Machine polishing - PeachParts Mercedes-Benz Forum

bgkast · #1 03-02-2007, 12:16 AM

I would like to machine polish my valve cover like the picture below. I have seen the process before but am not positive what it involves. I have seen it done using a drill press and some sort of polishing wheel, but only on flat surfaces. How would you do it on something as curved as a 617 valve cover?

MS Fowler · #2 03-02-2007, 06:39 AM

What you want is called "engine turned". I've forgotten what I knew about it, but I think you are correct; it involves using a spinning tool in a drill press.

#3 03-02-2007, 06:53 AM

Yes that is called engine turning. It is typically done in a drill press or a mill. For it to be shiny like that, however, you will have to polish out the sandblast or as cast finish and then do the engine turning.

I have only done engine turning on flat pieces. I did a few flat pieces of aluminum that I used for an instrument bezel on some late thirties Ford hot rods that I built. I can describe the process for flat stock and you will have to be creative for the curved portions.

What I did was chucked a 1/2 inch wooden dowel in a drill press. I turned it at medium speed and ran it down on a sheet of sand paper glued to a wooden block to flatten the spinning end. I then put valve grinding compound on the end of the dowel and pressed it against the stock while spinning. I then moved it over one radius and brought the dowel down again, and so on. As I recall I had to put a little more valve grinding compound on the dowel about every fifth swirl.

I also rigged a fence or guide of sorts, so that I could move the piece along a straight line as I moved over one radius.

I believe my procedure will work nicely except, of course, you will have to come up with something flexible instead of the wooden dowel since it is not flat stock. Maybe a rotary wire brush, but I think that would be way to course unless you made larger swirls.

I would think that you need to experiment on a scrap aluminum valve cover before attacking your own. Even if it's a broken one from a toyota or something, just any aluminum valve cover from the scrap pile.

Good luck and let us see the outcome.

RUN-EM · #4 03-02-2007, 07:16 AM

It does require a drill press. You must also mark off a grid on the part...each
X intersection will be the target area for the center of the polishing bit. The polishing bit looks like a dowel rod with an eraser on the end..which is covered with course grinding paste. The variable here is the diameter of the dowel chosen to vary the diameter of the swirl....but the same diameter is maintained for the entire project. If you choose a tool too large to get into the tight areas of your job, you might not find out until half way through that you are screwed. The burnishing tool is touched down onto each one of the target X's in an overlaping manner. Each row of swirls is ofset by half the diameter of the adjoining row of swirls. Running your drill press you touch the tool down ....making the swirl, pull up the tool surface, move your engine part over to the next target, touch the tool down again, make swirl, pull up tool, and repeat till the entire part is covered with overlapping swirl marks.

Another decorative process is the one used on Buggatti engines. The worker had the clean part and used a sharp chisel/screw driver device. This device was pushed down onto the part with some force, then hammer struck from the side at a 90 degree angle from the sharp face of the tool. The tool then made a "scratch" indentation into the engine part the width of the tool. The mark width could be varried as different tool widths were chosen to get into cramped areas of the castings, although a uniform tool width does look better (it is just not as apparent as different swirls in the first case). This was also overlapped until the entire part was scoured. Quite a bit easier to do than the overlapping circles as this method is quite a bit faster but harder on your hands.

I've heard of another method, but not seen too much of it, except on pistols. You use a punch (or many various sizes of punches) to make an indentation on the surface, stippling is what it is called, I think, not sure of the spelling. Anyway you wind up with a cratered overlapping surface that offers a super gripping surface. Suggest you powercoat clear to a smooth surface---actually smooth coat all of these methods as they can become fantastic dirt traps that are almost impossible to clean.

There is a file method of surface decoration. A grid of file serrations is marked out and the file cuts are made in uniform fashion (crosshatch actually)...this usually on a flat or slightly curved surface. You wind up with a surface coated with tiny pyramid shape decorations (side by side and row upon row).....this reflects light somewhat like a polished diamond.

Then there is engraving such as seen on many high class pistols. Skilled craftsmen are paid mucho dinero for this process...say about $25,000 for something as large as a valve cover... go for it

.

Hope these explanations help... not too sure of my ability to convey what actually occurs in each process though

.

Regards

Run-Em
1983 300SD- aka - SPARKY THE DIESEL

vstech · #5 03-02-2007, 09:10 AM

wouldn't a standard loaded buffer on a hand grinder work? TONS of polishing compound, but it should work...
John

TheDon · #6 03-02-2007, 09:39 AM

You will have to deal with the casting imperfections in the valve cover as well.

winmutt · #7 03-02-2007, 10:41 AM

Could you get the same results with a grinder and a sanding disc? Larger patterns of course.

#8 03-02-2007, 10:48 AM

You cannot do this with a handheld tool. You need a drill press or mill such that the part and the rotating component are held RIDGID.

murdockspencer · #9 03-02-2007, 12:37 PM

eastwood sells a kit to do aluminum intake manifolds, if a v-8 manifold can be done a valve cover can definitely be done. And Aluminum isn't that hard to polish being that it's a soft metal. http://www.eastwoodco.com/jump.jsp?itemID=960&itemType=PRODUCT

murdockspencer · #10 03-02-2007, 01:00 PM

sorry, I just looked closer at your picture and saw the kind of polishing you were talking about. And here I was thinking all these guys were crazy talking about drill presses and such.

bgkast · #11 03-02-2007, 01:07 PM

I have always called it engine turned as well, but this article called it machine polishing. Must be a Brit term.

Guess I'll keep an eye out for a test piece in the junk yard.