Have got carbon steerer forks and the Alu bung in there with serrated edges is just pulling upwards so I can’t preload the bearings.

What can I do to stop it slipping?

If you take the top cap bolt out there is usually a socket for a larger alan key, which you use to expand the bung before tightening the top cap

Shirley the OP has done that already?

The term bung is misleading. Should be ‘expanding steerer thingy’

No this is very simple. There’s a sleeve with the serrated edge. A wedge bung sits underneath that with a bolt thread in there. The bolt pushes through the top cap into the wedge bung and pulls it up. BUT as the bung moves up it pulls the sleeve with it. The sleeve is not staying put, so I can’t preload the bearings.

Groan.

sounds like you are missing an equal wedge bung to go on the top facing down into the sleeve.

without the stem on use a stem bolt in the bung whilst holding it in place with a screwdriver or something.

Once it starts tightening up it won’t slip any more. Undo the bolt, use a stem cap (but still no stem) on the top of the steerer and do the bolt up again until it’s fairly tight. this will lock the bung in place even when you undo it.

undo bolt, put stem on and then do up and preload bearigns.

wwaswas, just tried that. when i put the stem cap on the steerer and do up the bolt, it just pulls the whole lot up. no tightening.

here’s a picture of the wedge expander.

P1060962.JPG by cakefest, on Flickr

Not seen it like that before. I can’t see how you can tighten it up without it moving without there being another part to tighten and expand the sleave against.

This is similar
http://www.chainreactioncycles.com/vp-compression-adjuster-pinarello/rp-prod108087
and has a top part to do this.

looks like the old style of SFN-less headset, the one I had was a right faff to get setup.

my method – remove stem and spacers, use a top cap that sinks into the steerer tube a little, that keeps the expanding collar in place while you tighten the bolt, the collar should wedge into place, remove bolt and top cap, fit stem and spacers and bolt – use a shallower top cap or fit an extra spacer above the stem to give you room to preload the bearings.

not a great explanation but hopefully you can figure out what I mean

this is cheap and works a lot better

In doing the DONK/ wwaswas method, how does the sleave not just slacken off and the wedge drop when you undo the bolt? Is friction enough?

Is friction enough?

yes, it all tends to lock in place once you’ve tightened it sufficiently.

Is friction enough?

hopefully 🙂 be careful when threading the bolt back in lest you knock it out and have to start again

Ok – looks like a problem that has been solved by all the newer types. Also for a carbon steerer, the bung is v small, certainly smaller than the clamp area of the stem. Would the greater support of a deeper bung not be better? Presumably they are deeper nowadays for this reason as well as gripping better?

It might make no difference, just curious.

In short what you have is shite 🙁

I had same issue you need as mentioned the carbon bung that first you tighten into steerer to allow you a solid base to then tighten your top cap/bolt 😀

Get a BBB Powerhead which is deeper than most and use carbon assembly paste between it and the steerer http://www.chainreactioncycles.com/bbb-powerhead-compressor-adjuster-bap03/rp-prod29884

went to LBS and bought new FSA steerer bung for £8. inserted base part into steerer at correct depth, tightened nicely in there. put special top cap on with threaded column underneath that tightens onto base, and removed bearing play. fantastic!

thanks for help.