The invention relates to an internal combustion engine (1) comprising a housing (2) having at least one opening (4) into its inside, which is preferably the engine-oil feed inlet, and with a camshaft (5), mounted inside the housing for rotation about its geometric shaft. The camshaft (5) and the housing (2) have means cooperating with each other and with a device for locking a turnable shaft (6) with respect to the housing, insertable through this opening. In a second embodiment of the present invention, the device consists of a rod (6), the cooperating means in the housing consist in a bore (7) for receiving an end of the rod (6), and the cooperating means on the cam shaft consist of a notch (9) made in the surface of the shaft, which cooperates with the rod. In this way, when there is a need to adjust, repair and/or replace engine (1) components, the rod (6) is inserted through the opening (4) and locked in this bore (7) of the housing (2). In this position, the rod functions as a stop against said notch (9) in the plane surface of the camshaft (5), preventing it from turning about its axis. When this operation is finished, said rod (6) is removed from the housing (2) through the oil-feed opening (4), and the shaft (5) is unlocked. Additionally, the present invention relates to an engine housing (2), preferably for use with an internal combustion engine (1).