321 v 861 and the much talked about cost savings

Took several re-reads to fathom the operation but, I did find this extremely informative and educational. I will never get this deep into my watches but, it is still gratifying to understand how they function. Thank you for such a detailed and clear explanation.

Quick addition to this thread. While servicing a vintage Longines 30CH chronograph, I noted that like the 861, the minute counter has no sliding gear, and uses an intermediate minute counting wheel, just like the 861 does. However, it does not have a spring loaded finger on the chronograph wheel - it is a fixed finger that trips the minute counter, like on the 321, and not the spring loaded collapsible style that is used on the 861.

So how does Longines prevent the finger from crashing into the teeth of the intermediate wheel when the chronograph is being reset? The answer is again a spring, but this time under the intermediate minute counting wheel. Here is the spring at the red arrow on the right, and the red arrow on the left shows the hole where the wheel mounts:



Note that the spring actually goes under the bridge. Here the chronograph wheel, intermediate minute counting wheel, and the minute counting wheel in place:



Note that on the intermediate wheel, there is a fairly large diameter steel section visible. Now here it is with the chronograph bridge, and the other chronograph parts installed:



The left red arrow points to the upper pivot of that intermediate minute counting wheel - it sticks up prominently through the bridge. To the right of that is the flyback lever - this chronograph is a flyback, meaning that it can be reset without stopping the chronograph. Let's zoom in on this area in detail and watch the reset a few times:


Since it can be a little tough to see in the video, I cropped some screen shots to illustrate it more clearly. Here is the intermediate wheel when the chronograph is running - you can see the upper pivot sticking out, and the red arrow is pointing to the gap between the underside of the bridge, and the top of that large steel diameter on the wheel:



Now when the reset is in progress, the flyback lever has moved over, and has pushed the intermediate minute counting wheel down against that spring that goes under the bridge - the gap is now quite large:



This pushes the intermediate wheel down far enough that the fixed finger on the chronograph wheel spins back freely, spinning above the level of the teeth on the intermediate wheel.

This is very clever, and I suspect was done specifically for the flyback feature, but also significantly reduced the complexity of the minute recording system. This movement is earlier than the 861, so did Omega take some inspiration from this? Can't say for sure, but it wouldn't surprise me. In many ways I prefer this solution, because there's very little to go wrong here. The spring is just a simple flat spring under the intermediate minute recording wheel, and the chronograph wheel construction is still super simple.

If you have questions or anything isn't clear, let me know.

Cheers, Al

@Archer Thank you for the excellent explanation, photos, and video. I was familiar with this aspect of Longines' caliber 30CH, but I had not seen the movement in all of these states of assembly, nor videos depicting the angles that you showed. Also, I appreciate the comparisons that you drew with calibers 861 and 321.