Citizen BLS 8100 4-900031-TA - The Flyback Chronograph of the 1970s!
Introduced in 1972-73, the Citizen BLS 8100 (Ref. 4-900031-TA / Model 67-9577) is one of the Japanese watch industry's most technical and ambitious mechanical chronographs. "BLS" stands for Black Coating + Stainless Steel Bezel: The case is protected by a black hard coating, while the robustness of the stainless steel is preserved on the bezel and case back. This special coating not only provides a cosmetic appearance but also provides extra resistance to scratches and external factors.
The watch's black dial, with its contrasting orange chronograph hands, baton indices, and colored sub-dial at 6 o'clock, conveys a strong sporty character. The day-date window at 3 o'clock adds practicality for everyday wear. The approximately 38 mm case diameter is quite modern by the standards of the time and still represents the ideal size for a men's watch today.
Movement
Caliber: Citizen 8100A (Automatic Flyback Chronograph)
Jewels: 23 jewels
Frequency: 28,800 vph (hi-beat)
Functions: Hours, minutes, seconds, flyback chronograph, day and date
Technology: Column wheel + vertical clutch architecture
Rotor Engraving: "Citizen Japan"
Caliber 8100A was the most innovative Japanese automatic chronograph movement of its time. Thanks to its flyback feature, the chronograph hand could be restarted directly without resetting. This movement, with its durability and high frequency, put Citizen on par with its Swiss competitors.
Case and Case Back
Reference / Case No: 4-900031-TA
Model: 67-9577 (Challenge Timer series)
Case Diameter: ~38 mm
Material: Black hard-coated case + stainless steel bezel and case back
Back Brands:
“BLS 8100”
“4-900031-TA”
Model No: 67-9577
“Citizen Automatic, Water Resistant, Japan”
Why the Citizen BLS 8100 4-900031-TA?
Legendary Movement: Cal. 8100A with flyback function, with a hi-beat frequency of 28,800 vph, one of the most advanced movements of its time.
BLS Coating: The combination of a special black hard-coated case and stainless steel is not only stylish, but also durable and long-lasting.
Collectible Value: Due to its short production run in the 1970s, it is very rare today.
Sporty Design: Orange chronograph hands, multicolored sub-dials, and a clearly legible dial layout.
Suitable for Daily Use: Day-date function and robust case construction.
Condition Note
As seen in the photos, the watch is in excellent condition.
Dial: Original, clean, and all indices are clear.
Hands: Original, vibrant orange.
Coating: The BLS black-coated case is in very good condition, with only minimal signs of age.
Movement: Clean and functional, with the rotor engraved with "Citizen Japan."
Case Back: The reference number and model codes are clearly legible.
Strap: Refurbished leather strap, with a simple and harmonious clasp.
Final Word
The Citizen BLS 8100 4-900031-TA is not just a chronograph; it is a symbol of Japanese engineering from the 1970s. With its flyback feature, BLS coating, and modern dimensions, it is a unique watch for both collectors and everyday wear. This model is one of the most striking examples of Citizen's time in watchmaking history, standing shoulder to shoulder with Switzerland.
The item you are viewing was manufactured in 1972.
Professionally overhauled and FULLY SERVICED (the movement is completely disassembled, its components cleaned, oiled, and adjusted), your watch will function flawlessly without any surprises. (It is maintenance-free for 3 years unless exposed to direct water or high humidity for extended periods.)
Item Condition: Tested and fully functional.
