C24FUN

Does anyone know the percentage magnesium in the engine fan of a '90 964? Apparently if it is too high the part can't be powdercoated.

Thanks,

Jim

Sten

I've had mine powder coated with no problems, no idea what the % magnesium content is though

elbeee964

(stuff re this, I've got to hear...)

Dwane

I think you don't want to polish magnesium.
Pretty sure painting is fine.

Geoffrey

We've had issues with powdercoating magnesium and do not recommend it. We had a rare Cup mag wheel spoke crack due to the heat of the powder coat oven.

elbeee964

...oh, yeah. That makes sense.

(I remember being young and stupid, below. Outgrew the one.) [probably caused a nice thermal 'bloom' on any launch alert satellite flying by at the time.]

springer3

I have painted two 911 fans using the same procedure as painting alloy wheels: Wurth silver laquer and Minwax gloss spar urethane clear coat. One was on my long gone 1970 911T. The paint held up very well, but eventually i saw wear on the leading edges. I just did my 964 fan, and the only change was to put a little more clear on the leading edge where the wear is expected.

rollingjack

powdercoated, no problems till now. OK there is small error- center part of fan must be clean, not coated as you see in picture.

Indycam

File that under ,
maniacal laughter .

C24FUN

Yes, Geoffrey has experienced the same problem that the powdercoating company pointed out to me. According to the expert, if the magnesium content is too high the heat of the powdercoating oven causes the fan metal to become very brittle and lead to breakage.

Of course it's a big mystery what the fan's alloy makeup is and what specific content percentage might cause problems and really not all that important to know. I'm more interested if any of you have had stock 964 fans powdercoated and have experienced problems.

Thanks,

Jim

C24FUN

OK, so I used Archimedes displacement method to figure out the volume of the fan assembly, calculated the volume of the steel hub, subtracted the mass and volume of the hub from the mass and volume of the fan assembly and was left with a pretty good approximation of the mass and volume of the fan only.

The resulting calculated density is: 617.4 gm / 358.9 cc = 1.72 gm/cc, which is pretty darn close to the reference density of magnesium (1.738 gm/cc). Oh, and by the way, if you put vinegar on magnesium, it reacts and gives off bubbles. I tried it on the fan and, you guessed it... bubbles.

So, my money is on the fan being a 100% magnesium part, but where does that leave the powder coating question?

Further research on powder coating magnesium (valve covers, wheels etc.) talks about special powders, allowing for outgassing, pre-heating cycles etc, etc, etc...

Does anyone really know if there is a standard process for powder coating a magnesium part?

Please chime in if you have an expert opinion!

Jim

IrocMan

Hi, according to a guy I knew at Motorsport, to who I asked this question about my 964 and the magnesium race parts, 100% magnesium is not used for several reasons (I actually don't remember why, it was almost 10 years ago, but something like limit of elasticity).
According to another friend, it was probably 92% 'best case' (a more common magnesium allow according to him).
I don't know how true all this is. The way you calculated the density is a good idea, and 1.72 seems to be close to an allow of 92% magnesium and 8% aluminum, for instance. So why not.
And for using in some RS 92, it would make sense to use 92% allow

C24FUN

IrocMan,

I think you're probably right (and I'll be the first to say my estimation methods allowed for at least 5-10% error in the density). On further research I found that some of the most common Mg alloys that are used for cast parts are:

AZ91
9.0 % Al 0.7 % Zn 0.13 % Mn
General casting alloy
Good castability, good mechanical properties at T<150ºC.

AM60
6.0 % Al 0.15% Mn
High pressure die casting alloy
Greater toughness and ductility than AZ91, slightly lower strength. Often preferred for automotive structural applications.

ZE41
4.2 % Zn 1.2 % RE 0.7 % Zr
Specialist casting alloy
Rare earth addition improves creep strength at elevated temperatures. Pressure tight.

and

AS41
4.2 % Al 1.0 % Si
General casting alloy
Better creep resistance than AZ91 at elevated temperatures but lower strength.


These range from 5-10% aluminum and other metals so it could be any one (or none) of these.

In any case, as I said,it doesn't really matter exactly what it's made of, but only if it will cause problems if it is heated to powder coat the part. Still looking for a more definitive answer on this...

anyone...

Jim

Fred's 964

Powdercoated - yes, problems - no. I gently heated them to allow outgassing, then powdercoated being careful keep the part temperature as low as the powdercoat allowed. I watched the clock and temperature carefully using an infrared temp sensor. Check proper baking temp with powder manufacturer. Mine may have been 325 degrees, but can't remember right now. Did the valve covers and timing covers at the same time. (the old "while you are in there" syndrome.... it's an incurable disease, I swear it is...)


http://i202.photobucket.com/albums/a...s/DSC01717.jpg

Pesty

What prep did you do? I'm asuming no sanding just clean and sprey?

This on on my lits of stuff to do eventually. I know sombody who could do powder coating but if spreying is easy may give it a go.