Rotor lock system for a wind turbine

A rotor lock system for securing a main shaft assembly of a wind turbine in a substantially stationary position, the main shaft assembly comprising a main rotor shaft supported by a base frame and rotatable about a longitudinal axis relative to the base frame, and the rotor lock system comprising:

• a locking disk associated with the main rotor shaft and provided with a plurality of locking apertures, each of the plurality of locking apertures extending through the locking disk in a direction substantially parallel to the longitudinal axis;
• and
• a locking unit comprising a first end arranged to engage with one or more of said plurality of locking apertures and a second end supported by a mounting feature associated with the base frame,
• wherein when the first end of the locking unit is disengaged from the one or more of said plurality of locking apertures, the locking unit is adjustable relative to the mounting feature so that the first end moves linearly with respect to the mounting feature, and
• wherein when the first end of the locking unit is engaged with the one or more of said plurality of locking apertures, the locking unit is incapable of being adjusted relative to the mounting feature and the locking disk is incapable of rotating about the longitudinal axis.