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How to change door cylinder lock
Feb 11, 2005

Question: My front door has an old-fashioned mortise lock, the kind with a big escutcheon plate and a long-shafted key. Is there any way I can change this to a modern, pin-type cylinder lock without having to replace the door? 

Answer: Replacing a lock is not difficult. Lock replacement kits are available through locksmiths, building supply dealers, and hardware stores. These come with all the parts and complete installation instructions. 

The task has been greatly simplified with printed templates which are included and drilling rigs (which can be rented or borrowed from dealers) which assure correct positioning and size of drilled holes. 

Before you purchase a new unit, jot down a few notes about your existing lock installation. This will help the dealer in advising you in your selection of a replacement. Information should include  the type of lock and if it’s mortised or bored in. 

Take into consideration the diameter of lock mechanism hole and the distance of the back set — this is the distance from the edge of the door to the centre of the doorknob and is normally 2 3/4 inches, but can vary. 

Also, coinsider the type of latch front, the shape and dimensions of the part of the latch bolt which shows in the edge of the door, as well as the thickness of the door since most locks are designed to be accommodated in standard doors of 1 3/8 to 1 3/4 inches thickness. The installation procedure will vary, depending upon the replacement. Step-by-step procedures will be provided with the kit you purchase. 

Described below is the procedure for replacing an old mortised lock with a new cylindrical unit. 

Remove interior and exterior knobs and hardware from the old lock. A screwdriver and perhaps a pair of pliers should do the job. 

Remove screws and set screws from the latch face on the edge of the door. Next, score the old paint around the edges of the latch mechanism with a sharp knife, and slide out the old mortise lock mechanism. Cut a block of scrap wood to fill mortise. Glue the block of wood into door mortise, seal the holes on the sides and edge of the door with wood putty and refinish the surface of door to match. 

Using the template supplied with the new lock, mark off locations and sizes of holes for the new cylindrical lock. Drill new holes in the door for cylinder and latch mechanisms. Install and screw in the new latch. Remove the old strike plate from door jamb. Mortise as needed to accommodate the new strike plate and latch bolt. 

Attach the new strike plate in its position on the jamb. Slide the lock cylinder into place with its keyhole properly positioned and be sure that the lock housing engages correctly. Attach the mounting plate to the inside of the door and snap on the trim and the knob. 

Lock problems are apt to cause a great deal of inconvenience. They usually require immediate attention. 

Although failures seem sudden, lock problems tend to develop gradually. Many of them can be corrected with some preventative maintenance at the first time of trouble before they become serious. 

Over a long period of time, locks will age and wear out. When this happens, and the lock mechanism fails or malfunctions, it is often simpler and less costly to replace a lock than to attempt repairs.