In a message dated 5/26/16 7:58:20 PM, detomaso(a)server.detomasolist.com
writes:
> Larry,
>
> I've still got the story on my computer. I can post it when I land
> tonight.
>
>>>Found it, and text is posted below.
It's worth mentioning that I have a set of Larry's wheels on the front of
my car now. However, he goofed up and selected a way wrong color (DOH) so I
had to have them painted atop the powdercoating. They are bulletproof now
I think! Going forward, I would hope anybody who is contemplating doing
this sort of thing will take the extra time to research the color and ensure
tha it is what you want it to be....
BTW one of the really nice things about this list format is that I can whip
out my phone while dashing through the airport between flights and quickly
get caught up, whereas with a web-based forum I would realistically have to
stop and break out my computer, get onto a WiFi network, and then wait for
ages for huge pages to load. So thank goodness that the REAL forum is alive
and well!
Article text below. Note that this was written almost 20 years ago, and
at this point should serve as the starting point for a conversation rather
than being treated as though the words were taken from a burning bush....
Cheers!
Mike
====
Restoring Magnesium Campagnolo Wheels the Right Way
The Pantera was delivered wearing Campagnolo wheels cast in exotic
magnesium alloy. Campagnolo is a very old company in Italy, and the methods they
used were the tried-and-true types right out of the dawn of the Industrial
Revolution. Thus, our magnesium wheels were cast in molds hand-carved from
mahogany!
Naturally, wooden molds, however hard, could only withstand a limited
number of times that molten metal could be poured into them before sharp details
were blurred. Eventually, these details were lost, and casting quality
began to drop off as well so the mold would be scrapped. This short life of
the wheel molds may in fact be the reason there are at least four separate
models of Pantera wheels that are known to have been shipped at various times
during the life of the DeTomaso/Ford joint project in the '70's.
In the meantime, Campagnolo as a company was going through changes. The
light-alloy bicycle accessory business was spun off in the '70's, the wheel
company was sold (but kept its name the first two times), and new management
were brought in after being taken over by Technomagnesio (one of
Campagnolo's chief rivals in the alloy-wheel business).
Finally, the magnesium wheels made late in the Pantera project were
pressure-die-cast. This method is where the molten metal is literally pumped into
steel dies under relatively high pressure. The metallic dies are much
more expensive than the old mahogany ones, but they also last much longer,
quality is higher and the higher pressure during the metal solidification
results in a denser casting with fewer, smaller pore areas. Intuitively one
would expect that the very late Campy wheels are stronger for these reasons.
Magnesium, the lightest structural metal known, has one desirable and
several not-so-desirable attributes. On the plus side, it is only 65% as heavy
as aluminum while having as much strength as the better aluminum casting
alloys, meaning it can be heat-treated and welded like aluminum.
On the debit side, magnesium is a 'reactive' metal: when magnesium contacts
plain water or even moisture in the air, a chemical reaction occurs that
results in the outgassing of hydrogen gas from the water molecule; the l
eftover oxygen combines with magnesium to produce the familiar white mag-oxide
powder. If left exposed, Campy wheels will literally dissolve into powder!
At 650 degrees Centigrade, magnesium burns in air at such high temperatures
that most substances in contact with it melt or burn as well. Large
chunks are difficult to catch on fire but grindings or shavings should be treated
like gunpowder-and definitely kept dry! Fine mag metal powder will react
hydrogen gas off so quickly, the gas spontaneously lights off, catching the
rest of the metal on fire. Naturally, pouring water on a mag fire will
result in a hydrogen explosion (remember the Hindenburg?) and even more fire!
Sand or dry-chemical extinguishers are the only hope for stopping a
magnesium fire. In fact, it may be best to simply stand back and let it burn
itself out....
Magnesium alloys have the property of age-hardening-that is, a mag
casting will get harder and progressively more brittle as it gets older,
regardless of its use or storage. Magnesium expands some 2-1/2 times as much as
aluminum when heated. This means that for best results, the casting must be
physically restrained-bolted down-before heating or it will literally 'crawl
away' from the welding torch!
And due to its very light density, magnesium castings, especially open-mold
castings, tend to be porous, or at least have very large crystalline areas.
All wheels flex and bend slightly in use. Magnesium flexes too, but the
flex-energy is not dissipated 100%. Instead, stresses build up inside the
castings, eventually concentrating at an imperfection such as a casting
pore or a crystal grain. Such an area will eventually separate and connect
with another pore or weak spot. A few more cycles of this and you have a
crack growing in the casting, with the accumulated stresses concentrating at
the point-ends of the crack. This process works exactly like a micro
pry-bar!
