Seikosha 19 pocket watch

I have been wanting to dabble in watch repair for a while and one of the usual recommendations is to start with pocket watches rather than wrist watches – the principles are very similar but pocket watches are much bigger and easier to manipulate. So, I bought a Seikosha 19-Ligne railway-type watch – actually, as I so often do, I bought 3 of them.

• a 19-Ligne “Precision” (1930s-1955) works perfectly and actually keeps very good time. I’ll post about this one another time because it came with a little medal as the fob on the owner’s chain, which turned out to be very interesting in its own right.
• a 16-Ligne “Empire” (1909-1934) works fine but runs a bit fast.
• and the last 19-Ligne “Precision” (1930s-1955), inscribed by its previous owner, Fukuda san, on the dial gave all the symptoms of a broken mainspring – the crown turned but with very little resistance and the watch didn’t run.

This was pretty much the result I wanted – a few watches that I can play with and which work, and one dud that I can try to fix. I decided to fix the worst of them first and then when I have made all my mistakes on that, and learned how to get it apart and back together again, I can just service the other watches and make them run better. 

So today I started to take Fukuda san’s watch apart and clean the parts. I soon found that it had a lot of oil / grease in it and it hadn’t had a clean in a long time. 

The mainspring was clearly broken so I measured it all in the standard way:

• height (H) =2.70mm – this is the maximum for the depth of barrel but it can be a little thinner without flopping about inside the barrel or coming unhooked from the arbor or hook.
• thickness (T) =0.20mm (could have been 0.19mm as my micrometer isn’t the best quality) – this is the power the spring gives out and the range is largely governed by the barrel diameter because it has to be able to be coiled up. The old rule of thumb to work out the safe range is T = D/90 (‬‭=0.1889) to D/80 (=0.2125) (for my 17mm barrel)
• length (L) =540mm – more spring might, in theory, give more power reserve but to work out the range you can use an old Swiss method which involves multiplying the barrel diameter (D) by 35. In reality that is scaled back for safety and x32 (=540mm) or x33 (=550mm) is used. 
• barrel diameter (D) =17mm – this is mainly used to sense-check the figures above 
• end type (=DBH) – this one they don’t tell you about at first but it’s really important because it governs how the spring attaches to the barrel hook on the outer edge of the barrel. Get that wrong and it will just slip as you wind it. The DBH end uses a D-shaped hole that grabs the hook but also a T-shaped bit that engages 2 slots, on the base and lid of the barrel. Other systems use one or the other, generally.  

… and started to look in online catalogues for a matching spring, but that’s where hours of “fun” started because Cousins, one of the biggest UK watch parts dealers didn’t have anything in stock that was a good match. They had springs that were similar but I had to work out which numbers were important and which I could flex on. Inside the barrel you need about: 1/2 of the space for the spring itself and 1/2 for expansion space and the arbor in the middle. This means you can always lose a bit of spring – and many old-school watch makers would anneal the broken end, drill a new hole in the end and shape it to fit the arbor so they could reuse it. 

So, after asking the experts on the reddit r/pocketwatches group (very helpful!) and chatting a lot with Gemini & ChatGPT, I found the following contenders (eliminating generic springs):

• Seiko 401.913 mainspring for the Seiko Caliber 9119A at 2.70 x 0.19 x 540, T-end, which must be compatible springs but there might have been a little variation between models of watch.
• Elgin mainsprings for “Seiko 19” pocket watches (located in Japan) marked “2.75 x 0.19 x 550” so I’m guessing those are close to the original size as they were clearly made for the Seiko 19.
• Elgin 16 size #817 840-284 spring measuring 2.65mm x 0.19mm x 546mm and with the correct DBH-type ends!

The Seiko ones were only available from a trade supplier and the first Elgin ones were in a job lot costing £95 + import fees! So I ordered the second Elgin model from the US as it was not only supposed to be a good fit but it was what the experts recommended on reddit. I hope it lives up to expectations! 

As I mentioned, the watch was dirty and full of oil so I suspect the original owner had tried oiling it himself at some point. After stripping it down I put each piece in turn into a petri-dish of naphtha (Zippo lighter fluid) and gave it a gentle brushing to remove dirt and oil. The escape wheel & pallet fork were given their own bath of clean naphtha and the balance assembly was dipped into a “one dip” type of special solution made for hair springs. Then everything was left to air dry. 

The reason we use naphtha is that it is a good solvent and it does not contain any water, so it will remove the old oils and dirt very well while not introducing the potential for corrosion, which could destroy the delicate movement. 

MORE TO FOLLOW…