McGeehan, J. and Yamaguchi, E., "Gasoline-Engine Camshaft Wear: The Culprit is Blow-By," SAE Technical Paper 892112, 1989, doi:10.4271/892112.
We were able to identify engine blow-by as a primary factor affecting camshaft wear in gasoline engines. Using a 2.3-liter overhead-camshaft engine, we isolated the valve-train oil from the crankcase oil and its blow-by using a separated oil sump. We find that: with engine blow-by, the camshaft wear was high. without blow-by, the camshaft wear was low. with blow-by piped into the isolated camshaft sump, the wear was high again.Later studies identified nitric acid as a primary cause of camshaft wear. It is derived from nitrogen oxides reacting with water in the blow-by. But even in the presence of blow-by, camshaft wear can be controlled by the proper selection of zinc dithiophosphates (ZnDTP) and detergent type.