Detecting cracks in mag castings cannot be done by conventional magneflux:
magnesium is totally non-magnetic. So a fluorescent dye called Zyglow is
dissolved in a very thin solvent like petroleum ether. The casting is
dipped in the solvent, left for a few moments, then wiped off. A spray cleaner
is used to further clean the casting. Any cracks or deep pores will retain
some of the dye, however. Illuminating the casting with near-ultraviolet
light will show up any retained dye.
Porous, rough castings like our wheels require someone talented in the art
of interpreting florescent patterns that show up. The layman could look at
a perfectly good cast-mag wheel glowing in numerous areas and be afraid to
mount a tire on it! X-ray casting checks can also be done but are even
more expensive, require more highly trained operators to evaluate the film
records and are sometimes inconclusive, requiring a dye-check to be sure!
Cracked magnesium castings should only be welded after stop-drilling both
ends of a detected crack. This is a technique whereby the crack is outlined
and a small hole drilled through the casting just in front of each end of
the crack, not in the crack itself. This is so when welding or grinding heat
is applied, any growth of the crack will expand into the drill-hole rather
than continuing to tear the base metal apart at the front of the crack.
Then, the entire cracked area is V-ground away to prevent the crack from
progressing sideways, and to provide clean metal to weld on. The V-groove is
also necessary since vertical cracks in thicker sections don't weld very well.
Remember the cautions regarding the dangers of accumulations of grinding or
drilling chips from magnesium repairs! Magnesium welding is best done
only by an expert, with lots of experience and understanding of the nuances of
magnesium welding. The incautious can very easily start a fire that will
literally consume everything in its reach-including your house, garage and
Pantera!
And surprisingly enough, the act of welding or grinding a casting induces
even more stresses, so the repaired casting must be stress-annealed. This
literally bakes out the accumulated stresses or any additional ones from the
repairs and results in a like-new wheel that has many more years of safe
driving left.
Fortunately, the annealing temperature (recommended by aerospace users of
magnesium) is only 350-375 degrees Fahrenheit. The piece is put into an
oven, heated to 350-375 degrees, held for an hour or so, then very slowly
cooled to room temperature-the slower the better! Ideally, the heavily
insulated oven is simply turned off and left closed until the next morning. If the
oven cannot be turned off, wrap the hot casting in thick blankets and leave
it undisturbed for at least several hours. Note-this will discolor any
silver finishes painted onto the wheels. Do the decorative painting last!
After the wheel is cast or weld-repaired, if it is to be painted it must
first be protected from moisture in the air by painting it with a zinc
chromate solution. The zinc chromate reacts with the magnesium to produce a
barrier layer that tends to be self-healing to small scratches-the zinc chromate
literally spreads across the scratch, again protecting the underlying metal;
not as well as a full-thickness coating, but at least there is some
protection! Zinc chromate is widely used in the aviation industry, and should be
available at better paint stores, as well as at any municipal airport repair
facility.
Bare wheels that are simply painted with conventional primers and paint may
trap moisture between the wheel and paint, resulting in corrosion under the
paint, which eventually shows up in the form of bubbles in the paint.
In recent years, it has become very fashionable to powdercoat (or
powderpaint) wheels rather than painting them. The resultant finish can be superior
to paint, but only if the wheel is correctly prepared. Some people simply
strip the old paint and then apply a coating of powderpaint, without
actually repairing any damage to the surface, or checking the structural integrity
of the wheel. When powderpainted in this fashion, often the wheel will
out-gas during the painting process, leading to bubbles in the finish.
Larry Stock of the Pantera Parts Connection found himself with a collection
of Campy wheels from various sources, some of dubious ancestry (including
Mike Drew's old wheels!) Even though modern 17” wheels and tires are all
the rage right now, he has found there are a select group of individuals who
are looking for the best possible original factory wheels, and he set about
taking these cast-offs and bringing them up to better-than-new specification.
The wheels were first carefully bead-blasted to remove all the old paint
and underlying zinc chromate. The blasting process also removed any
oxidation which might have accumulated. Afterwards, the wheels were annealed at
375 degrees in a large oven, which was allowed to slowly cool overnight.
