The Certina 251 originates from the 1940ies. It is also known under its former designations, K.F. 251 and Grana 251. “K.F.” is the abbreviation for “Kurth Freres”, for the brothers Adolf and Alfred Kurth, the founders of Certina (at that time with the trade mark “Grana”).
It is a form movement of 7 3/4 x 11 lignes, which was used in Certinas own gents watches.
On the base plate, which is partially decorated with a perleage, you see, that all important bearings contain rubies, except those of the minute wheel and the large mainspring barrel.
The Certina 251 uses a classical gear train with decentral second a 6 o’clock and a directly driven center minute. Due to the tonneau shape, there’s a lot of unused space on the lower part, while on the upper half, most of it is used by the large mainspring barrel.
The also large screw balance beats slowly with 18000 A/h. It is not shock protected and regulates a conventional swiss pallet lever movement.
Of course, the Certina 251 uses a yoke winding system and is on the dial side nicely decorated with a perlage.
In the lab
Timegrapher resultIn the median, the timegrapher rates compensate watch other, but the rather large positional errors are the cause of the age and wear of the movement. The amplitude was about 260°, a better cleaning could improve it a bit. The beat error is 5,4ms and this is quite large, but its correction would be quite hard since this movement doesn’t have a moveable hairspring stud.
|dial up||+20 s/d|
|dial down||+34 s/d|
|crown right (12 up)||-15 s/d|
|crown up (3 up)||+7 s/d|
|crown left (6 up)||-16 s/d|
|crown down (9 up)||-41 s/d|
|Size:||7 3/4 x 11''' (measured: 17,0 x 24,8mm)|
|Number of jewels:||15|
Nickel screw balance|
|Balance bearing / direction hairspring:||Clockwise|
|Adjust mechanism:||Long regulator arm|
|Construction type:||solid construction|
|Winding mechanism:||yoke winding system|
|Setting lever spring:||2 hole(s)|
Flume: 1947 / 32|