WS 29 How To Replace An Acrylic Crystal of a Pocket Watch

Foreword

The GOLD COIN pocket watch from the SHANGHAI STOP WATCH FACTORY that I had purchased many years ago in Shanghai received a blow a couple of weeks ago when I was wearing it in my jeans pockets. The crystal did not break, but it started cracking with a pattern of parallel fractures. The fractures did not compromise water resistance (yet), however I decided to replace the crystal because I am living in a hot and humid climate. I would not want to expose the white dial to the local climate and then probably expect discolorations.
Acrylic is important in this context. Setting mineral or Sapphire crystals normally requires Silicone rings. They cannot pre-tensioned like acrylic crystals.

Reto Castellazzi, August 2009

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The fractured crystal and the replacement crystal (355 = 35.5mm)

A close-up of the parallel fractures

Opening the snap-on case back with a A&F case opener knife

Pushing down on the crown release button

Pulling the crown out of the movement and case

Removing the white plastic spacer

Preparing the movement pad for the "Omelette Move": Turn the pad so the black side lies on the movement and then turn over

Now the movement is out of the case and is stored on the movement pad

Always a good idea to store parts that are not needed away. You will spend less time on the floor

Here are the cracks viewed from the inside. This crystal sits in the case with a so called "press fit"

The new crystal has not exactly the same shape: it is edgier. I did not really about the shape, sufficient clearance for all hands is critical

The crystal can be easily pressed out with the thumb. If it sits very tight, use the index and press in the center of the acrylic crystal

Before inserting the new crystal, measuring the new and the old one is a helpful step. Tenth of a milimeter can be corrected with sandpaper

You can try to "pre-tention" the crystal with your index and see whether you can seat it. But in most cases, you will need the case press

Use a large dye on top and a straight walled (the smallest) dye at the bottom

This configuration will allow you to "pre-tension" the crystal. You will bend the center of the crystal upwards, thus reducing its circumference

Press down the case press lever with the left hand and at the same time lift the case. If the crystal cannot be inserted yet, press more

If you are uncomfortable with simultaneously pressing and trying to insert the crystal, you can also use the lock feature (arrow) of the press

The case with the new crystal is placed over the movement on the pad

The crown is reinserted

The watch can be turned over now and the spacer inserted as well

The snap-on case back is put back in place. If you cannot do this by pressing it with your fingers, use the case press instead

The GOLD COIN pocket watch from the Shanghai Stop Watch Factory with it's new crystal