Abstract: 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).