The MST 431 is a ladies’ watch movement with a very small diameter. With only 7 lignes (16mm) it hence can be found on the first pages of the movement listing books.
Its execution with 17 Jewels and a rather large anular balance, which is Incabloc shock protected, is up to date for a movement of the early 1960ies, when it was released.
The movement train is constructed counter-clockwise (seen from the the balance), this is a bit unusual, since here the seconds wheel is positioned around 12 o’clock, while on most other movements, it is positioned around 6 o’clock.
Since the specimen in the archive is NOS (New Old Stock), no further teardown was made and the dial was also not removed to avoid damages.
In the lab
The specimen shown here, including its watch, was New Old Stock (NOS), which
means, that it was stored for about 55 years.
Therefor its oil condition is pretty bad, which you can see on the
low amplitude values.
Nevertheless, the deviation values are very well, the maximum deviation over all positions is only 30 seconds per day!
It is not hard to imagine, how well this movement might perform after a revision with an oil change.
|dial up||+14 s/d||208°||0.4ms|
|dial down||-4 s/d||249°||0.0ms|
|crown right (12 up)||+12 s/d||239°||0.5ms|
|crown up (3 up)||-8 s/d||236°||0.4ms|
|crown left (6 up)||-16 s/d||216°||0.3ms|
|crown down (9 up)||-4 s/d||214°||0.4ms|
|Number of jewels:||17|
Nickel anular balance|
|Balance bearing / direction hairspring:||Clockwise|
|Adjust mechanism:||Hairspring key|
|Construction type:||solid construction|
|Winding mechanism:||yoke winding system|
|Setting lever spring:||4 hole(s)|
Flume: 1962 -|