How to Repair a Casement Window

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How to repair and replace a casement window crank or gear assembly.

Casement windows, you know the ones with the crank handle, can be difficult to operate after a while, especially if they are not maintained properly or painted shut. The longer you wait before you perform a few simple repairs the worse the problem will get until the mechanism is damaged and must be replaced.

Repairs can be slightly challenging, but by following these steps, it should be something you can handle.

Tools and Supplies

WD-40 or similar lubricant

Soft Wire Brush, brass not steel that is about the size of a toothbrush

Utility Knife

Replacement Crank

Lithium Grease

Paint thinner or other solvent


Trim Pry Bar

Paper towels or lint free rags

Since you will have to remove the assembly to order the correct replacement, you will need to secure the window until you are ready to install the new parts. Pull the window closed and latch it shut until you have the new assembly and are ready to install it. You may need to have someone push it closed from the outside.


1. Open the window and disengage the arm from the track. In some models you must remove the screws that attach the arm to the sash. You may need help or work from the outside.

2. Remove the mounting screws that hold the hardware to the window.

3. If there are no visible screws, remove the handle by loosening the setscrew that holds it onto the shaft then remove the crank assembly cover to access the screws.

4. If there is no cover, the assembly is mortised into the sill of the window under some trim. Use a trim pry bar to remove the molding that extends across the bottom of the window and is notched around the crank assembly. Most of the time there are no nails, but could have been nailed at a later time so use caution as to not damage the molding. You will probably need to cut through the paint with a utility knife to break the paint seal.

5. Clean the crank assembly with a soft wire brush and a solvent or WD-40.

6. Operate the mechanism to make sure the gears mesh properly and aren't worn. If a replacement is required, contact the window manufacturer. Most windows do not have the manufacturer's name printed on the hardware or window, but if you look carefully in a corner of the window pane you should find the name there. It can also be stamped on one of the edges of the window frame near the weatherstripping. You may also be able to find a compatible replacement at a home center or online. A few links are at the end of the article.

7. Clean the track on the sash's underside with the same brush and solvent to remove dirt, paint, and grime. You may need to work from the outside of the window.

8. Lubricate the window operator with lithium grease and reinstall it following the manufacturer’s recommendations. New components may come with a small tube of lubricant that should be used.

9. Lubricate the track on the sash's underside with lithium grease.

10. Reattach the arm to the sash with the reserved screws and operate the window crank. You may have to scrape away any layers of paint near the hinge side that can bind the window sash and damage the assembly.

11. Clean off any excess grease off the track with paper towels or a rag.

Typical Casement Gearbox Assembly and Arm