My 8520 had a bad motor when I got it.
I followed Billy G's example and replaced mine with a 1 HP motor from Grizzly, $190 plus shipping.
http://www.grizzly.com/search?q=(motor)+AND+(brand:Grizzly)+AND+(category:Motors)
Bolted right on no mods required, but did require buying a different belt due to larger motor diameter.
I went ahead and replaced both belt since I had it apart. Took a 1/2" x 24" and a 1/2" x 48".
Might consider replacing the motor mounts too, I'll see if I can find where I got them, they're cheap and made a world of difference in vibrations at high RPM..