Magnesium or Aluminium? Best way to restore?

I had some dymag motor bike wheels refurbished, a very specialized job , so if they are mags be sure they are done right. The guy who did mine used to work for dymag and now does refurbs

 

Talk to Dave at StickRx. He knows the correct process for mag wheels.

 

You can clean it up and repaint it yourself. Do a chemical strip of the old paint, do not blast it with sand, or anything that will ruin the surface. Primer, paint, clear coat. Done.

 

Lots of discussions here in the archives on this exact subject.

"Search Is Your Friend"

As your starting point, post no. 18 here: https://www.ferrarichat.com/forum/threads/dino-cromodora-wheel-refinishing-needed.275151/

 

Does it say “Magnesio” anywhere in the back?

 

This guy has it down.

https://stevekouracos.com/restoration/tips-and-tricks/aluminum-magnesium-wheel-restoration/

 

I know it's been asked before, but wondering if there's a more modern answer: Opinion on simply powder-coating the rims? I've got a local shop that produces great results with other parts; not sure if the rims are a good candidate or not.

 

I believe they are also a magnesium alloy. I had my set of factory 16” wheels professionally painted and the front left is showing signs of oxidation under the paint.


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The Cromodora 14” wheels are Mag alloy.

 

If you're in Australia post it in the Australian section too.

 

I'm far from a magnesium expert, but this talked a lot on an old Ducati forum I'm on. Apparently what you are describing is the issue with magnesium wheels. Actually, the magnesium can corrode substantially and not disturb the paint on top, this is far worse. Guys running the old mag motorcycle wheels on the track get them x-rayed every year. The concern with stripping down to bare metal and repainting them them is that you will trap a contaminant under the paint and it starts invisibly eating away the inside of the wheel.

 

That's because of incorrect primer and over stripping the Factory finish.


Body Shops are not invested in the time required , but I a begging mine to spray them after properly priming
The Zinc Chromate is key.

Carefully repairing the chips is key.
Not f^**^%ing them up, is key.

No WAY should you powder coat as the off gassing of these old wheels would probably crack them.
Be gentle, sand gentle, spray back with the proper color..

 

Oh you can see the corrosion, it looks like ant or termite trails under your new glossy but wrong, paint finish!!

 

The Dino and 308 wheels are a light alloy made up primarily of aluminum with some magnesium. From a paint perspective they behave like aluminum and do not require any of the special coatings magnesium requires to protect them from oxidation. I repeat, despite a small magnesium content the prep to paint the wheels should be rooted in good practices with aluminum (different to steel) in order to achieve a good result.

A few considerations:

- Chemically stripping the wheels is generally a bad idea because of how porous they are. Neutralizing the chemical can be near impossible with it leaching out during temperature cycles. As such media blasting or hand sanding is the best option for prepping these wheels.

- Powder coating is generally a bad idea again because of the porosity. The heating process will cause high temperature out-gassing that will cause the finish to fail. Often times the failure happens during the coating process.

- Once the wheels are stripped coat them with a good Zinc Chromate primer (preferably a mixed paint with hardener and not out of a spray can) which will give proper adhesion to the substrate. Colour can be applied to the chromate primer or another sealer coat/primer can be used before the colour.

- Most wheels are now painted in a two stage process with clear and you want to keep your clear to about 60-70% gloss to keep them looking like original.

 

I restored my magnesium bbs wheels. The process in the Steve k link above is what I used. I also brought the magnesium to get magneflux inspected for cracks at an airplane engine shop (near my local small plane airport) - they have to do this on engine rebuilds. Paint - do not powdercoat as the baking will weaken the magnesium - even if it’s an alloy. That coating step has to be done too. I think I ordered it from grainger. It came out well!
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I did mine and it's a ****ty job with hazardous chemicals (if you can get them-- aircraft restorers will know where to find them.) My descriptions is here about half way down:
https://www.ferrarichat.com/forum/threads/dereks-308-engine-rebuild.535247/page-16

 

...I found the zinc chromate at a Marine Supply...

A close up of one of my rims shows the pin holes in the finish, only sanding this open and investigating, will renew my confidence in the rim.
That said, I think the QC in the '70s was a far cry from the wonderful wheels we see today!
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