Essay on lubricating oils for BMW motorcycles, engine oils

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Applicable to Airheads, K-bikes, and most other engines.
Understanding how oils REALLY work/operate/function.
LUBRICATION you've never heard before!
What things you should consider in selecting oils; how often to change them, etc. 

© Copyright 2007, 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.    The BMW Airheads are MEDIUM-older technology.  The BMW Classic K bikes (K1, K75, K100, K1100, and some into K1200) are more modern.

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 even more not necessarily true for the ability of the particular oil to deal with acids that accumulate in the oil, and, a few other properties.

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 mileage per start, all lead to oil contamination and degradation.  Some synthetic oils are compounded with longer-lasting additives to deal with contamination, & oil change intervals can be safely extended, DEPENDING on your riding habits, whether you do many very short trips (less than 40 or so miles), etc.   

You may have heard that it takes 10 miles or more to heat up the oil enough to 'burn-off' accumulated moisture (moisture in the oil is VERY damaging over the long term).  The wording of those statements should be: "begin to burn-off".   Under about 8 miles or so, little moisture is burned-off, and it takes about 20 to be meaningful....and can take a lot more, in MANY circumstances.

Most modern seals are neoprene or silicone types, USUALLY not needing specialized swelling agents. Keep in mind that your Airhead, or even Classic K bike, might have early seals in it, that are NOT all that compatible with your full synthetic oil.

For Airheads, one of the important protective additives is some form of ZDDP/ZDTP for flat tappet (flat cam follower) type of operation, in enough...but not way too much...concentration.   The early classic K bikes, roughly 1983-1986 K100 type bikes, also need this protection.  Few seem to know about THAT.

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 of the additive.  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 and super-premium oils is sometimes warranted, sometimes not; depending on many things, especially including how long you will own the vehicle, over how many miles.   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 USUALLY 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 in those engines.  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, oil that is circulating in the HEAD is exposed to much higher temperatures around the valve guide, and other areas of the valve.   This is particularly so 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 250°C (yes, Centigrade).  That is 482°F !!     All engine lubricating oils will 'evaporate' or are '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 considerably higher with some oils that 'burn off' quickly...if you have-to, or want-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.

Special notes, regarding modern CAR oils IN CARS!

Things have changed since very approximately 1990, radically so in some instances, in what type of lubricating oil is needed for modern cars.   I am not speaking here of certain things in the following article about ZDDP and ZDTP that are needed in some old flat tappet cars, nor in the Airheads, nor in the earliest K 100 models, etc.  I am deviating for just a moment here to offer you some cautions, as failure to understand and keep these things in mind can cost you a HUGE amount of money.  There are several situations that have become big expensive problems for car owners.

1.  The use of small extremely high speed turbochargers is becoming very common.  While SOME
     designs have oil reservoirs to protect the bearings during engine turn-OFF, others do not.  This
     means that much more frequent oil changes and using ONLY approved oils (approved
     specifically by brand and model of oil by the car manufacturer) are a NECESSITY.
2.  Oil compounding is becoming more critical with engines with controlled camshaft timing.
3.  The use of NON-top-tier gasoline causes problems with carbon deposits that can, and will,
     produce real driveability problems that are $$ to fix.  For a list of distributors/refiners that
     sell Top Tier fuels, see:  Click around at the headings at the top.
4.  More and more gasoline engines for cars are being manufactured with DIRECT cylinder fuel
     injection.  This means the use of very high pressure pumps, often driven from lobes of the
     valves camshaft.  Oil has become critical for these engines. Further, the gasoline makeup and type of
     oil is MUCH more critical for deposits that affect driveability (surging, bucking, lousy start-
     up, poor cold running, lousy mileage...and more).  It is DIFFICULT on many of these engines to
     clean-up the carbon mess.  Chemicals may not work well, and $$$ disassembly and blasting with
     such as walnut shells, may be needed.  Removing and replacing a head or two heads for this
     is NOT CHEAP.

