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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Quickfix: Drill a hole in the barend bung and attach the hope topcap to it with a nut from below...

or check the diameter on the fsa carbon bung. I think it can be shortened a bit:

or
What is the inner diameter of the adapter?
Maybe you can cut an internal thread in the adapter and use a crank bolt like this (or glue in a tube like I did)
https://www.lfgss.com/comments/12869532/

@svenhöek Thanks – interesting ideas!

The internal adapter diameter is 20mm so too small for the FSA bung unfortunately. Drilling the bar-end cap is a good idea if I could also shave its sides, since it has a slight expansion in the body but the cap is a little too wide at the moment. And the threaded tube is a great hack – if I didn't already have a cap I wanted to use.

The next thing I'm trying is to make an DIY expansion bung from an M6 rubber cavity fixing, which I'm going to nestle inside some 13-20mm rubber washers. Hopefully introducing a bit of the bolt to that nut will expand it sufficiently to stay in the adapter. I've got some small M6 rubber washers to keep the nut away from the bolt head if necessary. Those bits should be arriving tomorrow so I'll let you know how it turns out!

Thanks again for the tips.

Did you manage to solve this? I have exactly the same problem..

This could almost work. Unfortunately it’s 1,5mm too thick :/

I did indeed – not a perfect solution but it works. Basically the DIY expansion bung idea that I mentioned above – a cavity fixing (M6 x 15mm) surrounded by 13-20mm rubber o-rings with a few 6mm flat rubber washers added to the bolt above the nut to act as spacers. The outer dia. of the cavity nut is 13mm and the inner dia. of the adapter is 20mm so the o-rings fit pretty well perfectly – but if I did it again I might try and get slightly wider rings for a tighter fit. When the whole thing is tightened up it just about grips the inside of the adapter, and I can push it in with my thumb to seat it. The awkward bit is that I have to clamp the stem onto the adapter higher up than I would like so as to provide enough vertical space for the whole cap bolt to fit inside. But if I was braver I would saw the bolt shorter.

Hope that helps!

The simple solution is as follows.
Replace the long wedge bolt with an even longer one that goes through your top cap, the adapter, and threads into the wedge.
Now you can remove or adjust your adapter just by loosening the bolt from the top, just like any old quill stem.

Any questions?

It's a good idea – only trouble in my case at least is that the top cap I wanted to use is one of the Hope ones that has a freakishly large hole and corresponding wide bolt head (see pics above). Not insurmountable but certainly an issue.

You can probably find some sort of cup washer to fit in the hole and shroud the bolt head.

Yup. This is the best solution assuming a suitable bolt could be found. I guess only downside is being unable to use the matching Hope cap bolt but on balance not really a deal breaker.

Also you Can buy this https://www.sjscycles.co.uk/stems/profile-design-stem-convertor-1-inch-quill-to-1-18-inch-threadless/
It should convert from 22,2 mm to 28,6mm. And then just add your own top cap instead of the supplied 😊

Good find!

Expanding on drøn's idea, put the long bolt in from the bottom of the fork and attach a long nut on the thread which you can screw your Hope bolt into