I'm in agreement with Marten. The crack is best terminated. I found two cracks under the seatstay attachment at the seat lug on my Windsor Profesional, and terminated both with drilled holes. Thousands of miles later, they haven't grown.
With the steerer, I'd think it depends to a degree what the frame size is, as smaller frame sizes have disproportionately shorter steerer tubes. Short steerers have much higher shear stress near the threads due to the fact that the bending loads at the crown are fully resolved into shear loading multiplied by the steerer's length, force times distance if you will. As well, a longer steerer also allows for potentially more overlap between stem quill and the cracked tube, keeping the expander further away from the split in the steerer.
I would err on the side of assuming the crack has progressed further along than it appears, again as Marten has alluded, i.e. "be sure of where the crack now ends".
David Snyder Auburn, CA usa
Marten Gerritsen wrote:
> It al depends on how long the crack is I suppose. If you can be sure of
> where the crack now ends you could drill a hole so the crack stops in a
> blunt hole instead continuing a sharp V.
>
> Kyle Brooks wrote:
>> I had an older Mercian where the slot in the steerer was actually cut
>> through -- when I sent the frame and fork to Mercian for other repairs, I
>> asked about repairing the fork They told me to actually not worry about
>> it and the repair wasn't necessary -- as long as I wouldn't be tightening
>> the stem quill in the threaded part (which you shouldn't do anyhow). Now,
>> since yours is cracking and not actually cut, I wonder if that makes a
>> difference -- since the crack might be inclined to keep spreading? I
>> guess I'm not helping much.