 Several manufacturers replaced pre-war side-valve engines with new overhead camshaft power-plants during this decade; the new Opel also carried its camshaft directly above the cylinders.The chain-driven camshaft still operated the valves using rocker arms because the camshaft itself was not positioned a sufficient distance above the cylinders to permit direct action from the camshaft on the valves.The configuration had been developed by General Motors in Detroit and was known as the cam-in-head (CIH) configuration.