The Cal. 343 has a few unusual features - the barrel is arranged in a strange way with the armour being permanently attached to the ratchet wheel. It’s also marked as a sealed unit, which Longines would originally have recommend replacing as a whole rather than just the mainspring.
The oscillating weight is also unusual; being attached to a large internal tooth wheel which runs round the diameter of the movement. We’ll look a bit closer at the automatic system later.
Finally something which is a watchmaker’s nightmare… a bridge which screws on from the back. This small bridge holds the centre wheel and a wheel from the automatic mechanism, it’s fitted to the movement side, but the screws hold it from the dial side. You can see them at about 7 o’clock and they will later be hidden by the calendar mechanism.
The movement squeezes a very large number of wheels in a small space. The third wheel is a double-level wheel because the fourth wheel pinion also drives the centre seconds pinion.
From the other side we can see the automatic train, which includes a wheel with unusually large teeth that is driven by the oscillating weight.
As always the escapement requires a tiny drop of oil in exactly the correct place.
With the movement assembled and oiled the automatic bloc can be fitted. Here you can see how the oscillating weight interacts with the movement. Not only is that large internal gear unusual but it’s also mounted off-centre, as you can see from the photos below.