>From there, the wheels were hauled to a sophisticated testing facility used
by NASA and Lockheed Aerospace. The wheels were dipped in a liquid
penetrant (Zyglow), then rinsed off and evaluated for possible cracks and
imperfections. Any such imperfections were clearly marked, and one wheel was
condemned and ultimately discarded.
Once the faults were identified, the wheels were then transported to a NASA
welder who carefully welded up damaged areas of the wheels. While none of
the wheels exhibited any significant cracks, several had large hunks
missing from the lip of the rim. These were caused by the fitment of
conventional wheel weights. The metal in the wheel weights reacts with the magnesium,
turning it to powder. Tire-shop monkeys who traditionally remove old
weights by hitting them with a hammer as often as not remove the lip of the
wheel as well! For these reasons, whenever possible stick-on wheel weights
should be used instead of clamp-on weights.
The welder went out of his way to put excess material back into the wheels,
so now they needed to be brought back into spec. But before any machining
would take place, they were returned to the oven and annealed again, to
restore whatever strength might have been compromised by the application of
high heat in only one area of the wheel.
Larry then took them to his fully-equipped machine shop. A rear
axle/brake disc/stud assembly was inserted into a large lathe, and the wheels were
bolted to the axle. Then sophisticated cutting tools were used to carefully
remove the excess material and restore the original contours of the wheel.
The average wheel required two full hours of machining in this fashion.
Of course, machining introduces its own heat factors, so back into the oven
they went! After annealing, the powderpainters sprayed on silver
powderpaint, which had been carefully color- and texture-matched with an original,
mint-condition factory painted wheel. Back into the oven to bake the silver
paint on, and anneal the wheels again! Finally, a protective clear-coat
was powderpainted atop the silver, then the wheels went back into the oven
for the final time.
The resulting wheels are absolutely flawless, exquisitely beautiful, and
literally much better and stronger than new. The entire process was
extremely labor-intensive and took almost six weeks to accomplish. Larry now has
several full sets of early-style (Pre-L) wheels and a few L-model wheels in
stock, which he'll sell for $325 each with the exchange of your old wheels.
Alternately, he can have your existing wheels repaired for $325 each.
Thanks to Larry Stock for providing the step-by-step photographs of the
Pantera wheel restoration process.
In a message dated 5/26/16 7:58:20 PM, detomaso(a)server.detomasolist.com
writes:
Larry,
I've still got the story on my computer. I can post it when I land
tonight.
>>>Found it, and text is posted below.
It's worth mentioning that I have a set of Larry's wheels on the front
of my car now. However, he goofed up and selected a way wrong color
(DOH) so I had to have them painted atop the powdercoating. They are
bulletproof now I think! Going forward, I would hope anybody who is
contemplating doing this sort of thing will take the extra time to
research the color and ensure tha it is what you want it to be....
BTW one of the really nice things about this list format is that I can
whip out my phone while dashing through the airport between flights and
quickly get caught up, whereas with a web-based forum I would
realistically have to stop and break out my computer, get onto a WiFi
network, and then wait for ages for huge pages to load. So thank
goodness that the REAL forum is alive and well!
Article text below. Note that this was written almost 20 years ago,
and at this point should serve as the starting point for a conversation
rather than being treated as though the words were taken from a burning
bush....
Cheers!
Mike
====
Restoring Magnesium Campagnolo Wheels the Right Way
The Pantera was delivered wearing Campagnolo wheels cast in exotic
magnesium alloy. Campagnolo is a very old company in Italy, and the
methods they used were the tried-and-true types right out of the dawn
of the Industrial Revolution. Thus, our magnesium wheels were cast in
molds hand-carved from mahogany!
Naturally, wooden molds, however hard, could only withstand a limited
number of times that molten metal could be poured into them before
sharp details were blurred. Eventually, these details were lost, and
casting quality began to drop off as well so the mold would be
scrapped. This short life of the wheel molds may in fact be the reason
there are at least four separate models of Pantera wheels that are
known to have been shipped at various times during the life of the
DeTomaso/Ford joint project in the '70's.
In the meantime, Campagnolo as a company was going through changes.
The light-alloy bicycle accessory business was spun off in the '70's,
the wheel company was sold (but kept its name the first two times), and
new management were brought in after being taken over by Technomagnesio
(one of Campagnolo's chief rivals in the alloy-wheel business).
