This is the 4130 Rolex movement, not the modified Zenith. The 4130 is a very solid, modern chronograph and generally a pleasure to work on.
We are going to go straight to the dismantling process on this one, and follow along with a step by step rebuild. The movement has been through the cleaning machine and is now separated in the parts tray.
Here we see the mainplate. I have installed the column wheel and spring.
I now install more of the chronograph components. The operating lever, which starts and stops the running of the chronograph, as well as the reset lever are installed and lubricated.
Next, the gear train is installed. I put the escape wheel, 4th wheel, and 3rd wheel in place, but not the center wheel just yet. The 4th wheel of this model has actually been updated and given ‘spring-loaded’ teeth on the top pinion to help with amplitude losses when the chronograph is running. Newer models come with that wheel installed. It is also upgraded at service when taken to RSC. There is nothing inherently wrong with the old wheel, it is just a more traditional chronograph style, whereas the new wheel does improve performance with the chronograph engaged. However, I have my own thoughts on that upgrade!
The balance stop spring is then installed. This is the spring used that stops the watch when the time is set. It connects to the setting lever on one end, and when the crown is pulled out the spring engages the balance and the watch stops.
I can now install the center wheel.
Before the bridge is installed we need to make sure the crown wheel is placed underneath. There is also another small bridge that is affixed to the underside of this bridge, but I forgot to photograph that after it was in place
The barrel is put in place and both the barrel bridge, train wheel bridge, pallet fork, and balance are installed. The ratchet wheel is then screwed onto the barrel.
All the winding and hand-setting components are put in place so we can wind the watch and check the hand setting functions.
The start/stop functions of the chronograph are where they should be, but now the actual wheels and pinions need to be put in place. The clutch wheel goes in, so do the lever that controls it as well as the spring. Does this look familiar? It is a very similar setup to the classic Seiko chronograph.
The spring and screws are put in place.
The hour and minute recording wheels, along with the intermediate pinions, are added.
Then the chronograph seconds wheel is put in place and so is the reset hammer. The chronograph seconds wheel has also now been upgraded to have those “spring-loaded’ teeth discussed earlier. The reset hammer acts against the heart-shaped cams on the tops of the wheels which allows the hands to reset to zero when the pusher is pressed.
The bridge to secure all the wheels in place is then installed.
The automatic winding work is then assembled.
The dial and hands are installed and the watch is cased up.