The motor I'm building up now had been pressure washed/degreased and left in a shed for a while. As a result it had a lot of corrosion. I used a 3M "Roloc" white finger disc to clean it up. It leaves some swirls but I does a pretty good job.
You need the white version as it is the finest - good for aluminum. A body shop supply place might have them. My local place didn't have the white ones though.
-Chris
