The present invention relates to the reciprocating internal combustion engine sector and more specifically concerns a mechanical system of linking to the master connecting rod for transmission of the motion of the pistons of an internal combustion engine consisting of a lever, which can be completely rigid or made up of a flexible part and a rigid part, and a connecting rod connected to it that rotates a crankshaft; two coaxial pistons with opposed heads that act practically in the same cylinder and have opposed combustion chambers are connected by two small connecting rods at the top of the said lever, which has its fulcrum—fixed or moving—in the engine bedplate.