A casement window crank is the component on the window that allows it to open from side to side. What defines a casement window from other windows which open on hinges is that the hinges are always attached to the side of the frame, not the top or bottom. A casement window will be opened by the use of a crank or by hand.
There is a ratcheting mechanism or friction mechanism in the crank which allows the window to remain open in the wind. Sometimes you'll have problems with the crank sticking, making it difficult or impossible to open the window properly. If you find that the crank is damaged beyond repair, or you simply want to change the look of the crank, you can replace it.
Step 1 - Remove the Arm and Assembly
The casement window crank works by way of an arm moving the window in and out. Open the window and remove the arm. It should be a fairly simple procedure. Depending how the crank is made, it may be necessary to remove some screws holding it in place. Remove the assembly from the window. Again, it is a simple procedure of removing screws. Some may be hidden and you might have to remove a cover to access them. In the event that your mechanism is attached by nails, you will need to carefully pry the assembly away from the window. Discard the mechanism, but keep the screws. You may want to use these in your installation.
Step 2 – Replace the Assembly
It's best if the new crank you have purchased has the same footprint as the old one. It's also ideal to use the same screw holes to mount your new assembly, including using the same screws. Install the window assembly first, screwing the screws back into the old holes. Be sure that the assembly fights snugly, but do not over tighten the screws.
If you can not use the same holes, you will need to measure how the new arm and assembly will fit your window. Line the new assembly against your closed window and mark the new screw holes. Your crank may or may not come with a template. Be careful when screwing new screws into the sash or frame, so that you don't damage the glass. You will want to fill the old holes in with a crack filler and allow it to dry. Then you will need to sand and repaint the repaired area. It is easier to do this before installing the new hardware, although it's not necessary.
Once the assembly is installed, replace the arm. The crank should work smoothly. Maintain occasionally with household oil.