Tom, very interesting thoughts on oil. Can we go a step further, and
consider that various forms of air-cooled motorcycle engines have
varying running and oil temperatures?
No question that air-cooled engines run hotter cylinder head
temperatures than water-cooled, that's fundamental. Hard-working bikes
with smallish fins on the heads would be the hottest, for example my old
500cc Velocette single in the '60s, cruising at 70 on a hot summer day,
I would swear the head was 400-450 degrees F.
On the other hand, my good old Vincent Black Shadow, 1000cc twin,
all-aluminum, on the same day cruising at the same speed, might have a
head temperature (just guessing) of 250-300 degrees F. I do know from
tests that the oil tank contents at the time would only be about 125
degrees F. Hardly enough to burn your finger.
My CB-750 Honda Four, with the cylinders across the frame, ran very cool
at that kind of cruise. Probably the cylinder head was about the same
temp as the Vincent, and the oil tank contents were probably around 200
degrees. Why the difference? Maybe because the Honda had a lot of
plain bearings, and a high volume oil pump, whereas the Vincent was all
ball and roller bearings, with a low volume pump.
In '74 I took a trip to Daytona for the races, riding my Honda Four. A
friend went along riding his Yamaha 500cc Twin, which had modest finning
on a smallish head. We cruised about 70-75 all the way from VA down and
back, My Honda ran cool and happy, and the Yam made it down and back,
but was anything but cool and happy. It was so stinkin' hot every time
we stopped for gas, that my friend (who was a slow learner) would fill
the gas tank up, and before he could pay for it, the roasting heat of
the engine heated the gas in the tank up so much that it expanded and
poured out of the cap vent all over tank and engine. Fortunately, he
didn't have a fire.
In the '60s, Ducati made a sweet little line of 250cc singles, which
handled like a dream. If you wanted to cruise one at 70 or so, it was
okay at first. But before long it would just start to overheat, and
detonate, and you'd just have to slow down. Or break something. Today,
my water-cooled 250cc Ninja can cruise forever at 70-75 and has 60K plus
on it, with no problems. The difference is air versus water.
I have very little experience with today's air-cooled Harleys, but I
imagine their running temp and oil temp characteristics are similar to
the Vincents of old, that they resemble.
A late friend of mine, who was a distinguished hands-on British
motorcycle engineer, told me he had found that every American male was
an expert on at least two subjects. One was sex, and the other was
lubrication.
Cheers from ArdunBill in the Great Dismal Swamp, Chesapeake, VA
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