Finally, the magnesium wheels made late in the Pantera project were
pressure-die-cast. This method is where the molten metal is literally
pumped into steel dies under relatively high pressure. The metallic
dies are much more expensive than the old mahogany ones, but they also
last much longer, quality is higher and the higher pressure during the
metal solidification results in a denser casting with fewer, smaller
pore areas. Intuitively one would expect that the very late Campy
wheels are stronger for these reasons.
Magnesium, the lightest structural metal known, has one desirable and
several not-so-desirable attributes. On the plus side, it is only 65%
as heavy as aluminum while having as much strength as the better
aluminum casting alloys, meaning it can be heat-treated and welded like
aluminum.
On the debit side, magnesium is a 'reactive' metal: when magnesium
contacts plain water or even moisture in the air, a chemical reaction
occurs that results in the outgassing of hydrogen gas from the water
molecule; the leftover oxygen combines with magnesium to produce the
familiar white mag-oxide powder. If left exposed, Campy wheels will
literally dissolve into powder!
At 650 degrees Centigrade, magnesium burns in air at such high
temperatures that most substances in contact with it melt or burn as
well. Large chunks are difficult to catch on fire but grindings or
shavings should be treated like gunpowder-and definitely kept dry!
Fine mag metal powder will react hydrogen gas off so quickly, the gas
spontaneously lights off, catching the rest of the metal on fire.
Naturally, pouring water on a mag fire will result in a hydrogen
explosion (remember the Hindenburg?) and even more fire! Sand or
dry-chemical extinguishers are the only hope for stopping a magnesium
fire. In fact, it may be best to simply stand back and let it burn
itself out....
Magnesium alloys have the property of age-hardening-that is, a mag
casting will get harder and progressively more brittle as it gets
older, regardless of its use or storage. Magnesium expands some 2-1/2
times as much as aluminum when heated. This means that for best
results, the casting must be physically restrained-bolted down-before
heating or it will literally 'crawl away' from the welding torch!
And due to its very light density, magnesium castings, especially
open-mold castings, tend to be porous, or at least have very large
crystalline areas. All wheels flex and bend slightly in use.
Magnesium flexes too, but the flex-energy is not dissipated 100%.
Instead, stresses build up inside the castings, eventually
concentrating at an imperfection such as a casting pore or a crystal
grain. Such an area will eventually separate and connect with another
pore or weak spot. A few more cycles of this and you have a crack
growing in the casting, with the accumulated stresses concentrating at
the point-ends of the crack. This process works exactly like a micro
pry-bar!
Detecting cracks in mag castings cannot be done by conventional
magneflux: magnesium is totally non-magnetic. So a fluorescent dye
called Zyglow is dissolved in a very thin solvent like petroleum
ether. The casting is dipped in the solvent, left for a few moments,
then wiped off. A spray cleaner is used to further clean the casting.
Any cracks or deep pores will retain some of the dye, however.
Illuminating the casting with near-ultraviolet light will show up any
retained dye.
Porous, rough castings like our wheels require someone talented in the
art of interpreting florescent patterns that show up. The layman could
look at a perfectly good cast-mag wheel glowing in numerous areas and
be afraid to mount a tire on it! X-ray casting checks can also be done
but are even more expensive, require more highly trained operators to
evaluate the film records and are sometimes inconclusive, requiring a
dye-check to be sure!
Cracked magnesium castings should only be welded after stop-drilling
both ends of a detected crack. This is a technique whereby the crack
is outlined and a small hole drilled through the casting just in front
of each end of the crack, not in the crack itself. This is so when
welding or grinding heat is applied, any growth of the crack will
expand into the drill-hole rather than continuing to tear the base
metal apart at the front of the crack. Then, the entire cracked area
is V-ground away to prevent the crack from progressing sideways, and to
provide clean metal to weld on. The V-groove is also necessary since
vertical cracks in thicker sections don't weld very well.
Remember the cautions regarding the dangers of accumulations of
grinding or drilling chips from magnesium repairs! Magnesium welding
is best done only by an expert, with lots of experience and
understanding of the nuances of magnesium welding. The incautious can
very easily start a fire that will literally consume everything in its
reach-including your house, garage and Pantera!
And surprisingly enough, the act of welding or grinding a casting
induces even more stresses, so the repaired casting must be
stress-annealed. This literally bakes out the accumulated stresses or
any additional ones from the repairs and results in a like-new wheel
that has many more years of safe driving left.
