Tucker:

Any discoloration can be polished off an aluminum casting. But unless the casting was shiny to begin with, it looks odd until you polish the entire engine. If the engine came with a dull finish a bead blaster will serve, if used with care. You will find a bead blaster tank at many auto repair shops, just be sure it is loaded with glass beads, the same tank will work as a sand blaster too, the sand is way too rough.

In heavy trucking the more weight you can fremove from the rolling stock, the more weight of freight you can carry. In this quest most modern trailers have aluminum skins on their bodies, and keeping them shiny was a problem, so they were usually painted. Until some smart fellow found how to keep them shiny with a chemical cleaner. This chemical cleaner is a very mild solution of hydrochloric acid. Go to or call your local truck stop, ask if they have the chemical wash for aluminum trailers. You might be able to bum a pint or so of their mix. It's not expensive if they want to charge you, and either way it's easier than getting reagent HCl and mixing your own. Be sure to use rubber gloves, and take care. The acid is mild but it will still give your hands a sunburn if you're careless.

The acid wash will restore the original finish, shiny will be shiny, and a matte finish will still be dull.

Bill.