity or cold weather perhaps...versus over 20 mile average trips.    Changing oil too often is also, contrary to popular belief, not a great idea. I know that sounds wrong....and the reasons are complex, so I won't get into them here.  If you do not believe, me, do some of your own research!! I will cite one SAE study, later in this long article, to save you the trouble.   

There is also a POSSIBLE problem with the word synthetic. Due to a lawsuit (not absolutely true, but best thought of as a lawsuit) won by Castrol (versus Mobil), a judge made a ruling that even today should be considered wrong (in MY opinion!).  He ruled, my words here, that a highly refined petroleum oil, not REALLY a complete full synthetic oil, can, if the manufacturer wished to, be called synthetic. Because of this ruling, so-called part, or even full-synthetic oils!! that are on the market may not truly be high quality REAL synthetic oils. Another problem is that there are several types of base synthetic lubricants, and they are NOT all of the same quality!  I will get into them later in this article.

Another problem is that, except for most of the specialty motorcycle oil makers (who are better at NOT changing formulas), commonly available oils can...and do.... have their formulas modified, without the oil makers telling you.   The bottom-line on "synthetic" oil is that for PRACTICAL purposes, if they contain reasonable amounts of ZDDP (for your AIRHEAD bike or other vehicle that really should have it), they are ALL likely going to be OK and you CAN go further than you may think before needing an oil change.

Diesel and/or 'fleet' oils like Rotella-T and Delo and Delvac are all likely to have SOMEWHAT reduced amounts of ZDDP in them now...and perhaps even less as time goes on. 
Delo is perfectly OK for a gasoline engine.  Do not think these oils are 'only for diesels'. If curious enough, get the manufacturer's literature and read the fine print, particularly the characters (letters and numbers) that describe the approved service for the oil.   While air-cooled motorcycle engines are much harder on oils than water cooled motorcycle engines (or car engines), these 'fleet' oils may well do just fine for you.  You may save some money, if that is important to you regarding engine oil.

Your Airhead NEEDS ZDDP; but does not need the very high dispersant and some other qualities of SOME diesel oils that might, especially in the past on CD diesel oils, give problems. I do not recommend willy-nilly all modern diesel oils for Airheads.  You might carefully select one, but I am not 100% endorsing them any longer. I do think that probably Rotella and Rotella-T, and Delo, are OK.. at the time I updated this particular paragraph (April 2011).     The ZDDP is not all that needed on Classic K bikes, although the first several years (1983-1986 perhaps) of the Classic K bikes probably do better with ZDDP in their oils, and ALL K engines can actually benefit a bit.  Modern car oils have little or no ZDDP, as the zinc component of ZDDP tends to poison catalytic converters.  Modern car oils are typically energy saving (and so marketed and marked), are usually in thin grades such as 5W30,...and are absolutely NOT compatible with your Airhead, and not good for your K bike either. 

There is a lot of confusion over SAE graded oils, and ZDDP.   Very simply-put, if a viscosity grade of oil is deemed by the SAE and vehicle industry to NOT be a car/truck grade, then the oil manufacturer may put such as a goodly dose of ZDDP into the oil.  Doesn't mean they HAVE.  20W50 is such a grade.  Thus, a premium motorcycle oil maker MAY put lots of ZDDP into a 20W50.   He may do it in 10W40, 15W50, these are not considered car oils by SAE.

More information is in my 52B article and my viscosity article.

Thick oils, that is, oils with higher viscosities, have more internal friction, and CAN support larger loads....but!...there's always a but!, EH?......HIGH mechanical pressures of/in the parts themselves INcrease oil viscosity.  This is another of those common sense things that says "WRONG"...but.... Yes, it is true.   When oil is inside a common bearing, and the bearing has lots of pressure (think conrods, as one example), the effective oil's OWN thickness INcreases.   This is so even with the ends of the bearing open.  This is a special property of "thin oil films", and has very little to do with mechanical pressure in and of itself as a trapped medium.  Yes, I know this all sounds wrong.

A THIN (lower viscosity number) oil is vastly easier to pump and thereby get through the 'system', and INTO VITAL AREAS QUICKLY, and will support massively heavy loads. So, a manufacturer uses tighter tolerances on those bearings, less clearance and a thinner oil.  This engine then needs more oil pump pressure, but that INcreases fluid friction.  No entirely free lunch here.   Another factor is high rotational speeds.  The faster the surface speed, the more the oil is formed into a cushion, which allows even higher loading.     There are many types of surfaces in our motorcycles.  Some slide, some roll, some are fluid-based.  There are a lot of forces and peculiar things at work.     

Oil and oiling/lubrication is HARDLY just some sort of liquid slippery stuff!

What folks sometimes want to know is how lubrication really deals with friction.  You can't eliminate friction on a practical basis; but, you can minimize it. Many decades ago, schooling about friction was a sort of 'hills and valleys' type of discussion in describing forces that resist sliding motion.  In other words, parts that looked smooth, really had microscopic hills and valleys and it was those that caused the friction of the parts.  That concept is rather obsolete now.  It still applies, of course, to such as breaking-in of new piston rings, and most other areas... to SOME extent.  BUT, today, with modern fine-machining, the MORE important concept is ADHESION; and, lubrication engineers may sometimes find extreme problems that they need to solve: cold-welding of surfaces in contact. When a full film of lubricant separates surfaces, the only friction is from motion WITHIN the fluid. When you stop to think about this, it DOES, YES, sound crazy!    Common Sense is wrong, for the 3rd time, in this article you are reading.

