The most rewarding projects in watchmaking are the ones you know are way beyond your depth, yet you try anyway (and most importantly succeed.) This Hamilton 37500 aircraft clock was undoubtedly the hardest and most complex piece I have worked on to date.

This clock was one of the most complicated pieces ever made for military aircraft and as such has a huge amount of parts. To avoid too much clutter and confusion, I decided to familiarize myself with the movement and find the problem by disassembling and reassembling it in segments.

The first goal was to replace the balance complete. I knew that this was not working because the balance staff was broken. Once that was done it ticked but stopped. Something more serious had to be going on so with that in mind I went about the rest of the process.

I first disassembled the mechanisms on the front. This included the civil date, date jumper, and the elapsed timer. Once I got all of these properly cleaned I oiled and reassembled them, I then wound up the movement, and although it ran it still stopped after a short time. The problem was not with the front.

I the set about taking the back mechanism, which was the chronograph. Here I noticed something was awry. There was way too much play in the fourth wheel (the gear that drives the second hand and by proxy the chronograph. A closer look revealed that the jewel that holds it had been shattered causing it to tilt and stop the movement.

Fortunately I had a harvester movement on hand. Although expensive, it was no where near as expensive as a service for one of these (almost $1200.) The harvested back plate was perfect and after swapping those out the movement worked perfectly.

Next I disassembled the entire clock. Ultrasonically cleaned everything and got it all back together. Although that only took two sentences to describe, it was way more work than the few words might suggest. After oiling and regulation I made sure that it runs properly through the full 8 day wind. A timing machine can only tell you half the story with large capacity mainsprings so it is always important (although time consuming) to let these clocks run through.

Pieces of WWII history like this are always a touch more rewarding than regular restores and come with an extra sense of pride. As does being able to restore such a complicated piece. That being said, it’s back to smaller pieces for a little while.