the seiko diver

7/28/2019 The Seiko Diver

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The Seiko Diver's 200 Meter SKX779

Featuring the 7S26 Automatic Movement

Appended 1-1-2003

by John Davis (ei8htohms) 2-4-2002

(click on all images to view a larger version)

IntroductionWatches are machines. While some of them may also be works of art, they

cannot escape their machineness. There is undoubtedly somethingfascinating about those examples of the watchmaker's craft, but there isalso something to be learned from the droves of micro-machines that aredesigned and constructed with only performance and economy in mind.

There is craft involved in the ability to engineer a movement forproduction runs in the tens of thousands that is wholly other than the craftinvolved in manufacturing a movement by hand. It is a skill that I respectand admire, while having even less understanding of its intricacies than I

do of traditional watchmaking skills. Being a fan of Seiko's watches
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Each of the three hands has a slightly different interpretation of a rocket-ship shape and when the hour and minute hand line up, the resemblanceis pronounced. They are painted with an ecru color that matches the hourmarkers and both are filled with Lumibrite (Seiko's proprietary version of

Super-Luminova) and, especially when brand new, glow as brightly as any

watch I've seen. I'm always disappointed when watch companies use whiteday and date rings on a black dial and this is one of the few complaints I

have about the classic Seiko Diver's. The color scheme of this watch's dialgets big points from me for the use of black rings with white

letters/numbers. Taken altogether, the shape of the hands and case andthe depth of the dial through the domed crystal have a vaguely ray-gun

gothic effect that I find very appealing.

The strongest feature of this version of the Seiko Diver is the bracelet andclasp [1]. The solid link, brushed steel bracelet with polished accents isincredibly sturdy and well designed. It is heavy enough to balance thehefty case well on the wrist and has a wonderfully secure, two-button

folding clasp with safety and a wet-suit extension. In addition to providingthe peace-of-mind that this bracelet and clasp will in all likelihood never

come off of your wrist accidentally (either by breaking or comingunhooked), it has the flexibility to be extended sufficiently to wear over awetsuit at a moments notice. The links are held together by solid pins with

sleeves that are a little tricky to remove and replace but not unduly so.Attaching this wonderful bracelet to the case are the two largest spring

bars I've ever seen.

In addition to water-tightness, the ability to withstand abuse is a highlydesirable feature for a utility watch of this nature. The Seiko Diver hasseveral features that contribute significantly in this regard and a few of

them are visible upon removing the solid steel back. The 7S26 usesSeiko's patented Diashock shock protection [3] on the balance pivots, hasa soft, plastic spacer ring [4] closely integrated with the movement and a

relatively low mass rotor [5] that is unlikely to bend or break even withvery severe shocks. The plastic spacer ring, combined with the sheer

massiveness of the case, provides a great deal of additional shockresistance and is a more economical solution than a metal spacer ring aswell. This combination of economic and sensible engineering is a trendthat persists in almost every facet of the design of the 7S26 movement.
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Under the Dial

While there is often much disdainamongst watch enthusiasts for plastic

components in mechanicalwristwatches, I propose that there areinstances where it is acceptable and

possibly even preferable. One particular

area in which plastic is a perfectlylogical solution is the calendarmechanism. These are parts that rotate

at very slow speeds (or sometimesintermittently) and with very little torque for the majority of their rotation.This combination of features makes them controversial with regards tolubrication. While lubricating them significantly will increase the drag on

the movement and possibly ultimately stop the watch, leaving themsparsely lubricated or dry will ultimately result in wear. Plastic is an ideal

solution for these components because it is light and self-lubricating. Iwon't pretend that Seiko's primary concern here is not one of economics,

but it is combined with intelligent engineering as well.
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The plastic parts in question are thequickset wheels, the intermediatecalendar wheel and the calendar

advance wheel [left]. The calendaradvance wheel [8] has two plastic

fingers to advance the date and daydisks that will easily slip out of the way

if the quickset is activated while thecalendar is advancing. The calendar

mechanism is secured under a very thin but nicely polished metal platethat is held in place with three standard screws and one Phillips head [7].

The presence of this one tiny Phillips screw in the movement is somethingof a mystery and along with the molded plastic and thin metal plates lends

the bottom plate the appearance of a very well made calculator.

