I'm having trouble replacing my broken chip ejector fan. I've got a new fan and I removed the old one but the old metal sprocket is still on the armature and I can't get it off. The new fan has a metal sprocket glued into the middle, so I need to get the old one off before putting the new fan on. I've tried PB bolt blaster, heating it up, tapping it, and pulling with vicegrips. Nothing will make that sprocket budge and I am starting to worry that it is supposed to stay on the armature.