Abstract: An internal combustion engine comprising: a piston (2) and a cylinder (3), the piston (2) being sealedly mounted to the cylinder (3) and being reciprocally mobile therein between a Top Dead Center (TDC) and a Bottom Dead Center (BDC); also comprising a combustion chamber (4) delimited by the piston (2) and the cylinder (3); a crankshaft (5) provided with a crank (5m) pin (5p); a connecting rod (6) having a small end (6p) rotatably connected to the piston (2) and a big end (6t) rotatably connected to the pin (5p) of the crank (5m) of the crank shaft (5), also comprising at least one cam (7), mounted, rotatably and freely mobile on the big end (6t) of the connecting rod (6) and on the pin (5p) of the crank (5m), which cam (7) by effect of inertia consequent to a rotation of the crank (5m), moves cyclically rotatingly with respect to the pin (5p) and the connecting rod (6) between two operative positions, in which it transmits to the connecting rod (6) an action which adds to the inertia actions of the connectin