Unlocking the Mysteries of Locks, Keys, and Safes

How To Fix A Mortise Lock

If your home is more than one-hundred years old, it may have mortise locks. Mortise locks install on the inside edge of the door and use a deadbolt and separate latch.

However, the lock mechanism can fail because of dirt and rust, but you don't have to replace it. Some simple fixes can restore the lock and preserve the antique value of your home. Fix a mortise lock by following these steps. 

Remove Paint

To fix a mortise lock, gather:

  • screwdriver 
  • heat gun or blow dryer
  • putty knife
  • utility knife or razor blade 
  • #0000 steel wool pad
  • pressurized air
  • vise grip 
  • graphite lubricant 

Check the mounting plate and screws for paint, which may prevent the lock from working. If there is paint, score around the perimeter with a utility knife or razor blade, and scrape the paint from screw heads using the flat-blade screwdriver. 

Take a photo to help you recall the lock assembly, if needed. Remove the mounting screws, and press the lower edge of the face plate with the screwdriver, and set the screws aside. Heat the paint to soften it, and use the putty knife to scrape it off the plate. 

Realign the Lock

If paint isn't the problem, try to realign the lock. Use a screwdriver to detach the screws on the lock cylinder. 

Insert your key in the lock to point up, and slowly work the lock to the front of the door. Reinstall the lock cylinder, and tighten the screws to realign the lock.

Clean and Lubricate the Lock

Detach the mounting screws on the base of the knob, and pull it from the spindle, the straight piece on the back of the knob. Check the spindle for damage. Be aware not all parts attach to the spring, so detach the parts carefully. 

Loosen the screws holding the lock case, and pull it from the door. Undo the screws on the case's mounting plate to expose the lock. To release the deadbolt, push the gate to the top, lift it over the cam, and decrease tension until you pop the gate from the pin.

Clamp a vise grip on the case body to hold it in place, but not too tight. Polish the case and deadbolt with a #0000 steel wool pad, and use pressurized air to blow dust from the case. Spray the lock mechanisms with lubricant where metal contacts metal. 

Reinsert the side cover, and test the lock by pushing the knob shaft into the hole. Then, try the key that works the deadbolt. Reinsert all parts when you get them working correctly, and tighten the screws.

If you are still unable to fix your lock, seek assistance from a locksmith. Locksmith services vary greatly, and they can offer the expertise you may be lacking.