A beat up old BSR motor

[Terry]

Those motor turrets only went one way so they always clunked there way round.

That was the point I was making. I think most people would take the short cut: 13, 12, 11, 10, 9 whereas the motorised turret could only go the long way round ...

[Refugee]

That is a good use for a TV guide. Only change the channel as often as needed and no more.
It was a couple of clunks or 10 odd clunks alternately.