1989Pre 

I took this expander bolt and expander from my Miche Primato 1" headset out of my steerer tube, and now, when I put it back in to re-tighten, the bolt at the headset cap just keeps spinning (no resistance). What am I doing wrong?

soyabean

Sounds like stripped threads.

You should be able to verify with the piece removed as in photo.

curbtender

Can you thread it down until seated and then install and tighten?

Andrew R Stewart 

If the threaded cone isn't contacting the expanding band with enough force to keep it from rotating, when the bolt is turned, that cone can easily just spin with the bolt and no tightening will happen. Of course the cone's threads could be stripped but that usually has a "it sort of tightens but not enough to hold in place" feeling when turning the bolt. It also should be easy to watch the bolt thread in and out of the cone as well as look inside the cone's threads to be sure of their condition.

BTW I grease the cone and band's contact surfaces. Al loves to gall and stick to itself when under pressure. Andy

1989Pre 

I have inspected, and the threads are not stripped, but they are binding. It is taking me some force for me to turn the compression bolt on the top cap against the wedge (holding the wedge with chan-l-locs), so that when I turn it in the steerer tube, it just spins with the wedge, instead of screwing down into it (to compress the spring). I have cleaned and re-greased the bolt and threaded section of the wedge. The bolt is still not turning as freely as is required. A bike shop got this headset installed, though, so I am wondering how they got the sleeve to expand.

masi61

That is not a very substantial steerer plug. 1” threadless designs I have seen never inspire much confidence. Designs that provide grip and expansion along their entire length eliminate a lot of the uncertainty.

I’m not familiar with the Miche Primato one shown but I am curious about the middle aluminum cup shaped piece. Is there any chance it needs to be reversed to allow the threaded wedge piece at the bottom to have more purchase? Another thought about that cup shaped piece is that the groove on it is for another O-ring. Any chance it had an O-ring originally?

Also, does your 1” threadless fork have a carbon or aluminum steer tube? You might be able to get the wedge pieces to stay put while tightening by applying some grip paste to the outside surfaces.

Andrew R Stewart 

This suggests that either the bolt or the threaded cone's threads are buggered up. Given the steel bolt and Al cone I guess the cone's threads. One could chase those threads with a tap (most likely a M6) to see if that helps.

We assume the steerer is a carbon one as otherwise a star nut would have been used. Andy

1989Pre 

What you are saying makes sense. The steerer is steel and the fork is aluminum, a 1990's Moser-branded fork.

Andrew R Stewart 

Then remove and toss the plug, install a star nut and don't look back. Andy

1989Pre 

You know, I didn't even think of that. Choice. Thanks, Andrew.