original finishing of the cylinder and cylinder head

jensen · Post by **jensen** » Wed Dec 16, 2009 4:10 am

I know this is maybe not the right place for this post, but it's also not in place under paint.

This time not a question about color, but maybe an answer.

When looking at pictures from the 60’s and 70’s (of dreams and cb’s) I always wonder why there’s so much difference in color or/and finishing of the cylinder head and cylinder between how these parts look on the pictures compared with these parts now. On pictures these parts look glossy, almost silver, but the structure isn’t smooth at all, so it’s not polished or so. Then there are questions on the forum if these parts should be painted or not, and if yes, what kind of color that would be. There are also questions about how to get that finish back on these old parts so that these look new again. Should I beat blasting, sand blasting, blasting with nut shells or blasting with cork?

Recently I acquired a few, never used, cylinder heads for a CB72. A few boxes where unopened, and where always stored dry and warm. The color of the cylinder heads from the already opened boxes where nice silver, but not as shiny (a bit dull) as on the pictures from the 60’s and 70’s. So I opened a box which wasn’t opened upon last week. It was an early cylinder head, and it is as shiny as good be, exactly as on pictures of that time.

It seemed to be painted silver, but it wasn’t painted, so I was wondering what was causing this very light silver shiny surface. I took off a very small part of the vins and gave it to a friend of my who is a metallurgist. The answer he gave was explaining everything. He found out that the aluminum was containing high levels of zinc (this I knew already because it’s difficult or almost impossible to weld). But his explanation how the surface was so shiny was indeed an eye opener. If you are casting this type of aluminum, there will be a layer of pure zinc formed on the surface due to the process. This layer will oxidize during the years, just as on bolts and other zinc plated parts, and will turn dull Grey, or even worse.

Knowing this, I compared the color of the head with the color of a new modern zinc plated bolt and the color matched almost perfectly. The head was a little “flattened” but this was the closest match I’ve ever seen. Most likely the color was a little shinier too, in the past.

Personally I don't like the shiny finish, it's too much bling bling, but now I've seen the original color and finishing I'll maybe turn around.

If you’re beat blasting it, no matter how fine beat you use, or which procedure you use, it will never get the same glossy, shiny silver surface. Painting is one way to get there (almost), but the surface just looks different (from my experience).

I will bring a nos, but dull Grey head, to a company which can zinc plate (electrolytically), and see what the result will be, I also will zinc spray a piece of dull aluminum to see if that is good solution to get that shiny look back.

If that doesn't do the job, I'll zinc plate a part thermally, if possible, because that's the closest you can get to the original finish and color I presume.

Maybe all of this was already known by the forum readers, but for me it is a discovery, just letting you know.

I’ll keep you posted, with pictures of course.

Jensen

bill440cars · Post by **bill440cars** » Wed Dec 16, 2009 9:40 am

Hey Jensen, sounds interesting to ME AND I'll be watching to see just what you come up with. My OWN feeling as far as the look goes, is that I like the silver on most, but now and then, I go with a black motor and some polished pieces to set it off. Anyway though, I'm interested in what YOU are doing.

Take care, Bill

jensen · Post by **jensen** » Wed Dec 16, 2009 3:16 pm

Pictures taken from two nos heads, one head is the one I spoke of in the prevoius email, the other one is a nos head but beat blasted with ultrafine beat (50 micron) and very low pressure (0.75 bar).

chico · Post by **chico** » Thu Dec 17, 2009 4:50 am

the bead blasted one looks great. would you seal it with WD-40?

jensen · Post by **jensen** » Thu Dec 17, 2009 7:37 am

Hi Chico,

For the record, in the last picture, the bead blasted head is the one with the bolt on it, the other one is the original look (without the bolt), to show the difference in color and finish between the bolt and the bead blasted head, compared with the nos not-blasted head. The difference is big, however, when pictured alone, with no reference, it nice.

Yes, I spray with WD40 directly after blasting, When you look closely to the picture (I can make a close-up) you will see a closed structure. The very small bead particles "hammers" the surface smooth. But don't forget, it is also a nos / new head.

Jensen

btw, it took me more then one our to do the whole head.

bill440cars · Post by **bill440cars** » Thu Dec 17, 2009 12:22 pm

I definitely like the look of the NOS head myself. I saw that it had a slight shine to it, but with it next to the bead blasted one, you could REALLY see the difference.

Later on, Bill

chico · Post by **chico** » Thu Dec 17, 2009 1:06 pm

Jensen, they all look better than my 43 year old.