Here is what really happens: The fluid splits into layers.  The top layer sticks to the surface, bottom layer sticks to the lower surface, and each successive layer travels at a lower speed, which shears the layers on either side.   Oil "film" is what does the lubricating (not absolutely true on a REAL engineering basis, but good enough for us, here). There are several types of 'oil films'.  The hydrodynamic film is only perhaps 0.001" thick in a 1 inch bearing.   Surfaces are kept apart by several functions, one of which is the hydrostatic function which is primarily from oil pressure from the oil pump.  Thus, ONE of the purposes of the oil pump is to provide this 'keep the surfaces apart' oil pressure inside the bearing, etc.  This is critical when there are slow heavy loads and also for starting up of the engine.  Please be sure to read this small paragraph again....Oil slipperiness is not really involved!   If you jump to the conclusion that poor oil pump pressure (or, same effect, from excessive bearing wear clearances) can cause problems would be correct.

If the oil film gets too thin, metal contact is possible.  Typically this won't happen until the film is ten times less thick than that 0.001" mentioned.  At that point, you want additives like ZDDP, etc.  Some additives found in larger amounts, in diesel oils in particular, can cause problems in HIGH SPEED engines.  Thus, one of the reasons I am hesitant to fully approve diesel oils in high rpm engines, is those problems.   Some of the old CD-x diesel oils were like that.

From what you have read so far, you now understand that you do not want too thick an oil, nor do you want too thin an oil.  There IS A REASON that 5W30 or 10W30...and possibly 10W40.....are all too thin (and have other not great characteristics).... for most Airheads and K bikes riding in mild temperatures.  There IS A REASON that 15W50 or 20W50 oil is most often recommended. This also applies to K-bike engines.

As parts speed up, other factors come into play. Required or specified oil viscosity can be juggled somewhat by the engine manufacturer.  INcreasing viscosity will allow more loading, but then you get higher temperatures; and less immediate oiling.  SPEED of the parts means faster shearing of all layers, but speed helps form a cushion, so higher speed means higher allowed loading (read that again, and think about what you have heard about 'lugging' an engine). The best approach for a manufacturer is usually to use a reasonably low viscosity oil, with very good thinning characteristics (high viscosity index) so it does not thin too much with temperature rise.  When the K bikes came out, BMW contracted with Spectro Oils to produce an oil specifically for the water-cooled K bikes.  BMW then promoted that oil (a bit slyly when they did that for Airheads, it wasn't the very best for them, although 'adequate').  The oil that Spectro made for BMW was NOT Golden Spectro, and was not standard Spectro either.

In the very beginning of the K-bike production, BMW was having problems with the K bike starter sprag drive clutch not engaging, and finally BMW redesigned it by adding more sprags and more holes for better oil flow. The updated assembly gave far fewer problems, but some problems still remained now and then.   BMW offered a full synthetic oil later on.   Mobil 1 works quite well, with VERY FEW reported problems with ANY starter sprag clutch.  What happened when the starter sprag clutch began to fail is that it would slip after some sort of unseen glazing film or wear (shape wear?) accumulated; and, perhaps, some loss of sprag clutch springs tension;...and synthetic oils helped a did some synthetic additives in the Spectro synthetic oil as well as the original Spectro from BMW. The Mobil 1 brand has 15W50 and 20W50 oils specifically for motorcycles; although Mobil does change, irregularly, on the exact formulation of what is being sold.  They do have an oil that was designed for Harley Davidson's, the V-Twin oil.....there have been various names for that oil over the years.  It has a goodly amount of ZDDP in it, and seems to be very good in Airheads.  I prefer the 15W50 Mobil 1 for the K1, K75, K100, K1100, K1200.  However, some have used that oil for the Airheads.  I haven't made up my mind on it.
Rislone, and a few other additives, perhaps the stronger CD2... used once if needed.... would sometimes free up the K bike starter sprag clutch, which is a VERY HIGH labor-charge job to replace; and the part is not cheap either.    It is actually possible to remove a failed later type starter sprag clutch and clean it (PROPERLY!!!) and have it work again...but few do that, due to the intense labor, if the cleaning does not work well.

Synthetic and Conventional Oils:
This particular section was plagiarized from several combined internet articles, and highly edited by me.
I claim NO copyright for this particular section.  Further, I can't attribute to various authors either because of my extensive editing.

Oils are categorized in groups by the type of base stock they are made from.

Group one oils. These are the old high paraffin (wax) base oils. They are not used for modern engine oils anymore but can still be found in those little bottles of all-purpose household oil you buy at the hardware store for stuff like oiling door hinges.

Group two oils:
This is the standard petroleum base stock that all modem conventional petroleum oils are made from. Quality varies widely depending on where it was "dug up from". Even in "finished" form it can contain various amounts of paraffin (wax), impurities left over from refining and from the ground it came from. Chemically it is a hodge podge of different sized hydrocarbon molecules, not all of which "get along with each other" to speak. The result of this is a product that produces sludge, varnish and mechanical wear as it ages and breaks down in service.    That does NOT mean that this is not a good usable oil for many purposes.  These oils have steadily been improved over the years as API services requirements have gotten stricter. However as modern engines pump more horsepower from smaller engines with less total oil sump capacity and the level of horsepower/torque transmitted though today's light weight fuel efficient drive trains continues to climb, lubricant manufacturers find that conventional petroleum oils really just cannot be improved any farther. Hence the move we see by automakers to synthetic fluids; both in engines and transmission/differentials. Combine that with the need to improve fuel economy (and synthetic lubricants have the ability to do just that) and you can see why "factory filled with synthetic" is becoming more and more common in cars and some bikes.

