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This is a genuine second wheel designed for MIYOTA FS20 and FS60 quartz chronograph movements. It serves as a central component of the movement‘s gear train, transferring power from the stepper motor to the central hour, minute, and chronograph seconds hands. Precise tooth engagement guarantees smooth, jitter‑free hand motion.
This part is intended for movement repairs involving wear, broken pivots, or debris‑induced stoppage.
The table below summarizes the main technical specifications of the MIYOTA FS20 and FS60 quartz chronograph movements.
| Parameter | Value |
|---|---|
| Compatible Calibers | MIYOTA FS20 / FS60 |
| Size (Ligne) | 10½‴ (approx. 23.3‑23.7 mm) |
| Movement Height | 5.10 mm |
| Jewels | 0 (quartz movement) |
| Accuracy | ±20 seconds per month |
| Battery Life | Approx. 2 years |
| Battery | 377 / SR626SW |
| Winding Stem | 065-549 (Tap 10 / 0.90 mm) |
| Stem Thread | M0.90 (Tap 10) |
The table below compares the main functional differences between FS20 and FS60.
| Feature | FS20 | FS60 |
|---|---|---|
| Hand Layout | Center hour, minute, chrono seconds; small seconds at 6 | Center hour, minute, chrono seconds; small seconds at 6 |
| Additional Display | 24‑hour sub‑dial at 3 | Day retrograde at 3 |
| Sub‑dial at 2 | None | 60‑minute counter |
| Sub‑dial Hand Hole | 0.26 mm | 0.26 mm |
| Date Position | 4:30 oblique (D430) | 4:30 oblique |
| Hand Part | Hole Diameter (mm) |
|---|---|
| Hour | 1.20 |
| Minute | 0.70 |
| Center Chronograph Seconds | 0.17 |
| Sub‑dial Hands | 0.26 |
Normal Operation：The second wheel, together with the stator and rotor magnet, converts the stepper motor‘s electrical pulses into rotary motion, driving the center hands in a smooth sweep.
Rate Deviation：If the watch stops intermittently, the seconds hand stutters, or becomes stuck, inspect the second wheel for gear wear, and rule out poor battery contact, dry lubricant, or foreign debris.
Hacking：Both the FS20 and FS60 have a hacking (stop‑seconds) function. Zero‑return of the chronograph seconds hand relies on a hammer and heart cam. If the hand does not return to zero after reset, check the zero‑return components.
Chronograph Reset：After a battery change, if the chronograph seconds hand does not return to zero, pull the crown to the time‑setting position, repeatedly press button “A” until the hand is zeroed, then return the crown.
Remove the hands, dial, and the faulty movement.
Clean the gear train bridge and remove the old second wheel.
Clean the bridge, pivot holes, and jewel bearings to remove old oil residue and debris.
Install the new second wheel, ensuring smooth gear meshing and that both pivots are properly seated in the jewel bearings.
Replace the gear train bridge and evenly tighten the bridge screws in a diagonal sequence.
Hacking/Zero‑Return Check：After assembly, pull the crown to the time‑setting position to verify the center chronograph seconds hand stops. Press buttons A and B repeatedly to confirm accurate return to zero.
After assembly, use a timegrapher to verify the movement‘s power consumption and drive pulse (essential for quartz movements).
Important Note：Movement disassembly and gear train alignment must be performed in a dust‑free, static‑safe environment. If you lack quartz‑movement repair experience, professional service is strongly recommended.
Q1: Is the second wheel the same for FS20 and FS60?
Yes, the basic gear train of FS20 and FS60 is identical; the second wheel is interchangeable.
Q2: How to test a suspected second wheel problem?
Manually rotate the rotor and watch for irregular stepping. Use a timegrapher to monitor the motor pulse; unstable timekeeping combined with abnormal current measurements points toward excessive gear‑train friction or a damaged second wheel.
Q3: Can I replace just the second wheel without special tools?
Yes, but it requires a full set of precision watchmaker screwdrivers, tweezers, and a loupe. Without quartz movement experience you risk bending pivots or misaligning the gear train.
Q4: Why does the chronograph seconds hand fail to reset to zero?
Inaccurate zero return is typically caused by a worn reset hammer or misplaced heart cam, not the second wheel itself. Inspect the zero‑return components together.
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