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Do It Yourself Project: Seiko 7S26 for Novice Horologists

Chapter 7: Disassembly of the Time Display Unit

Now that we got our movement out of the case, we are ready for more serious disassembly. To refresh your memory: a 7S26 movement consists of 5 major units. In this chapter we will cover disassembly of the time display unit.

DIY Seiko 7S26 disassembly of time display unit diagram

The time display (TD) unit consist of the following components:

    - dial and hands
    - day and date dial disks
    - day and date quick setting wheels
    - hour and minute wheels and cannon pinion
    - driving wheels for date dial
    - dial holding spacer, plates and screws

For more details and part numbers, refer to Parts Catalogue, page 2 position 1-15. Since dial and hands are not movement-related components, they are not listed in the movement parts catalogue.

NOTE: most components in the TD unit are made of plastic. Plastic is not a traditional "watchmaking" material but like many other manufacturers of mass produced watches, Seiko has opted for plastic components due to lower production costs and lower maintenance requirements. Unlike metal wheels, plastic wheels require no lubrication. Unfortunately plastic wheels are easily damaged and destroyed when handled inappropriately. Also they are far less forgiving when they are not placed correctly - even a relatively small amount of force can cause permanent damage if the wheels are not free to rotate, bent or misplaced. Failing to follow disassembly instructions will result in permanent damage.

The first step in disassembly is removal of the hands and dial.

Tools: hands removal tool, tweezers, screwdriver size 80.

Hands removal tool is a simple yet essential tool which is correct for hands removal.

DIY Seiko 7S26 hands removal tool

The core of the tool are two specially shaped levers. When springs are squeezed together, the levers are pushed against the dial upwards and the friction-fit hand is removed from its wheel.

Seiko DIY Project hand removing levers

Seiko 7S26 DIY hands removal procedure

Hands removal procedure:

With the mechanism placed in the movement holder, set the time so that the hour, minute and sweep seconds hand are "over each other," like in the photo.

Seiko 7s26 DIY disassembly - paper dial protector

In order to protect the dial from scratching (when in contact with the hands removal tool) make a paper dial protector as per photo.

The next step is crucial: place the levers of the hands removal tool UNDER THE HOUR HAND.

DIY Seiko 7S26 placing the hand removal tool

Note: the common mistake is to place the levers between the hands - for example, one lever underneath the hour hand and other between minute and second hand. Such placement is INCORECT and will result in damage! With the squeeze of springs, all 3 hands will be lifted at the same time. Another tip: make sure that tool is positioned vertically (not under an angle).

Note: once the tool springs are squeezed and hands are removed, DO NOT RELEASE PRESSURE! If you do, the hands will most likely fly away never to be found. The proper action is: squeeze-remove hands-keep the tool squeezed-bring it down to the bench surface-release the pressure.

The photo below shows the moment after removal, while the squeeze is still maintained.

DIY Project Seiko 7S26 with hands removed

Hands removed! Remeber not to touch the dial! Fingeprints are very difficult to clean off the shiny dial surface!

DIY Seiko 7S26 dial without hands

DIY Seiko Project - 7S26 hands

Next step is to detach the dial from it's holding spacer. The dial has two feet which are pushed into the spacer. To lift the dial, place tweezers in cutout underneath 3 o'clock position and rise the dial very gently for approx 5mm.

Seiko 7S26 DIY Project - dial holding spacer

Rotate 180 degrees and again, unsing tweezers as lever, lift the other of the dial.

DIY Seiko 7s26 detaching the dial

Seiko 7s26 detached dial

Place dial in a small paper bag and store away.

Seiko 7S26 DIY parts storage

Next step is removal of the Day star with dial disk (day dial). It sits on top of hour wheel and it is secured in place with a "snap".

DIY Seiko 7S26 day star with dial disk

Snap is really a C-clip which slots into the hour wheel. With tweezers, align the cutout in snap with the stem as per picture.

Seiko 7s26 day star with dial disk and date dial

To remove snap: place screwdriver underneath the snap EXACTLY 90 degrees from the cutout and twist very gently. Be careful! You need to position the screwdriver in a cutout which is located on the bottom of the snap. See photos below for enlarged shot of the snap. BEWARE: do not push or pull the snap. Any attempt to remove it in any other position than shown in the photo will result in damage to the very thin day dial. The snap must remain in shape, if bent it will not hold the day disk properly or it will not provide clearance for free rotation. However when removed as described, it will remain in perfect shape.

Seiko 7S26 cutout in snap

Here is another shot of the snap, showing the cutout to accept the screwdriver.

Seiko DIY repair - cutout in snap

Remove the dial disk.

Seiko DIY repair - removing the dial disk

Remove intermediate wheel for day correction. This wheel is held in place by the day disk so you can just lift it up form it's arbour. NOTE: this odd-shaped plastic wheel is very fragile, try to avoid touching the tooth!

Seiko 7S26 - intermediate wheel for day correction

Seiko 7s26 DIY repair - intermediate wheel

We are now going to remove another layer of wheels which are held in place by the date indicator maintaining plate (for shor: date plate). The date plate is held secured in position with 4 screws (3x A type and 1x B type). First we will unscrew one B type screw, part number 0016 705. It is a phillips head screw. (Another unorthodox component!). To be able to remove this screw, we would have to make a tool - a "halh phillips head screwdriver". :-)

Seiko 7s26 diy disassembly - date indicator maintaining plate

Place a sheet of medium coarse (400 or 600 grade) sand paper on to a flat surface and shape the blade of your smallest size screwdriver (40 or 60 / 0.40 or 0.60mm) as per photo.

Seiko DIY 7S26 - 40 or 60 screwdriver

DIY Seiko 7S26 - 0.40mm or 0.60mm screwdriver

Seiko 7S26 Date Plate screw A

Seiko Date Plate screw A

Seiko 7S26 Date Plate

Seiko Date Plate screw A

Seiko 7S26 Date Plate removed

day-date corrector setting wheel

date jumper 0810 300 seiko 7s26>
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seiko 7s26 date dial

seiko diy project 7s26 hour wheel 0271 483>
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seiko 7s26 - minute wheel 0261 006

seiko 7s26 - date driving wheel 0802 300

Seiko 7S26 DIY disassembly

Seiko 7S26 DIY assembly and disassembly

Seiko 7S26 DIY

Seiko 7S26 dial holding spacer

DIY Seiko 7s26 project

Seiko 7S26 cannon pinion 0225 005

Seiko 7S26 disassembled parts

DIY Seiko 7S26 disassembly

Seiko 7S26 DIY project

Seiko 7S26 DIY

DIY Seiko 7S26

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