Intake Manifold Painting
The intake and valve covers are made of a magnesium aluminum alloy which is prone to pitting and corrosion if not painted in some way - polishing alone would not be a good idea unless it was clear coated. Once the paint is removed and the surface is clean the metal is not very smooth and usually pitted - so I don't know how well they would polish. In addition, standard painting techniques are not sufficient to make the paint "stick" even for a short period of time. They must be bead blasted very carefully with new soft media, acid "conversion" coated to remove surface oxygen, then immediately painted. Even with proper painting I have heard that the paint will start coming off in 5 to 8 years - due to the nature of the metallurgy. The best advice is to find an aircraft painter who is familiar with painting this kind of alloy and have them do the painting. I just had these parts painted on my car and they look great - it cost me $400.
The covers and intake are magnesium. To make paint stick, the oxide coating needs to be removed first. Once the oxide is removed, you have just a couple hours before the newly exposed metal forms another oxide layer again. The procedure would be to blast the parts with walnut hulls or plastic or something like that, while avoiding sand and glass beads. Then go immediately to your paint booth and get a fresh coat of primer on them.
Regular paint procedures can follow, provided you don't expose bare metal during any prep steps. I have had good experience using scotch-brite pads for surface prep between coats. A little more work than sandpaper, but cuts down on the chance for scratch-through to metal on any steps.
Engine temps in the covers should not ever exceed 300f, and typically run a lot cooler than that except under extreme conditions.
I had the top of my engine apart a few months back and repainted the tubes, intake manifolds, etc. with paint that my company uses in high temperature applications. I had the parts glass bead blasted to remove the old paint, and taped up the surfaces that I did not want damaged. It worked very well and they look great. The paint is a silver-grey color...more silver than grey. It is a Warlick High Heat Spray Enamel good to 400 degrees F, Warlick # 1-8-6734. I believe there is aluminum in the paint. It has been on about 6 mos, and no flaking, etc. Looks like it is holding up good, and it looks good. The paint runs very easy, and after doing the first part, the paint guy actually cleaned the part again and sprayed lighter coats. We put 4-5 coats on and hung to dry. It takes about 1 whole day to dry completely.
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