Hi Miles;
I have to disagree that paint on the engine keeps the heat in. A
dirty engine keeps the heat in, a engine without a fan or one that is
missing the shrouds will also heat up. But, as I have had guages on Honda
600 engines to watch the temperature of oil and cylinder head on both
(painted and not painted), I can't tell the difference. If you bead blast
the aluminum it will corrode/oxidize with time and that too will result in
captured heat. If the issue is a smoother surface when painted allows the
air to move faster over the engine fins that may be true but then bead
blasting will initially give the same effect. I paint my engines with a
high temp (cures with the heat of the engine) and developes a nice aluminum
color with an aged patina after a few years. And I like the way they look.
Bill