Lawrie,
There are several variations for lubrication of multi cylinder IC engines.
Some have an oil pump and passages drilled to pressure lube the rod and main bearings. Throw off from the crank and rods lubes the rest of the internal parts. Lube for the rocker arms could be via drilled passages or just drip some oil on between runs with the rocker cover off. The high rpm engines, the model Offenhauser for example, are lubed this way.
By fitting small projections on the connecting rod caps to just barely contact the oil in the sump, there is enough splash to lube the rods, mains, and other internal parts. My Silver Bullet is lubed that way and it works fine.
I know of one builder who runs a 4 cylinder inline with an enclosed crankcase with no oil at all in the sump. He mixes just a bit of Marvel Mystery Oil (or similar product) into the fuel. There is enough lube in the blowby gasses, past the piston rings, to lube the bottom end. He has run many hours this way with no ill effects.
If the engine runs an open crank, you can drip a bit of oil on the rod and main bearings between runs. I do this with my single cylinder open crank engines and have never had a problem.
With the enclosed crankcase engines, getting the balance right between just enough and too much lube is important. Too much, and you flood the rings, giving a smoky exhaust.
It is my opinion that these lightly loaded model engines will run fine with a lot less lube than you'd expect. My experience is with low to medium speed engines, up to maybe 3000 rpm. High rpm engines are probably more critical.
Back in the mid 1950s, at our county fair, I remember a fellow selling an oil additive which he claimed offered great protection for gasoline engines. To prove his point, he had a small 4 cylinder hay baler engine running with the oil pan removed. He'd squirt some oil, treated with his product, on the rods and mains and then start the engine. The engine ran at idle, no driven load, with the crank running in open air. I think all he proved was that at idle loads, an engine will run a long time with minimal lube to the crank an rods.
Which multi cylinder engine are you considering?
Chuck
