How to Change a Mortise Lock Cylinder

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Last Updated: December 26, 2024

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

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Remove the two retaining screws and set aside.
Most likely it is at the bottom (six o'clock).

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On some applications there may be two set screws, one for the outer cylinder and one for the inner.
Use extreme caution not to cross thread the cylinder as this may ruin the entire lock!
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.
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.

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Tips

Purchase a few trim rings of different depths when you buy the new cylinder. You can make one trip to return them once you're finished rather than running back and forth and having to disassemble the lock multiple times.

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You can purchase cylinders that do not require keys to operate them to install on the inside if you have inner cylinders. Keep in mind that you may want keyed inner cylinders if you have a window or side lite in your door.

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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.

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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!!!!

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