Frame discoloration?

[ritcho]

I have a 7 year old (already???) Giant road frame made from 6061-T6 aluminium alloy. It has recently developed some small white patches (the bike has a silver finish) up to 4-5mm in diameter on the front of the head tube. I've not crashed the bike, but it has done a lot of miles[1], including some racing and triathlon.

I want to know if this discoloration is just some surface/cosmetic issue or if it is a sign that it is going to fail and make me fall on my face.

Can anyone shed some light on this?

Cheers,
Ritch

[1] The frame, stem, handlebars and seatpost are all that is left of the original bike...

 

[Allan Butler]

It sounds as if the protective finish on the front of the head tube has been
chipped in those places where you are seeing the white patches. By your
description there is either a layer of anodizing or clear coat over the
polished aluminum.

Clean off the white powder which is oxidation. Polish it best you can by
hand where you see the pitting. Immediately, clean it with something to
remove any oil and grease, then spray a clear coat of acrylic over the
spots.

If the pitting isn't too bad that should be all you have to do. If the
pitting at these sights is too deep then take it to a bike shop and have
them tell you what you should do.

 

[Werehatrack]

On Mon, 24 Jan 2005 04:34:22 GMT, Allan Butler
<[email protected]> may have said:

>It sounds as if the protective finish on the front of the head tube has been
>chipped in those places where you are seeing the white patches. By your
>description there is either a layer of anodizing or clear coat over the
>polished aluminum.

More likely the latter, and it's quite possible that the oxidation is
under the clearcoat, spreading out from small chips in th coating.

>Clean off the white powder which is oxidation.

To remove oxidation from aluminum, use ammonia solution. If the
oxidation in under clearcoat, then the coating must be removed in that
area.



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[Zog The Undeniable]

ritcho wrote:
> I have a 7 year old (already???) Giant road frame made from 6061-T6
> aluminium alloy. It has recently developed some small white patches
> (the bike has a silver finish) up to 4-5mm in diameter on the front of
> the head tube. I've not crashed the bike, but it has done a lot of
> miles[1], including some racing and triathlon.
>
> I want to know if this discoloration is just some surface/cosmetic
> issue or if it is a sign that it is going to fail and make me fall on
> my face.

Just a bit of surface oxidation. It happens particularly badly if they
use salt on the roads where you live. You can keep polishing it off or
have the frame refinished.