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This paper reviews historically-significant valve train developments and their combustion system/engine installation implications. It describes the ROTULAR TAPPET™, a simple invention which allows angularity between the valve stem axis and the operational plane of the valve actuator to produce hemispherical chambers with four radial valves. It compares modem conventional gasoline and diesel engines to upgrades utilizing this device. It concludes that a new prechamber on an advanced IDI engine, with DOHC, hemispherical chamber, four radial valves and variable effective compression ratio could provide the optimum solution for small automotive diesels. The new tappets can make these engines possible.

This paper reviews combustion system design and development of a very small diesel derived from a gasoline engine. It compares the results and discusses the special problems of small diesel engines through two displacements and a series of cylinder heads, valve trains, and injection systems. It concludes that for small engines on automotive applications of two-valve technology a classical swirl-chamber IDI combustion system, or an “M System”, offered substantial advantages, including fuel consumption, over a DI system.The paper also discusses solutions through the use of four valves, and the problems anticipated with those solutions.