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© Copyright, 2014, R. Fleischer I suggest you read article 51-C:
http://bmwmotorcycletech.info/oilessay.htm I STRONGLY suggest you read article 51A. It is near mandatory for an Airhead owner to know the things in 49 through 51D. This article below glosses-over the highly detailed information provided in article 51-A ...particularly about the oil canister and the so-called $2000 O-ring, the paper gasket, and the metal shim. The earliest Airheads, when not equipped with a BMW cooler, came with a three bolt outer plate, and an inner metal cap cover held to the canister center pipe by means of a single large bolt. This system is nearly foolproof. At least one or more Haynes books are wrong in not even illustrating this version! ....and Haynes wrongly labeled a later models sketch for the /5. For the cooler models, the canister, central pipe, and the outer cover were changed, and there is no internal metal cap cover and thus no single bolt at the internal cap cover. BMW later changed the oil filter chamber and cover parts for ALL models, and they became much more similar to the parts used for the cooler models. But, now, the general parts, with minor changes, were for both cooler & non-cooler.
It has information about engine oils that are becoming a problem for Airhead owners. You will be vastly better informed. It also has a very much in-depth discussion of how oils really work, and much more, including more information about changes.
Some notes on oil changes for your Airhead:
I suggest you read article 51-C:
I STRONGLY suggest you read article 51A. It is near mandatory for an Airhead owner to know the things in 49 through 51D.
This article below glosses-over the highly detailed information provided in article 51-A ...particularly about the oil canister and the so-called $2000 O-ring, the paper gasket, and the metal shim.
The earliest Airheads, when not equipped with a BMW cooler, came with a three bolt outer plate, and an inner metal cap cover held to the canister center pipe by means of a single large bolt. This system is nearly foolproof. At least one or more Haynes books are wrong in not even illustrating this version! ....and Haynes wrongly labeled a later models sketch for the /5.
For the cooler models, the canister, central pipe, and the outer cover were changed, and there is no internal metal cap cover and thus no single bolt at the internal cap cover. BMW later changed the oil filter chamber and cover parts for ALL models, and they became much more similar to the parts used for the cooler models. But, now, the general parts, with minor changes, were for both cooler & non-cooler.
This is some very simplified information, because it is not intended to be 'how to do an oil and/or filter change'. Please read the other oil articles, in particular: http://bmwmotorcycletech.info/oil.htm. Looking carefully at the other oil articles, including the oil sketches is also important!
In my opinion, for a normal oil only change (not changing the filter), I'd not drain the cooler. I'd not remove the outer cover at all. I would not loosen the banjo bolts if you have a cooler model. I would check the banjo bolt tightness with a torque wrench, and check that neither hose was touching the inside of the fairing, if one had a fairing. If a hose was touching your fairing (assuming you had one), I would loosen the associated banjo bolt only just enough to allow you to reposition the hose, with mild force on the banjo metal. If you have to remove or greatly loosen the banjo, then replace its two washers (two gasket washers per banjo). You must re-torque the banjo bolt to specifications. DO NOT reuse the 4 washers. Two types of washers are usable. The aluminum ones are 07-11-9-963-130, the better (less chance of cracking damage) are the copper ones 07-11-9-963-132. Keep reading::::
The cooler will drain some when you undo the banjo bolts for a filter change. Further draining is not necessary. The amount of old oil left in the cooler radiator is fairly small. Drain it further if you want to. I never do.
If the cooler was drained in any way, you should properly refill it. There are two basic types of outer oil canister area covers for those bikes having coolers. The original type has a cylindrical part on the casting, and it contains a thermostat. The thermostat opens when the casting and oil are hot enough to warrant oil cooling. The other type of cover came with the later GS models. It does not contain a thermostat and looks like a flat plate with two ports. Inside that plate is a bypass hole, which, in the early versions of the flat plate, should be drilled out a bit, per a BMW Service Information (SI) bulletin. The information is in the main article, http://bmwmotorcycletech.info/oil.htm
For the thermostat version, refilling was originally to be done by installing a special 23 mm nose radiused (no sharp edges!) special bolt, designed to lift the internal thermostat, so oil from the engine could pass into the cooler, whether or not the oil and thermostat housing were hot enough. You would crank the engine (not start it) until the oil light went out ...usually a few seconds. However, there were differing instructions over the years. There usually was no mention of not starting the engine. Information was sketchy, and in some literature, and even the owners booklet, there was conflicting information. There were also some too-long cooler bolts shipped ...they can ruin the thermostat. The too-long ones can be modified rather easily to be equal to the proper length ...and the nose properly radius'd. In fact, these special bolts could be called drain bolts, because, if used for that, the filter will supposedly drain some back into the engine, without the outer filter cover being removed. Do it if you want to. I never do. I use the 23 mm special bolt only to refill the cooler.
More ideas, presented in only some literature, were that the main reason to fill the cooler (assuming it had drained some) was so that in very cold weather the thermostat would not 'suddenly' open, allowing a sudden surge of extra high pressure cold oil into the cooler, and thereby break the cooler seams. There is a bit of truth to that story. The literature I am talking about never seems to say much, if anything, about the two types of outer covers in use. One has a thermostat that shuts off oil to and from the cooler, the other does not. These various 'ideas' never seem to mention that on a GS, with no thermostat, the cooler can drain a bit after engine shutdown. Obviously you are not expected to find some method of refilling the cooler in cold weather after any engine shutdown, overnight storage, whatever. In truth, a teensy bit of oil may move into and through the cooler on the thermostat models, even when the engine is very cold.
For the non-thermostat GS models, you are supposed to not over-rev at start-up (1500 to maybe 2000 RPM could, perhaps, be considered the starting-up limit). I suggest that the next time the cover is off, you check the size of the cover internal bypass hole, which may need enlarging. In fact, in cold weather, on a GS model (no thermostat) you are even supposed to put a cover over the radiator! ...lest the oil be OVER-cooled, once under way.
For myself, I do use the 23 mm bolt at every filter change, to refill the cooler, because all my Airheads have coolers, with thermostat type oil chamber covers. But ......I first refill the oil canister after a filter change, by engine cranking.
If you have a BMW cooler, any model of Airhead motorcycle, no matter the cover: Both filling the oil canister area, and filling the cooler (23 mm bolt on thermostat type cover), are done by cranking the engine without starting the engine.
I either ground the spark plug caps; or, more usually (since I don't like removing spark plugs unless it is necessary), I don't turn the fuel on, and I empty the carburetor float bowls. I recharge the battery after cranking, unless I am going to be starting the engine and riding.
