The Seagull ST-19

At Arcus we have two core values: transparency and quality. While marketing always aims to showcase the best aspects of a product, we believe that knowing the weak points is equally important. As such, we wanted to have an open discussion about the critical failure points of the Seagull ST-19 movement in order to explain why they fail, and why the misconception that they are low quality movements is not entirely true. In the process, we also look at how we deal with these issues as part of our quality assurance program.

A quick look through the Internet will yield horror stories of faulty movements, but also an equally large number of very satisfied owners. It is true that compared to its modern ETA/Sellita counterparts it is a more delicate movement, however a good ST-19 is very robust if adequately adjusted. The important thing to note is that this is not a chronograph where parts can be dropped in and things magically work; it is a complex mechanism that requires very careful regulation. When poorly done it results in the following common problems:

1. The movement keeps bad time.

There are two possible reasons for this:

The first: The lever marked E on the diagram below is responsible for regulating timekeeping of the movement. Moving it left or right adds or decreases the length of the hairspring thus altering the rate of the balance wheel. The ST-19 hairspring is incredibly sensitive to changes of position of the lever, more so than other movements. Moving the lever +/- 0.5mm left or right can affect timekeeping as much as +/- 45 seconds a day. Depending who does the adjusting, if the person is heavy handed, it can cause severe timing issues. Newer models of the movement can be purchased with swan neck regulators which make adjustment much more accurate.

The second: the chronograph mechanism is poorly adjusted. The screw marked “a” is an eccentric screw which is responsible for controlling the depth of meshing of the gear teeth at point “A”. If the gears are too close together, the movement can lose large amounts of time daily because of the resulting frictional forces, or in more severe cases it may even seize up the movement. A common symptom of this is that the running seconds hand stops in the same spot every time. Adjustment of screw “a” eliminates all these problems.

2. The movement loses time when the chronograph is running:

Similar to the previous problem, the screw marked “b” is an eccentric screw which is responsible for controlling the depth of meshing of the gear teeth at point “B”. If the gears are too close together, the movement can lose large amount of time daily because of the resulting frictional forces, or likewise seize up. Adjustment of screw “b” eliminates all these problems.

3. The central chronograph seconds hand has a choppy motion:

This is actually a case where screws “a” and “b” are not adequately adjusted and as a result the gears at points “A” or “B” are too far apart. This extra looseness causes play between the teeth of the gear, and that appears as a choppy seconds hand. Contrary to the belief of some, this is not the result of poorly made gears, the ST-19 gear profiles are actually very sharp and good quality.

4. The chronograph seconds hand doesn’t always reset exactly to zero:

This is a far less common problem but slightly more serious. The reset mechanism works in such a way that lever "F" hits heart shaped cams on the gears marked in red at points “D”. As the tip of the lever travels to the lowest point on the cam, this rotates the gears, bringing the hands back to their zero position. Every now and again, the cams may not be perfectly cleaned during assembly, and dirt on them causes friction at the point of contact. As the lever arrives at the lowest point on the cam, the speed of rotation decreases and the wheel may stop before it reaches its true zero position.