A stop disposed in the bottom of the shackle heel bore normally blocks movement of a pin holding the cylinder in the casing. Raising the stop when the lock is unlocked permits the pin to move away from the cylinder freeing the cylinder for replacement.

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a padlock having a replaceable cylinder. More specifically, the invention relates to a padlock having a cylinder assembly and which, when the lock is open, may be removed by the use only of an elongated element such as a wire, following which a second cylinder may be inserted and retained so that the keys used before the change will be ineffective to open the padlock after the change. 
     2. Description of the Prior Art 
     The prior art is replete with examples of padlocks wherein the cylinder may be removed and changed. Examples are: 
     Hanson U.S. Pat. No. 2,141,748, issued Dec. 27, 1938; 
     Dequick U.S. Pat. No. 2,430,391, issued Nov. 4, 1947; 
     Dies U.S. Pat. No. 3,187,525, issued June 8, 1965; and 
     Lippisch U.S. Pat. No. 3,793,856, issued Feb. 26, 1974. 
     The prior art as a body, however, does not really teach a structure in which the cylinder may be removed and replaced with great ease and, at the same time, offer maximum security, unyieldably retaining the selected cylinder in the padlock body. 
     SUMMARY OF THE INVENTION 
     Under the present invention, the bore receiving the shackle heel extends almost to the far end of the padlock body and is parallel to the cylinder. The partition between the heel bore and the cylinder opening is formed with an aperture in line with an aperture in the cylinder and a pin normally extends in the two apertures, retaining the cylinder in the body. A slideable spool-like stop member is provided in the heel bore. This stop member is stepped and a larger step normally aligns with the pin holding it in place. 
     When it is desired to change the cylinder, it is merely necessary to release the shackle and insert a wire or the like through a reduced opening from below into the heel bore and push upwardly on the stop causing the smaller step to align with the pin and permitting the pin to drop out, preferably by turning the padlock on its side and letting the pin drop against the smaller step. After the new cylinder is inserted, the reverse of these steps secures it in place. 
     Other objects, features, and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effective without departing from the spirit and scope of the novel concepts of the disclosure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a sectional view of a padlock embodying the invention showing the shackle in closed or locked position; 
     FIG. 2 is an elevational view, partly in section, showing the shackle in unlocked condition and with a wire W inserted to commence the cylinder replacement procedure; and 
     FIG. 3 is a greatly enlarged fragmentary sectional view of the padlock taken from FIG. 2 and turned 90° in a clockwise direction and showing how the locking pin may be manipulated and the cylinder withdrawn. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the embodiment of the invention illustrated, FIG. 1 shows a padlock generally designated 10. It includes a casing 12 having a shackle 14 generally U-shaped in form featuring the toe 14a and the heel 14b. The opposite end of the casing has a cylinder opening 15 which receives a key cylinder comprising shell 16 embracing a plug 18. The plug 18 has a slot for a key 20 opening to the bottom of the plug. 
     The casing 12 has parallel bores; the toe bore 22 and the heel bore 24 receiving, respectively, the toe and heel of the shackle 14. Compression spring 26 seated in the bore 24 biases the shackle upwardly out of locking engagement with the casing 12 upon the release of the lock. Both the heel and toe of the shackle have recesses 28 and 30 respectively, adapted to be engaged by locking balls 32 when the padlock is locked. The balls 32 are worked by the bolt 34 in the conventional manner. The bolt is held in place in the casing by a C-shaped ring 36. The lower end of the bolt 34 is slotted as at 38 and engaged by a tenion 40 at the upper end of the key plug 18. The heel 14b of the shackle is formed with an annular groove 35 which is engaged by its associated ball 32 when the lock is open. This retains the shackle and casing together. The shell contains the usual spring-biased drivers 42 which work in the conventional manner with the tumbler pins 44 and key 20 to permit the rotation of the plug to open the lock. 
     As shown in FIGS. 1 and 2, the heel bore 24 is provided with an integral slideable stop 46, the lower portion of which may be shaped like a spool with annular guide flanges 48 and a central stepped area having a circular larger step 50 and smaller step 52. Extending upwardly from the spool-like structure is a spacer 54 which is circumposed by the spring 26. Preferably, the spacer 54, when the stop is seated on the bottom of the heel bore, reaches almost up to the heel end of the shackle 14 when the lock is locked. This precludes the upward movement of the stop should an attempt be made by an unauthorized person to move it upwardly. 
     The metal of the casing between the heel bore 24 and a cylinder opening 15 is apertured as at 56 in line with an aperture 58 in the cylinder shell 16. In these aligned apertures is disposed a pin 60 which holds the cylinder firmly within the padlock casing. In its normal condition, the pin is held in place by butting against the larger step 50 of the stop 46. 
     Referring now to FIG. 2, it will be noted that the lock is shown in unlocked condition. The spacer 54 is thereby afforded clearance beneath the shackle heel 14b to permit the stop 46 to be raised by a wire or similar tool W inserted through the stop access hole 24a. The upward movement of the stop 46 is accomplished against the bias of the spring 26. As shown, the space is raised so that the lesser step 52 aligns with the pin 60. Because the pin 60 normally protrudes into the space between the two guide flanges 48, the travel of the stop 46 is limited as the pin hits the respective flanges. In FIG. 2, with the lesser step 52 lined up with the pin 60, the lock is now in condition for removal of the cylinder and this is accomplished as shown in FIG. 3 by turning the lock on its side so that gravity causes the pin 60 to fall against the lesser step 52. At this point, the pin 60 is completely out of hole 58 so that the lock cylinder may be removed leftwardly as shown in FIG. 3. 
     With the key 20, the cylinder 16 and plug 18 may be removed and replaced by a new cylinder and plug having a different key. 
     In securing the new cylinder in place, it is merely necessary to push the new cylinder into the opening 15 to a point where its flange 16a nests in the recess 62 about the cylinder opening 15. Holding the wire W in the position shown in FIG. 3, the padlock is then inverted (not shown) so that the pin 60 may drop down into the aligned aperture 58 to secure the cylinder in position. Thereafter, the wire W is withdrawn and the spring 26 urges the stop 46 to seat at the bottom of the heel bore 24. 
     It may be seen from the foregoing that a simple release for the key cylinder of a padlock has been provided, accommodating quick removal of the key cylinder to be replaced by a key cylinder having a different tumbler combination by merely unlocking the padlock, poking up through the access 24a with a wire W or the like to shift the position of the stop 46 and thereby permit the pin 60 to drop and then withdrawing the key cylinder for replacement with another key cylinder of a different tumbler combination.