Many older casement or awning windows simply have an arm with several holes along its length. As the window swings out, the holes fit over a peg in the window frame, allowing you to prop open the window at various positions. Newer casement windows replace this arm with a rod on a pivot mount, or with a crank mechanism.
With arm-type windows, the screws can work loose over time. To fix them, see the fix for loose door hinge screws in Chapter 3. Regular maintenance includes cleaning the rod of any grease that might accumulate on it and applying a few drops of lubricating oil to the pivot.
For crank-type windows, the crank mechanism can break or wear down. In this case, it's best to buy a replacement crank, removing the screws from the old crank and taking it with you to your home center to choose a replacement. Occasionally lubricating the crank with a machine oil spray can also smooth its operation (operate the crank several times after you spray to spread the oil throughout the mechanism, keeping a rag handy in case any oil drips out), as can keeping the extension arm free of dirt or grease.
To replace the glass in a wooden casement window, follow the same steps as for a wooden sash window, detailed previously. If you need to remove the window, first remove the crank mechanism, then the window hinges, making sure that you remove the bottom hinge first so that the weight of the window doesn't twist the bottom hinge screws. (It's helpful to have a second pair of hands here.) For newer metal or vinyl casement windows, you probably need to call a glass professional. These windows tend to have weather stripping and energy-efficient gases built into their design, putting them beyond a fix-it solution.