Movement Stories: One Platform, Two Watches — Bulova’s 11AF in Manual and Automatic Form
One of the real pleasures of vintage watchmaking is discovering how clever manufacturers could take one solid movement design and turn it into several distinct calibers with different capabilities. When you get the chance to study those variations side by side, the logic and creativity of the engineering becomes much easier to appreciate. That does not happen very often on my bench, since I work on such a wide variety of movements, but this time I happened to have two different versions of Bulova’s mid-century 11AF at once: the 11AFC, a manual-wind variant with indirect center seconds, and the 11AFAC, which builds on the same foundation by adding a full-rotor automatic winding system. Putting these two back together side by side seemed like an especially interesting way to explore how Bulova modified a common base movement to create two quite different expressions of the same design.
Let’s get started by taking a look at the two main plates. The 11AFAC automatic movement is on the left, while the 11AFC manual wind variation is on the right:
These main plates are nearly identical, with one small but important variation: the main plate for the 11AFC has a jeweled center wheel pivot, while the 11AFAC makes due with a simple bushing. This variation has little to do with performance, and much more to do with hitting the right jewel count. Both of these are 17 jewel movements — commonplace in the era due to the fact that the US import duty schedule at the time had a cutoff at 17 jewels, beyond which duties escalated rather dramatically. However, the 11AFAC employs two of its jewels in the automatic winding works, leaving a 15 jewel base movement underneath, while the manual 11AFC gets a full 17 jewel base movement.
With the mainspring barrels and train wheels in place, things still look pretty much identical, and these parts are all fully interchangeable with the exception of the mainspring barrel itself (as the automatic 11AFAC version has a smooth inner wall that lacks the hook for the tongue of the manual mainspring that’s found in the 11AFC):
After installing the train and barrel bridges, we start to see the first major design variations between these movements:
The bridges have the same basic shape, but there are significant differences in how they are finished. The 11AFC has a jeweled upper pivot for the center wheel which, again, is lacking in the 11AFAC. The 11AFAC train wheel bridge has additional threaded mounting points for the automatic winding module as well as a lower pivot bushing for the automatic driving wheel located immediately adjacent to the rachet wheel. The 11AFAC bridges also lack the decorative polished bezel seen on the 11AFC bridges, as the space that would have been taken up by the bevel is needed to create additional clearance for the automatic winding rotor. Finally, the 11AFC bridges are finished with caliber engravings. These are missing on the 11AFAC, since they would be covered up by with automatic mechanism. The 11AFAC puts these caliber markings on the winding rotor instead.
Next, we’ll flip these movements over so we can assemble the keyless and motion works:
Once again, the designs here are identical, with fully interchangeable parts.
Flipping both movements back over, we can now complete the primary assembly by installing the escapements as well as the indirect drive center seconds components. After a bit of lubrication both movements run happily:
The 11AFC movement is complete at this point, but we still ahve some work to do on the 11AFAC — namely assembling and installing the automatic winding module. The photos below show the automatic winding components and how they are placed, with the lower plate of the automatic module installed above the train wheel bridge:
The 11AFAC automatic mechanism uses a pair of reversing wheels, although these are relatively primitive compared to the contemporary ETA/Rolex style reversing wheels. They consist of two separate pieces that engage using ratcheting Breguet teeth. They rest on an external brass spring that facilitates the ratcheting action.
The thin, polished upper plate for the 11AFAC automatic module has two jewels, bringing the total movement count to 17:
Finally, with the 11AFAC winding rotor attached, we can see both complete movements side by side:
I hope you found this side-by-side comparison as interesting as I did. These movements ultimately found their homes in a pair of lovely Bulova watches which are listed for sale on my shop:
