I poached this from the above link:
"...First, let me qualify by saying that I'm an amateur in finishing. My work does involve painting steel and aluminum in the marine environment, but only periperially - I don't spec that out. I have been vigorously researching aluminum finishing for amateurs, in conjunction with my interest in homebuilt airplanes.

The process I suggest for most amateurs runs like this:

1. Alkaline degrease
2. Rinse
3. Mechanically remove oxidation
4. Rinse
5. Self-etch primer, applied as soon as possible after the rinse.
6. Top Coat
The degreaser can be anything, well, alkaline and degreasing. Dawn brand dishwashing detergent is fine. Your local auto parts store has something.

Rinses should be hot, if at all possible.

Maroon Scotchbrite pads are the best way to remove oxidation, either the hand pads, or the drill motor mounted "Surface Conditioning" pads. Degreasing and oxide removal can be combined.

Most auto parts stores can at least order self-etching single part non-chromate primers in spray cans or quarts for brushing with a foam brush (problematic, holidays are badddd), roller-brushing (roll an even coat on and tip it with a foam brush, better) dipping or spraying. NAPA carries Martin Senour 7220. Marhyde makes another one. These are one part alkyd systems that have very low health risks, a simple particle respirator is semi-adequate protection. It's crucial to apply the primer as soon as the surface is dry from the final rinse. A mild solvent wipe (alcohol) can be used to speed up drying.

Top coats with this simple system can be any single part paint, from latex to moisture cure epoxies. Acylics with strong solvents, and any two part polyurethane will lift this primer, and ruin the job. But amateurs shold not be using polyurethanes, and especially not spraying them. The isocyanurates will kill them without a supplied air respirator.

This is a "good enough" system. It will NOT produce the same level of performance you'd get by using more toxic forms of degreasing (MEK anybody?), acid etching/deoxidizing, conversion coating, chromate containing primers, and more expensive, nastier paint systems. But it reduces, substantially, the health risks and the toxic/hazardous wastes that consumers DO NOT carefully dispose of.

...
I see too many articles in the aviation hobbyist press advocating the use of "industry standard" practices of 40 years ago. The aircraft industry has done a tremendous job in the last 10 years of reducing it's hazards and it's waste stream, it's time the the hobbyists did the same."

Ryan R. Young

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89 300te 222,222
92 300e 190,000

The topic of painting aluminum comes up frequently with owners of Volvo wagons. The rear hatch door is aluminum, and can require touch-up on the lower portions.

People have had good luck using a self-etching primer, then a finish coat. I cannot speak to the heat resistance of this process, but apprently the primer is available through auto paint suppliers, and they should be able to answer any questions.

Jeff Pierce

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Jeff Pierce

Current Vehicles:
'92 Mercedes 190E/2.3 (247K miles/my daily driver)
'93 Volvo 940 Turbo Wagon (263K miles/a family truckster with spunk)
'99 Kawasaki Concours
Gravely 8120
Previous Vehicles:
'85 Jeep CJ-7 w/ Fisher plow (226K miles)'93 Volvo 940 Turbo Wagon
'53 Willys-Overland Pickup
'85 Honda 750F Interceptor
'93 Nissan Quest
'89 Toyota Camry Wagon
'89 Dodge Raider
'81 Honda CB 750F Super Sport
'88 Toyota Celica
'95 Toyota Tacoma
'74 Honda CB 550F

So here is a follow up of what I finally ended up doing & not doing.
As I mentioned earlier, I could not get the paint remover/wire brush method to really do the cleaning job in a satisfactory manner. The paint was very tough in places. So I decided to go for the alternative - blasting the cover. I think in hindsight I might have tried polishing the cover instead. I was even toying with the Idea of just leaving the sandblasted cover unpainted. The above comment is proof of how I was NOT thinking. Once blasted, I now know - it must be painted or corrosion will set in rapidly.
I did not get the cover degreased before the sandblasting thinking I would do that later before painting. That turned out to be a blessing in disguise. I only took the oil separator off so as not to get the sand embedded there forever. The better way would be to mount the cover, as was suggested here to a wood or metal plate.
Once blasted the cover looked clean, yet half baked…So I chose to have the same facility poder paint and bake it right there and then. Black or Dark Gray, which would have been my choice was not available and meant waiting for several days until they could fit me in with a large paint order. As this is my daily drive I went for the available - light Gray.
The paint stage is when a mounting plate, or not degreasing the belly in advance is the way to go. Even though they only paint the outside – some paint does find it’s way underneath. I lucked out because the paint did not stick to all the oil & crud.
The cover was powder coated and baked at 200 degrees celcious and put back on the car yesterday. Took the car out for a long run and so far the cover is not peeling or leaking. Here’s for another MB project I thought would take no time at all...

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Nice powder coat job! But it's the classic "If you give a mouse a cookie" situation . . . time for some brush on exhaust header paint?

Here is an image of my (fairly) well polished 107 cover. This is NOT perfect and it still represents a lot of work and probably $15 of materials. I could have done a better job if I had a bench buffer. Given that you can't really see most of it, I think it turned out OK; on the corrosion issue, polished items corrode less because corrosion can't get a "tooth"; also, I'm hoping that oil vapor in the compartment alone will help prevent corrosion. I don't drive this car if it's cloudy! I polished my air cleaner last year and it still looks very good with no sign of deterioration.

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86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm

Haasman has already made reference to my earlier thread dealing with this and other valve cover problems at http://www.peachparts.com/shopforum/showthread.php?t=73940. Other threads also worth looking at are http://www.peachparts.com/shopforum/showthread.php?t=79612 and http://www.peachparts.com/shopforum/showthread.php?t=84975 and this post http://www.peachparts.com/shopforum/showpost.php?p=725260&postcount=8.

The repainted valve cover on my M102 which I refer to in the above threads is still looking fine. No evidence of my DIY efforts failing 18 months down the track. With regards to polished valve covers, this is suitable for some but not all. As mentioned in some of the earlier threads some valve covers are aluminium alloy whereas others are magnesium alloy. I believe those on the M102 and M103 with the thick coating that flakes are the magnesium versions. The coating was to hide the imperfections in the casting. My DIY effort on my M102 looks like this http://www.benzworld.org/gallery/pics/W201_49666.jpg

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Polishing too looks like a task..
It has been several more days now and many more kilometers and all is well under the hood. Powder paint is supposed to be very durable. I hope so. "All is well" is relative - I am having a problem with the heating system, but will take that to a different thread.