Expert advice required - restoring 'cast' metal look

Not a restorer... But blasting with glass beads or walnuts works great...

 

Not an expert or a restorer but have had considerable experience addressing this challenge in a recent Dino restoration. The general idea is to do the least invasive things first and gradually increase the aggressiveness of your approach as required. It is often very hard or impossible to go back if you ruin/change a casting's natural appearance with overzealous cleaning or blasting. In order, I'd do the following:

1. Degreasing soap, warm water, brushes and lots of elbow grease

2. Alumabrite or similar chemical aluminum cleaner (not sure how this reacts with Magnesium so be careful with Mag.) You'd be surprised at how effective this type of chemical can be if you take your time and do multiple cleanings. Wear rubber gloves and safety glasses when using this stuff. In most cases, unless you are dealing with stubborn corrosion or are trying to go after the last concours points, you can stop here.

3. Blasting with ultrafine glass beads (NOT crushed glass which has sharp edges) at very low pressure. Don't get frustrated as this can be a time consuming process to do well. The glass beads do a wonderful job of getting in every nook and cranny and leaving a beautiful finish. One caveat is to be fastidious about washing any blasted parts to make sure no beads remain in hidden corners, esp. on engine castings. BTW I tried walnut shells early on and I did not get nearly as good a result as with the beads.

I wouldn't be surprised if there are other blasting techniques, like dry ice blasting, that might yield perfect results as well, but I am limiting my comments here only to those techniques with which I have first hand experience.

It isn't hard, it just requires patience. Good luck.

Best Regards,
Paul

 

More on step 1 Paul noted, try a solvent like lacquer thinners then a soft stainless steel brush.

 

I've seen successful results using ultrasonic cleaning on Porsche magnesium parts such as the gearbox housing. I've never used it myself.

Freeman

http://www.tierratech.com/US/cp24/automotive-equipment

 

Bead blasting will peen over the pores on the light castings. The NCRS guys know about this. It will not look original if that is what you are going for.

 

I use a commercial wheel cleaner fluid product called "ProX". It contains a slight amount of acid, just enough to remove light oxidation from the cast aluminum. This has proven to work like a charm and it does not make any permanent changes to the surface appearance. It is important to neutralize with plenty of fresh water a few minutes after appliance, other than that no further treatment is needed.
Best regards

Peter

 

For sand cast (rough and pores) aluminum and die cast (smooth and less pores) aluminum, I use very fine (flour like) glass beads at a lower pressure. This get the metal nice and clean and get in all the small areas. Then I follow up by vibratory tumbling in plastic media.

Dan - I thought your email was regarding wrinkle finish parted parts....

Here are some before, in process (only have this photo with steel parts) and after photos:
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Investigate ultrasonic cleaning. Chuck Stoddard (founder of Stoddard Imported Cars) showed me his personal ultrasonic cleaner in his workshop. He used it for everything from the magnesium engine case of his 917 to plastic interior assemblies of his 911's. They came out like new without any chance of damage. Chuck researches everything he does in his workshop.

Freeman

https://www.stoddard.com/aboutus

 

We have a pretty high end Ultrasonic cleaner and while it works very well, it does not remove heavy soiled debris on parts. Our machine cost $10K but it's only 110VAC. Perhaps the 220VAC power sources provide more scrubbing power.

 

Dan,

Based on your last 2 photos this part looks like a manifold. These are typically pressure cast (different surface finish, less porosity, etc.). The use of glass beads, or beads followed by plastic media as indicated by Dave at Sticky RX, works perfectly to restore these parts to as new condition. Don't get too hung up on trying to compare the restored part to a photograph. Clean, newly cast aluminum, particularly pressure cast, is silvery out of the box and typically acquires a darkened cast with atmospheric exposure in a short time. In fact, get a recently cleaned part and rub it with a WD-40 soaked rag and it will already darken a few shades. The photos posted by Sticky RX look absolutely perfect (i.e. as original) to my eye.

The chemical cleaners always seem to work best on the porous sand cast parts for some reason.

As others have noted, blasting can seal the pores of cast parts. If you use glass beads, I have to emphasize again to use the finest grade you can get and at LOW pressure. You are not blasting the part as much as using the media to very gently rub away the final bits of contamination and give the part an even finish. It is slow going work to do properly if you go this route.

Best Regards,
Paul

 

Thank you, Paul. I'm about as OCD as one can get

100% spot on

 

LOL - I just stated this in my email to you before reading this post....

I don't use glass beads on any parts such as cylinder heads, etc. I wish I could as cleaning my head is killing me in time....

 

Dan,

I used tape, and lots of it, along with rubber plugs in some cases. In spite of your best efforts assume that some of the beads always find a way through which is why you need to be fastidious about cleaning afterwards.

In my case I did clean the heads this way but before they left for the machine shop where they would be cleaned again and have all new seats and hardware installed.

Best Regards,
Paul

 

Here is a sample of the Vapor Blasting we do, I have looked for 20 years to find a process that gives me the look of new Cast Aluminum, this looks correct.
I have never been happy with dry Glass Beading, the parts printed and stained due to the porius nature of the process, Vapor Blast is the way to go.


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The vapor blasting looks good however, I think it leaves the part too shinny. When we glass blast, one, we use low pressure and second, we vibratory tumble after.