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How To Polish Your Manifold (and other aluminum)

By Rob Robinette

When I pulled my manifold to replace my rubber vacuum hoses with silicone I decided to polish the manifold (and turbo inlet pipe). It’s not easy but it looks great and I got a lot of satisfaction in doing it myself. I’m now eyeing my GReddy intercooler and wondering how tough it would be to polish the top of it. Some safety notes: You must wear safety glasses and a dust mask (aluminum dust is bad for you). I also recommend wearing ear plugs because you will be using the drill for long periods of time to sand down the metal. You can always find a Harley-Davidson dealer that can do metal polishing for you, I know I'd seriously consider going that route if I had to do it again.
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Polished extension manifold

What You Need

What you will need: 40, 80, 180, 220, 320, 400 and 600 grit sandpaper (40, 80 & 180 were 5 inch power drill disks ($17)), a drill, a mandrel for mounting polishing disks on the drill (available at ACE hardware $5), two 6 inch polishing wheels (ACE $13), a Dermal tool or high speed grinder to get at the hard-to-reach places, conical shaped sandpaper drums (Bright Works  $15), inch cylindrical sanding drums (ACE, course, medium, fine $8), conical shaped felt bobs for the Dermal tool (ACE $8), tripoli and white metal polishing rouge (ACE Hardware or Bright Works $13), and clean rags. Bright Works can be reached at their web site: www1.minn.net/~bright-1 and (612) 429-4439. They sell a good book and video on metal polishing. Home Depot also has a very good assortment of polishing supplies in its tool crib area.
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Polishing tools

Sanding

I started by using 40 grit (course) sandpaper on a 5 inch wheel in my drill. This will take off the rough sand cast finish on the manifold and remove the casting ridges from the sides of the two outboard intake tubes. I used a small 40 grit sandpaper drum to get to areas that I couldn’t reach with the 5 inch disk.
I then moved up to 80 grit (medium) sandpaper and went over the entire manifold. Do the same with the 180 (fine) disk. If you encounter an imperfection that you can’t remove with your current grit, go back to a heavier (lower number) grit sandpaper and remove the blemish. I used some conical sandpaper drums (available from Bright Works in many grits) to get to the hard to reach areas.
Next I used sandpaper sheets and hand smoothed the manifold by wrapping the sandpaper around a foam sanding block. You will need to step down from 120, 180, 240, 320, 420, and finally 600 to get the metal smooth enough for final polishing. Finish sanding with a gentle wet sanding using the 600 grit. This is time consuming. It took me about 5 hours for all of the sanding (drill and hand).
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Polishing

Polishing the metal was easier than I expected. The key is to make sure you have a consistent wet sanding 600 grit finish on your aluminum part before you start. Any scratches or imperfections visible will still be visible after polishing, it will just be a shiny imperfection. I used two, 6 inch polishing wheels that I got from ACE hardware (Dico #26 for the tripoli, #36 for the white rouge). The back side of the Dico polishing wheel package has a list of suggested wheels for the two rouges. You must use two different wheels for the two rouges.
Keep the manifold at room temperature or warmer. This is important, the rouge will goop up if the part gets cool. I used a propane heater in the garage to keep the parts warm. Gently put the stick of tripoli rouge against the rotating polishing wheel for a about two seconds to transfer the rouge to the wheel. Begin polishing the manifold with the polishing wheel. Don’t push so hard that the wheel slows down much. Polish a small, four square inch area at a time (the wheel heats the part and it shines up best when it's warm).
Be careful here, the wheel will grab unexpectedly and can propel the part or the drill across the room. The polishing wheel will also grab onto sharp edges, so go easy. Mounting the polishing wheels on a bench grinder is an option that works well but there are times when the drill mounted wheels are easier to maneuver. Reapply the rouge every couple of minutes. Keep going over the part until you get a good shine. I used my Dermal tool with a conical shaped felt bob to polish the hard-to-reach areas. You will need two separate bobs for the two polishing rouges. When you have a good, chrome-like shine, clean the part with a cloth and switch wheels/bobs and use the white rouge to bring out a mirror like shine. You have to clean the part thoroughly before you move to the white rouge. When you use a polishing wheel after it hasn’t been used for a few hours you must "comb out" the wheel by rubbing it against a wire brush or a flat blade screwdriver. If you don’t do this you won’t be able to polish the part to a shine.
This is hard work but the manifold (and turbo inlet pipe, intercooler pipes, etc.) look great. It really changes the look of your engine compartment. Good luck.
Rob Robinette

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