The first wheel in the quickset mechanism [9] is permanently attached tothe underside of the calendar plate. It's only after removing this thin plate

that the date ring can be removed and, subsequently, the spacer ring.Such close integration of the spacer ring with the rest of the movement isunique in my experience and sharply contrasts with the usual method ofsecuring the spacer ring to the case. This novel arrangement conceivablycontributes to the shock resistance by separating the movement and ring,

as one unit, from the case.

After removing the calendar plate we can also observe the oddly shapedteeth of the clutch and quickset pinion [10], all the more visible because of

the utter lack of keyless works on the bottom plate. Because there is nowinding pinion (no manual winding capability), in its place is a quicksetpinion. The square teeth of this pinion mesh with identical teeth on theclutch when the stem is in the second position and allow the quickset

pinion to turn in either direction: clockwise to advance the date andcounterclockwise to advance the day indicator. The second quickset

intermediate wheel (the white plastic wheel with traditional teeth) thenslides into engagement with either the date ring or the third intermediate

wheel (with the wolf teeth) which advances the day disk. This is a veryfunctional and robust quickset and calendar mechanism and, being largely

made of plastic components, requires no lubrication. Another thin plateholds the intermediate calendar wheel, c! alendar advance wheel and hourwheel in place and after removing them we can contemplate the top plate

of the movement.
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The Automatic System

One of my favorite features of Seikoautomatics is the Magic Lever windingsystem. Earlier versions of this winding

system involved only three movingparts: the rotor, the Magic Lever and

the pawl wheel. Currentimplementations use one extra wheel

for a total of four moving parts. Thissimplicity of design adds to itsrobustness while maintaining a high

level of functionality. Along with the lack of manual winding, it makes the7S26 one of the simplest automatics around. The basic functioning of theMagic Lever system can be understood from these diagrams [11,12] from

a Seiko Credor catalog. The coupling between the lever and theintermediate 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 cannotbe removed until the bridge is removed as the intermediate wheel is
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held onto the bridge with a semi-circular clip on the underside of thebridge [14].

For the sake of comparison, an ETA 2892 winds the mainspring arbor onerotation with 155 turns of the rotor. The current implementation of the

Magic Lever winds the mainspring arbor one rotation for 166 turns of therotor. Another factor to consider when contemplating automatic system

efficiency is the dead angle. The dead angle is the angle of back and forthmovements that the rotor can experience without any winding energybeing 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'tprecisely calculated either. There are many other subtle factors that effect

the efficiency of an automatic system but I feel safe in assuming thatSeiko's system is slightly less efficient than ETA's (at least the 2892, whichdiffers from the 2824 and 7750). ETA's automatic systems are remarkablymore complex and expensive to manufacture though and I've yet to hearof 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 intermediatewheel coupling in older versions of the Magic Lever system. This exampleshowed 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 thewhole, the automatic system is a triumph of simplicity that comes with

some apparent sacrifices to longevity as well as efficiency.

The Power Train

Upon removing the bridge, we canget at the barrel, the power train and

the oddly placed keyless works [left]. It

is quite rare to see keyless works on thebridge side of the movement and isfacilitated in this case by the absence ofmanual winding capability. By placingthe clutch lever, set lever and detentwhere the crown wheel would usually

be, the space on the dial side can be used for the quickset mechanismalone. This allows all of these components to be quite a bit beefier thanthey would be otherwise. The increased size of these levers and wheels

adds to their robustness as well as their ease of manufacture, owing to thelooser tolerances required. The set lever has a three-position detent and

pivots on a post, rather than a screw. It's tail end serves as a push-buttonto release the stem from the movement and can only be operated when
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the stem is in the neutral (1st) position. Most keyless arrangements haveone position in which it is most convenient to! replace the stem, it is nice

that the 7S26 dictates this by only allowing the stem to be removed in oneposition. The set lever acts as its own return spring by way of its extended

tail. This does away with the need for a wire spring, none of which are

found in the 7S26.

The click [16] on the 7S26 is also remarkably simple. It consists of a longsteel spring held in place by sheer geometry, without the use of screws. Itlies under the click wheel and is held in place by a brass pin on one side, araised portion of the mainplate on the other and the plate bridge on top.

The barrel [17] is circular grained on the top and bottom and isreplaceable as a whole unit. Although it is possible to open the barrel, it isnot designed with this in mind. These pictures [18,19] are of a faulty barrelmy friend Randall Bensen encountered. Inside we can see the insufficientlyapplied black graphite-laden grease [18]. He replaced it with a whole newbarrel (an appropriate precaution given the permanently sealed nature ofthese barrels) and proceeded to open up the bad one. After he took themainspring out and cleaned it, we can see that the inner surfaces of the

barrel are unfinished [19]. While this will undeniably effect the consistencyof the ! power flow from the mainspring, a host of other refinements

throughout the train and escapement would be necessary before evidenceof this effect could be noticed.

