The Zenith 405 is a true flyback. Just to avoid confusion, let me explain what that means… Lots of people think just because the hands on their chronograph “fly back” when they re-set it, it’s a flyback. It’s not. The difference between a normal chronograph and a flyback is that you can press the reset button whilst the chronograph is running, and it will instantly re-set the chronograph hands to 0, and continue to run from there. Apparently a feature that was useful to WW2 pilots, and, even though probably not of much use to you and me, something sought after!
A first look at the 405. It’s a 400 with a couple of modifications, so most parts from the 400 fit.
That’s not too bad.
The minute recorder hand is slipping and doesn’t reset to 0 properly, and that’s because the tube of the hand isn’t attached properly to the hand itself any more. I solder the tube to the hand to resolve the problem.
The bottom plate with the hour recorder.
I start off with the chronograph layer on the top plate.
This Zenith chrono has very little damage and abrasion, which is rare. Most of the time, it’s a battlefield in here, with lots of abrasion and worn down parts. Not in this case.
I just have to pull off the driving wheel for the chronograph, and then I can take off the wheel bridge.
Ready to take off the bridge.
The gear train with the winding gears.
Now it’s time for the bottom plate. The winding / setting / date quick-set mechanism is quite complex.
The unlocking date spring is still the old type, and I will replace that with the sturdier new construction.
All ready for the cleaning machine. You can only buy a complete barrel for £100, so I will re-use the mainspring.
Whilst the movement is in the cleaning machine, the case will go into the ultrasonic cleaner.
The old mainspring is still in very good shape, as you can see.
Now I put the balance jewels back in.
The gear train is in place, so I can put the bridge back.
Time for some lubrication. In this photo, I’m lubricating the escape wheel with Moebius 9010.
I put the winding gears in so that I can wind the mainspring.
That’s the beauty of Zenith chronograph movements. 10 beats per second, and an arrow-straight beat rate.
The base movement beating again.
Now I start on the chronograph layer.
It’s 5 o’clock, and time to go home. The movement goes into a dust-proof container.
It’s the next day, and I complete the bottom plate. You can see the new-style unlocking date spring in place.
Ready for the dial and hands.
The hour recorder looks rather sorry, with paint chipped off, so I will do something about it.
Firstly, I take off the old paint with a tiny drop of paint stripper.
And then I re-paint using highly diluted white model paint, applying it with a fine oiler.
When putting the chronograph second hand on, I notice that it slips as well, so I solder it to its tube, too.
Finally, the dial and hands are back on (bar the hour recorder hand, which is still drying).
Time to case the movement, and to put the oscillating weight back on.All back to its former glory, with the newly painted hour recorder hand.