Fortunately, the annealing temperature (recommended by aerospace users
of magnesium) is only 350-375 degrees Fahrenheit. The piece is put
into an oven, heated to 350-375 degrees, held for an hour or so, then
very slowly cooled to room temperature-the slower the better! Ideally,
the heavily insulated oven is simply turned off and left closed until
the next morning. If the oven cannot be turned off, wrap the hot
casting in thick blankets and leave it undisturbed for at least several
hours. Note-this will discolor any silver finishes painted onto the
wheels. Do the decorative painting last!
After the wheel is cast or weld-repaired, if it is to be painted it
must first be protected from moisture in the air by painting it with a
zinc chromate solution. The zinc chromate reacts with the magnesium to
produce a barrier layer that tends to be self-healing to small
scratches-the zinc chromate literally spreads across the scratch, again
protecting the underlying metal; not as well as a full-thickness
coating, but at least there is some protection! Zinc chromate is
widely used in the aviation industry, and should be available at better
paint stores, as well as at any municipal airport repair facility.
Bare wheels that are simply painted with conventional primers and paint
may trap moisture between the wheel and paint, resulting in corrosion
under the paint, which eventually shows up in the form of bubbles in
the paint.
In recent years, it has become very fashionable to powdercoat (or
powderpaint) wheels rather than painting them. The resultant finish
can be superior to paint, but only if the wheel is correctly prepared.
Some people simply strip the old paint and then apply a coating of
powderpaint, without actually repairing any damage to the surface, or
checking the structural integrity of the wheel. When powderpainted in
this fashion, often the wheel will out-gas during the painting process,
leading to bubbles in the finish.
Larry Stock of the Pantera Parts Connection found himself with a
collection of Campy wheels from various sources, some of dubious
ancestry (including Mike Drew's old wheels!) Even though modern 17a
wheels and tires are all the rage right now, he has found there are a
select group of individuals who are looking for the best possible
original factory wheels, and he set about taking these cast-offs and
bringing them up to better-than-new specification.
The wheels were first carefully bead-blasted to remove all the old
paint and underlying zinc chromate. The blasting process also removed
any oxidation which might have accumulated. Afterwards, the wheels
were annealed at 375 degrees in a large oven, which was allowed to
slowly cool overnight.
From there, the wheels were hauled to a sophisticated testing facility
used by NASA and Lockheed Aerospace. The wheels were dipped in a
liquid penetrant (Zyglow), then rinsed off and evaluated for possible
cracks and imperfections. Any such imperfections were clearly marked,
and one wheel was condemned and ultimately discarded.
Once the faults were identified, the wheels were then transported to a
NASA welder who carefully welded up damaged areas of the wheels. While
none of the wheels exhibited any significant cracks, several had large
hunks missing from the lip of the rim. These were caused by the
fitment of conventional wheel weights. The metal in the wheel weights
reacts with the magnesium, turning it to powder. Tire-shop monkeys who
traditionally remove old weights by hitting them with a hammer as often
as not remove the lip of the wheel as well! For these reasons,
whenever possible stick-on wheel weights should be used instead of
clamp-on weights.
The welder went out of his way to put excess material back into the
wheels, so now they needed to be brought back into spec. But before
any machining would take place, they were returned to the oven and
annealed again, to restore whatever strength might have been
compromised by the application of high heat in only one area of the
wheel.
Larry then took them to his fully-equipped machine shop. A rear
axle/brake disc/stud assembly was inserted into a large lathe, and the
wheels were bolted to the axle. Then sophisticated cutting tools were
used to carefully remove the excess material and restore the original
contours of the wheel. The average wheel required two full hours of
machining in this fashion.
Of course, machining introduces its own heat factors, so back into the
oven they went! After annealing, the powderpainters sprayed on silver
powderpaint, which had been carefully color- and texture-matched with
an original, mint-condition factory painted wheel. Back into the oven
to bake the silver paint on, and anneal the wheels again! Finally, a
protective clear-coat was powderpainted atop the silver, then the
wheels went back into the oven for the final time.
The resulting wheels are absolutely flawless, exquisitely beautiful,
and literally much better and stronger than new. The entire process
was extremely labor-intensive and took almost six weeks to accomplish.
Larry now has several full sets of early-style (Pre-L) wheels and a few
L-model wheels in stock, which he'll sell for $325 each with the
exchange of your old wheels. Alternately, he can have your existing
wheels repaired for $325 each.
Thanks to Larry Stock for providing the step-by-step photographs of the
Pantera wheel restoration process.
