Note the use of brass gears and bronze bushings. In the upper left corner you can see an off-colored steel gear with a copper clutch plate in it. When you turn the time dial, you are actually moving the clutch, not the entire gear assembly. The clutch has prongs that engage the holes in the steel gear and move it when the motor is turning.
The complete Wil-burt timer has a long life span and every individual part is replaceable.
In this case, the clutch was worn out from excessively turning the time dial by hand in the wrong direction. Each gear is removable and the assembly is built by hand.