The power train of the 7S26 is a direct-seconds layout of the simplest

configuration [right]. Quite remarkablefor a low-cost movement such as this,are the Diafix cap jewels on the thirdwheel and escape wheel [20]. These

jewels bring the total number to 21,quite sufficient for an automatic watch,especially with only two jewels in the

automatic system (for the intermediatewheel). The power train wheels are crudely finished and appear to be

made of nickel. This is the first time I've seen nickel train wheels.Traditionally, train wheels are made of brass because it is relatively

strong, cheap, easily machined and wears well in contact with steel. Nickelhas these same features while being slightly stronger and more difficult tomachine. It's use for train wheels does not seem to be dictated by cost so I

can only surmise that its greater strength is desired.
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All of the train wheels have properly shaped teeth although their faces arenot well polished with the exception of the escape wheel. The center

wheel [22] is actually a solid disk, having no spokes or even holes drilledthrough it (as do some train wheels in earlier movements). While this isnot ideal from the standpoint of inertia, the second wheel is the slowest

moving of the four train wheels, making its inertia the least critical.Disconcertingly, the lower pivot on the third wheel was completely floodedwith oil [21]. There was so much oil present that it had contaminated theteeth of the center wheel [22] and would have resulted in serious wear

issues, over time capturing the inevitable micro-metallic dust and turningit into an abrasive paste. Apparently one of Seiko's robots was asleep at

the wheel when applying lubrication to this pivot.

The Escapement

The escape wheel teeth [23], whileappropriately polished, are not beveled

at all, leaving a rather wide face to

impulse the pallet jewels. This meansmore friction and less power. One

possible reason for these wide impulsesurfaces is to prolong the life of thepallet stones. The wide faces of theescape wheel teeth are less likely to

groove the pallet stones even after years of use. Seiko escapements alsoseem to have an unusually large locking depth (the extent to which the

pallet jewels lock the escape wheel teeth). In all likelihood this is aconcession to looser tolerances in the manufacturing process and in my

experience often results in a lower balance amplitude.

The pallet bridge [24] is nicely shaped and supports a very homely palletlever [25]. The topside of the pallet appears to have had its insides

scooped out and is utterly unfinished. Interestingly, the underside of thepallet fork is fairly well polished, contrasting with the Swiss tendency to

finish the top of the pallet fork and not the bottom. At least I can say theyweren't trying to hide anything. I can only guess that the weird, semi-

hollow form of the pallet fork is an attempt to make the pallet fork lighter,something that is highly desirable in this critical component.
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The balance itself [27] has two arms and is of unknown composition. If Ihad to guess, I'd say it was made of a nickel alloy and the hairspring ismade of some form of elinvar. It is not as critical for the balance to bemade of a material that is stable over different temperatures as the

hairspring, but without a variant of elinvar for the hairspring, it would beimpossible for the movement to perform well in daily use. The hairspring isflat and is attached to the collet [28] in a manner that avoids the problems

inherent in traditional pinning methods. A pinned hairspring has itselasticity compromised in close proximity to the pinning point as the

spring's cross-section curves around the pin. In addition, the hairspringmust be bent profoundly from its even, concentric spiral shape to where it

enters the collet. Seiko's arrangement does away with both of theseproblems as the inner coil of the hairspring is crimped in a groove in the

collet without disturbing its! shape. The outer coil of the hairspring issimilarly crimped in a slot in the stud [29]. Although this is a perfectly

functional solution, it negates the possibility of altering the length of thehairspring in the future, resulting in a balance that is effectively

disposable.

The regulator uses a buckle [30] (as opposed to simple pins) to keep thehairspring from slipping out when subjected to shocks. Like all of the

components of the movement, it is crudely made but well designed andfunctional. A watch is said to be "in beat" if the tick and the tock are

equally distributed around the resting position of the balance and this iscontrolled by either rotating the hairspring collet on the balance staff or

changing the position of the stud. For ease of beat adjustment, thebalance cock of the 7S26 features a movable stud carrier that I fault only

for being a little too large. Its excessive, unbalanced weight can cause it toshift during shipping or when dropped, resulting in a significant rate

change as well as throwing the escapement out of beat. If the escapementgoes too far out of beat, its ability to self-start after running down will be

hampered in addition to positional performance problems.

