A rekeyable master keyable lock includes a plurality of key followers, a plurality of user racks and a plurality of master racks. One user rack and one master rack are associated with each key follower and are configured to be selectively disengaged from, and reengaged with, the key follower. When the user racks are disenggaged from the key follower, the valid user key can be replaced with a new user key. Reengaging the user racks with the key followers rekeys the lock cylinder to the new user key and invalidates the original user key. Similar functionality applies to rekeying the master key. Either the user key or the master key can be rekeyed without rekeying the other.

A cylinder lock assembly includes a lock cylinder inserted into a cylindrical chamber of a lock housing, the lock cylinder being formed with plate mounting slots, a latch slot, and a main key slot; primary locking plates inserted in the respective plate mounting slots, each of the primary locking plates being formed with a secondary plate recess, a first key slot, and a first latch groove; secondary locking plates inserted in the respective secondary plate recesses, each of the secondary locking plates being formed with a second key slot and a second latch groove, springs being provided between the primary locking plates and the lock cylinder and between the secondary locking plates and the lock cylinder respectively; and a latch inserted into the latch slot, a latch return spring being provided between the latch and the lock cylinder.

A rekeyable master lock includes a plurality of pin gears, with each pin gear engaged with a corresponding key follower. As each key follower rides up and down on the key bitting, it causes a corresponding pin gear to rotate. Each pin gear engages a user gear and a master gear so that, as the pin gear rotates, the user and master gears rotate. Each user and master gear, in turn, drives a corresponding user rack and a master rack. When a valid user key is inserted and rotated, the user racks or master racks are aligned along a common axis and held in alignment by a locking bar. Longitudinal movement of the user gear or master gear allows the rekeying function by decoupling and recoupling the user gear or master gear with the user racks or master racks.