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This is a MIYOTA (Citizen Group) 6T51 automatic mechanical movement, sized at 8 ¾‴ (approx. 19.4 mm) with a height of 5.98 mm. It features hours, minutes, seconds and a day/date dual calendar display, supports automatic and hand winding, and includes a quick date setting mechanism. With a frequency of 28,800 vph (4 Hz) and a power reserve of approximately 40 hours, it is an ideal choice for compact automatic watches. A gilt version (Cal. 6T51 Gilt) is also available.
The following table summarizes the main technical specifications of the MIYOTA 6T51 movement:
| Parameter | Specification |
|---|---|
| Caliber | MIYOTA 6T51 / Cal. 6T51 Gilt |
| Size (Ligne) | 8 ¾‴ (approx. 19.4 mm) |
| Height | 5.98 mm |
| Jewels | 21 |
| Frequency | 28,800 vph (4 Hz) |
| Accuracy | -20 to +40 sec/day |
| Positional Variation | ≤ 50 sec |
| Power Reserve | Approx. 40 hours |
| Functions | Hours, minutes, seconds, day, date |
| Winding | Automatic + hand winding |
| Date Setting | Quick setting (crown first position) |
| Gilt Version | Yes (Cal. 6T51 Gilt) |
Automatic Winding：During normal wear, wrist motion automatically winds the movement. For initial use or after stoppage, manual winding is recommended.
Manual Winding：With the crown in the normal (pushed‑in) position, rotate it clockwise to manually wind.
Time Setting：Pull the crown to the second position (time‑setting) and rotate clockwise to set the time.
Day/Date Setting：Pull the crown to the first position (date‑setting) – rotate clockwise to set the date, counter‑clockwise to set the day.
Quick‑Set Caution：Avoid quick‑setting the day/date between 9 PM and 3 AM to prevent damage to the calendar mechanism.
Hacking：The 6T51 does not have a stop‑seconds (hacking) function; the seconds hand continues to run during time setting.
Remove Old Movement：Open the case back and carefully remove the old movement; retain dial screws and other fittings.
Install Dial：Align the dial feet with the movement‘s locating holes, gently press into place, and tighten the fixing screws.
Install Hands：Install the hour, minute, and seconds hands in order, ensuring they are parallel, clear of each other, and have safe clearance to the crystal.
Install Winding Stem：Insert the winding stem into the movement, press the setting lever, and push it in until a soft “click” is felt.
Test Functions：Pull and push the crown to verify crisp detents and smooth operation in all positions (winding, date, time).
Case the Movement：Place the assembled movement into the case, secure it with a movement ring or screws, and install the crown.
Water Test：After closing the case back, perform a professional water resistance test (the movement itself is not water‑resistant; case sealing determines the final rating).
Important Note：The 8 ¾‴ size is a standard small caliber, commonly used in 28‑34mm ladies‘ watches or small men’s watches. Verify case compatibility before installation.
| Note | Details |
|---|---|
| Movement Size | 8 ¾‴ (approx. 19.4 mm) is a small caliber, suitable for case diameters of approximately 28‑34 mm. |
| Gilt Version | The 6T51 Gilt has gold‑plated bridges for a more luxurious appearance, with identical functionality to the standard version. |
| No Hacking | The movement does not hack; the seconds hand continues to run during time setting. Compensate by gently turning the crown after pulling it out. |
| Date Danger Zone | The calendar mechanism is engaged between 9 PM and 3 AM – do not quick‑set the day/date during this period. |
| Power Reserve | Approximately 40 hours when fully wound. Daily wearing or hand winding every 1‑2 days is recommended. |
| Factory Accuracy | Factory tolerance is ‑20 to +40 sec/day; actual accuracy can be improved through regulation. |
Service Interval：Professional movement service (cleaning, lubrication, regulation) is recommended every 3‑5 years.
Common Issues：Date sticking, fast/slow rate, reduced automatic winding efficiency.
Cleaning Method：Clean movement parts with specialized solution and ultrasonic cleaner – do not use corrosive cleaners.
Lubrication：Use Moebius series watch oils; apply precise, microscopic amounts to all bearings and contact points.
Rate Regulation：Adjust via the regulator index on the balance bridge; fine adjustment changes the effective length of the hairspring.
Replace Wear Parts：Inspect and replace mainspring, clutch wheel, date jumper, etc., as needed during service.
Q1: What is the size of the MIYOTA 6T51 movement?
A: 8 ¾‴, approximately 19.4 mm. This is a standard size for small mechanical movements, commonly used in watches with case diameters of 28‑34 mm.
Q2: Does the 6T51 have a hacking (stop‑seconds) function?
A: No. The 6T51 does not have a hacking (stop‑seconds) function; the seconds hand continues to run during time setting. You can set the time approximately, or pull the crown when the seconds hand reaches zero for a close synchronization.
Q3: How do I set the day and date?
A: Pull the crown to the first position (date‑setting). Rotate clockwise to set the date, counter‑clockwise to set the day. Avoid operating between 9 PM and 3 AM.
Q4: What is the power reserve of the 6T51?
A: Approximately 40 hours. When fully wound, it can run for nearly two days without wear. Daily wearing or hand winding every two days is recommended.
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