Slipping nut in carbon steerer tube

[tiger]

I posted recently about a loose headset that I couldn't tighten...
turned out that the star-fangled nut in the steerer tube had slipped and tightening the top cap bolt had just drawn the nut up to the bottom of the top cap, so tightening wasn't drawing all the headset components together.

My LBS pushed the nut back down the steerer and got the headset nice and tight. But now after just a few rides it's come loose again. I suspect the nut has slipped again. It's a long drive to the LBS, so
I'd like to fix this myself.

How do you tighten this nut? Is there anything special about tightening it in a carbon steerer tube?

[onearmsteve7]

Ok, Ive wondered this since I first heard of the star nut. Why not use an expansion plug on steel or aluminum too? The slightly higher cost of the part would most surely be offset by the simplicity of installation and the possibility of a screwed fork if done incorrectly.

[Sarcastic Apostle]

Before the sharp edges of the star nut cut up the inside of the steerer, get the correct setup. Assuming you have the 1 1/8" steerer, there are bike shops that sell the expander plug that goes into carbon steerers.

Hint: how tight are you tightening your bolt? Don't use the same methodology you used with threaded stems. The two bolts that clamp onto the steerer help to lock the stem, not the top bolt. Even with that, don't muscle it and crack the steerer.

[Hec-1]

Could be an issue with method used?

Just to confirm your work (pls excuse this if you are indeed very familiar with how a-heads function):

To tighten:
1. Handlebar stem binder bolts backed off
2. Star nut properly down the steerer tube (though star nut kind of dangerous in a carbon tube)
3. Tighten top cap bolt to eliminate headset play. If the h'bar stem does not move freely down the steerer tube while doing this, you may consider twisting the handlebars back and forth ever so slightly, in relation to the forks, to allow the stem to creep down the steerer tube while tightening top cap bolt.
4. Tighten h'bar stem binder bolts once handlebars are aligned with wheel/fork.
5. Loosen top cap bolt so that it is no longer stressed.
6. Ride like hell.

The basic principle is that once the binder bolts of the handlebar stem are tightened (and the headset has close to no play), it should be possible to back off the top cap bolt so that it is slightly more than finger tight (if fingers could've reached it). What holds the tension in the headset is the stem secured to the steerer tube. It should not move at all until you loosen the binder bolts. The top cap and its bolt should play no further part in the game, until next time you want to readjust the headset or remove the h'bar stem.

If all is working well it should be possible to ride without top cap and bolt at all, once everything's tight (though it looks better with them on).

If you cannot get sufficient tightness on the h'bar stem via the binder bolts (so that the stem starts slipping slowly up the tube, causing headset bearing play), then that problem should be addressed *without* using the top cap and its bolt as support. In my case (Deda Zero 1 inch stem on steel steerer tube), I used a small amount of masking tape on the inside of the stem and that stopped the stem from creeping up the steerer tube. Inelegant, but effective.

BTW you should have no grease in the mating surfaces between steerer tube and h'bar stem.

/Robert
Sweden (Colnago Chic, Campag veloce, does not grease tapers on centre bracket axle ;-)