Depending on how large the part is, you could try sandblastind or bead blasting in a cabinet. All those rust killing products are extremly hard. They tend to bond into the metal. If the parts are very small get a gallon can of carb cleaner (nasty stuff), and let the parts sit over night. Than using a stiff brush clean off the loose material. If needed, dry off the part and bead blast it right away.