The bottom line, for CARS, as a general rule, is:
Use ONLY! the brand, model, and grade, of engine oil and engine oil filter, that the car manufacturer has recommended.   
DO NOT DEVIATE, even if the oil retailer says it meets the specifications by the car manufacturer.  If the car manufacturer
has nothing about your proposed oil in its APPROVED oil and filter literature, PASS!!!

NOTE, especially, that modern oils for cars are usually classified as 'energy saving', which has connotations FAR
beyond those words! 
  Use of high dosage additives (30% is not unusual) and thin oils (5W30 or 0W30, etc.) is
common.  VERY strict attention to engineering the engines is necessary to support the use of such oils.  Modern engine
design and construction is SO GOOD that it is now considered 'normal and expected' for engines to not require
valve jobs or piston rings, etc., for 1/4 million miles.  Burned oil smoke coming out of the exhaust is mostly a memory
from the era before the eighties.  This is true for the BMW K bikes.  It is less true for the Airheads.  If the Airheads
had been water-cooled, they, too, could have lasted much longer.  As it is, Airheads usually need a top end job
by 80,000 to 120,000 miles.  The earliest Airheads, before the Nikasil cylinders, would usually be on the low edge
of those figures.  But, enough on this, because I could write more paragraphs, and bore you.

ZDDP (and ZDTP):

NOTE that these two additives are NOT in all engine oils,
and when they are, the concentrations vary...a LOT!

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 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 possibly 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, be called synthetic. Because of this ruling, so-called part, or even full-synthetic oils!! that are on the market may not truly be the highest 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 or characteristics!  I will get into them later in this article.  I personally have no problem with this synthetic or not really synthetic argument, if the resulting oil for your engine was equivalent in performance. UNfortunately, they are NOT, usually, very close.

I am going to be BLUNT here.  Castrol...and some other companies....know quite well that the Public is not knowledgeable about oils, and these companies know that the public is typically enamored with buzz-words, such as Synthetic, Laser, etc.  Yes, those words were once producing 'outer space' sort-of emotions.  Super-Tech ideas for the Public. These companies also know that the vast majority of products are purchased by PRICE, not quality.  Many companies have made quite a lot of money, for decades, by selling worthless products for vehicles, like certain additives you put in the fuel tank, or the engine oil.  I am NOT saying Castrol products are like this, not at all. What I DO want you to understand is that there is a lot of misleading advertising, part-truths, insufficient information, etc.    I suggest you be somewhat cynical about what you purchase.  I HOPE you have reasons to believe ME, over someone else, or some advertising.    Maybe, just maybe, you will read this article, and some of my other articles, and get the idea that I view myself, and hope you do too, as an educator, trying to help those who do their own work, or be knowledgeable about what is done to their vehicles by others. 

Another problem is that, except for most of the specialty motorcycle oil makers (who are better at NOT changing good formulas), commonly available oils can...and always do.... have their formulas modified, without the oil makers telling you.   

The bottom-line, SIMPLIFIED, about "synthetic" oil, is that for MOST PRACTICAL purposes, if they contain reasonable amounts of ZDDP or ZDTP (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.  Some will burn off faster at the beginning, and that costs-you; but you will probably overlook this.  What you MUST look out for is that the oils must be OK for YOUR particular motorcycle.  Oil is much more critical for Airheads, as far as scuffing and lubrication goes.  HOWEVER, FOR THE CLASSIC K BIKES, USE OF THE PROPER OIL, A FULL SYNTHETIC, IS VERY LIKELY TO GREATLY EXTEND THE LIFE OF THE STARTER MOTOR SPRAG CLUTCH, WHICH IS BURIED DEEP INTO THE ENGINE AREA, AND IS VERY COSTLY TO REPLACE.

