NineMeister

Magnesium.

jhg41977

So they can be safely powdercoated then? Outside only of course.

NineMeister

Yes, powder coated or etch primed and two-pack painted.

cobalt

I trust your expertise but I always assumed these were aluminum like the valve covers. I am surprised Porsche would use any Magnesium alloy without protective coatings especially after the problems they had with the earlier cars intermediate plates.

Exposed magnesium without proper protection will disintegrate in a few years especially in extreme environments. The fans are magnesium and are coated albeit not as well as they should be and as many have learned the hard way will disintegrate if debris hits the edge while spinning and exposes the raw casting to the elements.

What you posted appears to be a factory document although I find it hard to believe that these are magnesium alloy.

geolab

I think I got the info two years ago from Porsche system at dealer with the name of the actual manufacturer of the covers. I did not guess the bakelite word, must have come from somewhere.
I will look next time there.
Since I am in finance for 24 years now, and work essentially with figures. I think the covers weighted just less than 300 grams each.

JasonAndreas

I certainly can't say with 100% certainty! And I knew the source of some of Geolab's previous info so I tried to phrase it as a question. re Colin: he has probably held more in his hands than everyone in this thread combined!
I've just never seen anything from Porsche that specifically says, "these covers are magnesium", only the cases themselves. And short of burning/igniting the covers I wouldn't know how to tell the difference. I've held the cover and the cases in each hand, i've tried pushing a red hot pin into them (to test for plastic) and I've seen them cracked.

It is a screen-shot from the air cooled 964/993 engine repair manual from Porsche.

NineMeister

Would anyone like me to take a file to one and photograph the result? All the ones that I have seen are definitely some form of light aluminium/magnesium alloy, I know plastic when I see it and these are not plastic. The covers and housings are not bare metal, they do have some form of surface treatment, perhaps hard-anodised or similar, and are hence not prone to corrosion.

cobalt

I had sent JasonAndreas a response to a PM he sent me earlier apparently the TC covers including the valve covers on the 964 (not 993 which are some form of glass fibered Polyamide) are listed as magnesium in the document he referenced. My background is in aluminum and magnesium sand castings and I had 964 and earlier valve covers tested along with Ferrari cases tested for chemical composition years back since I was melting them for scrap and could not introduce it into the melt without verifying its content. What I found with the valve covers was they were made of an alloy that I have no record of but were predominantly Aluminum with high levels of Magnesium not unlike an alloy which never caught on called Almag35. I would consider it an aluminum alloy since the majority of the composition consisted of aluminum although many refereed to it as magnesium. I must assume they used the same alloy for both. The Ferrari 512 cases were most definitely magnesium alloy.

This would make sense because it is both strong and far less susceptible to corrosion. Magnesium has many pros but holding up to the elements is not one of them. Unfortunately I no longer have the certifications otherwise i would post a copy of the certification.

JasonAndreas

The original valve covers for the 964 were magnesium and then Porsche started using aluminum valve covers around the same time (i think around 1990?) that the intake manifold was changed to plastic?

cobalt

The batch of covers I tested consisted of covers from earlier 3.2's and 3.0's also.

There is no chemical conversion or anodizing that I am aware of that would not break down after a couple of years that would hold up to the elements as long as these parts have. A simple slip of the wrench or scratch with a screw driver would expose the magnesium and once that occurs just the moisture in the air is enough to start the corrosion process.

I know Porsche used magnesium alloys up through the 70's on the production cars but I believe other than the fans they stopped on most parts. Such parts like the fan shroud for a 914 or the covers and case halves on the earlier 911's but as you know finding surviving parts in good condition is rare. Even the wheels on my friends 935 and rear tranny and support on his 962 are constantly corroding requiring refinishing in environmentally controlled garage.

None of these parts exhibit what I am accustomed to seeing regarding magnesium. Here is a picture of two mag samples of navy grade low corrosion magnesium AZ91ET6 one coated and one not look at what 120 hours of salt fog testing can do and this is to simulate one year at sea. I can only imagine we would be seeing far bigger corrosion issues by now with these parts if they were magnesium. Cross section under 500X magnification

EDoyle

Bringing this back from the dead. My engine is not going to look like poop with crusty old covers and at $250 each new, I am going to ceramic high-temp paint mine. Here is a cover bead blasted next to one that was scrubbed as clean as I could get it.

AOW162435

I've refinished my covers, as well as three other sets for Rennlisters. In each case I bead blasted the outside of the covers (only) and washed them in hot soapy water. Once dry, I wiped the surface down with a prep solvent. Then the covers received a few light coats of etch primer followed by three coats of engine paint (in this case, DupliColor 'Cast Coat').

No issues with the finish after a few years of use.








Andreas

EDoyle

That looks great Andreas. Good to know that paint can hold up.

Did you notice the very rough and slightly piited inner gasket mating surface on these covers? Could it contribute to the fact that these things perpetually leak?!

AOW162435

Yes, and I paid attention to cleaning the channel as much as possible (a wooden chopstick works well to scrape the residue without scratching the parent material). Because of this less-than-perfect surface, I used some Curil-T on the new gaskets - no signs of oil.




Andreas

cobalt

The corrosion had gone pretty far and the black spots are a result of pitting. There is still dirt in there and i would try to get it better before coating. Another thing with Mag is after it is blasted you should wash and dry in a convection oven at around 125 degrees and paint ASAP. Corrosion will set in quickly if they sit around. I am not sure what a ceramic coating will achieve over a quality etching primer and a catalyzed paint.

Has anyone figured out what coating Porsche used on these and why they used it here but not on other similar parts? Apparently the earlier cars the timing chain covers are magnesium and considering how well they held up over the years the coating did a great job.