Double changeable key lock for safe deposit boxes and the like

A changeable multiple key lock for safe deposit boxes and the like, comprising a lock case, a locking bolt including an integral bolt plate slidably movable in said case between projected locking and retracted unlocking positions and having a pair of longitudinally spaced fence members projecting therefrom, first and second stacks of peripherally gated tumbler wheels rotatably supported about respective parallel center axes in the path of longitudinal unlocking movement of said fence members to bar retraction of said fence members from the projected locking position, the tumbler wheels having gating recesses for accommodating said fence members to accommodate retraction of said bolt to unlocking position, first and second sets of key operable sector levers pivotally mounted on respective pivot posts and having gear teeth couplings respectively with the two stacks of tumbler wheels and having key follower surfaces to be engaged by portions of a guard key and renter key inserted into the lock and rotated to unlocking position to drive the associated tumbler wheels to unlocking position, and said pivot posts for said first and second sets of sector levers having means mounting them eccentrically in the lock case and having change key receiving openings therein for rotation of said posts pivot to positions withdrawing the first and second sets of sector levers to decoupled positions relative to their associated tumbler wheels by a change key to free the sector levers to assume new positions corresponding to a new renter's key or a new guard key introduced and positioned to set the sector levers and their associated tumbler wheels while they are decoupled from each other.