Soaking it in a product called Evaporust for a couple of days worked for me. This BB shell was quite rusty.
More pics of this project on my Flickr:
http://www.flickr.com/photos/3915149...th/5189018750/
I liked the stuff so much, I purchased a 5-gallon quantity to do this:
More pics of this project here:
http://www.flickr.com/photos/3915149...th/5735724952/
Good luck!
Alex