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.  These oils are NOT '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 or ZDTP; but does not need the very high dispersant and some other qualities of SOME diesel oils that might give problems, especially in the past, on CD diesel oils. I do not recommend all modern diesel oils for Airheads.  You might carefully select one, but I am not fully endorsing any of them. I do think that probably Rotella and Rotella-T, and Delo, are OK.. at the time I updated this particular paragraph (April 2015).   ZDDP is not much needed on Classic K bikes, although the first several years (1983-1986 perhaps) of the Classic K bikes probably do better with more ZDDP in their oils, and ALL K engines can actually benefit.  Modern car oils have little or no ZDDP, as the zinc component of ZDDP tends to poison catalytic converters.  The substitutes in modern car oils are NOT adequate for Airheads.

Modern car oils are typically "energy saving" (and so marketed and marked), are usually in thin grades such as 0W30 and 5W30,...and NO Energy Saving oil, of ANY viscosity is fully compatible with your Airhead, and not all that 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, API, and vehicle industry, to NOT be a car/truck grade, then the oil manufacturer may put such as a goodly dose of ZDDP and other stuff 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 also not considered car oils.

More information is in my my and articles.

From this point onwards in this article, I will begin to get more technical at times.

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 makes you THINK that it is  "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 oil's effective thickness INcreases.   This is so even with the ends of the bearing open to 'release trapped oil'.  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 quite 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, stable alloys, and so on, 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, as ONE example. 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 (OIL) 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 the 'keep the surfaces apart oil pressure' inside the bearing, etc.  This is critical when there are slow heavy loads and thusly for the 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 gasoline engines, are those problems.   Some of the old CD-x diesel oils were like that.  NOTE that diesels are used in many cars, particularly common in Europe, and some of these engines are RELATIVELY high rpm types.  Thus, the specifications for diesel engine lubricating oils have changed over the years.  The Europeans were very much better at this than the Americans.

From what you have read so far, you 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.  There are even oils with a wider range, like 10W50.    While MUCH less true today; decades ago, multi-grade oils in the wider ranges were not all that good, not much better than straight grades, at least after some miles.  Not so today.   Today, straight weight oils have little use in 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 the oil 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.  Golden Spectro was a BETTER oil, than BMW oil, IMO.  There were problems with early K bikes with petroleum oils, that were mostly cured with the use of full synthetic oils, at the starter sprag clutch.  BMW modified that design more than once. 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 showed up 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 sprag shape wear accumulated; and, perhaps, some loss of sprag clutch springs tension;...and synthetic oils helped a lot (particularly with deposits buildup in the sprag clutch internals) 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.  BTW...Harley Davidson has gone to full synthetic oils.
Rislone, and a few other additives, perhaps the stronger CD2... used once if needed...for a hundred or so miles.... would sometimes free up the K bike starter sprag clutch, which has 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.

BTW...BMW is hardly the only company having starter motor clutch problems.  The common Honda Gold Wing uses what amounts to fat rollers or roller bearings if you wish, to provide a one-way clutch, and they have a habit of gumming up from oil residue varnishes, etc.  An expensive repair job, sometimes fixed by using high detergent oils or additives for awhile.  The BMW K bike starter sprag clutch is a high cost repair job, and the same high detergent additive routine can work here.    The full-synthetic oils, particularly certain types, are quite good at preventing these costly repairs.

SIMPLIFIED information on classification of types of lubricating base oils.
I will get into these things in more depth following this section.

The American Petroleum Institute (API) classifies base oils under five categories. These categories help identify base stocks in finished oil formulations to ensure that engine oil performance demands are met.

Group I: Conventional mineral oils derived from refining selected crude oil fractions. Solvent processing, first used in the 1930s to improve base oil performance, is still used today to produce Group I lubricant stock. While some automotive oils on the market use Group I stocks, they are generally used in less demanding applications.

Group II: With the development of “hydrotreating” and “hydrocracking” technology, refiners introduced highly refined, low wax base stocks, or oils. While refined to a greater extent than conventional mineral base oils, these hydro-processed base oils still have performance limitations due to the presence of undesirable impurities. Group II base oils are common in mineral based motor oils currently available on the market and have fair to good performance in lubricating properties.

