This next photo shows the lever pulled out. A set of gears has now rotated and moved to disengage from the mainspring arbor and instead engage with the gear that sits in the middle. This part in the middle is the cannon pinion.
This detail offers a better look at the cannon pinion and the intermediary wheel that will now turn it when the crown is turned, thus setting the hands.
The thing to note here is that pulling the lever out pushes the assembly toward the cannon pinion. These are really then just two gears whose teeth must engage in order to work. It is possible for the gears to happen to come together in a position such that they do not line up and engage.
If this happens, which is really just a matter of chance, a slight turn of the crown will move the wheels a little so the mechanism can engage.
If on the other hand, the lever is instead forced further out, the gears will press together with the teeth mis-aligned.
This next photo gives a better view of the other side of the cannon pinion. There is a tooth missing, and at least two others are badly bend over to one side. This is a result of the gears being pushed together with force when they are not aligned.
The gears will actually mis-align near to half the time when the lever is pulled out. Giving the crown a slight turn though, will drop them in place. Forcing the lever out on the other hand will crush the teeth of one or both parts involved.
Even under good conditions, the way these wheels come together makes the teeth on these brass gears subject to wear causing an uneven and rough feel to setting.
This is an old Elgin design (the model is similar to the first watch Elgin ever made in fact). But it represents the highest state of the art for this technology and manufacturing for its day. It's over 100 years old. The design is not like a modern watch would be, and it is far from perfect. Even just slightly later watches have a completely different clutch design, improved to better avoid such problems.
Parts for these watches are becoming more and more scarce. In the not so distant future it will become vastly more difficult to repair a problem like this.
Let's be careful with these old machines.
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