IN JAPAN, watch enthusiasts often refer to Grand Seiko as “saiko no futsuu” (最高の普通), which roughly translates to “the best of normal”. The 45GS (Grand Seiko) and the 45KS (King Seiko) is a prime example of a seemingly normal watch but at a closer look, a watch packed with historical and technical significance. Both watches employ the legendary caliber 45 family of movements - arguably the greatest movement made by Seiko. Introduced by the Daini Seikosha in 1968, the Hi-Beat caliber 45 was used in both the King Seiko and Grand Seiko models, and is loved by Seiko enthusiasts around the world for its incredible accuracy. The 45 family of caliber's consists of the 4502A, 4500A, 4520A, 4522A, and the 4580. Hi-beat (that is a movement with 36000 bph) movements existed before 1968, most notably constructed by Girard-Perregaux and Suwa Seikosha, but the caliber 45 was designed by Daini Seikosha completely from scratch, in house, and thus has a unique layout.
There were namely two reasons why this movement is so accurate even in today’s standards. One is the large balance wheel (the balance wheel of a hi beat movement is usually smaller than a low beat movement). The second reason is because of the thick and powerful main spring. Despite the balance wheel and main spring being large, the engineers at Daini were still able to make a thin movement by employing a unique layout of the gear trains. Specifically, the 2nd gear wheel was moved off center and instead the 4th gear wheel was positioned there.
Although this layout allowed the movement to be thinner, it would become the weak spot as well. The unusual layout is a bit tricky for watch makers during maintenance of the movement. In addition, given that the barrel was closer to the gear trains, any issues with the main spring meant that the entire movement could be ruined. Nonetheless, a well maintained caliber 45 is undoubtedly a machine to marvel at. As one Seiko engineer at that time noted, “it’s a mass produced movement, but inside it’s a racing machine”. In our humble opinion, the 45 caliber still remains the greatest manual wind movement ever produced by Seiko.
At Special Dial, we are always on the hunt for good conditioned 45GS and KS's. When we do source them, we usually have our watchmaker perform a full servicing of the movement so that you can enjoy the 45 caliber in all its glory. We've usually found that in most cases, the movement still runs within +/- 5 seconds per day when serviced and adjusted. Not bad for a + 50 year old watch!