Yes, you can tap the star nut down.
From step "F" in the owner's manual at cane Creek's web site
http://www.canecreek.com/manuals/Hea...structions.pdf
Quote:
Press the star nut into the steerer tube to a point 15 mm below the top. This should preferably be done using an installation
tool such as Cane Creek’s Star Nut Installation Tool Set (p/n TL0200). If this tool is unavailable, thread the compression bolt
into the star nut and lightly tap the assembly into position with a deadweight mallet or similar tool. Ensure that the threads of
the star nut are aligned with the steerer tube.
End quote.



Reply With Quote
... combined with the above careless maintenance. 
