oil viscosity

[jorrow]

I have all heard to use 60 w oil in old bikes especially here in texas where we see 90 -100 degree weather all summer long, however I have often questioned the need for such heavy oil. If you convert Harleys original "heavy use oil" you actually are closer to a straight 50w. Could it be the old" bigger is better" philosophy in action , or do these old machines really need the oil that heavy. I would imagine that starting these engines cold with straight 60 is a bit hard on the rods, cases, etc...Remember, thinner oil cools better, thicker oild holds its viscosity longer. I'm sure there are plenty of good opinions out there, and I would love to here from you. And...what of multiviscosity oil? A factory engineer at the daytona exhibition told me that 20w-50 would actually be excellent for the old bikes and would actually thicken up past its 50w margin....any opinions???

[yhprum]

20-50W oil is used for aircraft piston engines. Large displacemnt, air cooled engines. Aeroshell is one brand. Dont see why old aircooled motorcycle engines would suffer using similar oil.

[Kojack]

Last time I asked my Harley dealer this question he told me that Harley has never recommended multi-vis oils for pre evo motors. Nobody could tell me why exactly so I tried 20W-50 in my shovel. Oil consumption went up and my hydraulic lifters became noisy (which could have just been a coincidence, lifter problems aren't rare). I didn't really see an advantage so I switched back. I believe that a 20W-50 oil is the same viscosity as an SAE 20 oil at low temperatures. Harley recommended thinner oil for winter use but not that thin.