Refurbishing of magnesium wheels

[lukasdeopalenica]

Hi Guys,
Is there any special method to refurbish of magnesium wheels? My HPE has magnesium Cromodora CD53 originally designed for fiats 131 and argenta. They are slightly similar to the alloys CD51 installed in older berlinas and HPEs. CD53 are superbly lightweight and have a bit lower offset so the track is a bit wider. My 53s are straight and have no cracks and cavities, but the paint, especially from the outer side, needs renovation. I heard that magnesium wheels should not be sand blasted nor chemically treated. Also cannot be powder coated, as they are not resistant to heat treatment. Is that true? I have seen magnesium wheels devastated by chemical cleaning...Thanks for your tips 

[rossocorsa]

I had some wheels refurbished years ago by powder coating but didn't realise they were magnesium at the time. I don't remember the details very well but I recall the company saying that the wheels have a quite thin outer skin and under this skin they are not resilient so coating was a bit of a gamble, no idea whether that is so or not but what I can tell you is that the finish didn't last and the coating eventually crazed.   

[lukasdeopalenica]

Thanks Rossocorsa. Where they also cromodoras? Maybe I should rather resprayed them.

[rossocorsa]

yes cromodora, they were very light wheels possibly the same as yours although at the time I thought they were Beta wheels. I don't know if the problem with the finish was due specifically to their magnesium content or just because they were in relatively weathered condition?

Alan

[MattNoVAT]

I found this on PistonHeads, seems very informative.



 I refurb wheels, have done for a long time now, magnesium wheels are a complete bind.. and there's no easy answer, a lot of companys won't touch them and with good cause. magnesium as we all know is very unstable and oxidises very repidly when in contact with air/ water/ salt/ acids.. the process to redo them is not quite as straight forward as acid strip etch prime and powdercoat!!

firstly yes you have to be VERY wary of acid stripping, it has to de done, however the timing is critical.. stripping acid will not only etch magnesium badly, but will also soak into the metals pores, they have to be bathed and bathed and bathed and soaked in alkaline solution before the next stage!

bead blasting, this has to be done at a low pressure as magnesium is a soft and easily damaged metal, also the risk of blasting any residues deep into the porus structure of the wheel is an issue..

after the blasting stage the true extent of corrosion is VERY evident, particularly where wheel weights have been attached.. I have seen 50% + of the actual stock completely gone where the weights have been!!, the other prime damge area is where the brake disc sits, you tend to get 2 big grooves where the brake dust has been thrown out from the pads on either side of the disc, I'v seen this so bad before that its almost rotted the wheel into two pieces!!.. at this stage you have to decide if the wheel is even safe anymore..

next comes a process called out gassing.. most wheel restorers wont even know about this and wonder why when they paint the wheels big air bubbles appear.. magnesium creates gas.. deep in the pores.. when sealed in it will build up and pop up big air blisters.. the answer is to heat them, allow them to cool and paint them immediately!!.. this will 99% stop the problem..

corrosion removed and structural integrity ascertained you then etch prime, high build prime, and paint either with powdercoat (cheap and in my opinion not recomended for mag) or a good 2k base and clear..

job done.. problem is that even the slightest contamination, or chip or scuff will set the mag off again.. basically mags are an ongoing problem and to my best knowledge cannot ever be gauranteed to last problem free for years..

so there you are.. the (I think) definitive answer about mag wheels.. personally I hate doing them, I mainly do ferrari ones and maserati, chromadora's and campagnolo's, and frankly the results can be dissapointing, as even though structurally sound the end result invariably shows some level of deep pitting..

grindnshine.co.uk

[mangocrazy]

I don't know whether vapour blasting or soda blasting might be less aggressive than bead blasting. Having said that, one would have thought that the professional wheel renovater that Matt quoted would have known about that.

[peteracs]

Hmm

Sounds like a seriously expensive process with questionable end result. Think it may be worth rethinking and going for a different set?

Peter

[VXdeMayo]

Dear All,
whilst I would love a set of "Mags" myself, (due to the fact that they are rare and have a certain cachet about them), I would agree with Peter. All that work and expense and still you will not have correct wheels for the car! Look at it this way. The money you spend on the Mag project would buy many parts that you will actually need and be correct. Get some standard Beta's, they are surprisingly light and can look very presentable. (If in doubt, look up the "Lulu topic"). Pics of the wheels are on there.
Hang them on the wall, that's what I'd do!
Best,
Chas and Anne.

[lukasdeopalenica]

It sounds reasonably. Thanks. However my mags are not yet scrappy enough to retire

[mangocrazy]

Hi Lukasz, I have recently had experience of stripping magnesium castings - without realising it! I have a pair of motorcycle discs and carriers that I refurbished a couple of years back. The carriers (centres) are what I assumed to be aluminium, the disc rotors are ductile iron. I had the rotors passivated and the carriers coated with a material called Zylon (or Xylon - not sure). This seemed fine for a year or so until 'fur' started peeking through the coating.

I decided I'd get the carriers stripped and re-plated, but this time in electroless nickel plate. I sent the carriers off to a place that does vapour blasting and they did a beautiful job of it. The finish was excellent, smooth, no pitting - perfect. Then I took them to the platers, who assumed (like I did) that they were aluminium. It was only when they put them in the plating solution (which is acid) that they discovered the carriers were definitely NOT aluminium. Basically the plating solution started boiling and frothing, and my 'aluminium' pieces had turned black and pitted. The plating solution was completely contaminated and had to be thrown away, and my carriers are now scrap.

With the benefit of hindsight, I now realise that the carriers were magnesium, not aluminium. This explains why they were so light, despite being quite 'chunky' in appearance, and also why they furred up so quickly. The only positive I've drawn from this is that I now know that a) vapour blasting works really well on magnesium  and b) acid will kill magnesium in a matter of seconds...

[Ashley frater]

Am considering having Lepsons in Kent refurbish my wheels and am thinking about taking them back to silver, although I've learned to love the bling gold.  Can I just get confirmation these are not magnesium so will be straight forward to do. 

Also, I heard that S1 wheels had a different silver finish than later cars.  Does anyone know paint codes so I can provide to Lepsons.

Many thanks
Ashley

[lukasdeopalenica]

These are not made of magnesium, no matter if by Cromodora or FPS. Late models were a bit goldy, but not as gold as yours...

[smithymc]

When I had my FPS wheels stripped and re-finished, the company described them as semi- magnesium rather than 'standard' alloys and altered the spec accordingly.

[Ashley frater]

Thanks for the comments, glad they'll be easy to refurb

[carl59862]

"Also, I heard that S1 wheels had a different silver finish than later cars.  Does anyone know paint codes so I can provide to Lepsons."


Does anyone know the answer to this question? I have a set ready to refurb for my S1 Coupe and would like to get the correct colour.

Thanks

Carl