Slipping fork bung on PX track

I got the headset fitted on my PX track a couple of weeks ago,

used it a couple of times and seemed fine.

When i went to change my stem today the metal bung wouldn't tighten back up properly, it's not gripping the inside of the steering tube anymore. The bolt does up tight but the whole bung can still lift right out.

Any ideas why this might be? There was a red gritty type paste on it which may have rubbed off a little?

Thanks for your help,

Robin

Cornholio?

Is it a carbon steerer? If so you may need to tighten the wedge/bung inside the tube before reassembling the headset.

What brand is the bung?
With the Hope one you tighten the bung part into the steerer with a big allen key, 8mm or something, then the bolt goes through the cap and down into the bung and preloads the bearings as normal.

The red stuff is Tacx assembly paste used to increase the friction in component interfaces with carbon tubes so you don't have torque as much. A steerer bung is not the place I would expect to see it as you only need it finger tight anyway so no risk of over doing it. Maybe bung was faulty and somone added the friction paste to try and make it work?

Pull it out and tighten it up and check that it is operating properly. It should easily compress enough that you can't get it into the steerer at all. Lot's of stories of people splitting carbon steerers with over-zealous tightening. It only needs to be tight enough to just stop it pulling out when you adjust the headset cap.

If it's knacked a new one is only £4 or £5, M:Part ones are supposed to be OK and easily available in Evans etc.

The wedge/bun that came with my serotta was made of cheese. After six months it was so warped that all the straight edges were warped and the round bits ovalised

I think I now have an m:part one

Use TP.

Corny was not amused when referred to as cornholio

My bung gave me some gyp when I changed stem, but it was all solved by a bit of fettling.

Firstly, clean that assembly paste off the bung - you need friction between the bung and steerer.

Then check your stem/spacer configuration, esp as you say you changed stem. Do you have enough stack height to clear the steerer by a good few mm, so that when you tighten down, the steerer and bung do not interfere with the top cap before tension is acheived? You may need extra spacing.

Second, the position of the bung in the steerer tube before you tighten is important. It must be pushed far enough in so it does not expand out of the top of the steerer, but not so far as the bolt will not reach the threaded plate.

Good luck