The paper presents a qualitative analysis of a crank-and-rocker piston mechanism. In comparison to a conventional piston assembly the mechanism is composed of more elements necessary to convert the reciprocating motion of the pistons to rotary motion of the crankshaft. A greater complexity of the system is balanced by a greater number of advantages particularly visible in the module, composed of four cylinders coupled by the rocker with a single crank journal. A greater number of elements allow an obtainment of better functional flexibility of the mechanism, particularly in terms of the piston movement. This feature can be used to control the course of the engine torque, the heat losses to the cooling system, the reduction of the piston pressure on the cylinder liners (friction and mechanical losses) as well as variation of the compression ratio easily performed during engine operation. The natural characteristics of the four-cylinder module have been highlighted through an internal balancing of the mass forces. The analysis does not contain the elements of design. The design parameters in the analysis are random. They were selected to highlight the properties of the design and show negative and positive features. The relations and remarks included in the paper may turn out useful when designing the mechanism.