a fixation or stabilization of the rotor relative to the stator in the direction of the axis of rotation accordingly by inserting possibly screwing the fastening member 140 which may be a threaded bolt into the cylindrical element 112 and the hole 125 the rotor may be fixated relative to the stator in the axial and radial direction such that the main bearing may be disassembled without causing displacement or misalignment of the rotor and stator relative to each other thereby maintenance work can be performed on the main bearing without having to disassemble the generator and lowering the corresponding disassembled part to ground level the fastening member or members 140 may be stored within the main shaft 102 or nacelle not shown for convenient access by maintenance workers or they may be part of the tools that are carried by the maintenance workers fig2 shows a schematic overview of a wind turbine generator at an initial stage of a bearing maintenance procedure in accordance with an embodiment most structural elements are similar to those of fig1 and a repeated description of similar structural parts will accordingly be omitted more specifically fig2 shows a state where the rotor of the generator which is arranged at a bed frame 204 has been locked in an appropriate angular position by means of the brake disc 227 rotor lock 228 and a brake and lock bracket 229 which is fixed relative to the main shaft 202 and bed frame 204 a fastening member 241 has been inserted through a cylindrical element not shown and a hole not shown aligned therewith in the state shown in fig2.