Ventilation/lubrication system of the crank chamber of an internal combustion engine, in particular for vehicles with a rideable saddle

An internal combustion engine, of vehicles with a rideable saddle, wherein said internal combustion engine comprises a lubrication system, said system comprising a crank chamber in which at least one connecting rod is accommodated, and a basin or pan for collecting a lubricating liquid, wherein said crank chamber and said collection basin or pan are put in mutual communication by means of a first opening obtained in said crank chamber, wherein the flow of said lubricating liquid through said first opening from said crank chamber into said basin is adjusted by means of a first adjusting element adapted to be switched to an open position so as to allow the discharge of said lubricating liquid from said crank chamber into said collection basin or pan when the pressure inside said crank chamber is higher than or equal to a first predetermined pressure value;

• characterized in that said crank chamber is put in communication with a further zone of said internal combustion engine by means of a circuit which leads into a second opening obtained in said crank chamber, and in that it comprises a second adjusting element which is switchable to an open position in which it allows the introduction of air into said crank chamber through said second opening when the pressure inside said crank chamber is lower than or equal to a second predetermined pressure value, wherein said second opening is obtained in a compartment into which an introduction channel in fluid communication with the exterior of said compartment leads for introducing air into said compartment, and wherein said introduction channel is put in communication with a chain compartment and/or a compartment defined by the flywheel cover of said internal combustion engine, wherein a closed recirculation of air is thus generated from pan into the crank chamber without the need to draw in air or gas from the exterior.