How to Change the Mortise Lock on a Main Door

Mortise locks are installed differently than most common door locks. Instead of a lock cylinder, mortise locks feature a large lock case that fits into the door edge. They are more secure than cylinder locks and can be re-keyed without changing the lock trim. Because mortise locks are more expensive than basic key-in-knob or deadbolt locks, keeping the existing trim is an economic choice. If both the trim and case must be replaced, the new lock must be at least as large as the original lock in order to fit the existing lock holes.

Philips screwdriver

Instructions

- 1
  Lift the trim plates carefully, and remove all visible trim screws with a Philips screwdriver. Remove the edge plate screws and trim cover. Remove the strike plate screws and plate if you are replacing the trim.
- 2
  Remove the edge plate mounting screws with a Philips screwdriver. Pull the door trim and knobs or levers from the door panels. Remove all visible lock case mounting screws from the door edge and panels.
- 3
  Pull the lock case from the door edge. Measure the lock case, trim pieces and all lock holes in the door for replacement parts. Take the case to a professional locksmith if you cannot find a suitable replacement at your local home improvement store.
- 4
  Slide the new lock case into the door edge. Install all mounting screws in the door edge and panels with a Philips screwdriver.
- 5
  Insert the knob or lever into the exterior door panel, and secure it with mounting screws and a Philips screwdriver. Install the interior knob or lever, and secure it with mounting screws. Install the edge plate and screws.
- 6
  Replace or slide the lock trim over the knob assembly, and then secure it with trim screws.
- 7
  Reinstall the strike plate and screws.

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