How to Change a Mortise Lock Cylinder

Last Updated: January 22, 2021

Mortise locks are most commonly found in older homes and in commercial applications. There are many variations, but they all basically work the same. This guide should help you to be able to change the lock cylinder.

Steps

1
Open door partially to reveal the mortise lock cover plate at the edge of the door. Remove the two retaining screws and set aside.
2
Note the position of the keyway as it relates to the cylinder. Most likely it is at the bottom (six o'clock).

Advertisement
3
Remove the cover plate from the edge of the door and back out the set screw that is preventing the cylinder from turning. On some applications there may be two set screws, one for the outer cylinder and one for the inner.
4
Unscrew the lock cylinder from the body of the mortise lock by turning it counterclockwise (to the left).
5
Carefully thread the new cylinder into the body of the mortise lock. Use extreme caution not to cross thread the cylinder as this may ruin the entire lock!
6
Set the cylinder so that the keyway is in the same position as it originally was, usually to the bottom, and tighten the set screw.
7
Test the lock to make sure it is functioning properly. You may have to back out the new cylinder a turn or two so that everything works smoothly. The store where the cylinder was purchased will have trim rings that will compensate for this.Once the lock is functioning properly, re-install the cover plate at the edge of the door.

Warnings

Be sure to tighten your set screw. If the set screw is not tightened the cylinder may be easily unscrewed from the lock body and security will be compromised.

⧼thumbs_response⧽
Helpful 1 Not Helpful 0
If you have keyed inner cylinders you MUST keep a key within easy reach in case of emergency. You may want to tape it to a fire extinguisher or emergency flashlight. You should inform your personnel and anyone who may be locked inside your structure where these emergency keys are. THE KEY SHOULD BE AN ORIGINAL AND NOT A DUPLICATE!!!!

⧼thumbs_response⧽
Helpful 0 Not Helpful 1