When Vincenzo sent me an email asking if I would put together his Seamaster that another watchmaker took apart, I did of course decline. I don’t like to mop up other people’s mess, and think that whoever takes a watch apart, should put it back together again.
In this case, though, the watchmaker couldn’t put it back together, as he was late. So stupidly, I agree …
The first shock is the wheel bridge. There is a gaping hole where the thread for the hour recorder yoke used to be. On top of that, the tread in question is left handed. Now where can I get a 0.9mm left handed tap to cut a new thread??
In moments like this, I resort to the bible, or, to be more exact, to George Daniels’ book “Watchmaking”. And alas, there is a note on how to do this. You take a normal 0.9mm tap, and flatten it on both sides. 
Before I can bush the damaged bridge, I have to get a straight and round hole in. I drill with a 1.5mm drill, and I’m ready for a bush now.
Now for turning a bush…
The bush, and the screw that will go into the thread.
The bush is pressed into place, and I can cut the thread.
And here is the modified right hand tap, flattened. You just turn it left, and it will cut a left hand thread!
The thread is cut, and the trickiest part of the repair is over. Or so I think …
I run all the parts through the cleaning machine, and start putting the movement back together.
Vincenzo supplied a new mainspring.
The gear train is in, ready for the wheel bridge.
The base movement is ticking. Notice that the regulator is all the way set to slow, and that never bodes well!
And rightly so, the movement still beats too fast. So somebody before me had a problem here. Either the hairspring is too short, or the balance too light.
On close inspection, I find 4 balance screws that have been turned down in the lathe to make it lighter. Somebody poised the balance, but forgot that just taking weight off isn’t the brightest idea.
In order to fix this, I put two balance washers on opposite screws.
The balance is poised, and hopefully, all will be well now.
Phew!
The regulator is still a bit on the slow side, but there are limits to my suffering. 
Now the chronograph layer goes on.
And the bottom plate with the hour recorder.
The blocking lever screw that came with the parts was wrong, and I order the correct one.
I test and adjust the hour recorder…
… and then the minute recorder.
The dial and hands go on.
The case had non-original pushers, that also don’t move very easily.
Here a new Omega pusher (left) compared to the pusher that was in place.
The new pushers are in, and next is a new crystal.
A new Omega crystal (probably one of the last ones still around).
The movement is cased and a new gasket in place. 
I’m very happy with the result!
A side view with the crown and pushers.
Wow !
I dont even understand most of that, but amazing work to putball that right.
I bet the owner is very, cery happy !
Again a job well done and a very interesting read.
Sensational work.
You know, reading this blog makes me not even think twice about sending a watch to any other repairer. A true professional who knows exactly what he’s doing. God bless you!
I can’t understand the previous “repairers” idea that lightening the balance screws would be an improvement and it should be obvious that the left handed screw for the wheel bridge has a different head pattern.
Still we can all learn something new. I hadn’t heard of the left handed tap trick before, very clever. Another beautiful watch saved from wreckage.
Great job! And what a fantastic result!
Once again Christian fixes somebody elses screw up!
I have to hand it to you Christian;you are a clockwork genius.
Somebody used a lot of time and elbow grease turning that left handed screw the wrong direction! The picture with the bush next to the collet is the clearest image of just how small these bits and pieces can be- very nice work there.
It seems wrong blocking lever screws must be a common problem with the 321 calibre. I’ve tried and failed to source one for the movement on my bench twice now.
That’s a beautiful Seamaster Chronograph when it’s all said and done. The white dial is a nice contrast to the more popular Speedmaster of the same era. Very elegant piece.
all i have to say it’s: thanks for the great job you done with this blog. learning new stuff with every post
A lovely watch and another impressive job!