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; minor revision on 06/02/2014; edit again on 06/20/2018 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 pricey 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 SLIGHTLY less friction, SLIGHTLY 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.