[Geoff]

There is what looks like a clock main spring that keeps the play out of the tuning system as well as assisting to balance the tuning cap weight. It is attached to the tuning shaft. On the motorized sets it needs to have the right tension. On the earlier sets it is not critical. If it's too loose or tight, the motor will slow/speed up noticeably as you get to the higher frequencies on the dial.

Good point. I forgot about that spring. If I remember correctly I had to play around with that a little bit to get mine to work properly.