I just replaced the drive belt on a Guardian

There is a collar on the power nozzel elbow where the elbow goes to the nozzel. You need to pry it off with a screw driver. Don't worry about it breaking. It just snaps off and on. This will make it easier to get the top aligned. Make sure that the front of the cover is touching the rubber bumper and lay the cover down to the back side of the nozzel. You will have to lean the elbow up when you are trying to get the cover down in place. You'll see what I mean when doing this. When you replace the screws, you'll have one that is shorter than the rest. The short screw goes in the hole on the front side of the nozzel on the part that the motor is not on. Hope this helps.