Integrated headset topcaps.

[Joe]

Not the best topic title I'll admit.

Basically I'm just switching out the stem on my CR1 and I can't get the headset tight enough. The new stem appears to have a slightly smaller stack height which I guess accounts for this.
Anyway, I've never seen a topcap like this before and it needs replacing as in my eagerness to tighten it up I've mashed the head of the bolt up.
The now mashed up bolt goes through the topcap and into the silver bung pictured. Should this whole thing comeout when I unscrew it, as it has, or has the bolt been tightened hard enough to "join" the topcab with the bung?
Apologies for the rubbish wording etc but I'm not used to this - all my other bikes have a starnut in the steerer!

 

[bonj2]

at a guess, it looks like what may have happened is that the bung wasn't tightened enough into the steerer, meaning that with sufficient force it could slide up and down it, and when you tightened the top cap bolt, instead of applying compression it simply pulled the bung up to the top of the steerer tube and as you sensed it didn't seem to be getting tighter you took the top cap off which lifted the bung off with it which was now pulled all the way up and resting against the top cap?

what should happen is that the bung is inserted into the steerer tube to the right depth, and then it is tightened up so it can't move up or down, often with a 8mm or 10mm allen key. when it is tight enough that it can't move up or down when the force required to apply the compression to set the bearing preload is applied, you put the top cap on , and screw the top cap bolt into the thread in the bung and you can then tighten it up to apply the necessary compression and the bung doesn't move.

it isn't a terribly informative picture but it looks like part of the bung is still in the steerer tube and the other part of the bung is attached to the topcap bolt in your hand.
maybe you could see if you can get the part that is in the steerer out, and take the other part off the top cap, reassemble the bung and then if you can get to that stage then you can move forward from there. namely understanding how the bung is supposed to be inserted and work and then once it's in correctly you can put the top cap on.

you also need to check the top of the steerer is a few mm below the top of the stem, you mention the stack height being different so you need to make sure this is still the case because if not you won't be able to apply compression.

 

[Joe]

Cheers Ben. There is indeed part of it still stuck in the steerer but theres no way of pulling it out that I can see, and it can't be pushed out the bottom like a starnut as the steerer is closed off.
Should these two bits be joined together then, you think? And the carbon topcap seperate? It's just that the carbon topcap and the part of the bung not in the steerer are stuck fast together.
I'm wondering if they are supposed to be like that? From what I can tell it would still allow you to compress with the topbolt (providing there was enough stem above the steerer) and preload the bearings before tightening the stem.
I don't have any small spacers to hand to try it but I am waiting on a new stem with a larger stack height.

Either way I need to repace the top (or all) of it as the bolt head is mashed.
Is this the same thing?
http://www.chainreactioncycles.com/Models.aspx?PartnerID=79&ModelID=2218
Do you think the top of this would fit with the bottom of the one I have, or is there an easy way of removing the bung in my steerer?

 

[02GF74]

there is more than one design for these headset bungs. I can't work out what is going on in the photo but the bung should have a split wedge, usually in 3 parts held together with an rubber o-ring that when the bolt is done up, causes the wedges to expand and grip the inside of the steerer.

regaring the bolt - this is usualy someting like an M5 or M6 cap head - very cheap - your local fastener place should stock these. 8.8 tensile will do as this part is not under mcuh train, unlike the stem which use 12.8 grade bolts.

 

[bonj2]

can you not screw the bolt partially into what's left of the bung in the steerer tube in order to pull it out?