1. BMW made some simplifications of the filters, after years and years of confusing folks. NOTE that they still confuse some people. I am NOT surprised. BMW sometimes forgets to package a part, or adds extraneous parts in oil filter "kits". BE SURE you understand what goes into YOUR bike, and that any filter kit, or purchase of filter area parts, includes what YOU need.
2. I recommend genuine BMW filters. If you are in Europe, perhaps you can get quality Purolator or Mahle filters. Fram filters are NOT on my acceptable list.
BMW's hinged filters are BETTER than the one-length (one-piece) filters. Hinged filters are STRONGER, and FAR easier to install on some models! ...in fact, the one-piece filters are near impossible to install on some Airheads. If you have a problem installing the hinged two-piece filters, simply separate the two at the plastic strap! However, they almost always will install without separating them, without forcing them, if you find the correct angle AND the correct position of the hinge during installation.
3. By now, the REALLY OLD filters (hinged...and not....with the confusing duplications of parts and numbers), are probably long since sold and gone. Still, for reference purposes I have them listed. On this website you can read the lengthy article 51-A, which will inform you of every possible thing I know about ALL the oil filters, canister area, etc. I DO recommend folks read it completely through, and follow the advice given. That is not a how-to step-by-step article, nor simplified. It was NEVER intended to be.
4. NOTICE that Haynes and Clymer's, and BMW's OWN LITERATURE ...are either wrong, or highly confusing! ...in their sketches for the canister area. BEWARE of anyone's sketches!
5. Those motorcycles with the internal cap covers have a VERY simple, just about foolproof system ...baring a sufficiently talented fool.
6. The -570 filter is used for the NON-cooler later bikes. With this filter, with its rubber at both ends, you do NOT use the medium size no longer available ROUND sectioned O-rings, and also you do NOT use the medium sized SQUARE sectioned O-ring that replaced the no longer available round one. Since that is probably confusing to you, just be aware of this: The -570 filter is hinged, and if it comes with a BONDED RUBBER tube at BOTH ENDS, EITHER end can be inserted first. The -570 is sometimes purchased by owners as part of a kit, the kit is 11-009-056-145. USUALLY one does NOT use the paper gasket in that kit. SEE website article 51-A for details on WHEN to use the paper gasket. This -570 filter is SHORTER (both filter parts are shorter) than the next filter to be described, the -575. Thus, the -570 filter, with its rubber ends, needs no other O-rings, EXCEPT the large white one...which is always the critical one, and which must ALWAYS be replaced. One metal shim ALWAYS goes against the canister metal, unless you have a lipped canister and measurements of canister depth say no shim needed.
7. The other filter is the -575. It is hinged, LONGER than the -570, and this longer one is for cooler-equipped bikes. It has bonded rubber at ONE end, that end goes in first. The outer end is not rubber bonded, and that is where the square-sectioned black rubber O-ring goes, it fits onto the groove for it on the outer cover. The metal shim goes on immediately after the filter. The large white round O-ring is the critical one. This kit is 11-009-056-146. YES ...ONE DIGIT away from the first one! I have seen these kits come with one or two small coppery washers, I don't use them. The kit may not come with the banjo bolt gasket-washers; you will need FOUR.
8. Both kits SHOULD come with one engine drain plug metal washer gasket. 20 foot pounds, max.
Acceptable engine oils:
If you want more depth, read:
Preface...The importance of proper engine oil:
Most any engine oil will work reasonably well for the engine, but there are specific areas of the engine that WILL BE damaged, and perhaps expensively, if the oil is not of proper quality and that means proper additives that are blended by the oil makers. The author's website, http://bmwmotorcycletech.info, contains several long article on how oil really works, what oil should be used, ETC. Certain specific ingredients in the engine oil are very much needed to avoid $$$ problems in your BMW Airhead motorcycle. THREE are critical. One of them is ZDDP (or ZDP). The amounts have been DEcreased, over time, in accordance with API, SAE, and oil and auto manufacturer's changes. Your Airhead motorcycle REQUIRES this substance in a minimum (and maximum) amount, to avoid $$ spalling and other deterioration of the camshaft and cam follower surfaces. Another ingredient is needed to be sure that under storage conditions, the cam and followers (and other items in the engine) do not have the oil dripping off and leaving the metal unprotected at engine startup. The final ingredient (of major importance) is that the amount of detergents (Increasingly higher in modern car oils) should not be excessive, as that defeats BOTH long term storage metal protection AND defeats the protection of ZDDP.
For some years, BMW has recommended that you DO NOT use SJ and later oils. Many have been ...more will be ...sorry that they used later oils. There is NO guarantee that SJ and later oils offer the full package of protection that BMW wants your engine to have. Old Porsche boxer and VW beetle owners (as well as early Corvettes and other engines with flat tappets) have similar problems. You MIGHT get away with these later oils ...and you might be the unlucky one. BMW's heat treatment of some parts has varied (they don't publish nor admit this), and for that reason alone (let alone other reasons), I agree with BMW in NOT USING THE WRONG OILS ...although I don't go quite with what BMW said about ALL those acceptable grades. BMW says to use SF, SG, or SH oils. BMW says that these can have a suffix of CD or CE. BMW also approved of CCMC-G4 or -G5 oils, and BMW says if the suffix of PD2 is on the container, that is also OK. I believe BMW is correct for the SG. I use Golden Spectro #4, in grade 20W50 year round in my airheads; and it IS an SG oil, and you can disregard the container markings that makes you think otherwise.
I will now explain the confusion, or attempt to explain it:
This is somewhat difficult, so bear with me. Many specialty oils, including Spectro's, have wording on the containers that you MUST take with a grain or two of salt (or, with understanding). If a manufacturer's oil does NOT have the SAE starburst seal &/or does NOT have full approval RATING & SPECIFICATIONS for SL or SM, ETC., then it is NOT REALLY such an oil. If the oil IS a viscosity grade that is NOT a car grade ...anything goes, well, almost. A car grade either has the starburst symbol; OR, has certain specific viscosity grades. A 20W50 is NOT am official car oil for modern cars. What SAE, the car companies, and the oil makers have done is to totally confuse some of the public, particularly owners of old flat tappet cars ...and old motorcycles (like our Airheads).