Group III: Group III base oils are also manufactured using the hydro-treatment process but are subjected to higher temperatures or processing times. These highly hydro-processed, or “non-conventional” oils, have greatly improved oxidation stability and low temperature performance but still contain some undesirable impurities that cannot be removed. These high quality Group III base oils are now widely available in North America because they can be manufactured by most companies making Group II oils.

Group IV: API has classified synthetic engine oils made with PAOs as a special class of base stock. The term “synthetic” was originally used to refer to Group IV (PAOs) and V (see below) base stocks. With the growth of the PAO market, some base oil manufacturers began manufacturing Group III mineral oils that provide equivalent performance to PAOs, and marketing these as “synthetic” oils. In 1999, a ruling by the National Advertising Division of the Council of Better Business Bureaus broadened the definition of “synthetic lubricants” to include high-performing products made with Group III base stocks.

Group V: These specialized base oils, with few exceptions, are chemically engineered stocks that do not fall into any of the categories previously mentioned. Typical examples of Group V stocks are esters, polyglycols and silicone.

Note:  Terms and words used in the petroleum industry, to which you possibly have been exposed-to, are not very descriptive to laypersons, and I am going to mention some of these terms briefly here, and if you are interested in a more in-depth discussion, simply do a search by any common search engine, such as Google's.

MINERAL base oils MEANS petroleum-based oils, from crude oil, from oil wells sunk into the ground.  These types of oils replaced animal, vegetable and fish oils in the 1800's.  Mineral (petroleum) oils are made from crude oils by several processes, a few of the major ones are hydrocracking, hydrogenation of various sorts, waxes isomerization...but, always, the prime method is distillation.

"Paraffins" means the molecules are branch-chains, or straight-chains, of hydrocarbons.
"Aromatics" means the molecules are what is called Alkyl Benzenes.
"Naphthenes" are Paraffins in a RING form of molecules.
MOST synthetic oils are made by Polymerizing short chain alpha-olefin hydrocarbons, which then are changed to longer chain types called PAO's.  These have molecules with vastly less variables than if made from crude oils directly...although chemically they are similar in many respects.

Synthetic and Conventional Oils:

This particular section was plagiarized from several combined internet articles, and then 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 (American Petroleum Institute) 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 much 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.  I am not about to dig deeper in this Group Two into arguments about super-modified petroleum oils that are or are not to be considered synthetics.  Castrol won that argument in court, as you saw from reading much earlier and below in this article.

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 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, manufacturers are eager to jump up and grab the profits for the sexy-customer-grabbing-word "synthetic" on the bottle. Some car makers are starting to specify synthetic oils, particularly on turbocharged engines.   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 synthetic 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 or early K motorcycle (and many other motorcycles not just BMW) 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.  ZDDP is used generically here, as ZDTP is more likely to be in synthetic oils.


More...for the even more technically-minded, lots of nerdy stuff too.....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, another story), 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 applies to 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-small eccentric to each other...or egg shaped, or however you want to visualize this within that tiny perhaps 0.001" bearing clearance.
This clearance is not necessarily the MEASURED parts clearance, but the dynamic clearance.....  more or less.

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 totally invisible lubricant.

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 normal oils 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 these things......but!....some more, a bit simplified, is appropriate:

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 VERY considerably.  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!   Therefore, just raising the rpm range of an engine is NOT simple for a manufacturer.   Many modern engines have very high redline limits for RPM, it was NOT easy for the manufacturer to design and build such engines, and many have very high effective combustion pressures, exceptionally high compression ratios, etc.  The pressure on bearings is intense.

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, is still evolving.

I probably should quit here. Probably bored 90% of you anyway!!

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

ZDDP (or ZDTP) is important for Airhead engines.  ALL ZDDP is NOT the same.  Zinc dialkyldithiophosphate is both an antioxidant (you never hear about THAT) 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 $$$ catalytic converters 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) due to their design, which was changed in a few areas, and not really advertised as such for lubrication purpose.  Thus, use of ZDDP and ZDTP in K bike oils 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 anti-wear protection for engines with what is called "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 (good enough term for us here) 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.  Popular belief is that ZDDP protection does not even come into play until things are awful (such as metal-to-metal)... this 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 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.  Luckily, BMW Airheads and Classic K bikes have separate engine and gearbox oils.  However, SOME oil shearing does occur on these bikes.

