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Porsche Crest Input from magnesium mfgr on fan polishing.

I read all the posts on polishing vs painting engine fans and could not get a concensus on which way to go. So, I looked up a manufacturer of magnesium parts to get another opinion. I received some good feedback via email. I'm still in the middle of correspondence but here's the email data I have so far. Once I get the formulation and a firm path forward, I'll post again.

By the way, when I remove my fan and housing to have it coated, should I have any pre-emptive maintenance performed on the alternator or just put it back in. It is a rebuilt unit that I just installed last year?

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The short answer to your inquiry is that there is nothing I know that will give you that “polished look” on magnesium for the long term. This is the same issue people have for polished magnesium wheels. If you “polish” magnesium and simply apply a clear coat, the clear coat will delaminate (turn milky) from the magnesium at sharp edges and stone damage sites in even quite mild (humid/wet) conditions. This is because of the following factors –

Polishing with certain abrasives can contaminate a magnesium surface with cathodic (iron containing) impurities. This has the effect of further increasing the corrosion rate of magnesium alloys and aggravates the situation. Safe polishing media for magnesium would be high purity aluminum oxide, silicon carbide, glass or diamond. Do not use emery powder. Never use a wire brush to “clean” magnesium components.

Magnesium is an alkali metal and requires a conversion coating to be applied before painting. The conversion coating will passivate the magnesium surface and improve paint adhesion. This will slow or prevent delamination of the paint under corrosive conditions. All the best conversion coatings for magnesium are colored and most contain chromates. The “best” available conversion coating that would maintain a “shinny” finish is known as the # 21 Chemical Treatment (If you send me a fax number I can copy you with the chemical formulation which does contain hexavalent chrome compounds).

Magnesium is an alkali metal and epoxy based paints are preferred. Epoxy based paints suffer from UV degradation so should not be used as a top coat. Its probable best to apply a clear epoxy primer followed by a clear polyurethane for the look you are after. Cellulose paints on magnesium behave poorly.
Don’t know if this will help you – why not chromate the fan assembly using one of the better chromate treatments, rinse, dry the chromate film between 110 to 120 C, then apply a silver base/clear coat system.
Old 02-04-2002, 03:24 PM
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Thank you. Please post more on this subject as information becomes available. Thanks again.
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Old 02-04-2002, 03:34 PM
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Great information. I guess the bottom line is there isn't an easy way to do this. Maybe the 'natural' look is best! -- Curt
Old 02-04-2002, 04:01 PM
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You could spray the fan with a ceramic coating and polish that, it won't have the same luster, but it will look nice........
Old 02-04-2002, 04:50 PM
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You need to overhaul your alt. while you have all the fan and shroud apart. It would be bad news for you to have to go back into the fan and do it say 6 mos from now.


Bob 80SC
Old 02-04-2002, 06:18 PM
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Quote:
Originally posted by bob hodges
You need to overhaul your alt. while you have all the fan and shroud apart. It would be bad news for you to have to go back into the fan and do it say 6 mos from now.


Bob 80SC
You know, that's what I'm leaning toward. Half the effort is removing it, even though I just put it in a year ago. My last rebuild lasted 9 years, but maybe I can add a couple more years by servicing it.

I figure it will take a few weeks to refinish the fan once I decide on a direction and this would be a good opportunity to service the alternator.
Old 02-04-2002, 06:37 PM
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on my concourse car, i disassembled the fan housing and alternator. i used aluminum polish on the fan housing. i did it all by hand, and my hands were sore for weeks !

when i was done, i had a very polished look. upon further reflection (and before i reassembled the car), i thought the polished look was a little too UN-natural.

i used a very slightly abrasive wheel on my drill and buffed the housing to give it more of a matte finish. it really looked good. it has been over 1 year since i did this and it still looks excellent.

admittedly, my car isn't driven very much, so i can't say how it would have held up to daily driving. but i still like the way it turned out.
Old 02-04-2002, 07:53 PM
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Polishing fan

Compared to polishing fuchs, the fan blade is much easier. Took about 6 hours to finish.
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Old 02-06-2002, 01:44 PM
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89- that looks great... what is your secret?
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Old 02-06-2002, 02:07 PM
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I can't take credit for this, my brother, who just signed up, did it. Its nothing fancy, just bare metal polishing using 400 to 1500 wet and dry paper and then a metal polish like Wenol, Mothers, or others. The luster may not last, but it won't take much to polish.
Old 02-06-2002, 02:29 PM
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I had my fan and housing powdercoated grey (to try to match the stock color as closely as possible). It doesn't really look stock, it is obviously powdercoated, but it looks nice.

That was around 5 years ago.

It still looks perfect.

I had to knock down the coating on the ends of the fan blades. Not a big deal, literally took 5 minutes with some 180 grit sandpaper. It then fit right into the housing.
Old 02-06-2002, 02:36 PM
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Jimt

Is the powdercoat holding up on the leading edge of the fan? 5 years is pretty good. I've heard conflicting reports on the durability of powdercoat on the fan.

Since it is gray, slight chipping would not be very noticable.
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Old 02-06-2002, 08:25 PM
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We'll see. I'm taking the plunge. The fan, valve covers, chain housings and covers will be powder coated red like the shroud. The fan housing will be black. The strap and the center of the fan will stay goldtone. Should look nice I think.

One place had quoted me $160 for just the valve covers, and did not have good answers to my questions. the place I now found has good answers and the whole job will be $100. He'll bake the pieces for a couple of days first so the impurities 'gas out.' Then I think his process involves two thinner coats rather than one thicker one. I'm hopeful.
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Old 02-06-2002, 09:48 PM
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Super...IMO, the perception of color in small spaces is a consideration. Red, IMO, is the most striking, so the potental for real "punch" in an engine compartment is real. The contrast of the black and red adds excitment. So based on my previous BS the mix of ingredients is important. Therefore, will the red of the engine shroud clash with the P C red?? Will the P C red make your shroud red look "weak"?? Will to much red be boring?? Would a P C red fan housing strap offer good contrast and keep it exciting?? Would Por-15 clear on valve covers and chain housing make the red and black more "eye catching" and still look professional?? Will the gloss of the red and black be equal?? Will the air cleaner cover be black to match the fan housing?? Will you use $50 worth of stainless fasteners on engine sheet metal, shroud, and fan housing strap? The electric panel cover is away from the eye balls and can/maybe done at another time. I can't get away from the thoughts that a 911 is "ART".
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Old 02-06-2002, 10:54 PM
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Ron, I understand. The red is a good match to the shroud color, though the shroud is dirty and not easy to completely clean. This will be a great deal of red, and I wonder if it's too much. We'll see. I do like exciting-looking engines and this one is likely to be pretty striking. The black is quite glossy, although there is still time to choose a flatter finish. The red is glossy too. Perhaps I should coat the strap red. Hmmmm.

Hey, I have a question. JW told me that the hole in the back of the chain housing seals with an o-ring into the bore, and I can see the place where the o-ring sits in the chain housing. But what about the back of the chain housing? How does the cam tower seal to prevent oil from dribbling out between the chain housing and the cam tower? In other words, is there a gasket between the chain housing and cam tower, or can I quit worrying about this being a sealing surface?
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Old 02-07-2002, 06:51 AM
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Super...there is a 4 piece set up to prevent oil into chain housing around camshaft. It is under the shim. In order is washer, cover plate, O-ring, gasket.
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Old 02-07-2002, 08:14 AM
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