You might find the advertising or writing on the container saying something like this: "Meets and exceeds the quality requirements of SL". Be very sure you understand, that whether or not it says 'meets', or says 'exceeds', etc.....what it MEANS is that it is made to the QUALITY of the SL (or?) oil, but IS NOT ACTUALLY that grade NOR specification for that oil!!! You MIGHT see this for SG. Are you confused by this mumbo-jumbo? ...particularly the use of the word 'quality'?? Since Spectro, and other motorcycle specialty oils, were marketed for motorcycles, the wishy-washiness, in MY opinion, comes from them wanting to expand into CAR markets; or, just maybe, it is because it would take a number of paragraphs to explain just what they DO mean. I've never found it explained on their ...or anyone's websites, just here on mine. What I am telling you is TRUE about oil specifications and grading.
API does not allow older oil grades like SG to be sold nowadays FOR CARS; that is, no car maker approves them. VASTLY more important, SAE has exemptions from certain of its specifications, such as for 10W40 and 20W50 oils, and some others, as these viscosities are NOT specified for use in cars by the car makers ...and, SAE works with the car makers in making the SAE rules. Note carefully that nothing prevents an oil maker from producing an oil in such grades as 20W50, 15W50, etc., (these are NOT car grades), WITH friction modifiers in that oil. You are UNlikely to see those oils, they are quite rare. What we Airhead owners need is multigrade oils WITH ZDDP additive. ZDDP is being minimized, or eliminated, in CAR oils ...because the zinc component slowly ruins costly catalytic converters.
Grades 05W30 and 10W30 "starburst" "energy saving" oils ARE specifically designated as car oils ...so THEY likely have very low ZDDP, IF ANY!! Spectro does not make oils like those.
Golden Spectro in grade 10W40 & 20W50 are SG RATED AND FORMULATED, no matter what the container SEEMS to say about 'quality', or other weasel-words. These are NOT RATED NOR APPROVED as SL, SM, etc., for CARS. FURTHER, most Spectro engine oils generally contain 1800 ppm zinc & phosphorus. See my http://bmwmotorcycletech.info/viscosity.htm article for a listing of some other oils with ZDDP, etc. See the http://bmwmotorcycletech.info/oilessay.htm article also! Since these oils are NOT "car" oils, they can be sold with as much ZDDP in them...or as little in them, as the oil maker wants to put in. The reason behind all this mumbo jumbo, ETC., is that zinc products tend to poison catalytic converters, which are used in cars, but not in BMW AIRHEAD motorcycles.
It is possible that these oils COULD be sold with certain friction modifiers, yet NOT marked with starburst symbol, etc. Mobil 1 is found like that. Mobil 1 is a very good oil for BMW Classic K bikes, as its detergency and other properties are very good for a K bike weakness, the sprag clutch for the starter.
Nerdy: I use "ZDDP" almost generically here, as there are other forms of that zinc-phosphorus compound. ZDDP is usually not used with most pure synthetic oils, ZDTP is.
****If you have read the above, and some of what is below, you probably are wondering why SAE, API, and the car makers did not just allow oils to be marked for "Automobiles from xxx date only"; or "motorcycles only"; or something else. I have NO idea, and only some guesses; and I'm not listing them here.
Perhaps Spectro and other motorcycle oil makers will straighten out what its containers say, and clarify their websites some day. Don't hold your breath for that. I think this is ALSO a matter for clarification by SAE and API. Fat chance! To its credit (because this is surely messy), at least Spectro DOES ...or did ...explain SOME the seeming discrepancy ...but ONLY on its website; AND you have to search mightily to find the information ...and it is not the whole story. The latest bulk jugs of GS4 20W50 oil I received do not even list anything but meeting the quality of SF/SG (and some Japanese specification numbers). I truly expect this situation is similar with all motorcycle oil manufacturer's, and it is of no importance, unless you want to have facts and information ...so long as the oil you are going to purchase for your bike IS what IS NEEDED.
Golden Spectro 4, in 20W50 IS the oil I personally approve of, it IS SG, and it contains the right amount (HIGH! but, safely not too high) of ZDDP and other ingredients. You can use the lighter grade 10W40 if you insist on riding in weather below 40°F. Spectro Oils have been VERY good about NOT changing their oil ingredients, and only producing a very high quality oil. UNfortunately, Spectro, like others, is not so clear in its literature about what is in the oil ...meaning, is it REALLY an SG? ...and, what about the levels of zinc and phosphorus. But, you CAN get the information. NOTE: Spectro's website, spectro-oils.com, has a question/answers section, that does explain things much better, if not perfectly.
SG type (or rated) MOTORCYCLE SPECIFIC oils will likely have the correctly needed amounts of zinc and phosphorus, etc.
Castrol's 4T oil, (and Grand Prix oil, which is the SAME OIL) in either grade 10W40 or 20W50, as appropriate to your climate, is SG rated and formulated. Zinc component is 1100ppm; Calcium component is 1900 ppm; and Phosphorus component is 1000 ppm.
NOTE: Some folks still say that for certain transmissions and rear drives, that have bright metal (brass, bronze....) parts, one should not use GL5 gear oil. Gear oils vary, most GL5 oil is acceptable for BMW use. To be SURE, use a specially treated GL5, such as Spectro's. A fuller explanation about GL4, GL5, etc, is here:
Basically, in the AIRHEADS, there is one BRONZE spacer/shim in the rear drives, and BMW SAYS to use GL5. That covers it.
----- Original Message -----
.....there are some very recent changes in the API rules about what is stated on the oil bottles and HOW it is stated. The changes took effect June 30, 2008 and is one of the reasons reports flew back to me that the Spectro Golden 4 is now labeled API-SL and lacking the SG/SH rating labeling we desire to insure adequate cam and lifter protection. Now with the energy conserving oils and newer engine design changes, adequate ZDDP is no longer a guaranteed item when auto oils are used for older engines and/or motorcycle use. I made inquiry to my contact at Spectro Oils and explained the discrepancy in the published Web material versus what says on the bottle for the Spectro Golden-4 (10W40 and 20W50 ). My assertions in my July 10 post to the list are correct in that Spectro claims of their oil made strictly for motorcycle usage (their only products) haven't changed and are still OK to use, and you can believe what is published on the web site except for the official labeling discrepancies. Spectro wrote back regarding my query and indicated the web page changes will be looked into (in view of the most recent API rules change) and will be amended if necessary. The API people won't allow the publication of obsolete ratings on the bottle now and any labeling must be in conformance with the most recent rules ( effective June 30, 2008). The copout for Spectro is that since the engine oil chemistry additive rules apply only to automotive products, for motorcycle use they are exempt. As a result they stated the composition of their Spectro Golden-4 has NOT changed and still has all the more than necessary protective additives. Here is what I received as their present response:
>>>> Oak-- Our products still contain the full additive treatment they always have, if you are making viscosities like 10W40 and 20W50 the limits on additives don't apply, plus we are not making automotive products so API guidelines don't apply to our products.
