In-line two-cylinder engine

An in-line, two-cylinder engine comprises a crankshaft having crankpins at a 360 DEG setting and balancing means comprising a first counterweight rotating oppositely to, but at the same speed as, the crankshaft, such counterweight being so set that its center of gravity is remote from the crankpins when the pistons are at top dead center, such first counterweight being of a size and design such as to develop a centrifugal force whose amplitude is half the maximum amplitude of the reciprocating rectilinear inertia forces of the engine. Means are provided for compensating for the resultant of the centrifugal force of the first counterweight and of the reciprocating rectilinear inertia forces, such provision comprising at least one second counterweight rotating in the same direction and at the same speed as the crankshaft and adapted to produce a compensating force whose direction always passes through a point disposed in the central plane of the engine and symmetrical of the center of rotation of the first counterweight relative to the plane defined by the cylinder axes.