In general, for BMW Airheads, and most situations, a 4000 mile change interval....provided it is at least OK.  You might even go longer on a K bike, particularly if you use a quality synthetic such as Spectro's full synthetics or Mobil 1 in motorcycle viscosity grades.  Sometimes twice as long.  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 a reasonable answer to someone wanting a relatively INexpensive oil for their Airhead...but I can no longer make specific I no longer try to keep up with changes to them; which are hard to get details about anyway.    Another concern for oils is the moisture that collects in oils in engines that do not come up to proper operating temperature on shorter rides.  This is very particularly so with dino oils. If your typical ride is under 20 miles in cool and/or high humidity weather, and certainly if under 6 miles in any weather condition, you should consider changing oil sooner rather than later.  Vehicle makers used to include these types of usages in owner's manuals as being 'severe service'.  Another factor is the amount of sulfurs in the fuels, which varies by season, Country, manufacturer, etc., for which you will have a nasty time finding out about.

The following is for a BMW Airhead motorcycle: 
If you are going on longer rides, say over 50 miles in mild weather, and most of your riding is on such longer rides, and seldom quite short ones, you can likely SAFELY EXTEND oil changes by a fair amount.  In some instances even two years and 12,000 miles, but this would be about the LIMIT, under best conditions, and would be for a Motorcycle specific, High Quality, FULL synthetic oil.  For a high quality part-synthetic, such as Golden Spectro 4 in 20W50 or 10W40 grades, I advise changing oil at not over 1 year and 4000 miles, but SOME riders might be able to go 6000. 

Multiweight (multi-grade) oils are now 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.  Even back as little as ~1990, to get a good 10W40 oil was difficult (the standard was 10W30 for cars); today we have 10W50 oils that are excellent.    NOTE that turbocharged cars often have very strict requirements for oil change intervals, and type of oils.  Think about this....ask yourself WHY!  Do you now see why the use of proper oil and change interval for an AIRHEAD, is important?  YES, it is the HEAT at which the oil is exposed to, inside the engine, that degrades the oil!

The Europeans usually have tighter specifications for their oils...especially car oils...than we have here in the USA. The present 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.  
 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 recommend the following oils. NOTE THAT THESE ARE NOT LISTED IN ORDER OF PREFERENCE, except as noted specifically.

(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 or ZDTP, & 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.   A better substitute is Spectro's Platinum full synthetic.  It seems to be
       well-compounded, with no seal problems in Airheads.
(2)  Mobil 1 (not the V-Twin version) in 15W50 is probably usable, but I can't give a blanket
      100% OK.  BUT, if you want to use a full synthetic, this is likely one of the better ones (see
        #1, above).  If you want additional protection for an Airhead, use (1), above.
(3)  Golden Spectro 4 in 20W50.  A no-nonsense premium oil, it can also have SOMEwhat
       extended drain intervals, as it is a part-synthetic and is well designed and compounded.  I
       have considerable experience using this oil. Excellent quality & has an excellent base
       stock.  It is my favorite over-all 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 40°F.
(5)  BMW 20W50 NON-synthetic motorcycle oil. A good oil, not as good as the above oils.
(6)  BMW full synthetic oil:  I don't have experience & don't have enough information to
       comment further.
(7)  Valvoline 4-stroke motorcycle oil, in 20W50, or 10W40 for cold areas.  Not quite as
       good as (1) to (4), but good enough.  Phosphorus content is 0.103%; calcium 0.182%;
       zinc 0.112%; sodium 0.052%. For those not wanting to chance seal problems with Mobil 1
       versions IN AIRHEADS, yet wanting a less expensive oil than the BMW or Golden
       Spectro 4, this might be a good choice for AIRHEADS.
(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 also 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.
(9)  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.
(10)  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 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; Phosphorus component is 1000 ppm. 


