How to Convert Mortise Lock to Cylinder？

Upgrading your home's security often starts with the locks on your doors. If you have an older home, you might have mortise locks—those classic, rectangular locks set into a pocket on the edge of the door. While they have a certain vintage charm, they can be difficult to repair or replace, and they may not offer the same security features as modern locks.

A common and effective upgrade is converting your mortise lock to accept a more modern cylinder lock system. This process allows you to keep the sturdy mortise body while gaining the convenience and security of a standard cylinder, making it easier to rekey or replace your lock in the future.

This guide will walk you through the entire process, from understanding the different types of locks to the final steps of installing your new hardware. By the end, you'll have a clear roadmap for completing this valuable home improvement project.

Understanding Your Lock System

Before you start unscrewing anything, it's essential to understand the components you're working with. A solid grasp of the terminology will make the entire process smoother.

What is a Mortise Lock?

A mortise lock is a complete lockset that fits into a mortised-out pocket (the "mortise") in the edge of a door. The lock body contains the latch and the deadbolt mechanisms. Traditionally, these locks were operated by a skeleton key or a bit key, which moves internal levers to lock and unlock the door. While robust, these older systems can be less secure against modern lock-picking techniques, and finding replacement keys or parts can be a challenge.

What are Mortise Cylinders?

Mortise cylinders are the threaded, cylindrical lock mechanisms that screw into the mortise lock body. They contain the keyway and the pin-tumbler system that most of us are familiar with. When you insert the correct key and turn it, a cam on the back of the cylinder rotates and engages the locking mechanism inside the mortise body.

The primary benefit of using mortise cylinders is standardization. They are widely available, can be easily rekeyed by a locksmith, and are compatible with various security levels, from standard pins to high-security, pick-resistant designs. Converting to a cylinder-based system is a significant security upgrade.

Preparing for the Conversion

Careful preparation is the key to a successful conversion. Rushing this stage can lead to frustrating mistakes and extra trips to the hardware store.

Tools and Materials You'll Need

Gather everything you need before you begin. Here’s a checklist:

• Screwdriver Set: You'll need both Phillips head and flathead screwdrivers.

• Drill and Drill Bits: A set of standard drill bits is necessary. A spade bit or Forstner bit may also be needed to enlarge existing holes.

• Tape Measure: For accurate measurements.

• Pencil or Marker: For marking drill points.

• New Hardware:

• Mortise Cylinder(s): Make sure the length is appropriate for your door's thickness.

• Cylinder-compatible Mortise Lock Body: If your current lock body doesn't accept a cylinder.

• Trim Plates/Escutcheons: To cover old holes and give a clean finish.

• New Spindle and Knob/Lever Set: Ensure they are compatible with your new lock.

• Safety Goggles: Protect your eyes while drilling.

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Measuring and Assessing Your Door

Accuracy is crucial. Take the following measurements:

1. Door Thickness: Measure the thickness of your door to ensure your new mortise cylinders are the correct length. You want the cylinder to be nearly flush with the face of the trim plate.

2. Backset: This is the distance from the edge of the door to the center of the doorknob spindle or keyhole. Mortise locks have various backsets, so confirm yours to ensure compatibility with new trim.

3. Hole Spacing: Measure the center-to-center distance between the doorknob hole and the existing keyhole.

With these measurements, you can confidently purchase hardware that will fit your door, minimizing the need for extensive modifications.

Step-by-Step Conversion Guide

Follow these steps carefully for a smooth installation process.

Step 1: Remove the Old Hardware

First, you need to remove the existing mortise lock hardware.

1. Remove Knobs and Spindle: Locate the set screw on the base of the interior doorknob. Loosen it and unscrew the knob. The spindle and the exterior knob should then pull out from the other side.

2. Unscrew Faceplate: On the edge of the door, you'll see the mortise lock's faceplate. Remove the screws holding it in place.

3. Take Out the Lock Body: Carefully slide the mortise lock body out from the pocket in the door. It might be a snug fit, so you may need to gently pry it out with a flathead screwdriver.

4. Remove Old Trim: Unscrew and remove any old keyhole covers or trim plates from both sides of the door.

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Step 2: Adapt the Mortise Lock Body

Now, assess your mortise lock body. Some older models are not designed to accept a threaded cylinder.

• If your lock body is compatible: It will have a threaded hole where the new cylinder can be screwed in. You can proceed to the next step.

• If your lock body is not compatible: You will need to replace it. Purchase a new mortise lock body that accepts a cylinder and has the same dimensions and backset as your old one. Slide the new lock body into the door mortise and secure it with the faceplate screws.

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Step 3: Modify the Door (If Necessary)

This is often the most intimidating part, but with careful measurement, it's straightforward. The hole for the old bit key is usually smaller and in a different position than what's needed for the new mortise cylinders.

1. Mark the New Hole: Insert the new lock body into the door. Use a pencil to mark the center of the threaded cylinder hole on both sides of the door.

2. Drill the Cylinder Hole: Remove the lock body. Using a drill bit or spade bit that is slightly larger than the diameter of your mortise cylinder, drill a new hole through the door at your marked points. Drill halfway through from one side, then complete the hole from the other side to prevent the wood from splintering.

3. Test the Fit: Slide the lock body back into the door. Ensure the new hole aligns perfectly with the threaded opening in the lock body.

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Step 4: Install the New Cylinder and Trim

You're now ready to install the new components.

1. Install the Cylinder: Screw the mortise cylinder into the lock body from the exterior side of the door. Before tightening it completely, make sure the cam on the back of the cylinder is in the correct vertical orientation (usually specified in the manufacturer's instructions).

2. Secure the Cylinder: Tighten the cylinder until it is snug. There are usually set screws on the faceplate of the mortise lock body that you can tighten against the cylinder to hold it firmly in place and prevent it from being unscrewed from the outside.

3. Install Trim and Spindle: Place the new escutcheons or trim plates over the holes on both sides of the door. Insert the new spindle through the lock body and attach the new knobs or levers. Secure them according to the manufacturer's instructions, usually with set screws.

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Step 5: Test the Lock

With everything assembled, it's time to test your work.

• Test with the Door Open: Insert the key and turn it. You should feel the deadbolt engage and retract smoothly. Also, check that the latch operates correctly when you turn the knob or lever.

• Test with the Door Closed: Close the door and test the deadbolt again. Ensure it aligns with the strike plate on the door frame and locks securely. If it doesn't align, you may need to adjust the position of the strike plate.

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Your Next Steps for a Secure Home

Congratulations! You have successfully converted your old mortise lock to a modern, more secure cylinder system. This upgrade not only enhances your home's security but also gives you the flexibility to easily rekey your locks whenever needed. You've preserved the solid construction of the mortise lock while bringing its functionality into the 21st century.

If you encountered any issues or don't feel comfortable undertaking this project yourself, a professional locksmith can perform the conversion for you. They can also provide high-security mortise cylinders for an even greater level of protection.

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