Seiko 6309 movement

Both versions exist. Seiko USA publishes a guide for the 6309A, and Renou Watch Co. hosts a 6309B parts list. Boley’s parts catalogue lists a different date dial for each, 0801601 for the A and 0801602 for the B. That’s the only difference we’ve been able to confirm. We haven’t found a readable Seiko note on what else changed, and nothing suggests a change to the jewels, beat rate or winding.

The 6306 is the 6309’s better-equipped sibling. Mizeni describes the 6309 as identical to the 6306 except that the 6306 has a seconds stop, 21 jewels instead of 17, and a kanji day wheel. Adventures in Amateur Watch Fettling’s teardown of a 1979 6306-7001 confirms the 21-jewel 6306A and its English and kanji day wheel. The 6306 went into Japanese-market watches, including the 6306-7000 and 7001 divers.

Don’t judge a movement by its day wheel alone: wheels get swapped during repairs.

• The Turtle divers: 6309-7040 and 6309-7049, 1976 to 1988. See our 6309 Turtle page.
• The Slim Turtle divers: 6309-7290 (black), 729A (Pepsi) and 729B (orange), from 1982. The Seiko Guy records dial codes in the 6309-735 and 747 families on these, not the 704 codes of the big Turtle.
• Dress and Seiko 5 models, such as the 6309-8920 that Sky Corner restored.

This isn’t a complete list; Seiko put the 6309 in many everyday automatics. We’ll add references as each one is checked.

• A worn barrel arbor hole. The mainspring barrel’s arbor wears its hole in the bridge, so the barrel tilts and rubs. Sky Corner calls it a common issue with the 6309, and Adventures in Amateur Watch Fettling found the same wear on a 6309-7040.
• Dried, dirty oil, including on the pawl lever pivot jewels of the automatic winding (Adventures in Amateur Watch Fettling).
• On the divers, the case rather than the movement: Worn & Wound flags damaged crown tube threads on the 6309-704x as a serious problem.

We haven’t found a Seiko document giving a time window when the 6309’s day and date shouldn’t be set, so we don’t give one. The 9 p.m. to 5 a.m. rule you’ll see on forums doesn’t come with a Seiko source.

Seiko USA doesn’t list the 6309 among the calibers it no longer services, but warns other old calibers may be returned unrepaired. Its estimate for mechanical calibers like this one was $359 before tax and shipping in October 2026. Suppliers such as Boley still list 6309 parts, and watchmakers also use donor movements (Sky Corner).

Whether a service pays off depends on the watch: a Turtle diver and a plain Seiko 5 with the same movement sell for very different money. Check our price guide once sampling is in.

People do, but it isn’t a drop-in. A watch modifier notes date-alignment problems, and owners on r/SeikoMods point out that the dial feet won’t line up. We haven’t found a documented swap that keeps the original dial, hands and crown working as before. A 6309 watch with a modern movement is a modified watch, and it’s priced as one.

• Seiko, 6309A guide; Renou Watch Co., service documents; Boley, 6309A parts.
• Mizeni, Seiko 6309, and Caliber Corner, Seiko Caliber 6309: specifications and the 6306 comparison.
• Adventures in Amateur Watch Fettling, A Seiko 6309-7040 and a 6306-7001 from 1979; Sky Corner, a Seiko 5 6309-8920.
• The Seiko Guy, Guide to the Seiko Slim Turtle 6309; Worn & Wound, Affordable Vintage: Seiko 6309.
• WellingTime, Seiko Mod: Dreams & Limitations; Seiko USA, service estimates.