the -6 is comming along well,, the cold has made me done all the upholstery,, now the engine and trans,, surfing around,, I saw a nos 356 engine case and it has some sort of gold-brown finish,, I think the guy mentionned it still has the original plating,, what is it ,, how to make a new one ,, is stannate right ,, dont wanna paint , any idea and if you know , who has a source for the stuff

thanks guy

My theory is that the cases were cast, machined, and then a chromate process was used to provide a layer of protection (some may call this “pickling”). The chromate process gives them the tan/yellow color. Then after assembly a wax type coating was sprayed on. With the wax coating most likely being Tectyl. Tectyl also has a yellowish color.

I would love to hear from someone who knows for sure. Many people think that the Tectyl coating is the only thing that was done on Magnesium and I really don’t believe that.

I am interested as I would like refinish a magnesium transmission case just like the factory did. While Tectyl (or something similar) is relatively easy to source today, the various chromate processes (assuming I am correct about them using one) are hard to replicate as those are being replaced with newer non-chromate processes that may not replicate the color of the original chromate finish. The various favors of the chromate processes used years ago are very hazardous (watch the movie Erin Brockovich)

You might want to post this on the Pelican 911 technical forum. Many of those guys have superior knowledge in certain aspects such as this.

I cannot speak to what was done to "six" trannies. But I can speak to those on the fours - won't try to make a distinction/connection between the two either.

When I made the first serious concours prep for my 72 four I spent dozens of hours scraping a waxy substance from the transmission AND motor case. I was a QC chemist at the time & had access to loads of acetone - spray, scrape, wipe. I did this outdoors, which explains why I'm still alive!

Under the waxy substance was bare metal. No chromate or dichromate plating. In fact, several years later, when the motor & tranny where out of the car, I actually polished the casings with a Dremel & Simichrome. They were gorgeous, like chrome plating, then they oxidized to the original gray finish.
Pat

In my parts stash, I have parts of a 901/914 transmission including a differential side cover. The exterior is in typical rough condition (no trace of any coating), but the interior has a tan/yellow color that I think is typical of a chromate conversion. Usually this process involves the entire part being submerged, so I would expect that if the interior shows evidence that the entire part was probably done this way.

Then again, I am unsure of the source of my side cover (year, model, etc.). So I am going to pay real attention when I service my side shift transmission to see what it looks like on the inside on all of the castings.

I may open up this topic on PP to see what they say.

It is more likely that the interior yellow/tan colour is from 30+ years of exposure to Dino oil and what it contains, coating the interior. If the case was plated in any style, the exterior would be the same. Think about it ....why would the factory coat the interior and then remove it from the outside of the case? Wouldn't happen. That would cost time & money for no useable gain.

All I have ever read about it (case protection) was the factory shipped it with a protectant (Tectyl).

Easy way to find out is ask someone who has ordered a new case and ask them what it looked like. I know they were/are available as I remember a thread about someone buying one a couple yrs ago. Their case was worn out, so they bought a new one from Porsche and re used the internals.

All of this is theory on my part with not much if any evidence. So I don't discount that it could be a stain left by oil. But as it stands now, I would still bet that it is not oil as it just doesn't look like an oil stain.

I am also not saying that they removed the treatment from the outside. I suspect that the chromate conversion process was used as a very basic anti-corrosion barrier. Maybe even just to protect the case between the time it was machined and then assembled. That the protection it gave was never intended to deal with harsh exterior road conditions and that is why the Tectyl was used once the transmission was assembled. And that with the Tectyl applied, it would be hard to determine (visually) what is below the Tectyl as both the chromic process and Tectyle are nearly the same color. 30+ years later, I suspect that on most cases all of the Tectyl and chromic layer are gone due to normal weathering. All that is left on the outside is either caked on grease/oil or your standard grey/white magnesium corrosion layer.

I am not sure what I would do today to refinish a magnesium transmission case. I plan to test out a few things on that diff cover plate. I am going to clean different sections using different cleanersand then coat different sections with different coatings to see which hold up the best. It seems like Simplegreen is the cleaner of choice (it has a slight acidic component and it may remove the chromic conversion layer) and many people seem to like the "Gibbs" brand lubricant which seems to help prevent corrosion on magnesium. I will also probably try to get some Tectyl as well as the Tectyl like CRC product called "Marine heavy duty corrosion inhibitor"

Started a thread over there if anyone is interested...

http://forums.pelicanparts.com/showthread.php?p=3729721