Wheels/Tyres: Why do our alloys seem to corrode from the inside out ?

[AndyPants]

Excellent job I did a couple of T5 Columba wheels for my old 850 using BMW Titan Silver which I found a good match for the colour. Volvo lists a different colour for the Propus though. I'd definately echo the comments about trying to avoiding runs in the paint, its very easily done if you get impatient like me!

As I've got the same wheels as you I was just wondering a couple of things if you'd be so kind:

1. Is that a chrome paint you used for the outer rim? Think I've seen one in Halfords before and curious if its what you used?
2. Did you mask off the little split rim screws or did you separate the face and the rim?

[krussel]

Originally Posted by AndyPants

Excellent job I did a couple of T5 Columba wheels for my old 850 using BMW Titan Silver which I found a good match for the colour. Volvo lists a different colour for the Propus though. I'd definately echo the comments about trying to avoiding runs in the paint, its very easily done if you get impatient like me!

As I've got the same wheels as you I was just wondering a couple of things if you'd be so kind:

1. Is that a chrome paint you used for the outer rim? Think I've seen one in Halfords before and curious if its what you used?
2. Did you mask off the little split rim screws or did you separate the face and the rim?

I removed the paint on the rim with Nitromors and polished the alloy with a kit that has 3 grades of wheels which attach to a electric drill.

I did think about splitting the rims but they are bonded at the factory and require a fair bit of force. I was going to remove the 12 point torx bolts but read up on it and find that they often snap. A new set is around £100.

So in the end I cut up small strips of masking tape and carefully masked out. Took over an hour though.

[I-S]

This isn't galvanic corrosion, but simple oxidation.

Unlike steel, where the oxidation of iron is catalysed by iron oxide (ie rust accelerates the formation of more rust), aluminium self-passivates. That is, Aluminium oxide is very inert and once the aluminium is oxidised then it is protected from any further oxidation by that layer of aluminium oxide.

So... what is happening here?

You'll notice that these bubbles will tend to start from where a chip has gone through the paint to the metal. This chip then allows water and air to get to both the metal, but also underneath the paint. The metal oxidises which pushes the paint up (and aluminium oxide is notoriously difficult to get stuff to stick to properly), letting the water and air in further, and further, and further, creating these bubbles. The white powder is a mix of paint and aluminium oxide.

To best prepare aluminium for painting, use an acid etch primer, as this will bond into the aluminium rather better.

You see this effect much more on diamond-cut wheels.

Here's one of my old Honda Epsilon alloys, in the typical state they end up:

And after a bit of work (sand down all old lacquer, acid etch primer, high build primer, silver paint and lacquer):

[krussel]

Nice job !

Do you think using copper grease on the hub speeds up the process ?

[AndyPants]

Originally Posted by krussel

I removed the paint on the rim with Nitromors and polished the alloy with a kit that has 3 grades of wheels which attach to a electric drill.

I did think about splitting the rims but they are bonded at the factory and require a fair bit of force. I was going to remove the 12 point torx bolts but read up on it and find that they often snap. A new set is around £100.

So in the end I cut up small strips of masking tape and carefully masked out. Took over an hour though.

Nice, I assume you just lacquer it afterwards as normal to protect it from the elements.

I wasn't aware the wheels were bonded as well as fixed with the little bolts, so thats useful to know. And yep I can well believe it was time consuming masking them off - worth it though I think as I like the look of them and I think painting over wouldn't do them justice

Just to add to the copper grease debate - I've always put a small amount on mine and never noticed any problems. I have however seen what happens when you don't - when a friend came around in his mums Mondeo and the wheel was stuck on the hub!

[krussel]

I ve polished alloys before obtaining a mirror finish and then tried to spray a light coat of lacquer from a can. The result is disaster and ended up starting again. As my Volvo is a 2nd car and garaged in the winter I have found in the past that a coat of good polish on the alloy when you wash the car is enough to hold back corrosion.

Prev polished wheel with no lacquer.



Yes the wheels are bonded with a very strong adhesive tape. To break them you really need a press or hit them with a heavy hammer. You can use silicon when you re assemble. Videos on you tube.

The bolts kinda make the wheels really and it would be a crime to spray over them which is why I ve chosen a slightly darker silver to show them up. Did see a gold set on ebay which would look good but they were £120 and you have to get the old ones out as they are held in with thread lock.

[I-S]

I can't see copper grease making any odds - it won't eat the lacquer, nor change the process by which the lacquer is lifted.

With polishing as you have all that will happen is that as the wax/sealant that you have used wears away then the wheel will simply oxidise and go dull. Another polish will see it bright again. With no lacquer to lift/peel/become otherwise unsightly, it's probably a better look and one that ages more gracefully. Since you're prepared to put the elbow grease (there's a grease that does make a difference!) in to keep them looking good, it's the way to go.

Since I am merely a lazy beggar, I went for paint on those wheels. For the Volvo, I'd get them refurbed when necessary probably, but for now I'm just trying to keep on top of brake dust and treating them to some wheel wax, but painted wheels are generally so much easier to look after than diamond-cuts.

[AndyPants]

Originally Posted by krussel

I ve polished alloys before obtaining a mirror finish and then tried to spray a light coat of lacquer from a can. The result is disaster and ended up starting again. As my Volvo is a 2nd car and garaged in the winter I have found in the past that a coat of good polish on the alloy when you wash the car is enough to hold back corrosion.

Prev polished wheel with no lacquer.

/pic

Yes the wheels are bonded with a very strong adhesive tape. To break them you really need a press or hit them with a heavy hammer. You can use silicon when you re assemble. Videos on you tube.

The bolts kinda make the wheels really and it would be a crime to spray over them which is why I ve chosen a slightly darker silver to show them up. Did see a gold set on ebay which would look good but they were £120 and you have to get the old ones out as they are held in with thread lock.

Thanks, useful to know . Unfortunately mine are starting to bubble a little after 15 years, but I think they've done pretty well so far for quite a complex wheel. Not quite sure yet whether I'd DIY these or get them proffesionally re-furbed.

A friend had the same wheels done by a garage and based on what you've said, I can't imagine they separated the wheels. Having said this they did do what looks to be an excellent job but time will tell with these things. I've seen some 'BBS split rim kits' on eBay for like £100 but I wondered whether they were indeed specialist tools or just someone trying to make a quick 'buck'.

[Andy]

I refurbed my set of nebulas myself. Came apart no probs, no damage to any bolts using correct size torx bit. I've heard the Yanks use imperial torx bits that don't quite fit hence their problems. Stuff paint striper, tried that approach but didn't touch the yellowish primer, that then reacted with my 2K paint. Paid cash to get them acid stripped, took the bloke minutes and cost not much. Old thread lock on bolts polished off with a rotary polishing wheel.

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[krussel]

Wow nice job Andy. Looks like a new wheel.