Clean the keyway on both the shaft and clutch with brake clean or something similar. If the key is still too tall just grind it down with a dremel or grinder. It may also be that the keyway on the shaft is a different width than the keyway in the clutch. I retrofit my snowhawk with a team secondary last season and I had to modify the key. The keyway on my hawk was .3" and the secondary was .25". I used my dremel and ground down each side of the key so that the lower portion or snowhawk side of the key fits snug and the secondary side or upper portion fits snug as well.
Hope you get it,
cwh