Abstract: An air-cooled, reciprocating piston, internal combustion engine has at least two adjacent cylinder barrels with a plurality of cooling ribs lying substantially perpendicular to the longitudinal axes of the barrels on at least part of the periphery thereof. The intake ports of the cylinder heads are located on the cooling air inlet side while the exhaust ports are located on the cooling air outlet side, and an air deflection cover overlies the cylinder barrels on the cooling air outlet side. The cylinder barrels are provided on the cooling air outlet side with cooling ribs lying substantially parallel to the longitudinal axes of the cylinder barrels. The air deflecting cover is of a configuration such that at least some of the cooling air flowing, in the area adjoining the crankcase, around and between adjacent cylinder barrels, is deflected toward these parallel lying ribs, so that essentially the total flow of cooling air supplied may be used to cool the hottest area of a cylinder barrels.