Abstract: In an internal combustion engine its crankcase defines an oil reservoir and a pump receptacle. A crankshaft journaled in the crankcase carries a crank in the reservoir. A cylinder fixedly mounted on the crankcase is formed with a cooling jacket which communicates with the pump receptacle through communicating bores in the cylinder and crankcase. A pump shaft rotatably secured in the crankcase in the receptacle carries an impeller for common rotation about an axis parallel to the axis of rotation of the crankshaft, and the motion transmitting input member of a drive train, a toothed wheel, is mounted on the crankshaft next to a spur gear which meshes with a spur gear on the pump shaft.