[DeTomaso] Campy ?Powder Coat? Code Needed

[Peter Havlik]

I note that in this discussion no one has mentioned the need to crack 
test the wheels. As Jack has written, they work and age harden over 
time and, if the original finish was compromised in any way (as it 
always is), then contaminants leach into the porous magnesium. This 
causes corrosion and the resulting weakness, when combined with the 
work and age hardening, can cause the wheel to suffer cracks that can 
lead to failure. The wheels, therefore, need to be subjected to 
non-destructive dye testing (Zyglow) to find these often hairline 
fractures in order to repair them before the wheel is repainted. I am 
told a trained eye is needed to tell the difference between 
structural cracks and ones occurring naturally in magnesium, so my 
suggestion is to go to your local airport and approach the companies 
that test and repair magnesium aircraft wheels.

To prevent the outgassing (bubbling during powder coating or 
painting) problem mentioned earlier in this thread, the wheels should 
be baked before painting or powder coating so as to get rid of all 
the contaminants that have leached into the porous magnesium over 
time. About the same temperature and duration in the oven as for 
powder coating is appropriate. I was horrified when I spoke to one of 
our vendors, who quite arrogantly and disdainfully bragged about 
having refinished "thousands" of Campys by having baked them at over 
twice that temperature!

The article on this subject, written by Mike Drew and entitled 
"Restoring Magnesium Campagnolo Wheels the Right Way", should be 
mandatory reading for every De Tomaso owner.


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Message: 27
Date: Thu, 6 Aug 2009 13:59:04 EDT
From: JDeRyke at aol.com
Subject: Re: [DeTomaso] Campy ?Powder Coat? Code Needed
To: apache34 at embarqmail.com, detomaso at realbig.com
Message-ID: <cee.601b8cc2.37ac73e8 at aol.com>
Content-Type: text/plain; charset="US-ASCII"

In a message dated 8/6/09 8:41:55 AM, apache34 at embarqmail.com writes:

 > I dipped my original wheels (6) in 1990 or so and they came out of the
 > tank perfectly clean with a nice surface for painting. I then 
painted them a
 > 1992 Mercedes silver and after many years on the road they still look great
 > to this day. Nothing to it.
 >
Yup- painting is easy. The real problem in powder coating is the 350-375F
degrees used to fuse the powder grains together into a continuous sheet. The
high heat expands the very porous mag castings, opens up pores and stuff
thats been trapped inside for decades bleeds out, ruining the coating. Even
hot-tanking at 200+F won't reliably clean dirty, highly porous mag castings,
which is why many powder coaters won't handle mag castings: too many do-overs.
But if you find a shop that can do a good job on mag, the fusing
temperature can also be used to simultaneously anneal the magnesium 
wheel and get rid
of its slowly-accumulated internal stresses, so once done, its like a brand
new casting again. This alone is worth the price of powder coating. But the
whole process isn't something one can do correctly at home, usually... Good
luck- J Deryke