How to Change Mortise Lock Bodies

Removing the Old Lock

• 1

  Locate and remove the four screws in the lock plates on either face of the door. These are usually located in the four corners of the plate and can be removed with a flat-head screwdriver. Turn the screws counterclockwise to loosen and remove them.

• 2

  Remove the set screws under the edge of the inside knob, turning them counterclockwise as before. Remove the inside knob and draw the outside knob and spindle out of the lock.

• 3

  Remove the screws from the edge of the door, typically one at the top and one at the bottom of the lock. Pry the lock body from the door's edge with a small, flat screwdriver.

Installing the New Lock

• 4

  Insert the new lock body into the mortise, positioned similarly to the original. Install the two screws provided with the new lock into the plate -- one at the top and one at the bottom -- to attach the lock to the edge of the door. Tighten the screws by turning clockwise.

• 5

  Install the original spindle back through the square hole in the new lock and reattach the old handle. Replacement knobs are available if yours are damaged and are sold separately in several styles. Install them as you would the original, by inserting the outside knob and spindle, then attaching the inside knob with the set screw under its edge.

• 6

  Attach either the original or replacement plates to the door faces using the original screws or screws provided with the replacement plates. Turn the screws clockwise to tighten.