If anyone here goes to clean parts with those solvents Bikeguy Joe mentions and doesn't have much experience with them....do try to do it outdoors in a well ventelated area. I've worked with the MEK (Methal Ethyl Keytone) which is an inorganic solvent and "wicked" on one's lungs. The others are bad enough. The vapors are dense and linger on the ground and can build up on the floor of a closed garage in the winter.
Once my Dad and I were working in the garage and we were up on this pontoon boat deck we were building. Grandma's ol wiener dog was on the floor curled up by the gas heating stove as we started cleaning metal work with the acetone. We heard funny noises and it was the wiener dog with her nose in the crack at the bottom of the door huffing for fresh air. We simply forgot about her being there and the vapors. Dad and I were up higher and it didn't notice but it only took a few minutes to pickle the pooch.
Just a heads up.
I've learned that when working with aluminum and you want paint to stick to it.......using a mixture of "Lye" mixed in a strong solution with water and appied to the metal, it will create micro pits on the surface that the paint will hold to. It will be nearly impossible to ever get it off once painted on.
Another process for coloring aluminum is to anodize it. This is a process of dying aluminum. I think it could lend itself to the covers of the motor as well.
I have a book around here titled, "Formulas Methods, Tips, and Data that gives instructions on anodizing aluminum. The internet abounds with information on doing it too.
The first thing to do is to get the following things together: First on the list is the most expensive item: a 6 to 12 volt battery charger. They run from $45.00 to $110.00 depending on model, functions, etc.(The next item, though not that expensive, will take some effort to find: battery electrolyte, a.k.a. sulfuric acid. This should be available at a battery wholesaler for about $2.00/gal. To make the negative ground, you will need some aluminum ground wire and aluminum-foil. The wire can be found at an electronics store for about $35/spool, and you should have the foil in the kitchen. If you happen to be out of foil, you can pick up some more at the store when you go to buy the last item for this project. No super-special chemicals or solutions necessary to make the colors; just plain-old fabric dye. (Something like Rit dye, for about $5.00.) Rit offers something like 30-40 different colors, so you have quite a number of choices for what color you want your parts to be. An optional item is nitric acid: about $25.00/2.5 L. (This is used to clean parts prior to anodizing, but there are some cheaper alternatives. See end notes.) This is available at chemical supply stores. Should you not be able to find any, you can try to get on the good side of the high school science teacher. He may help you out since you only need a few ounces
Be careful with Nitric acid coming in contact with copper !
A solution of 1-2 ounces of nitric acid in a gallon of distilled water will allow you to clean the surface in preparation for the anodizing. Aluminum oxidizes very quickly when exposed to air, so the easiest way to keep it clean is to clean it just before you are ready to start working on the piece. (You should rinse the part with distilled water before you put it in the next acid solution.) Make your negative ground with the aluminum wire and foil. Shape the end of the wire into a paddle shape and cover the round part with the foil. What you want to do is create a flat, round shape to sit on the bottom of the bucket, with a lead that comes up out of the bucket. You will clip the battery charger's negative lead to the wire that comes out of the bucket. When you are ready to start, you will want to mix up your immersion solution. In your rubber bucket, combine the sulfuric acid and water to come up with a solution that is about 30% water. (1 part water to 2 parts acid.) Place the paddle in the bucket and attach the negative lead. Then attach the positive lead to the part, making it an anode, and immerse it in the solution. (Remember that thetwo leads the paddle (cathode), and the part (anode) should not touch.) This is the best time to turn on the charger: once the part begins to fizz, leave it in there for about 10-15 minutes. After about this time the part should no longer conduct electricity. (You can also use an ohmmeter to check conductivity, but this is not needed.) Turn off and disconnect everything, and rinse the part in cold water.
Read more about it here:
How To Anodize All Your Aluminum Parts - ThirdGen.org