A rotor positioning device in a crusher is arranged to adjust a rotational position of a rotor shaft. A shaft engager includes a female toothed mating surface for coaxial engagement with a male mating surface at an end of the rotor shaft, so they become rotationally interlocked. The shaft engager includes alignable indicator slots that are, when in use, alignable with markings associated with an end of the rotor shaft, such that the markings become visible through the slots as the rod is rotationally driven by a drive component. The markings correspond to hammer positions within the crusher, such that these can be maneuvered for maintenance (e.g. to top dead-center positions) before access to the crusher chamber is gained.