An engine includes a crankcase; an oil sump; at least one balancing shaft mounted in a balancing tunnel of the crankcase, which includes first and second end portions and a central portion extending between the end portions; and a blow-by gas recirculation system having an inlet channel communicating with the oil sump, an outlet channel communicating with an intake manifold, a centrifugal separator arranged between said inlet and outlet channels, and a drainage channel opening into the oil sump for discharging separated liquid. The inlet channel communicates with said first end portion, and said centrifugal separator is housed in said second end portion and is driven in rotation by said balancing shaft. The outlet channel communicates with a gas outlet of said centrifugal separator, whereby, during operation, blow-by gas flows successively through the central portion and the centrifugal separator in a path from the inlet to the outlet channel.