We had the rotor out. I think it could be installed with the rotor still in, but you would have to support it in the back to keep it from falling out. Definitely could not be installed with feeder on. Basically it takes the place of the elephant ears, but it is a single piece. It has a part in the front that slides up on the rotor shaft behind the bearing. So you would have to secure the rotor in the back, take the front bearing support off, remove front bearing, remove elephant ears, and install Axceller kit. If you've gone that far, you might as well take the rotor out and check the rear hub (ours was worn) and check your vanes.