There is a hidden message there. That is, conventional automotive oils now produced may not offer ample needed protection for the airhead engine. We talked plenty about that last January. You may never know for sure unless you have the oil analyzed. The rule changes coupled with all the chemistry changes in the past few years have really muddied the waters, with up to date information in an almost constant state of flux. The risk in using automotive oils, is if what appears to be OK in your motorcycle isn't OK, you won't find out until the damage is done. What it now looks like in general, is if you want good protection for the motorcycle engine, buy a motorcycle engineered oil ......not an automotive oil. The motorcycle oils are exempt from the automotive rules of chemistry that may be damaging to the 2 wheel machinery and can be custom designed for the application. The Spectro Golden 4 has some superb qualities, several being the exceptionally high flash point and viscosity index. You can examine those numbers on their web pages. They are very favorable in terms of low oil consumption and use of over a wide temperature range. Also, AFAIK, BMW gets their full synthetic engine oils from Valvoline, custom chemistried for the bikes. Although it is expensive, analyses have indicated it offers superb protection. Most of their other oils come from Spectro. ( Those things can change so don't hold me to it.)
First ... an UPDATE: BMW isn't purchasing its oil from the same old suppliers.
If YOU want to use REAL, RATED, LICENSED, SJ (or later) rated oils in your Airhead engine, that is your choice, and I hope you have REAL reasons to do so, rather than advertising hype. I have 'no problem' with you using the cheapest oils, such as SJ (or later symbol) car oils...it is YOUR bike, and the engines can be rebuilt, if expensively. Some have had good results over considerable mileage's with these car oils in the distant PAST. If you have a leak, camshaft lobe or followers wear, or other problems, it is not MY problem, it is YOUR problem. I AM TELLING YOU NOT TO USE CAR OILS IN THIS ARTICLE YOU ARE READING. It is MY BELIEF that some BMW parts are variable in factory heat treatment, which MAY account for large seeming discrepancies in service life of things like camshafts and followers, as some do get good life with cheaper oils. BMW also uses cam profiles and followers that are, essentially, similar to a rotating flat tappet engine. It is THOSE older engines, like in the sixties muscle cars, and some Porsche's, that are adversely affected by modern "car" oils. I simply will NOT take the chance. That is why I insist on a quality motorcycle type such as Golden Spectro. I simply don't want to take the chance on way too little ZDDP (or none) when my engine decides it needs it....AND, I want an oil with other good properties. Good properties include the oil sticking to the surfaces for long periods of inactivity; good corrosion resistance; good thin film performance, LOW boil-off (some oils boil off part of one quart very quickly...they are high volatility....); and other characteristics. I really want the oils to hold up.
A good oil really does cut down on wear, and in some instances is THE difference between lots of wear in extreme conditions (VERY hot engine, or very cold starting, etc....).
I don't use FULL synthetics in my Airheads, but have no objection to Spectro's full synthetic.
There ARE good motorcycle oils from Redline, Motul, etc. I also have no objection (BUT SEE BELOW!!) to your using CERTAIN types of diesel engine oils: Rotella, Delo, and Delvac.
If you ride in cold Winter weather, below freezing, you SHOULD consider a lighter grade, perhaps a 10W40. Your owner's manual has the grades suggested, although that is probably not in-date for what is available in modern oils (wider viscosity ranges).
Be advised that Rotella, Rotella-T, Delo, and Delvac oils, WILL be having much less ZDDP put in them, & this started in a small way in 2007. Some type of slow phasing out or a reduction was mentioned in a number of places; due to some diesel-equipped cars and trucks that are having catalytic converters installed. Diesel oils need more detergents and dispersants in them. HIGH levels of detergents are not necessarily the best for Airhead engines. The latest information I have shows that, at least for Delo, the ZDDP content is still OK. This was in 2011 and 2014 data.
Besides the heat treatment variability of some BMW parts like camshafts, followers, and rocker arms, which influence my recommendations ....ZDDP type additives TEND to come into their own (they do offer some help earlier) at the point that things are getting a bit extreme ...high rpm, hot temperatures, lengthy riding at high power levels ...etc. ZDDP is fairly critical when breaking in a new engine, or even just new rings or cam followers.
Some additives work at very cold temperatures for cold start protection. Most are not too good at this ...and most not good at all if the engine sat for a few months. Many cheaper oils are just not good at keeping an oil film on parts if the engine sits for some time. The proper additives of good quality will help here ...another reason to purchase a quality motorcycle specific oil.
ZDDP protection tends to come into play at cams, lifters/followers/cylinder bores, perhaps piston rings and rocker arms, possibly some other areas. Once there is enough of the compound in the oil, you get no more protection, only more cylinder deposits. 0.15% is probably just fine for full protection. 0.2% is likely too much and under .11% too little. I get into this deeply in my
http://bmwmotorcycletech.info/oilessay.htm article. I selected Golden Spectro 4 in 20W50 as my primary airhead engine oil DECADES AGO, as it has never shown the slightest problem with cams, followers, etc., and the additives do NOT burn off quickly like it does in cheap oils, and it DOES have many other desirable qualities. Oak liked that oil, I like that oil, every test seems to show it is a truly good oil. I don't intend to get into a lengthy argument on oils. Been there ....done that. I have nothing against you using the full synthetic version of the Spectro oils either...pretty good stuff! Do change it regularly, don't try to get 12,000+ miles on it; some of the additives will have burned off or converted or otherwise become ineffective ...if there are enough start cycles ...and miles. I think a reasonable change period is about 4000-8,000 miles, but not over a year (maybe two years if your trips are long enough to fully heat the oil). If doing in-city short trips, lots of stop and go; and especially with an older somewhat worn engine, generally do 3000-4000 mile changes, maybe up to 6000 on a FULL synthetic oil; but not over ~ a year.
You can change the filter every other change.
>>>A 20W50 oil is usually a better oil, from the same manufacturer, than their 10W40. The wider the range (divide the second number by the first) the worse the oil will be, long term (as miles accumulate).
