I bought a couple of very cheap Nukeproof ZS56 headsets as I needed to replace the lower bearing and the whole headsets were discounted.
The old headset had a plastic cup and tapped out reasonably easily as per normal removal. New headset cup is aluminium and can be pressed in / pulled out quite easily by hand and just isnt snug enough. I assume the plastic cup was used to take up poor carbon manufacturing tolerances.
Are there any retaining compounds that will work with Aluminium / carbon headtube?
Tried PTFE tape and it helps but not holding it well enough. May even try a coke can strip bodge.
Any other ideas?

Loctite green bearing assembly/retaining.

Not sure which number I used successfully for the same problem on a carbon felt.

Can’t you put the new bearing on the old cup?

1
BearBack
Free Member
Loctite green bearing assembly/retaining

638 iirc

638 as above. Check material compatibility though.

Any compatible epoxy adhesive will do the job. Clean the inside of the headtube thoroughly and wax/grease the headset cup so that it doesn’t stick and you can change it in future

Mix in some micro-balloons to fill gaps if it’s bad

Another for Loctite 638.

Had a loose headset (as in pushed straight in by hand) in a vintage road frame, not shifted since used the loctite.

Is your name Bernard Kerr and do you work for pivot?