embankmentlb

Adding a computer to my 3r today and noticed this mark on the stem. The photos are not that clear but looks like a stress crack to me. What do you guys think? Do these fail in this way? Thank you for your thoughts.

BrewsterII

Looks like a scratch to me.

repechage

I have found a "forging" crack on one of my Cinelli stems.
retired it, was an early one too before they started anodizing them.
crack check dye to be sure.

from my perspective, I really want the feeling of confidence. Test, don't guess.

embankmentlb

I took some steel wool to it and feel pretty confident that it is only a scratch.

Peruano

I polish rocks. To test for a crack versus a visual streak, I wet the surface. As the surface dries, the water will be drawn to a crack and that area will stay visibly wet longer. A shallower scratch or streak will not. It should work on metal as well.

rancho66 

scratch

oneclick 

You need a loupe.

A scratch will usually show metal displaced outwards from the surface, at the edges. Whatever causes the scratch will push metal as well as cut.

A crack will have no upwards displacement at the edges.

In your case:

a) that looks like a scratch to me;
b) it's a likely place for such a scratch; and
c) if that's a Cinelli XA it will crack across the front under the badge first, worry about that instead.

thinktubes 

Bad Lag

Push down on the bars. The stem will flex. If the feature opens up, it is a crack. If it a scratch, it will not open.

verktyg 

It's a scratch. You can clearly see how the thin hard anodized surface has been scraped away. A crack would show some division between the surfaces.

Cracks in forged aluminum parts are frequently the result of a flaw in the billet, blank or raw stock used for the forging. There are lots of different kinds of flaws: lap seams, laminations, incomplete mixing of the alloys and so on. Determining the cause of the flaw generally requires lab testing...

Within a 2 week period a number of years ago I ran into 3 different good quality forged aluminum components with cracks. One was in a brand new Nitto Pearl stem, their top of the line model. I was admiring the beautiful workmanship when I noticed what looked like a little scratch. I checked it at 10x magnification and it looked suspicious.



10x magnification



At 60x magnification the crack became obvious.



On the opposite side of the stem more cracks became visible at 60x



I found Nitto's email address and sent them photos of the stem. The next morning I received a replacement stem shipped overnight direct to me from Japan. They also enclosed return shipping for the defective stem!

Where do you find that kind of service and commitment to quality?

Anyway, Nitto makes premium quality components and that kind of crack was easy to overlook by their inspection department. There are several YouTube videos showing their manufacturing processes. I was surprised in this day of CNC machines, automation and robotics how much of their work is done on manual equipment.

I discovered this crack in a Stronglight crank arm I was installing. Again it wasn't obvious until I checked under a microscope.




The crack is the result of a lamination flaw in the billet. The layers were starting to separate around the pedal eye (delaminate). The cracks run parallel to the length of the arm so its not as serious as a crack that runs across the crank arm but still, there's is no way I would use this crank!




It pays to closely inspect highly stressed components like bars, stems, cranks, seatposts, etc. when installing or working on them. Consider this, many C&V components are getting long in the tooth and can easily be 40-50 years old. Unless you've owned them since new, you have no idea of what kind of use and abuse they've been through.

verktyg