Bodge recommendations sought: Attaching a top cap to a threadless headset adapter

Hi all,

I'm rebuilding a 2011 Fuji track frame I bought from a lovely LFGSSer and am attempting to reuse many of the parts it came with, in combination with a few bits from my spares box. Pic 1 shows the cast of characters in this part of the rebuild story. Slightly longwinded explanation follows, bear with me.

The frame has a 1" threaded headset into which has been fitted a threadless headset adapter. The adapter is tightened into the fork with a long bolt which runs through a (unthreaded) crown in the top of the adapter (pic 2) and screws into the "quill" plug. A regular stem then clamps to the top of the adapter (with a shim), and a simple plastic bung, which looks suspiciously like a bar-end plug, goes in the top of the adapter (pic 3). That was, at least, the arrangement that came with the bike.

I have a nice shiny Hope top cap and bolt that for silly and solely decorative reasons I want to use in this build. However, lacking the usual star-fangled nut to screw into, there's no (legit) way to secure the bolt and cap into the top of the adapter as one would normally secure it into the top of a steerer tube.

The solution I've got in mind for now is shown in pic 4 – I cut a plastic bottle cap down to fit the inner diameter of the adapter, poked a hole in the middle for the bolt to thread itself through, then if I move the adapter down a little inside the stem, there's room to work my little disc inside and tighten the bolt to "secure" the cap (pic 5). If the stem sits slightly higher on the adapter neck, there's room for the top cap bolt inside.

It does actually work, just not very well. The theme of many of my ideas. Actually, I can't claim credit for this one – it was Nelson at LBK who got me thinking about this.

So, any suggestions for a better way to do this? Ideally I do want to leave the adapter bolt (pic 2) accessible, or at least accessible with a little bit of effort. I did think about trying to use a tweaked star-fangled nut, but removing it to get at the lower bolt would be just about impossible, I imagine. I did just find these threaded expando bar-end plugs; I can't tell what the thread size is, but I wonder if that might work, or if some other kind of cunning threaded plug is available. Is there a way to somehow join the top bolt to the lower? Or should I try buying a new headset adapter that would support a standard top cap, shifting the problem to one of possible cap hole/bolt head diameter mismatch?

Edit: it seems I overlooked the existence of carbon steerers that need bungs of this sort – but the ones I'm looking at seem like they might be too long or too wide to fit into the adapter. Hope make a Head Doctor expander which I'm embarrassed I didn't spot earlier, but it seems it might be 1 1/8" so way too wide for this application. The internal diameter of the top of the adapter is 20mm.

Your creative solutions or other thoughts appreciated in advance! Yours in bodging,

James

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