Constructional improvements in a two-stroke opposed piston engine operating with stratified charge

A two-stroke engine with opposed pistons moving in cylinders of different before having a common axis, which are each fed separately by a relative crankcase-pump, the cylinder of smaller bore being fed with richer fuel-air mixture, and the cylinder of greater bore being fed with less rich mixture, the two cylinders communicating to form a combustion chamber, wherein the two cylinders are connected by a bell-shaped portion constituting the combustion chamber, and transfer ducts for the richer mixture open into the cylinder of smaller bore tangentially at its lateral wall, wherein the lateral wall surface of said combustion chamber is a surface of revolution, having a generating curve which is formed substantially by arcs of a circle which are tangential to each other, said generating curve being inclined to the axis by an angle of about 3.degree.-7.degree. at that end which connects to the smaller bore cylinder forming a first surface whereas this angle is about 70.degree.-80.degree. at that end which connects to the other cylinder forming a second surface, wherein at least one spark plug is located substantially at a junction of the first and second surfaces.