Group three oils:
Group three oils are petroleum oils that have been hydroisomerized, "hydro-cracked" as it is commonly called. This is the most stringent level of petroleum oil refining. Much of the paraffin and impurities have been removed and its performance on any number of industry tests is substantially better than Group Two. Although not made from truly synthesized engineered molecules and as such is not a true synthetic oil (as far as I am concerned!, see just below paragraph), it does offer a goodly portion of the benefits you would expect from a true synthetic and in fact is usually sold and marketed as a 100% synthetic product. The vast majority of synthetic oils on the market are actually made from group three oils because of a "lawsuit" some years ago between Mobil and Castrol, that totally changed the synthetic oil industry. Because of this lawsuit the buying public has largely been duped into believing that these oils are actually a real synthetic. Mobil Inc., makers of Mobil One (Mobil 1), sued Castrol Inc., makers of Castrol Syntec, accusing them of marketing a hydro-cracked petroleum oil as a synthetic. Mobil's primary argument was that Castrol Inc. had pursued an unfair market advantage because Group Three based oils are much less expensive to manufacture than true synthetic oils, yet Castrol was marketing Syntec as a 100% synthetic product. Castrol could make it for less, sell it for less and un-fairly under-cut ($) all it's competitors in the synthetic oil market with a oil that was not truly a synthetic product.

In the end though, Castrol convinced the judge that a Group Three based oil has been sufficiently refined that it should be able to be marketed along with true synthetic oils. Basically the court expanded the definition of synthetic to include group three based oils. Because the synthetic oil market is the fastest growing part of the lubricants industry, manufactures are eager to jump up and grab the profits for sexy-customer-grabbing-word "synthetic" on the bottle.  Group three oils do not have the performance of true custom engineered synthetic oils, especially in temperature extremes. The vast majority of what is being sold as synthetic are really Group Three petroleum based oils. The public for the most part doesn't know the difference.

Group four oils:
Polyalpha olefin and related olefin oligomers and olefin polymers. Synthetic hydrocarbon or PAO's as they are commonly called, are a true man-made-engineered base oil produced by catalytic reaction with various alpha olefin compounds.  PAO's are widely recognized as providing outstanding performance for many lubricant applications because of very high viscosity index, a wide operational temperature range and because they are thermal and shear stable.  PAO's also have low promotion of corrosion and are compatible with mineral oils and the range of materials that engines and other machinery are manufactured from.  The molecular structure of PAO's are easily customized for use in all kinds of applications from automotive to industrial and are widely used in motor oils, gear lubes, high temperature/extreme pressure greases, compressor oils and hydraulic fluids.

Group five oils:
This group comprises all synthetic oils other than PAO's. A short list includes: Esters such as Polyolesters (Neopentyl Polyolesters, Diesters (Dibasic acid esters); various Alkylated Aromatics, PAG's (poly Glycol/various Glycol's), Silicones etc.  This group of synthetics is primarily used for various industrial and aviation applications. Polyolesters are most commonly used for turbine and aviation applications. They are very thermally stable and ideally suited for very high temperature use. Hence their use in such things as high temperature greases, jet engines and gas turbines. They have a very low coefficient of friction and are sometimes added in small amounts to mineral oils and synthetic oils to lower the coefficient of friction of the finished product.  Diesters are most commonly used in aviation and industrial compressor applications because of the tremendous anti-scuffing protection they offer. They are often added in small amounts to PAO-based two-cycle oils as this feature is very beneficial to a two-cycle motor oil. Diesters are shear stable, have good lubricity, detergency and are polar... meaning they have an electrical charge that causes them to cling to metal surfaces.  THAT is a desirable trait for most lubricants. Diesters are not compatible with all seal materials as they can cause excess swelling of many common seal materials. Because of this they are often added in small amounts to automotive PAO based oils to provide positive seal function.  Silicones offer wide temperature performance and are sometimes used in compressor applications although this use has fallen out of favor in recent years. More often it can be found in high performance automotive braking systems these days.   I HIGHLY suggest you do NOT use DOT5 silicone brake fluids.   A discussion of why is in the brake and chemicals articles.

Why Choose Synthetic Lubricants?
Motor oils are comprised of two parts, the base oil and additive package. The base oil comprises 80-90% of the oil by volume and the additives the remaining 10-20%. There are five groups of base oils stated above: Group I, II, III, IV and V. Groups I to III are refined from crude oil containing tars, asphalts, waxes, aromatics & other things. These crude oils are "cleaned up", to the extent possible, by hydrocracking and filtering. The group III base oils are the best of this genre. However, they still contain variably-sized molecules and some contaminants that can result in sludge, varnish and other deposits in your engine. Moreover, the quality of group III base oils vary greatly due to differences in the feedstocks and refining methods utilized.
Synthetic oils are group IV (PAOs) and group V (esters) base oils. These synthetic oils are "man-made" synthesized uniform molecular structures that significantly improve the efficiency and effectiveness of these oils relative to their petroleum oil competitors. More specifically, these oils have lower coefficients of friction, better thermal (heat) and pour-point (cold weather performance) properties than do petroleum oils. Synthetic oils have no waxes, tars, or other contaminants to sludge or varnish your engine.
Synthetic lubricants are initially more expensive, but may pay off when you consider their extended oil life (and engine-life) capabilities, in addition to their improved performance.

One must be very cautious about using the various Group IV and V oils; they may not be compatible with seals in some vehicles, and as seals are usually made by more than one manufacturer, the seal material may not be necessarily compatible with an oil even though the seal has the SAME part number.   Still, these are THE best performing oils. 

