A Beginnerís Guide to Aluminum Polishing
By Stephen Gordon and Mark Strembicke
Youíve seen it at the car shows. Peering down into an event-winning engine compartment you see the reflection of yourself in the valve covers and intakes. Probably cost the guy a fortune sending those pieces out to be chromed. Look a little closer; chances are those valve covers, intakes, and carburetors have simply been polished and you can do this yourself.
Chrome is nice, but it is hard to beat a nicely detailed engine compartment with all of the aluminum parts polished. Contrary to popular belief this does not require a hefty investment in specialized equipment; chances are you already have everything you need in your garage already. Sure, people will send pieces out to be chromed but chroming can end up looking gaudy if not done tastefully and it is very expensive. Polished aluminum on the other hand looks clean and functional.
The theory behind polishing aluminum is similar to any type of polishing. Essentially you are attempting to replace large scratches and imperfections with finer and finer scratches until the scratches are so fine the human eye does not see them. As a final step on metal, the surface is de-oxidized to remove any tarnish.
The length of time it takes to polish a piece is proportional to the complexity, size, original quality, and the standard of results you want to see. Parts with complex inside curves will take longer to polish than relatively flat pieces. Large pieces will take longer than small ones. Parts that begin as rough castings will take longer than those that are machined. If you insist that all surfaces of the part (such as the underneath of intakes which canít be seen) need to be polished then you can considerably increase the time taken to polish the part. Generally speaking, and unless you are attempting to win the Ridler Award at the Detroit Autorama, it is entirely sufficient to polish showing surfaces only.
What tools are needed for polishing? The short answer is sandpaper and elbow grease. There are a few additional power tools that will help the job immensely: an electric orbital sander, an electric drill, an electric detail sander, and a Dremel tool.
Well the short answer is no. The reality is that these machines can substantially reduce the work involved though.
If you have access to a buffing machine, or you are thinking of purchasing a machine, consider the following. The same initial preparation of the metal must be done. Rough castings should be removed and pitting from the casting process must be removed. The advantage of a buffing machine comes into play the closer to final polishing you get, considerably reducing the amount of effort required to get that final shine. By using progressively finer compounds on the buffing wheels, these buffers take the place of the intermediate to final sanding grits and tarnish removers. There is no guarantee of a better result, in fact, if used carelessly they can blunt fine edges on pieces.
So what parts are good candidates for polishing? On the early 70-83 L-Series motor start with carburetor bodies, float chambers, intakes, valve-train cover, front engine cover, and distributor housings. Intakes on later vehicles are aluminum too. Generally, the clutch master cylinder and brake master cylinder can be polished as well. Original Nissan oil pumps on the L-Series motors are aluminum and polish nicely. Even Ďpot-metalí, a mixture of metals, can be polished. If the part rusts, then you probably donít want to polish it.
The part should be cleaned and fully degreased. You have a fairly wide choice of cleaning products at this stage. Products such as SOS pads and Castrol Superclean work very well for cleaning but these cleaners and others will actually etch the surface of aluminum and ruin a polished piece. Use them now to get the part thoroughly clean but donít use them again in this process or any time thereafter.
You may want to remove casting numbers, casting flash, and rough edges. On the other hand it may be important to you to retain the originality of the part. Generally it is easier to grind down the numbers than it is to try to sand and polish around them. Tools of the trade at this stage are rough and fine files, and 40/80/120 grit sandpaper on orbital sanders or drills.
If you need to remove large amounts of material, then a high speed drill/grinder with 40 or 80 grit can be used. A hack-saw or file can be used as well. These are particularly handy for removal of casting flash.
Photographs 1&2: Note the curves on this intake manifold are interrupted by casting edges. This piece will look much better with a bit of work with the Dremel tool.
If the part is a cast part it will likely have a rough, pitted texture. It will be necessary to remove this. Start with the coarsest grit of sandpaper. Power tools can significantly reduce the effort at this stage. An orbital sander comes in particularly handy but you must be extremely careful as you may not have a clear view of the back-edge of your sandpaper. It is quickest to take off as much as possible with power tools and keep hand sanding to a minimum. As you are still working with relatively rough sandpaper and power tools, wet sanding is neither necessary nor advisable.
Photograph 3: Youíll need to decide
80-120 grit sandpaper is a good starting point. Anything lower should only be used for removing large amounts of material quickly.
Opinions vary on sanding technique. Sanding in the same direction can make it easier to identify deep scratches from coarser grits of sandpaper, but runs the risk of creating deeper grooves to remove. With practice you will end up using the method that you feel works best for you.
Stop and clean your sand paper often. If it starts to appear the colour of the metal you are sanding, it is time to replace it. Softer metal like aluminum will plug up sand paper and turn your 120 grit into 40 grit.
Move up to 320 grit and repeat. Once the 240 scratches are completely removed, you can move up to 400 and do it again. From 400 grit, you can usually move directly to the buffing machine if one is available.
By now you will have realized that this is a long process and somewhat frustrating. Sometimes you just need to stop, put the part down and come back to it another day. Sanding with the heavy grit provides fast rewards, but when you drop down to 240, you are removing much less material, so it takes longer.
Donít fret. Over time youíll find you develop your own tools to help you sand your parts correctly and more quickly. Sanding rolls, drums, discs, etc. will all help you.
The progression of sandpaper will depend on the material you are polishing. The softer the material, the larger jumps you can make. Softer material will also plug up sandpaper faster. Again, you will need to test your method for your part.
Photograph 4: The outside edge of this part has been sanded to
400 grit . It is ready for the buffing wheel or finer sandpaper.
For this step you will need clean rags. Dip the rag into the tub of polish, pick up a little, and begin rubbing it in a small area. You will notice the cloth begin to blacken. Rub it in well and then take a clean cloth and rub all the blackened polish back off the piece. Continue this process over the entire piece. You may find that once over is enough but you will get a better finish if you go over the piece two or three times.
If what you see is a bright sparkling finish then congratulations! On the other hand if what you see is relatively dull with thousands of scratches of different coarseness, then you havenít been thorough enough in the sanding process. You will need to go back to the sandpaper.
If you have the money, then a buffing machine can be a real timesaver. I paid under $450 CDN for the machine, some buff pads, buffing compounds, and a heavy iron stand. This machine has proved more than adequate (it is a Ĺ hp unit and works on standard 120V) for the job.
When using a buffing machine, correct compound and buff selection is the key to good results. A variety are available and it really is as simple as following the manufacturers guidelines. Do not mix compounds between wheels and always clean all residue off a piece before moving on to a different wheel. Failing to do so will contaminate the buffing wheels with coarser compound and they will never work effectively.
A buffing machine can also be used to restore chrome and plastic. These arenít easy to polish by hand (I am not sure it is even feasible). If you have plastic lenses or taillights to polish it may be worth purchasing a buffing machine for these alone.
It is also possible to install buffing arbors on inexpensive grinding machines. This works too, but there are some drawbacks to keep in mind. The longer arbors create more side load on the motor bearings when leaning the piece into the buff and you may find that this shortens the life of the motor. This is likely fine for occasional polishing work but may not be suitable for extensive polishing. If longer arbors arenít used, it becomes difficult to buff pieces as there is very little room to maneuver the piece into the buffing wheel. Also, it may be difficult to find a grinder that works at the right speed. With all this said, you can buy a grinding machine for very little money so it is certainly worth a try.
Polishing aluminum is relatively inexpensive if you do it yourself. It isnít for everyone - it takes a fair amount of time and it isnít as durable or shiny as chrome. With this said, it has a unique look and can transform an ordinary engine compartment into something Ďextraordinaryí.