Abstract: The cylinder head has a conventional spark plug, therein, for engine start-up, and has a precombustion chamber unit mounted therein as well, for cleaner, more stable normal running of the engine. The method defines the reaming out of spark plug apertures in the head to accommodate the installation of the precombustion chamber unit.

Abstract: A main combustion chamber and a pair of dual ignition antechambers are contained in the engine head associated with each of the engine cylinders with the antechambers in flow communication with the main combustion chamber. A main fuel injection valve is positioned recessed within the cylinder head displaced from the surface of the main combustion chamber for discharging injected fuel in an axial direction to stratify the fuel with respect to air contained in the chamber. During the subsequent compression stroke, a quantity of air surrounding the stratified fuel is forced into the antechambers for mixing with combustible quantities of fuel subsequently supplied. Ignition thereafter of the air-fuel mixture in the antechambers in turn ignites the air-fuel mixture in the main combustion chamber to effect the expansion stroke of the engine.