You can use wider range semi-synthetics and full synthetics, the 15W50 are generally good.
Castrol GTX in 20W50 is NOT a great oil for Airheads, no matter the hype. I do NOT trust many Castrol engine oils ...since "the lawsuit". It is DIFFICULT to find out what the ZDDP level is in many Castrol oils these days, and their 'full or partial synthetic' oils may not have ANY REAL synthetics in them (I am NOT kidding, that was the thing in the lawsuit that an unsophisticated judge ruled on). NOTE, however: Castrol's 4T oil, (and Grand Prix oil, which is the SAME OIL) in either grade 10W40 or 20W50, as appropriate to your climate, is SG rated and formulated. Zinc component is 1100ppm; Calcium component is 1900 ppm; and Phosphorus component is 1000 ppm. If you like Castrol oils, or others are hard to find, these two should be OK, if just a bit sketchy on ZDDP content %.
As oil gets miles on it, the bigger molecules are sheared by various engine items, and the oil is no longer the viscosity you had when the oil was fresh. That does NOT mean that you should use single weight oil! This is one of the reasons to not try for 8000-10000 miles on oils unless you are careful about the situation.
Another problem is that ZDDP is actually used up and no longer has the necessary levels in SOME oils containing it ...after maybe 4000 miles, in some cases even fewer miles. ZDDP originally was invented for corrosion preventing purposes in old plain bearings, and its protection against metal-to-metal contact/wear was later recognized fully.
With reasonable usage, and not too many short trips under 10 miles or so, you can probably change oil at 4000 to 5000 mile intervals, and change the filter every second oil change with any quality oil. You can go farther with full synthetics in general, although the ZDTP tends to decrease, perhaps too much of a decrease. I personally have NO problem with going to 6-8000 miles on Golden Spectro 4, which is a PART synthetic oil ...on a long trip ...in which all or nearly all the mileage is in large amounts per average day. This is because the oil works best, and is VASTLY less contaminated by moisture, in this type of riding.
http://motorcycleinfo.calsci.com/Oils1.html is a hyperlink to a LONG article by a layman, on oils. I disagree with a FEW things, and a few conclusions, but VAST majority I DO agree with. The article has a tremendous amount of information. This is THE BEST article I personally know of (outside of my own!) dealing with oils. Articles point towards sales, but quite decent in most respects for the zddPLUS products.
Additives, more on engine oils, some nerdy technical things, gasoline's, ETC. :
There are hundreds of additives that one can purchase to doctor up one's ENGINE oil.
Please do NOT purchase and use ANY of them regularly ...but, read on:
....some for your gasoline are GOOD now and then. The use of Standard/Chevron's Techron additive (cheaper and better overall to get it by purchasing the gasoline, I've done the math for you, assuming you start with a modestly decent combustion chamber) is a good idea. NOTE: Techron additive was a polybutane amine compound. There is a boron component, I think. Originally identified as F310, it was reformulated many times, and in 1980 it became a polyether amine, and so remains today, with minor changes in overall formulations. FYI, for modestly coked up combustion chamber/heads, use of bottled Techron as found at your auto-parts store, and FOLLOWING THE INSTRUCTIONS, gives a mixture that is about TEN times the strength of the Techron in Chevron Gasoline's at the pump. You CAN use this bottled stuff a couple times a year, and it WILL keep your combustion chambers far cleaner, and it DOES help clean them if already carboned up. Use of the Techron containing pump gasoline WILL help keep your combustion chamber cleaner. Once cleaned, it is probably cheaper to purchase the Techron, for overall effect, at the pump, in the gasoline. The bottled formula is not just concentrated, but is a slightly different overall formulation, to work faster. As a bit more background, California was the leader in the U.S. to require various formulations of gasoline's to reduce smog. The California Air Resources Board (CARB) REQUIRES deposit control additives, this was set in stone in 1992, and modified in June of 1999 for even more additive levels. Intake valve deposits are under a certified testing routine, ASTM-D-5500 for all gasoline. I believe that Techron works better than other additives, and the bottled additive, used to help clean already coked engines, contain light aromatic naptha, stoddard solvent, benzene's, xylene, cumene,... all are besides the main working ingredient. Another thing about gasoline's: So-called "Tier-1" gasoline's ARE better. Do a Google search and read up on them. You may be surprised that SOME discount brands ARE Tier-1.
Additives, that YOU add to your tank, are hyped. People do NOT want to face up to the FACT that THEY are influenced by advertising. People WANT to feel like they are effective in life, have done something good, have an inner need. Don't bother with most additives that YOU would separately add. They are a waste of money, and in some instances can do damage to an Airhead. Techron for gasoline is an exception.
BMW camshafts and followers are very conservatively designed and built, with long life, quietness of action, etc., as goals. The cam lobes are mild in rate of lift rise. Still, heat treatment appears variable, and that is why I recommend NOT using cheap, or even expensive, "car" oils. Besides this, BMW cam and followers are mechanically manufactured in an old style ...such that a good oil film with a good dose of ZDDP is a necessity.
SOME oils are NOT good if the engine is run INfrequently. Some oils will NOT hold up to the very hot temperatures in the Airhead valve areas. Just because the crankcase oil measures 225°F perhaps, does NOT mean the oil is that temperature at the valve guides. Some oils will drip off parts until the parts rust. In particular, this is a trait of single weight motor oils. There have been instances of moderately frozen-up engines from sitting with car oils in them.
Oil changes need to be done more often in high power high temperature riding. For short, say under 10 miles commuting trips, also change the oil more often. Filters generally are OK for two, sometimes three, oil changes ...perhaps even up to 9000 miles, or more, in a reasonable length of TIME. That does not mean I approve of 9000-12000 miles between filter changes, except under very specific situations.
For severe cold or extreme hot weather use, a synthetic like Mobil 1 with lots of ZDDP may be best, in their V-Twin version.
I suspect that the Airhead rear drives may not like the new wider range hypoid oils that are available, such as 75W140, but have no proof, and yet I think those oils might be better in our Airheads for extreme situations, such as pulling a trailer or sidecar, or VERY hot weather at speed. I may have more to say on this in the future ...probably in my essay article on oils. Until then, my recommendation is to NOT USE THEM.
I am very suspicious of some magazine reports on oils testing. They do not test for actual long term engine wear; nor usually for usage (some cheaper oils are burned off much faster, particularly initially). Reports from a lab on metals wear as seen when analyzing oils, is NOT enough information.
