Orient 55740

Description

The japanese Orient 55740, which is only 7 3/4 lines in diameter, belongs to the smallest automatic movements for ladies’s watches and is even equipped with a date display.

With such a tiny movement, it is important, the that all bearings (here even including minute wheel bearing) contain rubies.

Even if the design of the gears is more reminiscent of a quartz movement, so we are dealing here with the classic gear train structure, where the mainspring barrel drives the center minute wheel, followed by third wheel (which at the same time drives the indirect center second), fourth wheel and escapement wheel.

Also interesting is the simple ratchet for the mainspring barrel, which is only a straight leaf spring, which unfortunately wears out over time.

The crown is decoupled via the movable crown wheel, far left in the picture.

The Orient 55740 uses a two-legged Glucydur balance wheel, which is mounted under a balance bridge, and beats at 21600 A/h.

It is stored in two Diashock shock absorber bearings and regulates a classic pallet lever movement.

The lever is not solid, but consists of a metal hollow body.

At 8 o’clock you can see the drive, which takes up the automatic wheel, in which the two claws of the eccentric lever later engage.

Similar to Seiko, the Orient-movement also uses an eccentric changer with two levers. Nice to see how it is mounted eccentrically on the inside of the rotor ball bearing.

An effective decoupling of the self-winding mechanism when hand-wound is not possible, which is why manual winding should not be used too often in order not to wear down the filigree claws of the eccentric.

The yoke winding system can be seen on the still empty dial side, as well as the preparations for the calendar mechanism.

The ratchet wheel at 6 o’clock (still without a shift finger here) is responsible for the progression of day and weekday display, the latter, however, is not installed in caliber 55740.

The date can be quickly corrected using the crown. For that, the vertical shift lever in the right half of the movement is responsible, which moves up or down via a cam on the Breguet clutch wheel.

You can now see the plastic shift wheel at 6 o’clock and at 1 o’clock the spring holding the quick corrector shifter to its home position.

Technical data

Usage gallery