If you need ZDDP in the oil, that is, you have an Airhead cautious, be sure the oil has ZDDP, perhaps at least 1000 ppm, and not over perhaps 1800 ppm.   There are other characteristics that are important too.


More...for the even more technically-minded, on oil functioning:

Looking at extremely tiny irregularities in as-machined and broken-in surfaces, a LOW viscosity oil allows the oil to creep into very small microscopic areas.   As the load increases, the oil is squeezed between the parts and dynamically increases the oil viscosity; which allows higher load carrying.   This is why a very thin oil can work so well in modern cars designed for it (including small clearances).  This is why a 10W30 or a 5W30 or even 0W-30, all being very popular or SPECIFIED today for cars, works so well in modern cars (which don't have flat tappet designs), and modern engines last so long (precise machining, proper selection of compatible materials, expert design for lubrication, improved oils, etc.).   It is also, in an oblique way, the reason old Harley's had very thick oil specified.    I'm NOT putting Harley down here, just telling real facts.  One could say the same thing about many old engine designs. ...and some of this really does apply to such as flat tappet old performance cars, Porsche boxer engines, and so on (and Airheads) I described earlier herein.

Oil wedging is a fundamental principle.   Let me begin by discussing a rotating crankshaft; a crank journal, and a conrod big end.

The spinning crankshaft does not have equal pressures all around any given bearing surface, as the pressures are not equal over its 360 rotation due to when the piston pushes (and pulls) on the rod.   In the bearing area itself, the parts are ever-so-tiny eccentric to each other...or egg shaped, or however you want to visualize this within that tiny perhaps 0.001" bearing clearance.   This eccentricity drags oil into a wedge-shaped layer between the journal and the bearing, which LIFTS UP THE SHAFT, so the shaft is SUPPORTED by the oil film.   Yes, all this happens in that oh-so-thin mechanical clearance. AND, yes, it is true that the eccentric-ness comes mostly during, another reason that break-in oil is changed sooner, rather than a 'normal' mileage.

Some shafts that rotate inside of bushings are supported by a wedging of AIR...there is either NO lubrication medium like oil at all!....or just some to allow no excessive friction as the parts START spinning-up.  Most old-time aircraft spinning instrument gyroscopes were like that...and many turbines work that way (granted, with huge loads and oil to keep things cool).   You are probably sitting at a computer screen, and the computer next to you has a FAN, and a HARD DRIVE, that use AIR bearings, to some extent or other.  Yes, air can be a lubricating medium.   Any problem MIGHT BE just as the device starts up....before the bearing is air supported. THAT is usually handled by a very TINY amount of lubricant, perhaps totally invisible.

An even deeper discussion would describe how oil leaves the wedge at a higher velocity than it enters, and then a discussion of fluid back-up.  Since oil can't really be compressed into a smaller volume, its pressure builds up instead; but, this is not intended to be a course on lubrication engineering and fluid I'm not going to get too deep into things...just a wee bit more!

These things about rotating parts also occur in sliding parts....just not nearly as easy for me to describe and for you to understand.  So, no sliding discussions (pun intended!).

In a reciprocating engine some parts are changing direction, a shaft is shifting position, and things move about, perhaps until equilibrium, and the shaft essentially centralizes in the oil film...well, ALMOST!  The oil film is squeezed, forced to move around the shaft, but the viscosity (thickness) pushes back against this change, and that resistance ADDS to the load supporting capability....up to a point anyway.   The high-brow term here is 'squeeze film'.  
As rotational parts speed increases, there is a point reached where oil friction suddenly increases...a LOT.  This critical surface speed is where the oil lubricating film starts ceasing to be a laminar flow (layer-like), and becomes a turbulent flow.   This MIGHT give you some idea about why some race-bikes have oiling failures under some conditions.  You can increase oil viscosity, or decrease it, you can change types of oil, you can increase oil pump pressure, you can do all sorts of things including changing clearances...but, there are limits for each bearing, and many a racer has found those limits!

Getting deeper into how thin oil films work in the molecular region is way too nerdy for even this article.  It would get into what is really meant by oiliness, adsorption, more on hydrodynamic lubrication, how the film can be penetrated, and so on. When I studied this sort of stuff, I kept my notes; and my industry information, and they, mostly typewritten on both sides of the paper, are several inches thick.   Lubrication is a VERY complex subject, it is still evolving.

I probably should quit here. Probably bored 99% of you anyway!!

I'll make it simpler from here on....

ZDDP is important for Airhead engines.  ALL ZDDP is NOT the same.  Zinc dialkyldithiophosphate is both an antioxidant and an antiwear agent, and most formulations are somewhat volatile to a bit too volatile.   As the oil standards specified by car makers and the SAE went from lower to higher letters (SG to SM, as example), the oils had less ZDDP.  Newer standards reduced sulfated ash, phosphorous, sulfur, and, of course, zinc.  The reduction in zinc was to keep the $$$ catalytic converter from being contaminated which reduces or eliminates their prime function; the other reductions were to lengthen the lifetime for the Oxygen Sensors on modern cars and bikes.  Think about what I just said about oxygen sensors.  You DO know that your K1100, etc., has one?   Yes, that means you do not want a high ZDDP level for K bike oils, but you need SOME on the earliest of the K bikes (1983-1986).   It is a trade-off.  

Most SM oils still contain some ZDDP, but in a less volatile formulation.  This prolongs cat converter life, but still provides some antiwear protection for engines with high slide-to-roll ratios.   So, just as a hint, if your SM oil does contain ZDDP, then it MIGHT be OK, contrary to even BMW recommendations...but you need to KNOW.

