Casement windows are great options for many homes because they allow you to open your window and get good ventilation however there are some problems with this design. They normally can not use screens and additionally you are dependent on a mechanical crank to open and shut the window where sliding windows don’t have this problem. On the other hand they are pretty secure and weather tight so many homes do use them.
A friend writes about a problem they are having with one of their casement windows. Over time the window has shifted due to wear and settling of the house. At this point closing the window completely is very difficult and often requires intervention from the outside to give it a nudge while cranking inside. This is not really a good situation and it means that the window stays closed more often than they would want.
As you can see in the image there is a small groove that is being dug into the bottom flashing of the window sill. When the window is closed it is hanging up on the heads of the screws that are protruding slightly from the bottom of the window where the mounting arm for the crank attaches.
The first thing to do is to make sure that the screws are in as far as you can get them. This may mean removing the window from the frame. If the screws are protruding in a way that is not normal then you will have to repair the mount so that they are flush. If they are protruding in a normal way then the settling of the window may have caused this issue vs wear or maintenance.
The best option in this case would be to remove the moldings around the inside of the window and look for shims that are installed around the window to make it square and fit the framing opening. If you have shims at the bottom of the window you can try adjusting them by removing a screw that holds the window in place.
Making this adjustment can be difficult and if you find you can not work just on the area below the window you will end up having to remove the entire window to remount it.
Another option is to do a temporary fix by using a wood dowel and forming a channel where that gash is in the bottom flashing. This will give you some room for the screw or nut to clear the flashing and should work for at least a few years.
Only do this if you know the flashing can be bent without causing damage to the window. You do not want to cause a leak or make the problem worse.
Check the flashing with a screw driver and see if you can bend it down or if it flexes down before you try forming the groove with your hammer and dowel. Be as minimal as you can just so you can get the window closed.
Final Note
Situations like this are never really perfect. The best repair means removing the window glass frame from the unit and repairing it and possibly rehanging the window in the framing opening.
The last thing you want to do is make problems worse so work slowly and if necessary you can call a window repair person to do the work. However always ask for an estimate before work is done so you can justify their cost vs you taking the time on your own.