Polishing 101 - Cast
By: Duane Bertrand
Just bought a cobra kit, life is good, find a donor, life is great, want to detail the engine, ok, start polishing the intake and valve covers, life is hell! So you're thinking of polishing those aluminum parts?
Here's my story and do it yourself instructions.
While checking out some build sites early on, I noticed a couple people who had polished the upper intake. Man it looked good! Well, I've got some time before the kit arrives, might as well polish the intake, and what the hell, let's do those stock valve covers to. Roughly 60 hours later I've got great looking covers and an awesome intake ? however my kit has since arrived and been sitting, and my garage looks like Mount Saint Helen's went off in it.
First note regarding polishing; Al creates tiny dust like particles of buffing compound and aluminum particles. This "dust" is very light and suspends in air, allowing for a nice full coverage of your workspace, in my case the entire garage. Hey, no problem ? I'll just dust it off ? Wrong! this stuff is greasy because of the buffing compound. Take a swipe and you get a nice greasy streak, now it looks 10 times worse than before the swipe. It's now time to get out your best grease cleaner and play "Mr. Clean".
Not only does the "dust" cover your garage, but it also covers you! On the weekend I would start polishing at 9:00 in the morning, and stay in my garage until 9:00 at night. My wife literally had to bring meals out to me as I was covered in this stuff and dare not enter the house. Here's a picture of me after I'd already cleaned off in the garage with grease cleaner, then moved to stage two, wash at the kitchen sink.
This is followed by stage three ? Scrubbing away in the shower. I would have worn long sleeves and pants, but the heat in Houston during the summer is a killer.
The author, if you dare, click to
The other note, prepare to spend ~ 20 hours on your upper (it took me 30 but did not use the sanding method enough thus took significantly longer than it could have), and 10 hours per valve cover (took me 15 hours per cover but you can also nock this down). It just doesn't happen quickly though.
So you're still interested, a sucker for punishment ?
Ok, I'll be your guide through the fiery caverns of buffing hell. First off, check out
www.caswellplating.com. This is the best polishing site I've found. Go to the buffing page and download the polishing guide, How to Buff and Polish Booklet, and buy their recommended materials. Once you've read their guide, you're equipped with the basics. But your journey needs some more tools. Here's a list:
80-220 grit sand paper sheets with sanding block, small sandpaper cones (~1/2" diameter at the widest point, and cylinders (diameter of approximately 1/4", ½", and 2"), bench grinder or bench polisher, the recommended buffing wheels and compound from the Caswell guide (for Al) and it's nice to have a small reciprocating type electric sander like the "mouse" or in my case, B&D's "Sand Storm", and finally, a big tub full of patience.
After reading Caswell, I thought I could start with the Sisal buffing wheel and the Emery compound to take down the cast profile. Did this for one whole valve cover and it took forever. Lesson learned, start off with coarse grade sandpaper, much faster at removing material (they added the sanding and greaseless section in a later version of their guide). Plug in that sander (or sandpaper and a sanding block) and start taking down the casting profile of the flat surfaces. This works great at ensuring a uniform surface. I used this technique on the top of the upper intake runners to get them all even in height. While doing this, switch to your drill, die grinder or dremel and use the cylindrical and conical rollers to bust down the rough profile of the remaining surfaces. Be careful not to "gouge" the surface while using the coarse grid rollers. If you do, you can blend it or work it out completely; it just will take longer. Once you get that looking good, work down to 220 grit. It still will take some creative sanding in the tight corners, that's up to you to figure out as I never found an easy way.
All right, it's looking pretty good, a nice brushed aluminum look, but don't stop now, the fruits of your labor lie not far beneath that surface. Get your Caswell buffing supplies out. I used 8" buffing wheels and put them on a standard 8" ¾ hp bench grinder (with all wheel covers removed). I also ordered the large brick of compound for each level of buff. It turns out you use a lot of the Black compound a medium portion of the brown and not too much of the white compound. I'd get the large brick for the black and brown and a small one of the white (this is assuming you're doing both the intake and valve covers). It's nice to have at least ¾ hp so as not to bog down the beast. If in a garage, tape up a plastic sheet to your ceiling and "curtain off your work space". This will save the rest of your garage from being covered with buffing dust.
Start off with your sisal wheel and work every surface you can get to. At the same time, you can be using the polishing cones and cylinders on a Dremel to be getting into the tight places. Work down to the more delicate wheels and compounds, again per Caswell. When you're finished with the Loose wheel (or Canton Flannel that I used) and white buffing compound, you should have a beautiful shiny intake.
- Click to enlarge any of these
Use the same process for any of the other Al parts on the engine. I also used this technique with the buffing wheels on a drill, and did the machined surfaces on a set of turbines, really makes them look better.
You're probably thinking, now how do I keep the shine. Well I tried the Easton's clear coat for bare metals, and well, it in my case dulled the surface. Didn't like it. So I removed the paint and have left the aluminum bare. They've sat for over 4 months and to my surprise, they still look good. My plan is to leave them bare and when needed, do a quick Mothers
In summary, this was something I was glad I did, but would never want to do it again. However as I'm a glutton for punishment, I'm sure I'd end up covered in grease if confronted with the situation again. Good Luck!
If you're interested, let us know here at
and we can provide a guide to polishing and painting those turbines to get the best look possible.