I recently "refaced" a Groco pump cover that is about the same as our water pumps and it took about 20 minutes. Starting with 400 grit paper on a sheet of glass I took it down at least .024" and then went to finer paper stopping at 1500 which was overkill I know. The Flitz polish then was really over the top but it was very pretty. The point is that the whole project took less time than a good machinist would take and the results were perfect.