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Discussion Starter · #1 ·
I have my top end with TOOLS right now who is doing the machining work for a thorough rebuild. The cylinder jugs, head, and valve covers will be bead blasted and I had planned to paint them with duplicolor's aluminum engine paint. I have some reservations though. For one, especially because there is ceramic in the paint, I wonder what the insulating effect will be like on the cooling fins. Can anyone quantify the difference from experience?

For another, I find the painted finish a little sterile compared to the rawness of 45-year-old aluminum. I like a little bit of "touch" in the metal finish and for that reason most of my side covers are hand polished but I don't completely remove scrapes, nicks, and dents. I don't know what the blasted surface will look like after fully oxidizing and if it's just too ugly I guess I would want to paint it. Anyone have pics of what a blasted aluminum surface looks like after developing an oxide layer? Or can anyone recommend for or against it on the pure basis of appearance?

Thanks!
 

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It will start to get an ugly IMO appearance with the white oxidation starting to appear on the surface. I would use the DupliColor on the engine and in my experience there are no issues with cooling. I have used this paint on a variety of air and water cooled bikes for years with no problems with cooling or the finish. Use the DupliColor self etching primer which is an army green colour on the bare metal first.

All the side cases I buff with a buffing wheel and they can then be clear coated with the same DupliColor clear engine enamel to protect the shine and reduce the need to clean and polish regularly. If they were originally painted then just prime and paint with the engine enamel like the rest of the bike.

Look at my restoration of the CM450A Hondamatic (Under the Pictures and Video section here) as it shows the engine that I bead blasted and then painted with the black DupliColor GM low gloss engine enamel.
 

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Discussion Starter · #3 ·
I may avoid the clear coat because I like the look of polished aluminum as it gets a patina. I don't have a buffing wheel so I've been destroying my hands by hand-sanding with varying grades of sandpaper. Anyone have suggestions for the most economical way to polish these short of actually buying a buffing wheel? I have a dremel tool but it only seems useful for polishing the tight corners.

Which duplicolor self-etching primer is rated for high engine temps?
 

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I may avoid the clear coat because I like the look of polished aluminum as it gets a patina.
Without the clear coat, you'll have the look of a half-done engine paint job. The silver by itself just looks really shiny, but not much like polished aluminum. Going over it with clear coat dulls it down a bit and does a great job of replicating the factory finish. Just silver paint alone tends to look kinda cheesy, IMHO.

I've done the silver + clear coat on air cooled engines for a full 50 years now, never once had an issue with heat retention.


One other consideration- ever notice that a lot of the old air-cooled motorcycles had a black finish on the engine? Bead blasting roughly doubles the surface area of an engine by creating zillions of small pits and spikes. If you bead blasted the cases, then applied a -thin- coat of flat black engine enamel, it was supposed to be good for dropping oil sump temperatures because between the extra surface area and black body radiation, the engine shed heat more efficiently. Might be something to consider if you want to go retro-race look.
 

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Discussion Starter · #6 ·
Old Putz, I should clarify that I am polishing the aluminum side covers, panels, and cam case covers while painting the case and cooling fins. what can be polished relatively easily will be polished. I meant that I didn't want to apply clear over the polished aluminum as I like the raw look. I'm open to clear coating the painted parts.

For those of you who've used the self-etching primer, I'm still wondering if it is rated for the temperatures it will experience on the engine cases. Or if the painting surface is bead blasted, is it even necessary to use primer?
 

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They have self-etching primer for engines right next to the engine paint. However, I never use it. I like the paint to be as thin as possible. Never had any problems with the paint, but I thoroughly clean/prep the surface. Also, I do not clear coat polished aluminum. I have aluminum parts on the toolmatic I polished 8 years ago and they still look good.
TOOLS
 

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Discussion Starter · #8 ·
Thought i would tack this question onto this thread--- can anyone tell me what material the starter motor housing is? The end caps are definitely cast aluminum but main body looks like steel to me. I stripped the paint and was hoping to keep it raw but if it is steel then i will paint it.
 

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Discussion Starter · #10 ·
Thanks tools. I was going to try that but thought i might get a false positive from the motor magnets.
 
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