A crankcase scavenged and lubricated four-stroke engine (1) comprising especially: a mixture-preparation device (15) for supplying an air-fuel-lubricant mixture; an intake channel (16) connecting to the crankcase or cylinder to supply at least air (13) to the crankcase volume (12); an overflow channel (17) connecting to the crankcase or cylinder and to the intake opening (7) with intake valve (8) to supply to the intake at least air and lubricant from the crankcase volume; a valve drive assembly (18) driven by a crankshaft (4) for actuating the intake valve (8) and the exhaust valve (10); a valve drive assembly housing (19, 20, 21, 21', 22) comprising one or more sections (19, 20, 21, 21', 22) which is/are separate from the crankcase but in communication exclusively with the crankcase volume via at least one small size passage (23, 24, 25, 26, 27), and each section (19, 20, 21, 21', 22) of the valve drive assembly housing has a lowest part situated closer to the combustion chamber, than the lowest part of the crankcase.