A rotor positioning device (113) in a crusher (1) for adjusting a rotational position of a rotor shaft (6). A shaft engager (105) includes a female toothed mating surface (120) for coaxial engagement with a male mating surface (121) at an end of the rotor shaft (6), so they become rotationally interlocked. The shaft engager (105) includes alignable indicator slots (128) that are, in use, alignable with markings (129) associated with an end of the rotor shaft (6), such that said markings become visible through the slots (128) as the rod (104) is rotationally driven by a drive component (107, 108). The markings (129) correspond to hammer positions within the crusher, such that these can be manoeuvred for maintenance (e.g. to top dead-centre positions) before access to the crusher chamber is gained.