I don't trust some 100% synthetics for maintaining seals size and condition. Golden Spectro4 20W50, a PART synthetic, which I trust, having years of experience with it, including engine teardowns, is very good.
Full synthetics with lots of ZDDP seem to be the better choice for truly severe conditions. Some of the better full synthetics are quite good these days at all temperatures and conditions; so I have reduced my previous cautions about them.
Some manufacturer's change formulations without telling anyone. This is QUITE common. Castrol GTX changed. Castrol won a lawsuit, dealing in what the word 'synthetic' really means. BEWARE of Castrol engine oils! ...except 4T and Grand Prix (at least, they seem to be OK, but not superior).
For touring use, with longer mileage between engine starts and stops, in mild to moderate conditions, 5000 miles between oil changes is very reasonable. On one long trip, over some weeks, I would not object to even a longer drain interval, if using a quality oil. With a full synthetic or better quality part-synthetic, and long trips, rather long drain intervals are probably OK. Just do not go overboard here ...remember, you want the ZDDP and other oil additives to remain in your oil.
Slick 50 is dangerous to your engine's health. It is TRUE that some types of additives will give less friction, and maybe a small bit of higher fuel mileage. That does NOT mean less wear!!! Some additive products will clump out, plugging oil passageways, this usually happens at sharper bends in the oiling system. Especially worrisome are additives containing Teflon or similar.
Bardahl, Rislone, Marvel Mystery Oil ...are not usually used for Airheads. In rare instances, these, including CD2 engine cleaning detergent additive, are used for cleaning. This is particularly so on K bikes, with the notorious starter sprag clutch, where Rislone or CD2 can possibly be of help. Keep in mind what I said earlier herein ...very HIGH detergent levels are NOT good for your Airhead engine. There is an article on this website about using this in a classic K bike: http://bmwmotorcycletech.info/kstartersprag.htm
I have actually gotten into the technical area of oils to great depth. Jigs, test engines, additive types, temperature effects on residues, neutralization number, channeling, shear strength, film strength, foaming, detergency, oxidation, etc.
The only area I could never get 100% agreement on, with engineers, is seal compatibilities ...due to all the variables.
Ashland Oil Company makes Valvoline brand products. Valvoline 4-stroke motorcycle oil in 10W40 (COLDER climates) or 20W50 for moderate to rather warm/hot climates, is still a good oil for Airheads. The zinc content of these two oils is 0.112%, phosphorus is 0.103%, calcium is 0.182%, and sodium is 0.052%.
For Shell Rotella-T, in 15W40, the calcium is ...or was ....0.27%; zinc is 0.135%, and phosphorus is 0.120%. A GOOD oil.
Do NOT use single grade oils in your BMW airhead unless you have a VERY good reason ...such as being someplace in the world you cannot find a proper multigrade oil. In almost every respect, modern multigrade MOTORCYCLE oils are vastly better than single grade oils, especially in NON-car viscosity grades.
Most engine wear is in the first minute or so of cold weather startup.
Changing the oil regularly is THE most important thing. That does not necessarily mean every 1000 miles (unless you put on 100 miles a month) ...and it might be 5000 or longer. Depends on conditions and usage.
Do NOT run your engine every month or so for a few minutes in your garage during Winter storage. This will result in moisture condensation in the oil, and perhaps sulfur-based acid buildup; better to not run it at all; don't rotate the engine.
SE oils were LONG AGO specified by BMW. SE oils were not, however, held to tight enough tolerances by manufacturer's ...there were real abuses, and SF replaced SE. BMW Airhead engines need a GOOD quality REAL SG oil.
'Viscosity index' is a number that indicates the RATE of change of the thickness of the oil, within a given temperature range. A HIGH index number means the thickness varies LESS with temperature changes. ENGINE oils are specified, generally, at 210°F (98.9°C), except that engine oils with a "W" are specified at 0°F (-17.8°C). This means that a 20W50 oil is specified at TWO temperatures; for 20W at 0°F, and for 50 at 210°F. For the really nerdy, SAE ratings are measured or specified in centipoises at 0°F and centistokes at 210°F ...and, let us not get into Saybolt Universal! If you are interested, look up these things.
What 20W50 is SUPPOSED to mean, and generally DOES mean, is that at 0°F, a very wintery temperature, that oil should be the same thickness (viscosity) as a UNcompounded (single weight) oil (that would be called SAE 20) is at that same cold temperature. The "50" means that at 210°F, that oil should be as thick as a SAE 50, AT that temperature. Think about this paragraph for a minute. If you DO think about what I said, you will understand that even a 20W50 oil can be rather thick at cold temperatures and not great at flowing through your engine until the engine warms up. You will also understand that 20W50 is better than a NON-multigrade oil for our engines. You might even be thinking of just HOW the oil manufacturer managed to make a 20W50 (or 15W50, or 10W40, or 0W30, etc.) oil...and, then, perhaps think about whether or not the multigrade (or a single grade) oil will, or will not, remain in the viscosity grade for which it is being sold.
Cx oils (replace the x with the latest letter) have specifications for sulfur content, and for temperature for release of various activity of additives, etc. Cx oil rating is concerned with many factors, some of which are pertinent to Airhead engines, some are not. A problem with Cx oils is that most of the active agents for protection of metal to metal contact are for vastly higher temperatures and some pretty extreme pressures (after all, they ARE diesel engines) than in Airheads. Thermal stability and breakdown point of additives are different. It was fairly critical, many years ago, that Cc oils NOT be used in diesels that needed Cd oil. We had oils, most are like this today, that are rated for gasoline engines and diesel engines, and you will see the rating as, perhaps SE/CD, etc. These crossover oils, when sold for cars, tend to NOT WELL favor the high temperatures of the turbocharged diesels, and the additives, or some of them, do NOT work well at gasoline engine temperatures. Just to complicate matters even more, there is a TREND since ~year 2010 ... towards cars having smaller displacement engines, direct cylinder injection fuel systems, and even turbocharging, .....yet even having high compression ratios. The result are sometimes oil wash-down on cylinder walls, deposits in the upper piston groove/lands and heads, ....and pre-ignition and thus exploded engine problems. Specially compounded engine oils are being used to help with such problems. These oils should NEVER be used in your Airhead motorcycle!
Sx oils have changed VERY considerably over the years, and the additives and compounding is quite different from earlier oils. Many characteristics are for increasing fuel mileage and decreasing damage to catalytic converters, and in some instances to help with decreased clearances and other lubrication and deposits problems, see prior paragraph, in very modern engines. All sorts of considerations are made, antioxidants, pour point depressants, anti-foaming, anti-scuff, detergency, slipperiness, AND MORE...etc.
