I would get all that crud off first with stuff like carb cleaner and if it "rough" do you mean like corossion? Like water was eating away or pitting the alluminum? Don't know what to tell you about that.
The procedure we use here at the shop is to first glass bead the manifolds, and then paint them with a product made by Seymour Paints called Dull Aluminum Engine Paint. I think the part number is SS71 but dont hold me to it, I can get it in the morning if you need it. I would also advise against sand blasting as it will actually remove material, which you do not want to do. Glass beading will clean off all the corrosion, stains etc. but will leave the aluminum very dull and sort of "porous". If you don't paint it with something, any thing that gets spilled on it soaks in and really is hard to remove. We have found after trying a bunch of products, that the Dull Aluminum Engine paint works the best. We use the product on all the aluminum cylinder heads we rebuild also and it really works good. It is also very easy to keep looking nice. If something does happen to it (it is pretty tough stuff) you can just clean it with 409 and spray a touch up coat on it and it looks lik e new. Hope this helps, if you can't find someone who has the Seymour paints, let me know and I will try to hook you up with a can. Your best bet will be to try a machine shop as that is who they market thier products to most. By the way thier engine paints, and thier cast blast are about the best I have seen.
Advanced Automotive Machine
Bulk; I've tried about everything over the years. Even used sugar and salt in a sandblaster to see if that would do it without risking engine damage. Best thing I've found is to clean good with gunk or kerosene first. Then use a product called Naval Jelly. Pink looking gel that is used to remove rust on steel. Has an acid base that will clean and whiten the aluminum. Just put on a thick coat and brush with an old toothbrush. Rinse well. If the intake is a valuable, original piece, or if the gel won't do the job, the bead blast might be better if available in your area, but I've cleaned several with the gel. tom
For best results, try professional restoration. Check Hemmings Motor News. Sorry, I cannot recommend someone specific.
If your going the low buck route, clean the intake best you can with carb cleaner and a small brass wire brush (by hand, not in a drill). Mix water and baking soda into a thick paste. Use a hand brass wire brush and a LOT of elbow grease. Did that on my BBC intake... it works!
If you have glass beaded an aluminum intake on any surface other than the exterior remember that the aluminum IS porus and will hold tiny schards of glass beads in the pores. They should be thoroughly cleaned in VERY HOT soapy water to open the pores and allow the glass to come out. If you don't do it now your engine oil will do it for you later! A guy who rebuilds Jaguar heads told me about this years ago and I could not believe the amount of glass left in the bottom of the bucket the first time I did it. I had already washed the intake thoroughly with solvent after blowing it out completely with compressed air.
I had some success with mag wheel cleaner, but was disappointed when the aluminum came out with a dull finish. Personally, I would only recommend it as a last resort. I haven't had the intake on the car yet, but I'm guessing it would have the same effects that BillK described.
I used Eagle One Etching Mag Cleaner. Unfortunately, I didn't notice the 'Etching' part till later. Also, DO NOT leave this stuff on too long. At first, the intake didn't gte real dull, but I let it soak for awhile and that must have caused the dull finish. Maybe just a little at a time might work better.
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