Repairing a Full Mortise Lockset

Carpenter Nathan Gilbert takes us on a house call to help a homeowner with an antique lockset. After the homeowner explains her troubles, Nathan removes a century-old mortise lockset from the door before disassembling it to investigate.

Mortise Lockset Parts

Multiple parts make up full mortise locksets. Nothing was standard during manufacturing 100 years ago, so each lock may be slightly different. Here are some general universal parts:

• The lockbox is the carcass that contains all of the small parts within the lockset. It’s also the part that slides into the door.
• The latch is the part of the door that opens and closes with the twist of the door knob. It catches in the door frame and prevents the door from opening without the twist of a key or the knob.
• The lever is typically the doorknob assembly, but there are many parts within the lockbox that work together to make up this part.
• The deadbolt is the heavy-duty version of a latch that slides in and out of a door, and sits deeply into the door jamb.
• The cylinder is the keyed portion of the lockset. It locks and unlocks the door for passage, and connects to the other parts within the lockset to allow for operation.

Repairing a Full Mortise Lockset

Note: Whenever removing parts from the lockset or the door, place them in a small container. These parts can be easy to lose and expensive to replace.

1. Start by removing the set screw holding the key cylinder in place. This is usually on the jamb-side of the lockbox, highest and closest to the keyed side of the cylinder. Also, remove the screws holding the thumb turn to the door and remove the thumb turn. The cylinder should spin loose.
2. Remove the set screw holding the door knob to the lockset and remove the doorknob. Remove the exterior half of the door knob and its shaft passing through the lock, and then remove the entire mortise lockbox from the door.
3. Carefully remove the screws holding the cover onto the lockbox. Be sure to put these small parts in a separate container or trays. Remove the cover and take a picture of everything within the lockbox before removing anything.
4. Survey the lockbox for broken or worn parts. There are many parts in a mortise lockbox, so be sure to perform a thorough inspection. Look for rounded pieces, broken tabs, or parts floating loosely within the lockbox. Carefully remove these pieces from the lockbox and take them to a local locksmith shop for replacements.
5. Spray all of the moving parts within the lockbox with white lithium grease. Be sure to pay attention to any pivot points, springs, or other areas which might experience friction.
6. Carefully reassemble the lockbox using the new parts. Refer to the picture taken in step 3 for any clarification needed. Place the cover back on the lockbox and fasten it with the screws.
7. Survey the door for damage. Older doors can wear down with years of repeated locking and unlocking, so fill any stripped screw holes with the putty knife and wood putty. Allow it to dry before re-drilling the holes.
8. Reinsert the lockbox into the door but leave it loose. Carefully thread the lock cylinder into the lockbox until it is hand-tight before tightening the set screw on the jamb side of the lockbox. Next, reinstall the thumb turn on the inside of the door.
9. Reinstall the exterior door knob, sliding the shaft through the lockbox. Place the interior door knob on the shaft and tighten it in place.

Resource

Nathan removes and repairs a full mortise exterior lockset. All parts and hardware were supplied by Mack Designer Hardware.

Materials

• Small trays
• Various repair parts
• White lithium grease
• Wood putty

Tools