I'm doing the traditional and necessary cleanup on the Wonderbus's new heads: opening the air channels, filing out the casting flash between the fins, etc. The surface for the valve cover gasket came with a few scratches and I want to make it flatter and scratch-free. My initial attempt is to use a mill-cut file, held flat against the surface and pushed away from me. While this works okay, little balls of head material seem to suddenly accumulate between the file and the head during a "push", leaving new lengthwise scratches.
What's going on, and is there something that can be done to keep it from happening?