There ARE just-for-diesel-engine oils that are now OK for gasoline engines, such as Rotella, Delo and Delvac. These oils, at least through 2011 (and probably 2014 at least), had quite adequate amounts of ZDDP, which car oils after SG did not.
MOTORCYCLE oils in 20W50 and 10W40 do not have to eliminate ZDDP, ...those grades are EXEMPT from the SAE and API requirements, and thus they can be REAL SG oils ...and can state on the container that they meet the quality (not specifications) of SL ...or anything else. Yes, CONFUSING!
Gear oils are specified for different temperature ranges, and their additives are most active in those temperature ranges. This is particularly so with the W rated gear oils. Do NOT think that a 80 weight gear oil is as thick as a 80 weight engine oil might be at the same temperature; ....NOT SO!
BMW fork oil, the old original red oil, was a military specified hydraulic oil; the mil-spec was MIL-5606. Quality fork oils available today are better, especially for viscosity index and anti-foaming (nice to have those forks handle the same after a few miles of bumpy road) and anti-stiction qualities (nice to have the forks, if properly aligned, to not act like solid steel ...no suspension....over tiny irregularities in the road surface). Generally, BMW has manufactured the various hole sizes, and clearances, etc., inside the forks, for use with a rather thin oil, roughly SAE 4. In another measuring system, it would be about a SAE 7. Use of oils of 7.5 is fairly common, but 10 and up usually means something is wrong (except on the R100GS, etc., with 10 in one fork, 15 in the other, per spec). Some oils that are OK for use in BMW forks may be marked as Suspension Fluid ...OR ...fork oil. The proper viscosity for the fork oil in all but the R80R, R100R, R80GS, R100GS, is SAE 4 ...but to be more exact, the viscosity should be 13.2+- at 40°C (104°F). You need to know the viscosity at that temperature area, and can mostly forget the other temperatures that are often quoted. One manufacturer's SAE 5, or any other fork oil, is not the same as another's! ...so see their specification sheets. When trying different fork oils, use the SAME manufacturer. There is more on fork oils a bit further down in this article. I also have an article, http://bmwmotorcycletech.info/viscosity.htm, that gets DEEPLY into fork oils (and some on engine oils), naming the brands, models, viscosities, etc.
Friction is a difficult, many-types consideration. Oil separates potentially rubbing surfaces by very complex means. Read: http://bmwmotorcycletech.info/oilessay.htm. Thick oils have more INternal friction, but can support heavier loads, but that is a complex thing to understand, but is covered in that oil essay article. An ideal oil would not change viscosity appreciably with temperature change for friction purposes. High pressure ALONE INcreases viscosity of an oil ...this is why a THIN oil can support heavy loads, like in the rod bearings. A thin oil is far better for COLD STARTUP. Because of these things, use of thick oils is not a good idea in BMW Airhead engines. It is just ONE reason, of many (including generally being poorer at sticking to surfaces during storage), that single-weight oils are NOT a good idea, at least nowadays, when multigrade oil performance is vastly better than 50+ years ago. I can see almost no use for single grade oils, except maybe for first 50 miles of break-in; or, where you cannot find good multigrade oils.
If quality multigrade oil was not available, for example in Latin America or in the very hot deserts of the Middle East, a single grade, perhaps 40 wt., would be OK.
RPM of moving parts influences the heat developed, and high speeds of those parts means faster shearing of the oil itself, but, conversely, high rpm helps form a cushion in bearings, so higher rotational speeds generally allow higher loading. That is why lugging your engine by using lots of throttle at low rpm is not a good idea; and there are other reasons, such as at the piston and rings, but no need to get into that here.
AIRHEADS: After the oil warms up, and you are at idle rpm, there is, depending on engine wear, etc., very little oil or even NO OIL, coming out of the pressure relief valve area, to lubricate the chain and sprockets. This is why lengthy idling ...and especially too low an idle rpm ...is a BAD idea. This is in addition to the bearings in the engine not having enough pressure with lengthy idling, to support the oil film at low rpm ...especially on a well-worn engine.
Transmission, driveshaft, rear drive oils; GL4? GL5?:
I generally use 80W90 GL5 petroleum oil at the transmission (and driveshaft on models requiring oil in the driveshaft) and rear drive. Note that dino oil and synthetics are available as 75W90 which are also generally OK, but some full synthetics are not 'sticking' to metal surfaces all that well after some storage time, and because of that, I am generally recommending one use a premium GL5 petroleum gear oil in either of these viscosity ranges. There is some controversy about using SYNTHETIC oils in the TRANSMISSION. I am in the middle of the arguments. More on this a bit further down this article.
There are also much wider viscosity oils, such as 75W140; 75W145; 80W140 and 85W140, etc. These extra wide range types in GL5 type are OK under certain SEVERE circumstances, although I have mixed feelings about them. You might consider using these wider range gear oils if you live in the very hottest climates and travel fast, or pull a trailer or sidecar at highway speeds; all these types of things being done most of the time. OTHERWISE, I can NOT recommend the use of such wide viscosity ranges. Use of extra wide ranges like these can result in strange happenings in both transmission and rear drive and driveshaft. Poorer lubrication in the driveshaft area. Improper spin-down of the gears and meshing speeds in the transmission meaning weird shifting ...and poorer lubrication. There may be cold overflowing or poorer lubrication in the rear drive.
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, and, even then, only with certain early bikes. 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). Confirmed.
BMW AG, recommended lubricant changeover: oil to hypoid.
