Mr.Alex

In the near past there have been many fan threads and I usually never paid much attention because it seemed mine was alright, but while doing some things in the engine bay I took a closer look and saw some flaws. However, the fan shroud seems free of any cuts or scrapes to imply that the bearing is loose.

#1: A few of the tips of the blades are gone, a very tiny portion but they are not sharp anymore just look cut off.

#2: There seems to be some very tiny pitting in some areas.

#3: Another fan tip seems to be slightly disintegrating slowly, I touched it and it seemed to gently flake off.

The way I see it there are three options, which would you do?:

A) Take it off and have it powdercoated to have it protected for good. The caveat is what if the media blasting prior to the powdercoating damages the fan or causes too much pitting.

B) Ride this fan out until time comes to get a new one.

C) Try the powdercoat, and if it all goes to crap, then get a new fan.




Some pics of some damage, not all.

John McM

That's nothing. This is the one I replaced

Spyerx

those look very minor
pulling the fan and inspecting it is a good thing
soda blasting or other methods of blasting are very gentle

paint or powder coat, which is suggested for these?

Mine will be coming off soon and either be replaced or refinished.

Talking with rothsport recently the said they are seeing a lot of fan issues lately. Time is the culprit.

LPMM

If the tips are breaking and flaking off, it may be time to replace as corrosion may have crept in and is slowly disintegrating the blades. If you prefer, you could try to refurbish it but you'll have to make sure the blades are solid and to neutralize the corrosion so that it does not creep further. Here is mine before I replaced it, this is exactly what happened to some of the blades, flaking and breaking off. I then started hearing a ticking noise but could not figure out where it was coming from until I found out that the fan was out of balance and scratching the housing.

FeralComprehension

C. If it's not cracked or horribly delaminating blast it and coat it.

cobalt

Any media blasting will not cause additional pitting. If the magnesium has started to corrode than the pitting is already there and will just show up as it is cleaned. It si better to remove it all and have some pitting than leave it behind and cover it up. I don't see anything that throws up a red flag but these cars and parts aren't getting any younger and certain items like fans Magnesium valve covers, Fuel/oil lines etc should be inspected on a much more regular basis.

Spyerx

There's a reason porsche/bbs stopped using mag... it oxidizes badly.

curious if they've found a process for the 991 RS roof or if that will start to corrode off the car in 30 years :-)

FlyinTomato

Got a new fan in... debating if i should paint it.... but what color. i dont want red

cobalt

It is based on many factors. Alloy used will make a huge difference. I used to manufacture parts for most of your helicopters. I made the same parts for the Blackhawk as i did for the Seahawk but the Seahawk uses a low iron or higher purity alloy known as AZ91E vs the standard AZ91C. It is far more costly to manufacture and requires salt fog testing to verify corrosion rates of less than 50mils per year. In the past the raw material suppliers offered both alloys now they just produce the AZ91E and the remelt can be used for less applications requiring AZ91C. So this will probably improve longevity however does anyone plan on owning most of these cars in 20 years? No doubt they are built to be driven under warranty and recycled.

Another huge aspect of how well magnesium will hold up relates to proper chemical conversion or surface treatments prior to painting. Most of what I see Porsche did skipped this process and once the paint or coating is damaged it is only a matter of time and is amplified in climates that have snowy wet winters. Road salts and debris can really make a mess of things.

I recently started working with a new foundry and we came up with a new sand system that is far more permeable and creates a nice skin on the material if not disturbed seems to be holding up quite well for prolonged periods without protection from the elements. Should be interesting to see how this works.

Also there are many types of magnesium alloys. The common ones we see on the car's built in the 90's are the aluminum zinc based alloys. Then there are the rare earth or zirconium based alloys that will handle corrosion differently. They have a tendency to be used for different applications like F1 racing wheels for their mechanical properties. Then there are the WE alloys which were first being introduced back when these cars were being built and they exhibit far better corrosion resistance than the Aluminum and Zirconium based alloys with very high strength. No doubt this is the prefered alloy used today for these applications but are again more costly to produce.

Spyerx

^^^ Very cool stuff. I think you hit on it thought, the surface prep/protection had some sort of timeline in mind and that timeline has been exceeded.

Couple Questions: is powder coat or paint the better process once stripped down?
And would you take a new fan and strip it down to prep and paint?
Once the corrosion has started (visibly) can it really be stopped on these parts?

onceover

Mine was looking pretty good when I purchased the car but it wasn't pretty enough for my liking

I glass blasted mine, not sand blasted. It's much more gentle. And got it powdercoated red.

Untitled by Patrick Derkacz, on Flickr

Untitled by Patrick Derkacz, on Flickr

Untitled by Patrick Derkacz, on Flickr

cobalt

Good questions

Honestly the fan is a tough application. If cleaned and checked for damage periodically the fan will be in like new condition even after all these years. The ones on my C2 and turbo are original and other than the typical change in paint color on the C2 look like new. The majority of issues come from damage by owner/mechanic or lack of care by owner.

A huge issue that is common amongst all 911 fans is the improper use of a pry bar/screwdriver placed between the fan blades to hold the fan while tightening and loosening the nut on the alternator shaft. This usually is the result of cracked blades or housings. Second is the lack of cleaning or care. Cleaning the engines is always a good idea. It allows you to spot potential issues much easier and sooner and in the case of the fan any damage to the fan blade edges which will allow access of moisture to penetrate and eventually corrode the magnesium. Simply touching up any damaged areas to keep the elements from attacking as soon as possible is always best.

If corrosion begins you will need to remove the fan and clean the area thoroughly. For Military application we would do an acid pickle at elevated temperatures to etch the surface. This was called a Dow treatment also known as Dichromate and or Chrome pickle. The acid would etch and clean the surface and sodium Bichromate would bond to the surface which would protect the casting until it awaited final finishing. Bead blasting and or grit blasting will also remove any corrosion however if it is extensive it might be time for replacement. There is no counteracting the damage done by corrosion only preventing the corrosion from happening.

I would not strip a new fan. I am not so sure powder coating is any better than paint. Powder coating is hard and if the fan at speed hits something hard it will shatter as where paint will chip. Keep on top of any damage and a painted fan should last a lifetime.

FlyinTomato

my fan

Mr.Alex

Thanks for all the input. While the salt trucks peppered the streets around me, I feel like I might take it off and see if there isn't anything worse. If all clear, I might see if it holds up on powdercoating and what method of blasting my local powdercoater offers.

Ken, you already swapped your fan?

FlyinTomato

I haven't. still waiting for the big day to do everything together. I am coming to brooklyn tomorrow night. You still got my rear shock? I need to disassemble it to use some of the stock parts for my new suspension.