Abstract: An orbital internal combustion engine including a pair of rigidly interconnected opposed cylinders having a pair of rigidly interconnected pistons reciprocally mounted therein with the pistons each including a rigid piston rod rotatably journaled to a crank throw on a crankshaft. The rotatable cylinders and the crankshaft rotate about axes that are spaced in relation to each other whereby the cylinders orbit in relation to the crankshaft and crank throw to impart a power stroke of 360 degrees to the crankshaft when the cylinders have orbited 180 degrees. Each piston includes a crown with recesses on each side thereof associated with a pair of spark plugs in the cylinder head to shape the charge formed by the combustible mixture for imparting a greater expansion force against the piston rather than against the cylinder wall.