Conclusion
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There are many positive things I can say about this movement, but themost relevant is that it is exceedingly honest, almost to a fault. It is an

economic design and construction that is created for maximumperformance and robustness at minimal cost. It has no pretenses of

decoration or "fineness". In fact, it uses this very freedom from tradition to

incorporate engineering solutions that would otherwise be shunned, likethe plastic calendar wheels and spacer ring. It is heartily true unto itself asa low cost, low maintenance, long lasting and well functioning automaticmovement. It is not pretty and it is not glamorous. It is in all likelihood

untouched by human hands in its manufacture. There is, however,significant accomplishment in its conception and implementation. Withoutthe Seiko 7S26 and comparable movements from Miyota (Citizen), Orient,

and Swatch, many people would not be able to experience the joy ofowning a mechanical watch at all.

Given the reliability and robustness of the 7S26 movement, the quality ofexecution and general massiveness of the SKX779's bracelet and case,and it's striking looks, this is a lot of watch for the money. I would nothesitate to recommend it to someone interested in a watch that will

perform well under any circumstances (ok, maybe not with a tux) whilerequiring no special attention. I will not be shocked in the least if this

watch runs for twenty years without service (maybe fifteen now that I'vereplaced the Seiko lubricants with Moebius greases and oils) and fully

expect to read extreme stories in the future regarding 7S26 based SeikoDiver's. It is a fitting addition to the illustrious Seiko Diver line.

_john

Addendum

In commenting on the wear I found in the automatic system, I believe Iover-emphasized its significance and the likeliness of long term

repercussions. While the amount of wear present under the pawl wheelwas more than I would expect to see in such a young movement, the

Magic Lever system remains only slightly modified from earlier designs,many examples of which have been observed to perform well for 10, 20 or

more years without service. I think the amount of cosmetic wear issignificant but I don't believe that it will adversely affect the longevity ofthe automatic system or movement overall.

Since publishing this review, I have come to better understand the actionof the Magic Lever and how its dead angle relates to winding efficiency. Inthe discussion of the Magic Lever in the review, I said "The dead angle of

the Magic Lever is slightly larger than in the 2892" but I now realize that isnot exactly true. While most automatic systems have a dead angle that is

more or less consistent regardless of the position of the rotor, thegeometry of the eccentrically mounted Magic Lever results in a dead angle

of varying size, depending on the position of the rotor.


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anywhere along that section of its rotation. This translates to a very largedead angle in the short portions of the drive wheel rotation between thesefour points. That is to say, if the Magic Lever wobbles back and forth in thisregion for a while, no winding action will be transferred to the mainspring.

Conversely though, the larger portion of the pawl axis' motion betweenthese four points results in a very small dead angle. When the pawl axis ismoving between A and D (in either direction) or between B and C (in eitherdirection), the action of one pawl is complimented by the slipping action ofthe other, translating the maximum amount of winding action to the pawl

wheel (keeping in mind that the pawl wheel teeth in the diagram aregreatly exaggerated and are in actuality very fine).

The dead angle is at its smallest when the pawl axis is halfway between Aand D or halfway between B and C (approximately where it is in the

diagram). By attaching the rotor so that the minimum dead angle of therotor corresponds to its natural, relaxed state in the crown down position,the winding efficiency is maximized. In this way, the normal movements of

the arm (particularly in activites like walking, where the watch is crowndown most of the time) will result in the greatest winding action.

While it is true that in certain rotor positions the dead angle is quite large,in other positions it is incredibly small (relative to other automaticsystems). If the rotor is positioned properly when installed in the

movement, the dead angle is minimized when the rotor is in the crowndown position (approximately). This ensures that the minimum dead angle

zone is capitalized on during wear (when the majority of the time is spentin the crown down position) to maximize winding efficiency. To assist thewatchmaker in positioning the rotor correctly, there is a small hole in thedrive wheel that lines up with a hole in the balance bridge when the rotoris in line with the crown. This capitalization on the idiosyncracies of theMagic Lever geometery likely accounts for the efficient winding action

most Seiko wearers experience in actual use. Unfortunately for us it alsomakes it impossible to compare its efficiency with that of other automatic

systems without exhaustive real world testing.

_john

January 1, 2003

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Copyright February 2002 - Mr. John Davis and ThePuristS.com - all rights reserved
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