Oil drain intervals, etc: This is a vastly misunderstood item.  My information comes from REAL industry experts, not just my personal opinion.    It is true that car makers tests show that drain intervals of 7500 miles are usually OK, even more in some instances. NOT NECESSARILY SO for your Airhead, especially with conventional dino petroleum oils. Oil wears out from high heat in air-cooled engines (particularly around the valves areas).  NOTICE ALSO, that ...and this is hardly widespread knowledge!!......fuel economy DEcreases quite a bit after about 4000 oils burn off the protective anti-friction additives.  Contrary to popular belief, that is, that ZDDP protection does not even come into play until things are awful... it is not so. 

There are quite a few things that degrade oil over time and mileage.  This includes fuel dilution, contamination from combustion byproducts that escape, typically through rings leakage; incomplete scavenging of crankcase vapors; oxidation, and the shearing action of the engine's mechanical parts.  For water cooled vehicles, it takes very little in the way of a cooling system malfunction, to shorten oil life.....and, a stuck-open thermostat is one of the worst things to have happen...the engine cooling water runs too cool, and so does the oil.  For air-cooled engines, the heat around the base of the exhaust valve (spring area) can be so hot that oil that passes by this area is degraded rather quickly.  This is VERY VERY COMMON.

I have mentioned how not changing oils TOO often is better...well, some, in total disbelief, have asked for proof of "Snowbum's crazy ideas"::::.......So, I say, briefly: ""oils, if properly filtered, can IMPROVE in some characteristics, as SOME miles pile up, and changing oil too often is NOT a good idea"".  For just one of a number of articles on this subject:

Obviously, there are limits.  Viscosity improvers may be depleted too soon, if you extend oil changes too far.  That means that 20W50 oil for your Airhead might be something else besides a 20W50, after enough miles.  If you had a motorcycle with the GEARBOX being lubricated by the engine oil, things can be much worse for the oil, as the gears WILL shear the longer-chain-molecules of the oil.  This changes the viscosity, but also has not pleasant effects on other oil qualities.   Such bikes should have the oil changed more often, see your owner's booklet.

In general, for BMW Airheads, and most situations of use, a 4000 mile change interval....provided it is at least probably OK.  You might even go longer on a K bike, particularly if you use a quality synthetic such as Mobil 1.  Older worn engines need oil changes sooner.   Diesel oils have a lot of dispersants in them, to deal with the soot and particulate formation and greater level of crankcase gases.  A quality diesel oil, with ZDDP, may still be the best answer to someone wanting a relatively INexpensive oil for their Airhead...but I can no longer make specific I no longer even ...well, keep up with changes to them; which are hard to get details about.    Another concern for oils is the moisture that collects in oils in engines that do not come up to proper operating temperature for a long enough ride.  If your typical ride is under 20 miles in cool weather, and certainly if under 6 miles in any weather condition, you should consider changing oil sooner.  Vehicle makers used to include these types of usages as being 'severe service'.

Multiweight (multi-grade) oils are generally vastly better than old-time single weight oils, for a variety of reasons.  Multiweight oils are typically manufactured using pour-point depressants to THIN the base it flows and pumps easily when cold.  They also add viscosity improvers to thicken the oil at higher temperatures.   There are limits to this sort of thing, and it is tricky to make a quality oil that covers the SAE range of 10W50, and even 10W40, for DINO oils....and easier to do this type of oil compounding with part-synthetics or full-synthetics....which, naturally, cost more. 

The Europeans usually have tighter specifications for their oils...especially car oils...than we have here in the USA.  I won't get into it any deeper in this article, it will only confuse you.

Oil recommendations for AIRHEADS:

 For Airheads, due to the variability (I think!) of some heat-treated parts, and due to the type of cam and followers;
 I can recommend the following oils:
(1)  Mobil 1 V-Twin in 20W50 grade.  You can usually extend the drain intervals due to this being a full
      synthetic oil.   This oil can be pricey, and I am not sure it is worth the money; but drain intervals,
      assuming longer touring miles than city traffic miles, could be quite long.  This oil has
      plenty of ZDDP in it, is a good formulation in all respects.  I have one big reservation about this oil IN might get some leakage at the seals.  Only SOME FEW have reported this.  I don't use
      this oil myself in my airheads.  
(2)  Mobil 1 in 15W50 is probably usable, but I can't give a blanket 100% OK.  BUT, if you want to use a
      synthetic, this is likely one of the best (see #1, above, too). Perhaps, in mild to hot weather, (1), above, is better.
(3)  Golden Spectro 4 in 20W50.   This is a no-nonsense premium oil, it can also have SOMEwhat extended drain intervals, as it is a
      part-synthetic.  I have considerable experience with using this oil.  Excellent quality.
      This oil also has an excellent base stock.  It is my favorite Airhead engine oil.  It's formulation has
      remained constant.  There are NO seal problems with this oil, on ANY Airhead, of ANY year.
(4)  Golden Spectro 4 in 10W40.  Same comments as above, but use only when the weather is under
      perhaps 40F.
(5)  BMW 20W50 NON-synthetic motorcycle oil.  This is a good oil, but not quite as good as the above
(6)  BMW full synthetic oil:  I don't have experience and don't have enough information to comment further.
(7)  Valvoline 4-stroke motorcycle oil, in 20W50 (or 10W40 for quite cold areas).  Not as quite as good as
      (1) to (4) but plenty good enough.  The phosphorus content is 0.103%; calcium 0.182%; zinc 0.112%;
      sodium 0.052%. For those not wanting to take a chance on seal problems with Mobil 1 versions,
      yet wanting a less expensive oil than the BMW or Golden Spectro 4, this might be a very good choice.
(8) Shell Rotella-T in grade 15W40; calcium 0.27%; zinc 0.135%; phosphorus 0.120%.  This is a good oil,
     can be purchased at quite a savings, in larger than quart sizes.  It is often referred to as a 'diesel' oil,
     which it is. It is possible that the formulation will be changed, but that is the latest laboratory test
     information I have on it, and due to those tests...which also cover other qualities of this oil, I STILL
     think it likely quite decent-enough for Airheads.  This comment is being made in October 2012.

