Mauro,
I have had a lot of experience with the Porsche, having owned a new 1959
356 then sold it for a new 1966 2.0 L 911S.
As I recall, the 911 cylinder walls were dimpled to hold oil, and chrome
plated for long wear life. Yes, the crank case was a bit "yellow". I
had to sell the car after it was 10 years old due to a relocation across
the country, and it was as strong as ever. My son was still quite young
(see "My Life with Cars"
http://tigersunited.com/articles/sl-mc/SteveLaifman.asp
Have your sound on, lots of good music!
As far as "rotting" is concerned, this is an extreme misuse of the
word. Steel rusts (oxidize), as do aluminum and magnesium. Magnesium is
much more susceptible to metal fatigue, causing early failure. Fatigue
is the condition of sudden failure to to work-hardening of the
material. Even steel is susceptible, but after a great many more cycles.
This is why they have limited race life. All the other materials are
subject to this, but at many, many more cycles. You can see this
happening if you bend and unbend a wire coat hanger. After just a few
cycles of extreme bending, it breaks in your hand. Mostly through
work-hardening, rather than fatigue, but a similar principle.
Oxidation is a normal response for these materials (including steel,
where it is called "rust").
The only thing I know of that has unlimited life is the unending hope
for better things.
Steve
Steve Laifman
Editor
http://TigersUnited.com
Would U.Believe wrote:
> Michael,
>
> The Porsche 911 air cooled engine was a dry sump engine; the whole
> case was made of magnesium. In all my experience with Porsche, over
> many years, I have never, ever heard of an engine case "rotting" or
> breaking randomly. Certainly, though, magnesium has a much greater
> tendency to fracture before some other metals and alloys, but it would
> take some doing to get that to happen even to a 40 year old magnesium
> engine case. Having said that, I know the Porsche magnesium engine
> cases can definitely corrode and become pitted badly, but only when
> completely neglected with water sitting on or in them for a very long
> time. The reason Porsche eventually moved to aluminum engine cases
> was only because the magnesium cases, which started out with a 2
> liter displacement tended to warp increasingly more (and leak oil) as
> the engine displacements grew from 2.2, 2.4 to 2.7 liters, increasing
> the engines' heat generation with each step up. I would never have
> guessed it, but aluminum cases are stiffer than the magnesium cases.
>
> Anyway -- back to wheels -- could it be that real magnesium wheels
> were a bit porous to begin with, even when new, which is part of the
> reason why the old mag wheels needed tubes in the day (beyond the bead
> design)?
>
>
> On 5/19/10 7:52 PM, "michael king" <michael.s.king@gmail.com> wrote:
>
>
>
> On 20 May 2010 08:24, Would U.Believe <mcdangerous@verizon.net> wrote:
>
> There are going to be a whole lot of Porsche 911 engines
> disintegrating if
> that's the case. They were magnesium until the 3.0 liter
> engine came out in
> somewhere around 1980. This is the first I've heard about
> magnesium
> "rotting".
>
>
> Mauro
>
> Magnesium wheels are well known for turning porus "rotting" they
> become very brittle and fracture. As for other magnesium parts..
> its not an uncomon issue on magnesium sumps.
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