<<These bikes do NOT normally run hot, unless you are asking for max HP all the time and not giving the engine air flow over it. Normally, the engine is over-cooled, as there is no regulation and there are more fins on the engine for the event when is does create more heat (high power settings). ...synthetics have a higher temp withstand. So, if you do cook the oil, it still gives some lubrication.
You do NOT want modern auto oil that has any labeling about "Energy Conserving" or one dedicated for use in engines with catalytic converters.>>
True! Should not have used the term HOT just to describe an air cooled engine. & Yes, auto oil = bad for motorcycle's with wet clutch, which the SOHC/4's have.
<<<There will always be an engineer or really tech saavy guy tell you that going to synthetic oil in an old bike or car that's never seen it, will do no harm. Yet I've seen it happen. stuff starts leaking, something happens to seals, these are not ALL made up stories.>>>
I've heard these stories as well. Never understood why the blame is on the oil?! All synthetics (no matter what brand) are high detergent oils. Basically meaning they keep the engine clean. No wax / paraffin fillers. So when seals start leaking after switching to your favorite synthetic, its the high detergent synthetic oil that is getting rid of all the varnish, crap, sludge in the engine. So likely the seals, even though they've been bad for a long time, weren't leaking because the owner is using a cheap oil that helps seal those old seals. (Which is what high mileage oils are engineered to do).
<<<Full synthetics will run thinner, lower viscosity, but still provide adequate lubrication as compared to petroleum base stock oils. That feature reduces the "cushion" available between internal parts and can result in leaks, as well as more noise. No harm done usually. Full synthetics also won't "varnish" internal engine parts as readily which is not an especially good thing as the varnish prevents rust when the engine is innactive.>>>
Viscosity is viscosity. It is not determined by the engine brand. 10w30 is 10w30. SAE 50 is SAE 50. Approved by API. (which is a stamp on all bottles of oil, showing it has been independently tested and meets specific API standards for viscosity) Synthetics flow very well even when very cold, so sometimes folks will say they oil is thinner. That's not the case.
"Varnish". Not sure of the value of varnish. Can't see rust getting in a normal operating engine. (not counting bikes left outside with no air filters, water getting in mufflers, etc.). I'd like my engine to be spotless. When rebuilding an engine, one of the things we do is polish the crank. Kind of don't want varnish anywhere. Which of course leads back to quality of oil. Bottom tier oils leave varnish (due to having high content of paraffin). Top tier oils leave engine bearings, etc. clean, and the dirt, varnish, crud- in the filter where it can be removed.
It is interesting that all Oil Brands have a synthetic in their line-up. Castrol, valvoline, Amsoil, Mobile1, etc., even NAPA has their own synthetic (made by valvoline). And, all oil brands that I've seen @ my local Motorcycle Shop, also have a synthetic motorcycle oil. Pick your favorite brand.
