To be fair, you deserve an explanation as to what you are looking at. The shiny polished chrome valve cover was what was known in the NAVY as a " show cover " and it was made out of tin. When there would be top brass that would be coming to do an inspection of the ship, the non polished aluminum valve covers would be taken off and the " show covers " would be put on strictly for show. After the inspection, they would be stowed away and the regular more beefy non polished valve covers would be put back on. Now you know the rest of the story.