A cylinder lock includes a lock housing receiving a plug assembly that has a key hole, tumbler pieces having respective toothed parts, and a re-keying unit. The re-keying unit has rotatable gear wheels engaged releasably with the respective toothed parts to reposition the respective tumbler pieces. The gear wheels disengage from the respective tooth parts by moving transversely of a longitudinal axis of the lock housing. Re-keying methods are also disclosed.