Mysterious top cap - any advice?

[edocaster]

Hello all - I very recently bought a secondhand, early-noughties Thorn Nomad. A previous owner had used a stem raiser, but when I got the bike it had the stem mounted without the stem raiser. However, it didn't have a normal top cap or bolt either.

The pictures below show what's at the end of the steerer tube. It appears to be a cap with the same diameter as the steerer tube, with a recessed bolt in it. Has anyone seen something like this? I removed the stem and bars to take the shot - the only thing holding the stem to the steerer was its own two bolts.

I can't detect any play in the headset, and I can't see how the headset is secured when the stem isn't on, other than via the cantilever hanger.

Should I leave it, or should I install a normal top cap and bolt? If I leave it, how would I adjust the pre-load in future if I needed too? If there's a star-fangled nut in there will it be too deep for a normal top cap and bolt?

Thanks in advance. I'm sure the collective wisdom of the board can offer some advice!

[Redvee]

On one of my previous bikes I had an FSA set-up like this. IIRC you can undo the bolt in the picture and remove the assembly to fit a normal star fangled nut.

[531colin]

The pinch bolt in the cable hanger will be maintaining headset bearing pre-load.
I think what you have got is a wedge top with its top cap missing....you need the top cap to set the pre-load.....so yes, replace it with either a complete wedge top, or a star fangled nut.

[Brucey]

If you use a 1" spacer and a 1-1/18" spacer beneath that top cap, you may be able to adjust the headset preload in the normal way (once the hanger is released) if the cap doesn't have a no-travel wedge. I have seen similar caps with a no-travel wedge. It is almost impossible to adjust the headset preload with this cap type; I have no idea what they were thinking of when they designed them.

I would fit a standard top cap if you can do so.

cheers

[531colin]

I would expect the wide deep recess which houses the visible bolt to have a female thread which accepts the male thread of a top cap.....so you can adjust the pre-load with the top cap....unless somebody has thrown it away....

[edocaster]

Thanks for all the replies. Yes, turns out it was indeed an expander wedge without the top. Sourcing the specific cap seemed an unnecessary trawl, so I had an LBS replace it with a normal star fangled nut, bolt and top cap.