Having been tasked with helping someone replace their tired Tourney kit, and not having come into contact with it before – I have to ask – how the hell do you get the cassette off?

Is the small cog a lockring?

That’s a freewheel, not a cassette. Freewheel removal tool in vice, locate freewheel on tool, turn wheel.

As above or use a large adjustable with the freewheel remover and turn anti clockwise.

You need one of these:

http://www.chainreactioncycles.com/shimano-freewheel-remover/rp-prod23264

Then as he said above 🙂

Ahhh, I getcha, thanks.

In fact, I have a sneaking suspicion I have one of those removal tools in my toolbox that was bought in error for a hypergilde tool years ago…. 🙂