Originally Posted by
hankj
So headtube conforms to cup, not vice versa? The cup I pressed in was perfectly round on the bearing before install. Cup went in dead square. Then after that the little bit of fore aft slop happened, exactly like the OG cup.
If manufacturing defect then the cup will conform to the tube?
Thanks
BEFORE doing anything, confirm that the problem is between the cup and headtube, and not elsewhere.
To answer your question----- the weaker member conforms to the stronger one. Cups are well braced while headtubes aren't so the headtube does the flexing.
Imagine for a moment a piece of string. Tie it around a cylinder tightly. Slide it off and you can shape it any way you want, but it will still slide back onto the pipe and be just as tight as before.
The same with headtubes. Being ovalized doesn't change how it will fit onto a cup. The ONLY ways it could end up loose are if actually stretched (possible but very rare) of if material is shaved off from the ID.
I've seen this dozens of times, and it's obvious, because the ID will show the evidence of reaming on the sides, but not front and back.