by the rear end drive assembly 18 but by the toothed belt 24 as the balance shaft 9 is driven by the primary drive 18 of the engine 1 the drive is transferred to the front end 3 of the engine 1 via the balance shaft 9 and is used to drive the second balance shaft 10 via the synchronous belt 24 thus the second balance shaft 10 is drivable by the secondary drive 24 an engine accessory 30 in the form of an alternator 31 is located at the front end 3 of the engine over the first balance shaft assembly 7 the alternator 31 is provided with an alternator pulley 32 for engaging the belt 24 so that the alternator 31 is drivable by the secondary drive 24 a lower idler pulley 33 is mounted at the front end 3 of the engine 1 below the first balance shaft assembly 7 the lower idler pulley 33 may alternatively be an accessory drive pulley the front end 3 of the engine 1 is further provided with a water pump pulley 34 which facilitates passage of the synchronous belt 24 between the first balance shaft toothed pulley 22 and the alternator pulley 32 the water pump pulley 34 and the alternator pulley 32 are in communication with respectively a water pump 35 and the alternator 31 to drive the water pump and the alternator it will be appreciated that in an alternative embodiment of the invention the second balance shaft 10 could be directly driven by the rear end drive assembly 18 the belt 24 is provided with teeth 27 on a top face 28 and a bottom face 29 thereof so that the first and second balance shafts 9.