Abstract: A four-stroke reciprocating piston internal combustion engine with an intake valve an exhaust valve and a valve drive assembly (18) driven by the crankshaft (4) for actuating the intake valve (8) and the exhaust valve (10). A mixture-preparation device (15) supplies an air/fuel-lubricant mixture to the crankcase, which together with the piston functions as a pump for the mixture charge. A valve drive assembly housing (19, 20, 21, 22) comprising one or more sections (19, 20, 21, 22) and the intake channel (16) is supplied with a connecting duct (17) communicating with the crankcase volume (12) either by being connected to the crankcase or the cylinder, or by being connected to the valve drive assembly housing (19, 20, 21, 22), which communicates with the crankcase volume (12), and the communication from the intake channel (16) to the crankcase volume is arranged through at least one valve.