Removing Oxidization from Aluminum with Chemicals

Recently, I acquired an 18 year old motorcycle. As I am restoring the "bike" I am interested in finding out if there is anything that can clean the oxidation that has formed on the side plates of the motor? When new, the side plates were somewhat polished and then sealed with a clear coat. In areas where the coating has failed a heavy amount of discoloration and oxidation is present. Using various types of polishing compounds and hours of work the aluminum cleans up, but there must be something that works better. Any information is appreciated.

It is possible that your part was Anodized originally and that it has worn off. If you polish aluminum normally within a day or so the finish is tarnished by oxide (blackens a bit). the only way to get rid of it is change the part or get it anodized again. Changing the part to say a better metal might be an easier or cheaper long standing answer.