Do NOT use cheap energy saving (so marked, and probably have starburst symbol) car oils in your motorcycle, particularly NOT in Airheads.  You CAN in an emergency.

If you make MOSTLY short trips under 10 miles, change your oil every 3 or 4
months and 2000 miles.  If you ride now and then for over 20 miles (especially well over), you might be able to extend the changes to 6 months...or even a year.  If using PART synthetic oil, you can add a few months or so.  If using FULL synthetic oils, doubling the recommendation is likely OK, but since this is iffy, perhaps you had better NOT.

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 MAY BE only fair for our bikes, and it is very difficult to find CJ-4 oils that actually have the proper ingredients and amounts, such as ZDDP.  

Remember, if you use synthetics, that they are NOT all the same!  Be SURE yours has ZDDP or ZDTP, 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 is my recommendation.    Consider even a 10W50 synthetic.   Use a motorcycle specific oil, such as a Spectro product, preferably a part or full synthetic.

***Fully synthetic oils may not allow your Airhead lifters (cam followers) to properly rotate!!   I have NO direct experience!  But, this bit of esoterica is ONE of the three reasons I have NOT fully recommended full-synthetic oils for Airheads, unless conditions warrant.  I believe the oils I have recommended, above, are OK in this regard.

Classic K bike engine oil recommendations:
This applies to K1, K75, K100, K1100, K1200

Because of potential $$$ problems with the starter sprag clutch, and some other things, I am recommending ONLY FULL SYNTHETIC OILS for the engine.  The owners booklet has a chart of the recommended grades.  My  article has the chart too...a late version.  My recommendation includes Mobil 1, and you do not need the V-Twin version of Mobil 1, but if you have a 1983-1986 K bike, that oil is better.
  Spectro Platinum is also recommended.

Do NOT use non-premium 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 filter is upside down, so there is no need for a drain-back valve in its filter.  NOTE:  I do NOT like ANY FRAM oil filters.

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

WHY a mention of an AIR filter in an OIL article?....because ordinary atmospheric air is somewhat (to 'considerably') 'dirty', and those contaminants often are very hard microscopic particles, and CONTAMINATE THE OIL, and DO wear your engine out.

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

Just what really 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; the one YOU have probably head about. 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.  Much of that is not fully true, this is a simplified explanation.  The wiping action of cams and tappets are particularly hard on oils.  YES, 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.  I earlier in this long article mentioned some of the ZDDP/ZDTP characteristics and why JUST thinking about it as The Last Resort protectant, is WRONG. 

Yes, it is true, that that ZDDP has excellent anti-scuff properties.  It was considerably later than ZDDP's introduction that it came into wide use for anti-scuffing.  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 any sort of what you might want to call 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, as I have noted, 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. 
Modern CAR oils with little or no zinc (zinc poisons catalytic exhaust converters) use substitutes, often phosphates...but the establishment of the glass layer is not good at all, for AIRHEADS.   Airheads have parts that vary in factory hardening, so SOME have had no problems using car oils for vast mileages.  If YOU try that, YOU are the Test Pilot for YOUR engine.

That is why ZDDP or ZDTP is also helpful for K bike engines, but particularly the earliest ones, which had different metallurgy but more important, different cam characteristics, etc.

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. 

So, ZDDP has that glass-forming coating, established at break-in, and this is quite microscopic, and then it protects in other ways, as time and miles accumulate (not to mention that it renews that glass like coating as needed, one hopes).

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.  Additives cost more than the oil stock does.  You can read into THAT quite a lot!  You can also think about the fact that it takes ZINC to establish the proper glass layer from the phosphorus (Phosphates), and ZINC is bad for cat oil mfrs make compromises, that are not necessarily good for your Airhead bike!

