This Quartz powered Seiko Sports 100 came in recently to have a problem with the crown and seconds hand looked at, it also was in need of a service. Like many quartz calibres it’s probably never had one in it’s life and it certainly needed doing.

The back of this watch doesn’t have the more usual Seiko tsunami logo, it’s a rather stylised wave version on this one. This is because it’s not a divers watch, Seiko divers are water resistant to 150m minimum and carry the tsunami logo usually on the caseback but also on the rubber strap in a lot of cases. These Sports watches are water resistant to 100m and carry the simplified wave logo, again it can be found on their rubber straps. Now you know!

With the back removed the two jewel calibre 7123 movement is revealed, it also had the wrong size battery fitted.

A quick look at the dial and handset, the gold tones go nicely with the chocolate brown dial.

A view of the day/date rings underneath the dial.

With these removed you can see the keyless work and calendar components.

With the movement turned over this is the motion work after the circuit and coil have been taken off.

The wheel train and hacking/set lever exposed here.

It was soon fully stripped ready for cleaning.

After cleaning and inspection it was time for reassembly, here the motion work is rebuilt.

The circuit and coil are back on here.

The calendar work going back together.

The calendar side coming together. The problem with the crown not screwing home was that the thread was worn on both the case and crown, a new crown was sourced, albeit one in gold not stainless steel but this has allowed it to now get purchase on the case threads.

The seconds hand was loose on the pinion so that was tightened up and watch was placed on test for 24 hours. I noticed it was 25 minutes slow in the morning which was odd as it was bang on at 11pm in the evening. The time was corrected and when checked the next day there was a 45 minute loss. I had my suspicions that the canon pinion was too loose causing it to slip at date changeover time. With the watch stripped again I removed the offending component and re-inspected it. The canon pinion on a lot of quartz calibres aren’t the same as a canon pinion on a mechanical one, the way they are constructed is the wheel’s a separate component to the pinion and is crimped into a groove in the bottom of it. This allows it to slip when setting the time but holds firm when running. The canon pinion on this one had a crack in two places on the actual pinion which left the wheel a very loose fit, in fact when I prodded it with a piece of pegwood it fell to pieces!

This was a nuisance as these pinions aren’t available any more so I had to find a donor movement to harvest one from. One was tracked down at the right price and eventually it was delivered to the workshop! You can see how the canon pinion should look in this shot.

The watch was rebuilt with the replacement part and thankfully it survived the date changeover without any issues. I think the gold crown on this actually looks a better match for the watch with its gold accents on the dial and hands!