Originally Posted by
panzerwagon
Overtightened stem expander/wedge? Repair threads, drill a hole at each end of crack to stop the spread, file the edges smooth. Use a taller stem and insert slightly deeper, but remain above any steerer flaring near crown.
Not sure it’s worth it— I would replace the steerer, or even the fork.
Maybe. But that expander/wedge should be below those threads, not completely above where they start. That silly minimum insertion line is there for that reason. Also, the bottom of the stem being there means it is too high, so a larger than intended maximum bending force (that would push back on the stem bottom when you press down on the bars hitting say a pothole). And that greater than intended bending force is resisted by a shorter lever. The force at the bottom of the stem resisting bending is in proportion to the inverse of the lever length. Say this stem was only inserted 2/3s of the way to to the min insertion line. Well, that's 1 1/2 X the bigger than designed for bending force applied at the weakest part of the steerer.
If that crack is not at the back of the steerer (your picture doesn't give any clues), I'll put on my dunce cap and go sit in the corner.