Several embodiments of air-liquid cooled internal combustion engines for powering vehicles such as motor scooters. In each embodiment, the engine is provided with a finned cylinder for air cooling and a cylinder head having a liquid cooling jacket for water cooling. A radiator is provided for exchanging heat from the cylinder head cooling jacket and the atmosphere and a single fan circulates cooling air across both the radiator and the cylinder. In all embodiments, the flow across the fan, radiator and cylinder is in a series flow fashion. In many of the embodiments, the components are axially aligned. The fan is driven by the crankshaft either directly, through a gear train or through a flexible transmitter and in one case this flexible transmitter also drives the camshaft. A water pump is driven off of the camshaft for the liquid cooling system.