How to Replace a Mortise Lockset

Mortise locksets are an old-fashioned dead-bolt/spring latch combination door fastener. They are used instead of having a cylindrical lock separate from the existing doorknob. A mortise is a hewn rectangular groove that is carved into the door, into which the lockset is recessed. Mortise locksets are often found in older houses, and replacement becomes necessary if the existing hardware is broken or rusted, or if you would prefer a different style from what is currently on the door.

• 1

  Remove the existing lockset by taking out the upper and lower screws on the face plate, removing the handles and dead bolt button, and sliding the apparatus out of the mortise.

• 2

  Fit the new lockset into the existing mortise. Try to purchase one the same size as or slightly larger than the old one. If it is larger, you may be able to enlarge the mortise with a chisel; if the lockset is much smaller, you may have to replace the whole door.

• 3

  Install the cylinder plug, if there is one, by screwing it into the available hole. Apply a piece of tape after lining up the notches to hold it in place.

• 4

  Slide the lockset into the mortise and secure it with screws. If necessary, place a shim on the cylinder side of the door between the door and the lock to prevent the bolt from pulling the lockset off-center when engaged.

• 5

  Push the spindle through the door from the inside if using handles over levers or knobs (follow the instructions for your lockset if that is the case), facing the V-groove toward the lower hinge on the door. Secure by inserting the screw and washer from the outside and tightening.

• 6

  Cut the thumb piece to size so it engages the lever at the base of the lock.

• 7

  Thread the cylinder into place until it sits against the trim on the opposite side of the door.

• 8

  Install the provided bolts to hold the exterior trim.

• 9

  Measure and saw the thumbturn tailpiece to the length that it extends halfway through the lockset.

• 10

  Install the trim and handles according to your lockset's included instructions. These all vary by manufacturer and style.

• 11

  Tightly screw the cylinder set screw, located just above the deadbolt on the face plate. Use a handheld screwdriver to prevent over-tightening. If provided, put the armored front or face plate in place and secure with screws.