This sprocket is a slip fit...it slides over the shaft and key....and as you have found, it is very brittle metal. A conventional gear puller may work if the fingers are small enough to get between the flange and the engine...what most guys do is spray the crank with PB Blaster or other penetrant, let it soak, then gently use a wide slim piece of thin metal (a little heavier than flashing)on Opposite sides of the sprocket at the same time and gently and evenly pry it forward..the key is evenly. I have repaired my sprocket using silver solder (just like you the first time I chipped the inner flange)and filed it smooth. Another method and the one I recommend is to put on a heavy glove and pull on the sprocket HARD while wiggling it. If you use the penetrant, it will come off. No need to remove the key....and I would NOT use heat or a hammer on it. Hope this helps. One guys opinion.