      DELO 400 oil contains 0.119% phosphorus and 0.148% zinc.  Last time I looked the spec sheet was
      showing those values, and dated in 2011.  It has always been a good oil.
(9)  I cannot recommend Castrol motor oils, of ANY type EXCEPT for: Castrol's 4T oil, (and Grand Prix
      oil, which is the SAME OIL) in either grade 10W40 or 20W50, as appropriate to your climate.  These
      oils are SG rated and formulated.  Zinc component is 1100ppm; Calcium component is 1900 ppm;
      and Phosphorus component is 1000 ppm. 

Do NOT use cheap energy saving (so marked, and probably have starburst symbol) car oils in your motorcycle. 

If you make ONLY short trips (under 8 or 10 miles), change your oil every 3 or 4 months.  If you ride now and then for over 20 miles (especially well over) at one time, you might be able to extend the changes to 6 months...or even a year.  

The Euro specification that is tighter and more strict than what is in the USA, is ACEA-A3.  Look for it on some products in the USA nowadays. 
  Do NOT use the latest CJ-4 oil, as it is only so-so for our bikes.  

Remember, if you use synthetics, that they are NOT all the same!  Be SURE yours has ZDDP, and a goodly amount, for your Airhead. 

If you ride a fair amount in rather cold weather, especially below freezing, I strongly suggest a lighter grade than 20W50, or 15W50.  10W40 perhaps.    Consider even a 10W50 synthetic.

Do NOT use cheap oil filters in your Airhead.  Use the two-part hinged filter, if you can.   The K bike can safely use all sorts of filters, I use BMW branded ones, you don't have to.  The K bike has the filter upside down, so there is no need for a drain-back valve in the filter.  NOTE:  I do NOT like ANY FRAM filter!!!


****DO NOT use K & N air filters!! *** .. if you want to know why, see the K & N filter article:  click

ZINC....ZDDP; 'special' break-in oils, etc......expanded section...:

Just what is ZDDP....ETC.:
ZDDP is zinc dialkyl dithio phosphate.  ZDDP was originally developed in 1930 and introduced for the purpose of oxidation stability in engines with plain bearings...protecting the copper-lead material.   ZDDP still has that purpose, but it also has at least one other use. It is usually considered to be the lubricant of last-resort, when two metal surfaces rub each other....and the 'protection' begins just at or around the time actual metal contact is about to, or does begin, that is, the oil film is failing to protect as intended.   For reasons far beyond this reasonably short (??) reply, the wiping action of cams and tappets are particularly hard on oils.  ZDDP (or ZDTP) is in the oil to prevent oil film failure (or give protection if the film fails).  ZDDP has other characteristics, and its protection really begins long before real metal contact begins.

It was found that it has excellent anti-scuff properties.  It came into wide use much much later.  In the 1960s, high performance flat-tappet camshafts were common.  It was found that a zinc level of 0.07% was very helpful.    Back in the 1960s, all new camshafts were generally phosphate-coated, and together with the ZDDP in the engine oil, the brand-new camshafts and lifters were protected from premature wear, particularly during the critical break-in period.   As engines became more powerful, and pressures on parts increased, the level of zinc was increased to 0.09%.  Oils changed too, becoming much more complex, and additives for friction modifications, antioxidants, detergents, etc., became common and more sophisticated.  Fuel economy began to be of some concern, and the zinc content was continually increased, with premium oils commonly having as much as 0.2%....into the 1980s and 1990s.

Zinc Phosphate is not really a direct lubricant....UNTIL IT GETS QUITE HOT.   When two metal surfaces rub each other, the microscopic top layers can be extremely HOT, yet the part be quite cold in comparison.   ZDDP is often called the "lubricant protector of last choice"; which is NOT entirely true, it actually has good properties long before that point.
However, most folks talk about ZDDP as the Last Resort:  so.....   That means that when the oil film fails, ZDDP should be taking over, giving you some goodly added protection.  The actual way ZDDP works is not easily found in literature.   When it gets hot at the surface interfaces, it creates a phosphate glass on the surface.  Extremely thin, but it IS THERE.    It has been compared to a painter's primer coat.  The engine oil is the top coat in this scenario.  YOU NEED A HIGH LEVEL OF ZINC DURING BREAK-IN TO ESTABLISH THIS PHOSPHATE GLASS COATING.  You also need an adequate amount of zinc for long-term cam, followers, etc., protection, even after the glass layer is established.  It is well recognized (within the performance engine builders community) that a high ZDDP level is very beneficial for roller camshafts, lifter bodies, lifter bores, roller rocker arms...especially where high spring pressures are used at the valves.........not just flat tappet applications.  ZDDP protects valve tips and pushrod tips.  Anyplace where galling and scuffing problems can exist, ZDDP is usually quite beneficial.  However, on a practical basis, large amounts of ZDDP are not necessarily a good thing for such as a water-cooled BMW K bike engine.

