A very good review of the Seiko 7s26 movement - Watch Freeks

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Old 10-03-2011, 03:48 PM   #1 (permalink)
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Here is an awesome review and description of the workhorse 7s26 movement from Seiko. This guy certainly knows this movement frontwards and backwards!!!


A sample of contents:

The Automatic System

One of my favorite features of Seiko automatics is the Magic Lever winding system. Earlier versions of this winding system involved only three moving parts: the rotor, the Magic Lever and the pawl wheel. Current implementations use one extra wheel for a total of four moving parts. This simplicity of design adds to its robustness while maintaining a high level of functionality. Along with the lack of manual winding, it makes the 7S26 one of the simplest automatics around. The basic functioning of the Magic Lever system can be understood from these diagrams [11,12] from a Seiko Credor catalog. The coupling between the lever and the intermediate wheel functions on the same principle as a locomotive (or a choo-choo as shown in the diagram). The two arms of the Magic Lever [13] then drive the pawl wheel. They alternately pull and push the pawl wheel in the counterclockwise direction as the intermediate wheel rotates in conjunction with the rotor. The intermediate whee! l and pawl lever cannot be removed until the ¾ bridge is removed as the intermediate wheel is held onto the bridge with a semi-circular clip on the underside of the bridge [14].

For the sake of comparison, an ETA 2892 winds the mainspring arbor one rotation with 155 turns of the rotor. The current implementation of the Magic Lever winds the mainspring arbor one rotation for 166 turns of the rotor. Another factor to consider when contemplating automatic system efficiency is the dead angle. The dead angle is the angle of back and forth movements that the rotor can experience without any winding energy being transmitted to the barrel. The dead angle of the Magic Lever is slightly larger than in the 2892 (by five degrees or so) although I haven't precisely calculated either. There are many other subtle factors that effect the efficiency of an automatic system but I feel safe in assuming that Seiko's system is slightly less efficient than ETA's (at least the 2892, which differs from the 2824 and 7750). ETA's automatic systems are remarkably more complex and expensive to manufacture though and I've yet to hear of a Seiko automatic that does not w! ind sufficiently in use. It is not at all uncommon to find some wear around the lever arms and intermediate wheel coupling in older versions of the Magic Lever system. This example showed some wear [15] underneath the pawl wheel. This amount of wear is fairly significant for a watch that is less than two years old. On the whole, the automatic system is a triumph of simplicity that comes with some apparent sacrifices to longevity as well as efficiency.

Not everything that can be counted counts, and not everything that counts can be counted.

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Old 10-03-2011, 03:52 PM   #2 (permalink)
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A good thread on regulating the Seiko 7s26:


Posted 10 April 2007 - 05:35 AM

Written by Mtech[/b]

Well my latest Seiko has now reached 5 weeks of age :shock: so it's ready for a Mtech tweaking. You may recall that when this watch was new it had amazing performance, it was actually performing well within COSC standards at +3 seconds or so in 2 days !!

As would be fairly typical for a new watch, with having it running 24/7 for the last 5 weeks, either on my wrist or on the winder, it is now (I hope) fully broken-in. The timing performance has now become +10 seconds in 24 hours. This would strongly suggest that the initial performance was due to frictional affects, and now all the moving parts have settled in and the watch is ready for a minor regulation. Manual regulation as you will see.

The tools, I have about $ 400 invested in watch tools, I don't expect that many other people could justify what I have spent, but tools are my other OCD disorder :shock:

Before I start to unscrew the caseback, I like to give myself a reference point of exactly where the factory tightened the back, in this example I am referencing the "S" in Seiko painted inside the display back. When I complete the timing work, I just tighten to till the reference mark lines up and then I know it's as tight as it was when it arrived at my collection.

Here's the movement exposed, it doesn't feel the same when you remove the back of a watch with a display back, sort of anti-climatic ~ you already know what to expect I guess? :biggrin:

Here I am holding one of my expensive screwdrivers parallel to the plane of the regulation lever, notice how my finger and thumb are restraining the blade against the side of the watch case? this prevents me from jamming my screwdriver into the balance spring. I am actually just squeezing the fleshy (yup I'm too heavy!) part of my fingers to give the screwdriver a slight pressure on the regulator lever. Since this watch is fast, I am going to move this lever to the "-" side. I don't want to move it more than " . " because in my experience with Seiko's, less is better.

Just in case the movement got some dust inside, I give it a nice gentle blow....then I put the case back on, twist it with those fingers until it's snug, and then wrench it home to my reference point.

It may take me 2-5 times to get this watch performing to my OCD WIS standards, it takes me about 4 minutes per attempt and 24-48 hours between attempts to see how I did. If you try this yourself, make certain that when you measure the timing performance that the watch is at a fully wound state, otherwise you are introducing a variable that will drive you FREAKIN INSANE, as I can attest.

Not everything that can be counted counts, and not everything that counts can be counted.

Go check out the Dive Watches FBG -->> https://www.facebook.com/groups/1131038630296057/
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