If it's not something that you'll be able to polish out to a high sheen (i.e. porus cast aluminum), try some WD-40.
The solvents and oils will help to dissolve and lift away grime from the pores. Be generous, but watch where you are spraying--you don't want it all over your belts and you don't want it to dissolve all the lube out of any bearings. While it is an oil, it is a very light one and tends to evaporate relatively fast, so don't count on it to replace whatever permanent lube you just flushed out of any bearing you may spray. That said, it will work well on bare metal surfaces, to clean and leave a very light temporary, protective coat of oil. Soak up excess with paper towels or rags, use a brush to scrub out cracks and crevices. Of course an oily surface could attract more dust, so limit exposure to dusty areas until any excess has been wiped off or evaporated.
Here's a good example of cleaning with WD-40--my stainless steel range hood will get a layer of cooking grease on it, especially after frying stuff. Most soap-based cleaners have a hard time emulsifiying and removing this, but spray on some WD-40 and wipe with a paper towel--the grease will come right off! :thumbsup: