Master Watchmaker, Clockmaker and Jeweller (since 1981)
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Do It Yourself Project: Seiko 7S26 for Novice Horologists

Chapter 14: The assembly of the train

We'll start the assembly of the train by attaching the first reduction wheel and pawl levers to the bridge plate.

Lubricate the contact surface between the wheel and pawls by applying a very small amount of lubricant as per photo.

Place the pawls onto the wheel as shown - pay attention to the orientation.

Apply a very small amount of lubricant inside the jewel holes as per photo.

Place the bridge of the reduction wheel as shown on the photo

Slide in the reduction wheel holder

Note the position on the arbor where the holder is placed.

It might be easier to do so if you support the wheel from underneath.

Completed assembly of first reduction wheel.

Place the main spring barrel in to the main plate.

Insert the click spring in to the main plate.

Insert the wheels in the following order: third wheel, escape wheel, then the fourth wheel.

Third wheel

Escape wheel

Fourth wheel

Bring the bridge over the main plate keeping the cut out section of the bridge parallel with the click spring - as shown in the photo.

Place the bridge, hold it gently in one hand without applying too much pressure, and then with the other hand move the click spring slightly so the bridge sits over the alignment pins. If necessary slide the click spring away to allow the proper alignment of the bridge plate.

Insert two plate screws approximately halfway down.

Align third, fourth and escape wheel.
The procedure of mounting the copper plate and wheels is described in chapter 12.

After checking the end shake of the components under the bridge, tighten the screws.

Check the rotation the barrel and wheels by gently turning the barrel. The escape wheel should spin fast even with just the slightest amount of force applied to the barrel.

Another way to check the freedom/end shake of the gear is to pump a bit of air towards the escape wheel from a few centimetres away. It should rotate freely.

Lubricate the pawls which hold the second reduction wheel and main spring barrel arbor.

Install second reduction wheel.

Check the winding action of the first and second reduction wheels.

Turn the barrel to position the slot in the barrel arbor as per photo.

Note the slot in the ratchet wheel.

Place the ratchet wheel so that both slots are aligned.

Before inserting the ratchet wheel screw, gently lift one end of the pawl above the second reduction wheel.

Insert the ratchet wheel screw - to preserve the alignment, hold the ratchet wheel down while doing this.

Once again, check the winding action - the escape wheel should rotate freely as the main spring is wound. Note: You will apply lubricant to the pawl at a later stage of assembly.

Turn the main plate.

Lubricate the jewels as shown below. And also, lubricate the centre wheel arbor. Note: Do not lubricate Jewel A.

Place the canon pinion over the centre wheel.

Push the canon pinion down as far as it can go. This is a friction fit assembly and you might need to apply a reasonable amount of force.

This image shows a correctly installed canon pinion. Observe the assembly from the side when the canon pinion is installed properly the third wheel arbor will protrude slightly.

It is important to apply a sufficient amount of lubricant on the centre wheel arbor. This will allow the canon pinion to rotate, allowing for the smooth setting of hands. (There will be difficulty in setting the hands if there is no oil.)

When it comes to applying lubricant into the jewel holes/caps, apply as little oil as practically possible. The amount of oil required to lubricate light wheels like the third, fourth and escape wheels, is miniscule. Over-oiling will create undesirable effects and finally, the oiling method of the bridge plate is less than ideal. The proper way to oil the fourth and escape wheel jewels is to remove the cap jewels. However, this operation requires a set of skills which are most likely beyond that of DIY participants'.

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