Pelican brain trust question regarding bead blasting magnesium

Jared at Pelican Parts · 05-03-2011, 03:52 PM

Someone here has got to have an answer for this one.

I've been working on a MBZ M104 for a new series of Pelican technical articles. I've come across what appears to be powder coating on both the inside and outside of the valve cover on what appears to be magnesium. As soon as I pulled the valve cover gaskets off, the coating lifted off with it. I can't seem to find anything on any MBZ board about this.

I've been trying to figure out the best course of action here. The magnesium seems to be in decent enough shape, but is quite powdery under the bubbled up sections. Would bead blasting be out of the question?

I havent worked enough with magnesium to really know how to tackle this one. Any ideas?

Mr.Puff · 05-03-2011, 04:04 PM

Maybe some Klean-Strip paste stripper?

red-beard · red-beard's Garage

I would try walnut-shells first. Glass bead is pretty soft, but walnut shell media is even softer.

DanielDudley · 05-03-2011, 05:08 PM

Don't know if baking soda is rated for Magnesium, but it sure does eat paint.

304065 · 05-03-2011, 05:23 PM

Might as well glass bead it-- the beads will eat up the corrosion and you will have a clear sense of what the substrate is. If you don't do that you will have corrosion under whatever you coat it with.

I went through this with my magnesium carburetor manifolds. In your case, if it's concours I would replicate the original finish- if not, I would have the manifold polished and then send it to Millenium plating for electroless nickel plating, then lightly scuff the top side and paint it M-B gray (which is what I assume the coating is.)

A930Rocket · 05-03-2011, 05:47 PM

Here's what a search brought up. It's all I have to offer.

http://www.magnesium-elektron.com/data/downloads/DS256SU0.PDF

Magnesium and magnesium alloys - Google Books

LSA · 05-03-2011, 07:22 PM

Quote:

Originally Posted by DanielDudley

Don't know if baking soda is rated for Magnesium, but it sure does eat paint.

Yup, soda blasting works great. My intake manifold on my 87 944S looked similar to that picture paint was chipping and flaking off. Soda blasted it and powder coated it. Unfortunately due to the porosity of softer metals like mag and alu if it's bubbling under the paint now the heat involved with the powder coating process might make it difficult to get it perfect as the new coat will bubble in similar spots. Happened to my manifold twice they stripped it both times and offered to keep doing it till they got it perfect (family friend on him) I said it was fine and just had them shoot it with some high temp paint been a few months now and still looks great.

Superman · 05-03-2011, 08:32 PM

blast away. Then have them bake it once or twice in the oven to address the out-gassing problem that causes bubbling later.

sammyg2 · 05-04-2011, 05:51 AM

I have a glass bead cabinet and a baking soda cabinet in my shop at work,
if I had magnesium valve covers to blast I'd use the glass bead cabinet and just go easy.

Now, blasting titanium is a whole nuther story ...

Two Rivers · 05-04-2011, 08:19 AM

Thats a sound deadening materiel. MB didn`t want its buyers to hear how noisy there top ends are. If you remove it the top end will be noisier.

Jared at Pelican Parts · 05-04-2011, 08:37 AM

Quote:

Originally Posted by Two Rivers

Thats a sound deadening materiel. MB didn`t want its buyers to hear how noisy there top ends are. If you remove it the top end will be noisier.

I don't have much of a choice as it's alreading flaking off inside and into the valvetrain. At the very least, I'd need to strip the inside surface. It's not paint. it's certainly a coating.

Two Rivers · 05-04-2011, 08:58 AM

I see that a lot on BMW valve covers also. Glass beading should work OK. The machine shop I use have coarse glass and it seems to work fine. They told me the coarse glass generates less heat because it cleans faster but I have not used it personally.