That is rust or iron oxide from the inner surface of the steerer.
Luckily, an anodized aluminum surface like your Technomic Deluxe stem is
pretty tough. Some vinegar and fine steel wool should remove it without
any further damage to the anodized surface. If yours was a regular
Technomic, it probably wouldn't be anodized, and thus could be scratched by
the steel wool. To prevent problems like this in the future, it is
important to grease the inside of the steerer before assembly. (A regular,
non-anodized stem would be even worse, as the aluminum-steel interface sets
you up for galvanic corrosion. In that case, the stem would be attacked
preferentially, leading to large volumes of aluminum oxide, and possibly a
stuck stem in bad cases.)
San Marcos, CA
On Sunday, October 16, 2016 at 12:29:46 PM UTC-7, Lungimsam wrote:
> Came off my Sam. Exposed stem is clean as you can see.clean. Stem sunk
> into steerer tube has some surface corrosion of some sort on the aluminum
> Technomic deluxe them. How do I get the corrosion off the stem and restore
> it to its original lustre?
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