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The movement is an 8L35, an undecorated and unadjusted version of the high-end Grand Seiko 9S55. Rhodium-plated, 26 jewels, automatic, 28800vph (4Hz), handwind and hacking, 50 hour power reserve. The size of the balance wheel was increased to provide the torque required, as the hands are heavier than a dress watch. The 8L35 is also used in the Landmaster, which has the same hands.The movement by all accounts keeps excellent time, and in 9S55 trim is capable of exceeding COSC specs. Anecdotal reports on various fora indicate less than five seconds’ daily error is typical. The spec is -10 to +15 seconds per day.The 8L35 is completely in-house Seiko, and is descended from the 6159 300m diver, circa 1969. Everything from oil on up, including mainspring, is Seiko. Kinda cool. What they call a ‘manufacture’. John ‘ei8htohms’ Davis is a big fan of the 8L35, and had this to say about it:My understanding is that the Seiko 8L35 is pretty much the same movement as the 9S55, but perhaps missing a few refinements and not as thoroughly adjusted. As such, it is one of the finest automatic movements Seiko makes. The machining is of the highest quality and the design and construction is informed by Seiko’s many years of experience. I believe the 8L35 even has a Lossier inner coil on the hairspring. A very nice touch you will not find in any modern Swiss watches to my knowledge.
 

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Interesting Reading!
I just cannot get this part:
minidriver said:
...The size of the balance wheel was increased to provide the torque required, as the hands are heavier than a dress watch. ...

In my understanding the balance wheel has nothing to contribute to the torque. To increase the torque you should rather modify the main spring.
What is wrong with my thinking?
But anyway it's hard (for me) to believe that a modification like that should be made just because of increased mass of the hands, but I'm more than willing to learn more about it.

Cheers,

Axel
 

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Being hard as it is to get any info on Seiko JDM's movements, I can only say that I am a very satisfied 8L35 user so far - accurate, steady variation, nice crown action.
 

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Axel66 said:
Interesting Reading!
I just cannot get this part:In my understanding the balance wheel has nothing to contribute to the torque. To increase the torque you should rather modify the main spring.
What is wrong with my thinking?
But anyway it's hard (for me) to believe that a modification like that should be made just because of increased mass of the hands, but I'm more than willing to learn more about it.

Cheers,

Axel
I agree. The only source of energy in the movement is the mainspring. If more torque is required to drive the hands, you would need to use a mainspring with a higher spring constant. I'm not a watch maker, and I'm not questioning the accuracy of what was written by our esteemed watchmakers. I'm just looking for some clarification on how a larger (or more massive) balance wheel is needed when heavier hands are used.

Myles
 

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It would seem to make sense that the more back pressure you put on the pallet jewels,the more energy would be needed to cleanly disengage them- if you didn't I think you'd end up with decreased amplitude and possibly loss of accuracy,hence the bigger balance wheel with more potential energy to cleanly "switch".
 
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