Oil Discussion for BMW Airhead Boxer Engines (and some good information for BMW Classic K bikes & Oilheads)
This discussion is also likely applicable to most old flat tappet engines, including some VW, Porsche, old Corvettes, etc.
Revised by the Author 11/05/2007, 11/01/2009, and minor revision on 06/02/2014 and again on 05/20/2017
Over the years, oils have been a popular subject for discussions in our motorcycle publications, club magazines, & on-line LISTS & Forums and Facebook, etc. I am not sure just why that is, but I suspect it has to do with our society of easy fixitus, or 'I need to do something to feel good', maybe a panacea for the masses...and maybe male ego, ..and who knows what else! Certainly there is a large amount of placebo effect. REAL facts are hard to come by, and so-called 'evidence' abounds, and may be quite difficult to verify. There is a considerable amount of so-called 'information'. Some is good, some is anecdotal, some based on testimonials, some sort of like 'my brother told me of his friend who has a friend who told him that...'; or, 'my mechanic who has decades of experience, says....
Did you ASK that person just HOW he REALLY got that information he is giving you? Does that mechanic friend have a sweetheart 'deal' with a particular oil's distributor? Has he ever REALLY seriously tested oils in Airheads? How did he test them? Has he looked at hundreds of Airhead cams and lifters? Do YOU believe the stories often heard>>that "car oils are plenty good enough, you hardly need pricier specialty oils?". Some information even seems scientifically derived, and implies itself to be definitive; in MANY instances this is NOT SO. In addition, there is all that advertising. SORRY, but those hyped additives like Slick50, QMI, etc., and those tests on TV of engines run without oil....these are sideshows; you never hear the entire story of the tests. DO NOT believe these folks. YES, it is true that you MAY (or may NOT) have less friction, higher fuel economy, etc. HOWEVER, you will also likely get much increased WEAR (YES, you can have LESS friction and considerably MORE wear!), the product may settle out or 'clump', thereby plugging oil passages and oil filters, and LOTS more ills. This can lead to oil starvation and catastrophic engine damage. As for additives like Bardahl or Rislone or Marvel Mystery Oil: don't use them, they can remove the protective coatings on your engine parts.
BUT: There ARE A FEW places that Rislone can be of help, and one is temporary use in a Classic K-bike, to hopefully free up a slipping starter drive clutch....aka Sprag Clutch.
OK, have I got your attention yet? Have I offended everyone?
In preparing this article on oils I not only relied on MY background experience, but that of several very well known and RECOGNIZED experts on Airheads. I also did a fair amount of research, and I actually did some tests on pour temperatures, slipperiness, and shearing just for my own information. I made up some jigs & tests to do this. I spoke to some petroleum engineers and obtained some typically off-the-record information. I looked into some specifications not normally available, on additive types, actual temperature effects on residues, neutralization number (a measuring method and answer dealing with how well the compounded oil neutralizes acids), channeling (when an oil is so thick at a low temperature that it does not flow at the gear meshing surfaces, and so the metal is starved for lubrication), shear strength, film strength, shear resistance of the VI improvers (additives), load carrying, corrosion resistance, foaming problems, detergency, oxidation resistance (oil, particularly petroleum, will oxidize at higher temperatures and gets thick and flows poorly).
I also dug rather deeply into testing done by various biker magazines, and found a lot of fault with these tests, which can be extensive and appear to be definitive and are NOT. Motorcycle Consumer News did a very decent set of testing (more than once) on many oils, and while one of the best, if not THE best reporting, it was very faulty in regards to AIRHEADS, which have flat tappets and special considerations.
...AND, lastly, the one item that I could NOT get 100% straight & definitive answers that I wanted: seal compatibility.
I paid a considerable amount of attention to lubrication effects