(By Model and Serial number/engine/frame No.:)
Oil Change Intervals, engine, gearboxes and forks ....in brief. Fork oils: non-racing, quality oils, 15,000 miles. Fork oils: I prefer Spectro's fork oils & suspension fluids. They are GOOD, have low stiction, wide temperature range (decent VI too), & the viscosities can be depended upon. NOTE that back in the early Airhead days, the BMW fork oil was red, was really a military hydraulic oil, you could find its full specifications using a search engine for: MIL-H-5606E (or D). Just to save you the trouble, the viscosity specifications for that oil are: Due to how it is specified, and the lack of superior stiction fighters, and some other characteristics, you are MUCH better off with a REAL fork oil ...especially a full synthetic fork oil. But, some synthetics may not be compatible with rubber parts in some BMW forks. For the various fork oils and suspension fluids, the various manufacturer's do not agree on measuring viscosity. Because of that, stick with ONE manufacturer if playing with viscosity grades. Except for some GS models, all the old BMW's needed a very thin oil, roughly SAE 4 or 5. For the most part, you can translate that to modern 4 to 7-1/2 fork oils. Note the 4.9 and 13.2 at the temperatures cited; compare those figures with YOUR manufacturer's figures. A formula to convert Cst to SUS is in the viscosity article, link just below. But, HEED my remarks about sticking with ONE manufacturer. ****NOTE!! On this website is an article on oil viscosities, and other characteristics, by brand, etc. Lots of information on shock and suspension fluids/oils and some on engine and gear oils too. http://bmwmotorcycletech.info/viscosity.htm
revisions: © Copyright, 2014, R. Fleischer Last check/edit:
Monday, January 15, 2018
Note that the above are not considered "Airheads".
AIRHEADS: There is ONE BRONZE, not brass, shim in the rear drives in the Airheads. BMW specified a GL5. BMW knew that is correct, & I agree. Use GL5. NOT GL4! in ALL AIRHEADS.
I have changed my recommendations on using only a dino oil in transmissions. My present recommendation is that IF YOU DECIDE to use a synthetic gear oil, it should be of very high quality. It is my belief that it can extend transmission time before overhaul by a considerable amount. At least one other supposedly knowledgeable person strongly disagrees with me, and seems to think that synthetic gear oils DEcrease reliability; I am not at all convinced, and he offers no proof, nor technical information.
DO NOT use any additive with synthetic oil, such as the Dow Corning moly type additive. In some cases, an additive is warranted to "try" to improve poor shifting. Be very cautious. Keep in mind that poor shifting can come from several things, including improperly adjusted clutches! Use MUCH LESS than the containers call for. About 2% (or not over 3%) of Dow Corning M Gear oil additive (do NOT use it with synthetic oils), or Guard Dog GD401 for petroleum oils; and same amount of Guard Dog GD421 for synthetic oils (Guard Dog is out of business). For the Dow product, SHAKE THE CONTAINER REALLY WELL and use ONLY the concentration I recommend ...and absolutely not the 5-10% Dow suggests on the container. If you decide to use this additive, 18 to 20 cc is about correct for your transmission (~800 cc total oil). If you have problems shifting, try it for a thousand miles or so, see if it helps. If not, you have other problems. DO check the clutch adjustments first. It may increase the lifetime for the bearings, etc. ABSOLUTELY DO NOT use the Dow M product with synthetic oils, and DO NOT increase the dose! For the rear drive, you can use about 2%.
For synthetic gear oil I am presently recommending only the Spectro brand, in 75W90, in the type called "Platinum". It can be used in the transmission and the rear drive of Airheads and Classic K bikes. It is OK for the driveshaft.
Oil changes depend on use, storage, riding styles, weather, quality of oil, and a LOT more. Without knowing all YOUR details, my recommendations would be:
Dino multigrade oils: engine oil change at 3000-5000 miles for mixed riding (short trips, long trips, mixed weather).
Semi-synthetic multigrade oils: engine oil change at 4000-6000 miles, with same conditions as above; up to 7,000 with long trips, few stop and go miles.
Full synthetic multigrade oils: engine oil change at 6000-7000 miles, short trips, long trips, mixed weather.
Gear oils: 10,000 miles for quality dino oils and semi-synthetics.
Gear oils: 15,000-20,000 miles for full synthetics.
MINimum 4.9 Cst at 100° C
MINimum 13.2 Cst at 40° C
Maximum 600 Cst at -40° C
01/16/2008: revised to include latest information on oils, and to clarify details on canisters, etc.
01/22/2008: updated for clarity only
07/12/2008: revised item 2, add more information on oils. Oak's comments added. Entire article edited a bit.
07/14/2008: revise the article in line with latest reports on diesel oils.
04/13/2010: slight updating, adding some oil characteristics content; + adding a hyperlink to my viscosity article.
04/24/2010: Go through entire article and fix typos, and bring up-to-date. A tad more on 11/12/2010.
11/18/2010: Add Castrol 4T zinc amount
02/24/2011: was 52B
10/11/2012: Add QR code; add language button; update Google Ad-Sense code; minor other editing
11/05/2013: Edit article for better clarity
03/03/2014: Correct the information reference from 51A, 51B, 51C, 51D, to 52x. clarify some details. More on 03/12/2014.
05/01/2015: Updated, and a few clarifications on 09/01/2015
03/10/2016: Update formating and metacodes, plus a few slight clarifications
09/22/2016: Update metacodes, scripts, add tables, clean-up.
05/31/2017: Clean up fonts, colors.
08/14/2017: Minor clarifications. Add section on clarifying outer covers and refilling oil coolers. Reduce some colors, fonts, bolds, etc., in favor of underlines, etc.
Oil Change Intervals, engine, gearboxes and forks ....in brief.
Fork oils: non-racing, quality oils, 15,000 miles.
I prefer Spectro's fork oils & suspension fluids. They are GOOD, have low stiction, wide temperature range (decent VI too), & the viscosities can be depended upon. NOTE that back in the early Airhead days, the BMW fork oil was red, was really a military hydraulic oil, you could find its full specifications using a search engine for: MIL-H-5606E (or D). Just to save you the trouble, the viscosity specifications for that oil are:
Due to how it is specified, and the lack of superior stiction fighters, and some other characteristics, you are MUCH better off with a REAL fork oil ...especially a full synthetic fork oil. But, some synthetics may not be compatible with rubber parts in some BMW forks. For the various fork oils and suspension fluids, the various manufacturer's do not agree on measuring viscosity. Because of that, stick with ONE manufacturer if playing with viscosity grades. Except for some GS models, all the old BMW's needed a very thin oil, roughly SAE 4 or 5. For the most part, you can translate that to modern 4 to 7-1/2 fork oils. Note the 4.9 and 13.2 at the temperatures cited; compare those figures with YOUR manufacturer's figures. A formula to convert Cst to SUS is in the viscosity article, link just below. But, HEED my remarks about sticking with ONE manufacturer.
****NOTE!! On this website is an article on oil viscosities, and other characteristics, by brand, etc. Lots of information on shock and suspension fluids/oils and some on engine and gear oils too. http://bmwmotorcycletech.info/viscosity.htm
© Copyright, 2014, R. Fleischer
Last check/edit: Monday, January 15, 2018