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Discussion Starter · #1 · (Edited)
Touching up Campagnolo wheels

Has anyone had experience touching up the coating and paint on these magnesium alloy wheels? I have looked up using a dichromate treatment on magnesium (Dow #19) and have sourced a small amount of Chromic Acid flake to make the Dow 19 solution. Overall the wheels are very good but there are a couple of spots that I want to protect from further corrosion and the back side of the wheels do need to be protected from galvanic corrosion with the rotors.

Also after I apply the treatment as a base coat, is there a closest match paint that would work as a touch up paint. One post stated that BMW Polaris Silver was a close match.

Thanks
 

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Result

Hi, here is my before/after comparison. Some of my wheels were in bad shape then it took about an hour per wheel to clean, brush, sand, clean again and paint. I've put 3 coats of "wheel paint" with a spray can. I didn't have many color choices but this one was ok for me. I can give you the paint brand if you need it. I bought it at an auto parts store.

Alloy wheel Rim Wheel Tire Auto part

Alloy wheel Tire Wheel Vehicle Car
 

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Hi, here is my before/after comparison. Some of my wheels were in bad shape then it took about an hour per wheel to clean, brush, sand, clean again and paint. I've put 3 coats of "wheel paint" with a spray can. I didn't have many color choices but this one was ok for me. I can give you the paint brand if you need it. I bought it at an auto parts store.]
Wheel looks nice. Would you mind posting some more detail, like what grit paper you used, the brand of paint, etc.?
My wheels are peeling like yours were, did you use a primer or just smooth them up and shoot?

Thanks,
 

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Bruce, I still have the 15" Quad wheels but last year I bought a Veloce in bad shape for parts with brand new tires on it. Thanks for the compliment for restoration work. I hope to update soon, I will have more spare time in few weeks.

Phil, I use "Dupli-Color High Performance Wheel Coating" Color was "Silver". I cleaned the wheel with abrasive pads, sand with 320 grit paper and I did not use a primer, just 3 coats of paint.
 

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Discussion Starter · #9 ·
Well I tried the Dichromate treatment this weekend and had mixed results. The metal is supposed to turn a brassy gold to brown color depending on the alloy. Some of the areas did turn color but others were barely affected. The temperature was less than the ideal range of 70 degrees and I may need to wait until we get some better weather to try again.
 

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Discussion Starter · #11 ·
End result was very good in my opinion but I ended up repainting the entire wheels rather than touching them up. Although one wheel was very good and two of the others were fair, one was too messed up to just touch up.

I had mixed results with the dichromate treatment and really would not recommend the process. It was a bit like working with a witches brew. I you look at the MSDS on the chromic acid flake you will see that it is really nasty stuff.

In the end after a couple of tries with the Dow 19 process, I used a SEM self etching gray primer (39683) followed by a couple of coats of Alfa paint code 33904 Silver Poly, and then followed that up with SEM 40903 clear coat. I will pull out the spare tomorrow so I can take some side by side photos to show how this color compares to an untouched wheel. The colors in these two photos are not a good comparison since they were taken in very different light conditions
 

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I'm not sure these wheels are magnesium at all. THe original Campy 60's GTA wheels were a magnesium alloy, but most of these are aluminum alloy, simply painted with an aluminum primer and a good poly or enamel color coat. Usually not clear coated.

Easy to repair - dyes for crack checking, heliarc welding, and standard primers and paints.

The original magnesium alloys were very light, but vulnerable to cracking and catastrophic failure.

Robert
 

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Discussion Starter · #14 ·
Here is the picture of the spare and a painted wheel. The spare is completely original and even has the original 29 year old tire on it (that has to be remedied). Overall they look close with the original wheel looking a wee bit darker to the eye.

The spare sure appears to have a clear coat on it and the paint guy that mixed up and helped me match the paint seemed to think there was a clear coat on the wheels as well.

The debate over the materials of the wheels made me do some backyard science. Using the Archimedes Principal I measured the volume of a wheel at about 195 cubic inches. Density of Aluminum is about .0975 lbs per cubic inch and the density of magnesium is about .0628 lbs per cubic inch. That means if they are aluminum they would weigh about 19 lbs and if they are magnesium they would be much lighter at about 12 pounds. Weighing the wheel on my home scale I got 12 pounds. Scale only measures in 1/2 pound increments and I measured the weight as an incremental adder to my weight so I wouldn't be at the bottom end of the scale. I have to admit that I expected this to tell me that they were aluminum.
 

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if you really want to tell if your wheels are real magnesium alloy or just aluminium, put a drop of Tinners fluid (plumbers use it for soldering) on a spot somewhere out of sight and it will bubble and turn black - on aluminium wheels there will be no reaction at all.
 

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The debate over the materials of the wheels made me do some backyard science. Using the Archimedes Principal I measured the volume of a wheel at about 195 cubic inches. Density of Aluminum is about .0975 lbs per cubic inch and the density of magnesium is about .0628 lbs per cubic inch. That means if they are aluminum they would weigh about 19 lbs and if they are magnesium they would be much lighter at about 12 pounds. Weighing the wheel on my home scale I got 12 pounds.
Nice work, That's convincing enough for me.
The Alloy reference i found was this... not confirmed, but supported by your measurements. Composition limits of AZ91D:
8.3-9.7% Al
0.15% Mn min.
0.35-1.0% Zn
0.10% Si max.
0.005% Fe max.
0.030% Cu max.
0.002% Ni max.
0.02% max. other (each)
balance Mg.

Nice looking wheels too, thanks for posting.
 

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Wow! Yalls wheels rock! Now I have to do mine. Nice! Hey wonder if my 84 spare is a full size. With wheel. Reckon I need to check in the morning. That would be great as one of my wheels is a bit warped. Seems they can never balance correctly. If my spare is a twin then awesome. Again folks nice job! Really makes the car look good.
 
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