Four-stroke engine

An oil-in-fuel lubricated four-stroke engine comprising:

• a cylinder;
• a piston movably mounted in said cylinder;
• said cylinder and said piston conjointly delimiting a combustion chamber;
• said cylinder having an intake opening and an intake valve for opening and closing said intake opening;
• said cylinder having an exhaust opening and an exhaust valve for opening and closing said exhaust opening;
• a valve housing connected to said cylinder;
• said intake valve and said exhaust valve movably mounted in said valve housing;
• a crankcase connected to said cylinder and communicating with said valve housing;
• a crankshaft rotatably journalled in said crankcase;
• a connecting rod interconnecting said piston and said crankshaft;
• said piston reciprocating in said cylinder to rotatingly drive said crankshaft via said connecting rod and alternately generate an overpressure and an underpressure in said crankcase;
• a valve drive assembly driven by said crankshaft for actuating said intake valve and said exhaust valve;
• a mixture-preparation device for supplying an air/fuel-lubricant mixture;
• an intake channel conducting said mixture to said intake valve;
• a connecting channel connecting said valve housing to said intake channel;
• and,
• said crankcase communicating with said mixture-preparation device exclusively via said valve housing, said connecting channel and said intake channel to facilitate movement of at least a portion of said mixture between said crankcase and said intake channel via said valve housing in response to said overpressure and said underpressure.