Best cyclocross bike under £1000 and other CX chat

With the top cap removed you can see that the hole into which the stem cap bolt screws has hexagonal flats surrounding it at the top- i.e. a large alan key can be used to tighten it in.

This I believe is how the expanding function of the bung is effected.

So I should be able to loosen that, drop/hammer the bung down, then re-tighten it.

What sort of torque value am I going to be looking at here- 5Nm or thereabouts?

Sounds exactly like my Headdoctor. Loosen slightly, untill you can tap it dowm 1-2mm, and then retighten. I guess 5Nm would be fine. It only needs to offer enought resistance to apply preload to the headset bearings. The stem holds your bars on.