INSPECTION: Just as with the housing and cover plate, it's not uncommon to see numerous radial scratches in the outer rotor's hardened peripheral surface. The internal surfaces may even have minor gouges from debris in the oil over time. Unless deeply gouged, most of these wear marks or machining imperfections can be satisfactorily smoothed over and polished to a glass like slippery surface.
SMOOTHENING: First take a 6" length of 80 or 100 grit emery cloth and begin evenly sanding the surface at a 45 degree angle to the grooves to better sand them "over". Do not concentrate too much in one particular spot so as to not create any slight deformations, but rather evenly sand the entire perimeter. The goal here is to smooth out the scratches and grooves, not necessarily remove them. Since oil pressure loss due to leakage through the grooves is not a concern here, the goal here is to provide as smooth and slippery surface as possible to reduce friction and heat.
Once the outer perimeter is satisfactorily sanded, move to the inside of the gear teeth. Once again, smooth over what you can but you do not want to remove any appreciable amounts of metal but rather just take out any burrs and make the surface as smooth as possible.
The top and bottom face of the rotor is another story, here you can remove more material (as long as it matched the final height of the inner rotor) since you can adjust the headspace of the assembly in the housing later. Take a 8x11" sheet of coarse grit emery paper in 80 or 100 grit place it on a known smooth surface such as a marble counter top. Lay the flat face of the outer rotor on the emery paper and begin evenly sanding the surface being sure to move the rotor around the paper and not just in a single back and forth motion. Do the same ot the other side.
Once you have the entire outer rotor sanded move up to 240 grit emery cloth and cover the same areas, thus smoothening the surfaces you just prepped. The 80 grit removed some minute material while the 240 removes the scratches left by the 80 grit. One that is completed, you can use a finer grit paper with a dab of oil to make the surface smoother and smoother before the final buff. Finish sand the outer surfaces, the inner surface and the top and bottom flat surfaces.
Once you have completed the sanding procedure your outer rotor should look like the illustration to the right. Notice that the original deeper grooves still remain in the surface but are much smoother while the minor scratches are gone. This illustrates you did not remove too much material but you dramatically smoothened out what was there. Also notice the flat faces are much smoother indicating more material we removed here which can be adjusted later during assembly. Also be sure to deburr the sharp edges of the pump to reduce stress risers and eliminate these edges to chip off under operation and be sent into your oil supply.
POLISHING: Once you have completed the sanding procedure your use a bench grinder mounted buffing wheel to further smooth the outer rotor and the flat top and bottom surfaces. First use Tripoli rouge compound for a coarser smoothening, then use the softer White rouge for the final buff to a high lustre. Then use a felt fob mounted to a high speed drill press or Dremel tool to buff the inside gear surfaces. Remember once again to buff all the surfaces evenly and uniformly. Buffing compound can remove additional metal as did the sanding operating, so care must be taken not to concentrate only in one area instead of evenly across the entire surface.
The illustrations to the right show the high lustre that can be achieved and the incredible amount of smoothness that is able to be achieved. While only the deepest grooves may still remain, there is a significant reduction in oil leakage potential across the previously numerous scratches and a dramatic improvement in friction reduction and cooling benefits as a result.
FINISHED PRODUCT: The photo to the right clearly shows how smooth and slippery the surface now is and most of the scratches and grooves are removed and the one or two that remains are fairly insignificant and will not adversely affect the pump's sealing characteristics.