In the 1950ies, it was en vogue, that ladies’ watches had to be as small as possible. From that very time originates the form movement IWC 431 with it’s really small size of 4 3⁄4 lignes (11.6 x 14.9 mm).
The base plate of this form movement shows, that the balance wheel and the mainspring barrel have as much place as possible, nevertheless, there’s quite a lot of wasted space, for example next to the mainspring barrel.
All fast turning gears (escapement wheel, fourth and third wheel) are ruby beared, especially the large golden toned Glucydur screw balance. The balance beats relatively fast with 19800 A/h and is secured in two Incabloc shock protection bearings.
The gears are of a very high quality, and the rest of the movement gives a really pleasent view with its decorations!
A speciality of that movement is, that the crown wheel does not directly drive the ratchet wheel, but uses two intermediate wheels, the first one with a slanted toothing. I don’t know the reason for that construction and why the crown wheel wasn’t made larger to engage directly with the ratchet wheel.
The click spring is a very clever construction: It is completely located under the ratchet wheel and consists of only one piece including a flat ball joint. Only an additional spring is used to hold the click in position. So, this is a clever, space and cost saving construction, which works very efficiently.
The dial side with its beading and the IWC hallmark gives a beautiful view. The helical toothing of the clutch wheel can also be seen here. Only few high quality movement offer this!
In the lab
The specimen shown here was pretty sure taken off a melted gold watch, and since it was still ticking, no service was made.
Nevertheless, the technical condition of the movement is pretty poor, on the timegrapher it showed bad results, which are not representative for that movement, so they aren't shown here.
|Number of jewels:||17|
Glucydur screw balance|
|Balance bearing / direction hairspring:||Counterclockwise|
|Adjust mechanism:||Long regulator arm|
|Construction type:||solid construction|
|Winding mechanism:||yoke winding system|
|Setting lever spring:||3 hole(s)|
|Size:||4 3/4''' (measured: 11,6 x 14,9mm)|
Flume: K2 -|