now all over the top of the engine.
Bingo!
The engines you mention have something important in common. Single valve covers with volume a fraction of that of the oil pan. After making room for the valve-train, I'm sure the remaining volume of those valve covers is way less than a gallon.
I'd bet money the engine was pumping oil up to the valvetrain faster than it could drain back down into the sump, until it eventually spilled out the filler cap or even out a pressure-weakened gasket.
The oil, especially when it and the engine are very cold, probably moves up to the head in substantial volume and under significant pressure. It's likely the path of least resistance even in a warmed-up engine, but I'd think more so in a cold one. The only other place it's got to go is through the crank and camshaft journals, and the bearings create substantial back-pressure.
But only gravity brings it back down to the sump, through a few smallish passages. And the oil was likely flowing back to the sump about as fast as 50-weight in January. Filling the area under the valve cover faster than it could drain.
Edit: That made me think of something else. Clear valve-covers would be SO trick! I'll have to ask my son about the possibility of him making some, starting with my R 75/5 since it has such simple and visible valve covers. Since it's too cold to ride it, he can just use the existing ones to make molds.
Edit 2: I really wish it'd warm up because I've been dying to use something he built for me recently. A 40-square foot (4x10) welding table. This thing is seriously massive. Everything about it. He said it weighs a little over 700 lbs.
I've set it pretty far from the welder and want to run power over to the table for plugging in the welder and other things and hit auctions to pick up a massive vice. Finally have a table that can handle one.
