The Official 356Talk Forum

Hello
I started the restoration of my 1954 bent window last november.
I need the help of the porsche 356 community about the anti corrosion treatment of the gearbox and engine case.The result should be a light brown colour. (see pictures) there is one proceeding from dow chemicals called dow 7 and a second one from henkel in germany called alodine.
Is there anybody out there with experiance in magnesium case treatment ?
thank you for any response

Schaefer - there is someone in the Southern California area that does this treatment, but I can't remember who.
Anyone?

Look up Mr. Okrasa on thesamba.com. He's in SoCal and does it.

Cheers,
-Greg

Or look up a plater which does magnesium chromating

Was magnesium chromating done originally by Porsche on the engine and transmission cases, or were they bare? And what did VW do in the early 50s, the same thing?

Martin Benade wrote:Was magnesium chromating done originally by Porsche on the engine and transmission cases, or were they bare? And what did VW do in the early 50s, the same thing?

Those are VW pieces, so that's what VW did.

Does the chromate disappear over the years? Sacrificial coating?

I have used alodine for years on airplane parts. It's pretty much a standard anti corrosion treatment, most FBOs will have a tank. Go to a general aviation airport ask who has a alodine tank. EPA put the process on the HAZMAT list so it's getting harder to find. The basic material comes as either crystals or a liquid. Mix with water at the ratio recommended by the MFG. then clean the aluminum, dip it in the solution, soak, dwell time varies by alloy.

Rinse then prime and paint.

It leaves a gold/brown coating a couple microns thick. Thoes motor cases must have been in the tank for a few hours. It is darker than we would do for an aerospace treatment. I would describe it as formic acid rust converter for aluminum.

John; does the alodine have the same effect on magnesium, as was asked here?

Vic, I believe it does not.

Vic
Let me go look in the repair manuals. Its been a while, cast magnesium seat legs on older airliners, we used a clear version of the alodine. All the process does is like an acid etch chromatic coating couple of microns on the outer surface. This layer reduces the oxidation of the metal. It Comes in several strengths. Mil-C- 5541 says it works on MAG/ALU alloys.

Since the EPA started monitoring chromate, the process is getting harder to fine. The plating industry has developed several better replacement non chromate processes. Ref MIL-DTL-32459, DETAIL SPECIFICATION: COATINGS, ANODIC FOR MAGNESIUM AND MAGNESIUM ALLOYS (25-JUN-2013)

With bauxite being one of the earth's readily available minerals, why did VW use magnesium rather than aluminum in their crankcases and transmission cases? Yes, it is minimally lighter than aluminum, but it's constantly trying to return to its original form. Aluminum is stronger.

Anybody have any idea why? Inquiring minds want to know.....

Magnesium easier and faster to machine; simple as that.

The original cases were aluminum, they went to magnesium later. I remembered reading it had to do with weight.

Henkel Alodine and Dow 7 are both hexavalent chromate treatments for magnesium and produce the same result. This is what VW originally used back in the 1950s on their magnesium engine and transmission cases. John's advice above to find an aerospace plater is a good one. You have to get the case very, very clean though.

Here's a photo from the Porsche factory in early 1956 showing a 519 magnesium case with dual-mount aluminum nose.