Without teardown, its pretty manual. First make sure all openings are well sealed with duct tape or other means so dust doesn't get inside. After that a small wire brush on a drill, sand paper and a pick of some type to scrape out the corners will get most of the rust off.

A thorough de-grease is important also.

If its very rusty, I would consider a first prime coat of rust stop primer. Rustoleum is available in spray bomb (red) at the home improvement store or rust encapsulator (black) from Eastwood. Then a light coat of grey automotive primer for a neutral color then finish paint.