It is not zinc, but phosphorus content that is the biggest item of importance in ZDDP, as far as wear goes. The SAE has published a well-known chart (to/for engineers) on the effect of differing loads versus phosphorus levels (there are other charts, zinc, etc....not important right here).  Most of these types of charts (there are a lot of them) are presented as lifter loads, in pounds, versus ZDDP or Phosphorus, and the criteria is scuffing of parts.   What is interesting about the charts is that the curve is NOT linear, particularly so at LOWER concentrations of phosphorus.    At lower loadings, only a concentration of maybe 0.03% is needed.  At higher loadings...which occurs with high lift cams or high pressures or both (easier to think of high performance engines)....concentrations of 0.08% are needed.  What is needed means that MORE than that amount is required, due to burnoff of the additives, and for a safety factor.  One last thing on that concentration business.  Way more than needed is NOT good.  The charts show that if the Phosphorus concentration goes over 0.14%, then wear starts to INcrease.  At 0.20%, wear is definitely accelerating fast.   This means that there is an optimum range of ZDDP concentration (and, for the revised modern oils, the Phosphorus concentration).   That is why you will see that many makers of motorcycle oils keep the phosphorus component down AROUND 0.12%.   BTW.. .that is same as 1200ppm.

ZDDP amounts have been reduced in MOST ALL car engine oils, in fact, now are almost completely eliminated.  That is because the zinc and phosphorus contaminate the $$$ catalytic converters.  At the early stages of reductions, phosphorus limits were lowered to 0.10%, and zinc levels were dropped also...but quite long ago.  In 2004 came the so-called Tier 2 emissions standards, and OEM warranties changed to 10 years or 100K miles, and phosphorus dropped again, to 0.08%...and zinc went down to 0.09%.   The levels are much lower now....or, gone.

Note that it is the phosphorus that gives the main protection in our motorcycle engines, but that requires the zinc to establish the glass layer.  For cars, it is the zinc that is damaging to the catalytic converter.   That means that car oils with the lower or no zinc formulations, do not allow formation of the phosphorus glass protective layer in our motorcycle engines, no matter how much phosphorous is in the oil!

There is no question that, for modern engines, modern oils are VERY SUPERIOR.   These oils and the more precise automated machining are a big part of why engines can last 250K+ miles these days.  Improvements in metallurgy and machining, even cooling of parts, etc.   The BIG problem is break-in of the cam and followers and other parts, when brand-new.  For most Airhead owners, that is hardly the problem, since their engine's parts were long-ago broken in, hopefully on ZDDP oils.  BUT, the zinc (and phosphorus) are needed continuously in Airheads; and if the cam, etc., was NOT heat treated well-enough, or perhaps not broken in on a proper oil....deterioration will set in.  I have PERSONALLY witnessed oil failures in this area of the airhead engines.     High spring loads compound the problems.  In a nutshell, EPA regulations, SAE and engine makers and car makers have all 'conspired' against the type of oil YOU NEED for your Airhead.   Luckily such oils are available.  One of the reasons for the availability (besides specialty makers of 'motorcycle oils') is that there are a few quirks in the rules, which recognize only certain viscosity grades as 'car oils'.   There is a break-in article on this website.  Yes, that was a hyperlink.  You want proper ZDDP levels in your break-in oil, and still in your regular oil after break-in.


Racing:  break-in, etc:


Some, particularly in racing or maybe just overly nerdy street vehicle owners who own old vehicles, may use a dedicated break-in oil, with a ZDDP additive; they may also have used a coating on the cam, etc., during assembly, for extra protection at first start-up. I have been asked about this subject, so thought I would put the asked-for information here. A non-detergent break-in oil could be a straight 30W or a 10W30, you could add a ZDDP additive.   You do not have to do that.

Your regular engine oil needs to be AT LEAST 1000 PPM of ZDDP.   Many diesel and fleet oils contain adequate ZDDP.  There are specialty oil makers who have oils specifically for flat tappet engines, break-in and regular running.  
So, for the EXTREMELY NERDY.....

Joe Gibbs oils...BR and BR30.  They have a special break-in oil, with 2800 ppm zinc...!!!...this oil was developed for quick break-in and dyno runs.    They have a BR oil in 15W50.  These specialty oils are often used where the oil is preheated, the new engine started, and is put on the dyno right away. 
They also have a Hot Rod Oil, with 1200 ppm ZDDP, in 15-50, 10W30, etc.  It is LOW detergent...did you know that HIGH detergent levels can wash-away the ZDDP somewhat?  This oil has extra additives for especially long term storage for classic cars...rust protection, corrosion protection, etc. One change a year for the typical classic car show type use.   The Joe Gibbs MicroZol BR and BR30 are good oils.

Brad Penn company.   American Refining Group makes Brad Penn Racing oils.  They offer a straight 30W oil with high levels of zinc and other antiscuff additives, called Penn Grade 1. ...specially formulated to help rings seat fast.   
Royal Purple company...makes a Engine Break-in Oil.

ZDDP additives from such as Comp Cams (159 ZDDP additive).

Red Line has a high-ZDDP break-in oil additive.

Trick Flow TFS-9400.

Eastwood 50332Z.

Isky Racing ZDDP PLUS. 

Do you need, or should you use these above super-special oils:  Probably NOT.

Miscl. section:


***A GOOD rule of thumb for decades, and still good, is that you should NOT use a full-synthetic oil for break-in....especially if new piston rings were installed or a fresh cylinder boring or honing job.  

