I remember reading that a good deal of engine wear (in car engines) happens at start up, when the engine parts have little, or no oil on them. I would think this is also the case with motorcycle engines. I've been running 5w20 oil in my Caravan (as per manufacturer specs) for around 110,000 miles now, and it's been through a new radiator, and one of the craziest droughts in Texas history, and it's still going strong.
I realize the dynamics of motorcycle engines are slightly different than that of a car engine, but the principle is the same. If a 20 hot rating is good enough to last in a 3.3 V6, wouldn't a 40 (hot) weight in a parallel twin be plenty? My concern is with 20w50 being TOO thick if the temp should drop, unexpectedly.
Last edited by neviander; 08-04-2013 at 12:23 AM.