I have a set of valve covers and a carb I would like to polish. To date I have tried everything from compounds, to 1 micron slurry, to muriatic acid, all of which worked well and did get rid of white oxidation, and did give a glossy look. However, especially on the valve covers (aluminum) there are dark splotches I just cant seem to rub out. Any ideas or products out there to take care of this?

Are you hand rubbing or using a buffing wheel? Try a buffing wheel and compound.

hand rubbing for many hours with blue magic liquid metal polish, and 1 micron aluminum oxide powder mixed with a little water

If you do not have a buffer buy a buffing wheel for your electric drill. It does not work as well as a bench fixed buffer but in a pinch it will work. Be sure you get a thick buffing wheel and use 3m heavy duty buffing compound but first you can use 2000 grit wet sandpaper and that will cut your buffing time in half. After buffing with the heavy duty compound switch to a med grade polish and the finish it off with a very fine alum polish for that great shine.Keep your wheel clean every 5 min of polishing clean your polishing wheel and add a small amount of moisture to the pad. When you are finished you may want to clear coat to prevent oxidation.

Rod

Every serious car enthusiast needs a buffer motor but the prices of a good one are high. A few years ago I picked up a used bowling pin resetter motor (or whatever it's called). It was 1.5 hp at 3600rpm with a long 3/4" shaft. Even with a large 12" sisal buff and lots of pressure I can't slow it down. Other friends have used washing machine motors but had to extend the shaft. I got a real powerful buffer for less than $25 although it has only 1 shaft but at the price I could afford another one.

Can you post a picture of the valve covers?

Before you scratch the daylights out of your aluminum covers by using the wrong equipment and aggressive compounds let me get this straight... you say they are shiny and bright except for some brown spots? If that is the case then you may need a specialty polish for those discolorations. Another option is to bring them to a metal polisher to do professionally, you should be able to find one in the yellow pages.

Perhaps it may be cheaper and better in the long run to just replace the covers?