One last thing on this 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 CAR 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 saying 1200ppm.
NOTE that some very pricey specialty oils are made with VERY HIGH concentrations.  They are marketed for special break-in purposes primarily.  I am NOT AT ALL in favor of these FOR YOUR BIKE.
  The prime purpose of using these oils is for racing, where fast break-in is needed at times for the ultimate maximum possible horsepower, etc.....note how often these engines are overhauled!  There is a section, later in this article, that gets deeper into these oils.

ZDDP amounts have been reduced in car engine oils, now ZDDP is almost completely eliminated.  That is because the additive contaminated 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, again, 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 full phosphorus glass protective layer in our motorcycle engines, no matter how much phosphorous is in the oil!
   If you do not have the zinc and phosphorus, you will not obtain the protective glass layer.

There is no question that, for recent generation car engines, modern oils are all that is needed.   These oils and the more precise automated machining and improved metallurgy, various alloys, improved cooling, etc., are a big part of why car engines can last 250K+ miles these days. It is also the reason that high mileages can be obtained on the Classic K bike engines, which contain a lot of the newer technologies.  

Establishing protective layers or very hard layers, on cams and followers, is dealt with by many small changes in modern engines, allows break-in of the cam and followers and other parts, when brand-new, without needing ZDDP. 

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 valve spring loads compound 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 still 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
article on this website, that covers a LOT more, on HOW to break-in an engine, assemble it, ETC.

There is some information on oils, with the heading title of "Information on acceptable engine oils:"
in this linked article:
I DO suggest you stop here, read just that section in that article, then resume, here.

Racing:  break-in, long-term storage, 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.....and DO keep in mind that I recommended earlier in this article that you do NOT USE SUPER HIGH ZDDP OILS as there ARE problems with using too much ZDDP! is some information for reference purposes:

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? (Yes, regular CAR oils have HIGH detergency).  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, if used for the design purposes.  The Hot Rod Oil is good for long term storage.

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, unless conditions warrant.

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. I use Golden Spectro 4 usually in 20W50, more rarely in 10W40.  Break-in an engine that is newly rebuilt, or overhauled, or a top-end has been done, according to my break-in article.

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 Energy Saving 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 because they '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 the future.  The Classic K bike really SHOULD have a good synthetic will 'burn' less, and have less-likely problems with the starter sprag clutch, a pricey repair job.

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 do Snowbum use?  I settled on one trusted oil for 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 V-Twins oil, 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 (maybe not for the 1983-1986 K models), but very good for the Airheads.  These are hardly the only good (IMO) oils available.  Should the day arrive when I can't easily obtain Mobil 1, I will use Spectro Full Synthetic in my K bike.

Disregard information you may have heard about sulfurs in GL5 being bad on Airhead rear drive brass or bronze parts. NOT TRUE.
The bad information is a hold-over from PRE-Airhead days.
Here is the information, in case you want it:
This is where BMW advised about the changeover on early BMW bikes from engine oil or early versions of gear oil (usually we say GL4) to GL5 hypoid rated oil.
From Barrington Motor Work: Chris Betjemann's
BMW/2 Motorcycle Restoration and Service Manual
(A Guide for the BMW /2 Owner/Restorer)

BMW AG Recommended Lubricant changeover: oil to hypoid
(By Model and Serial number/engine/frame No.:)
                     R50               R60                     R69
Trans         646358         1814032                663565
Boot           646 486        1814032                    "
Shaft               "                   "                          "
Final Drive  641 986       1810001               661445

More information on this subject is in my other oil articles.

Here is a link to an article about oils, especially for motorcycles, and it has some different, and interesting, viewpoints.  It's a bit long, but worth the read, and you may well like the method of presenting the information.

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. 
You will do that anyway.


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.
09/03/2014:   Clarify some areas, and do a further cleanup on 09/07/2014 and finish on
12/26/2014:   Add lengthy note near top about modern car engines and their needed oils and
                        filters.  Revise article, eliminating some font sizes, adding minor notes and corrections.
04/03/2015:   Add simplified section.
05/01/2015:   Update article

© Copyright 2007 and 2014, R. Fleischer

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