Abstract: A chain drive assembly for an internal combustion engine comprises a chain tensioner (6) that acts upon a chain (2) that is used to drive the cam shafts (4) of the engine. The tensioner has a hydraulically actuated plunger (30) which is moveable within a housing and biasing means in the form of a solenoid (34), compression spring or motor that urges the plunger outwards of the housing at least when there is no hydraulic pressure. The tensioner is controlled by means of a control unit (8) that receives signals from various transducers that transmit signals providing information in relation to the performance of the engine. The control unit receives the measured information, calculates the desired tension to be applied to the chain and transmits the control signal to the chain tensioner so as to operate the biasing means or control the hydraulic pressure so that the desired chain tension is applied.