***Fully synthetic oils may not allow your Airhead lifters to properly rotate!!   I have NO direct experience!  But, this bit of esoterica is ONE of the three reasons I do NOT fully recommend full-synthetic oils for Airheads.

For Airheads:  Some past 'wisdom' was that the cam, rings, etc., will be broken-in within 500-1000 or so miles, and then you can switch to a decent ZDDP-containing non-break-in oil.    Frankly, don't bother, just start and break-in the Airheads on one of the recommended oils in my list above. I use Golden Spectro 4 usually in 20W50, more rarely in 10W40.

If you are a nerd or quite anal...go ahead and coat your cam, etc., with a good ZDDP protectant, during assembly.

***Under NO circumstances, but an emergency, EVER use a car type engine oil if the container has a API starburst symbol; NEVER EVER for break-in...and try to never use it at all....

Cam lobe profiles differ from engine design to engine design.  Some cams have relatively a fast acting 'ramp', some do not, and some have lobe characteristics that are very hard on oils.   Cam lobes may look identical to the casual #1 eye-ball, but they may be vastly different, even when they look the same, right next to each other.  Cams and followers/tappets also vary in heat treatment.  It is my belief that the oil film failures seen on some Airheads, and likely some VERY EARLY K bikes, are, at least partially...and maybe the major cause.....due to the variability with the cam and followers heat treatment.   I know of some motorcycles with VAST mileages, run on cheap car oils, that have had NO problems.  I know of failures from common car oils.  Note that 'energy saving starburst marked' oils have been on the market long enough, I think, for enough problems to be reported on motorcycles.   I do think we will see more and more problems reported as unknowing owners use car oils.   I think this will slowly accelerate as more riders do their own maintenance on old bikes, and use the cheaper car oils, for either convenience or cost or both or, as said, 'just don't know'.  What you will likely see with the oiling failure is scored cams and followers/tappets, possibly microscopic (to larger) cracks in the surfaces.   Actual engine failure will occur on some engines.

ZDDP versions 'activate' at differing temperatures, and by temperature I am not referring to crankcase oil temperature as much as I am referring to near-contacting surfaces.   Differing versions of ZDDP are used in heavy-duty diesel engine oils and different versions in synthetic oils for compatibility purposes.   There are real reasons some oils were specified for some engines and some oils forbidden in others. This was a problem a number of years ago.    There are numerous European (and """Japanese""") specifications for oil, as well as our U.S.A. SAE and API folks (together with the oil companies AND THE CAR MAKERS) ideas on labeling and specifications.   There are "substitutes" for ZDDP used in many, if not most, modern oils.  They are NOT adequate for some engines, such as our Airheads.

For a vehicle out of warranty, it is the owner's choice as to the brand, type, and grade of the oil.  You may....or may not.....get away with using an unapproved type of oil in your engine.   K bike engine internals have a deservedly good reputation for not needing attention, other than oil changes and rare valve clearance adjustments, for huge amounts of matter the oil.  This is likely changing, and will likely change for th p

Zinc content is usually expressed as a percentage or parts per million.  Either way is OK.  For engines that really should have ZDDP in them, my personal feeling is that concentrations near 1500 ppm are likely optimum, and over 1800 is not needed and detrimental, and under maybe 800 or 900 is not enough.

What oils does Snowbum use?  I settled on one trusted oil for the Airheads so I have not used any other oils for decades:  Golden Spectro 4, usually in grade 20W50.  I use only one oil for my K bike, a synthetic, Mobil 1, in grade 15W50.  I don't bother to differentiate between the several Mobile 1 types, extended or not, gold cap or silver cap.  I sometimes get it from Wal-Mart in gallon jugs when they have it.   Mobil also makes a 20W50 for V-twins, that one is good too (Airheads also), but I prefer a 15W50 for my K bike, and the protection levels of the additives in the "Harley oil" is likely overkill for the K, but very good for the Airheads.  These are hardly the only good (IMHO) oils available.  Should the day arrive when I can't easily obtain Mobil 1, I will use Spectro Full Synthetic, in my K bike.

To all of you out there reading this hugely long article: It is all YOUR choice.   I have only tried to inform.
Believe what you want.


01/25/2007:  slight revisions and editing for clarity.  Remove poor formatting.
01/22/2008:  edit slightly for clarity
07/12/2008:  minor clarifications
07/14/2008:  more clarifications
02/27/2009:  Update by adding the entire addendum #1, and making minor corrections otherwise, in line with changes by SAE, etc.
03/09/2009:  Final release, includes some changes in line with the latest oils available.
08/09/2009:  updated
11/16/2009:  Add last section
01/21/2010:  minor updates and clarifications; add script to code
04/13/2010:  updated
04/21/2010:  Add to section on ZDDP
06/18/2010:  Updated the airhead oil recommendations to include the caveat on Mobil 1 V-Twin oil, and changed the commentary slightly for the Spectro GS4 20W50
09/01/2010:  added hyperlink to SAE article
11/12/2010:  slight updating, mostly for clarity and poor grammar.
11/18/2010:  add ppm of zinc for 4T oil
02/24/2011:   was 52C
04/10/2011:  Fix K & N article internal hyperlink and clean up entire article SOME
08/03/2012:   Get much deeper into synthetics, etc.
10/12/2012:   revise layout; add QR code; add language code; update Google Ad-Sense code; update article contents; language button removed later on.
11/05/2013:   clean up article...still is messy!......clarify a few details...
03/03/2014:   Revise article for clarity; add Ph and Z info on Delo, etc.
07/16/2014:   Minor additions, no revisions.

Copyright 2014, R. Fleischer


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