How to Install the Domed Sapphire Crystal on SEIKO 6309-7040

One of my friend sent me a SEIKO 6309-7040 and asked me to replace the original crystal with a new domed sapphire crystal with blue AR (anti-reflection) coating on the inside. The new crystal together with the new crystal gasket arrived few days ago. So I spent my quiet Saturday morning to do crystal replacement. I took some photographs during the process and think it would be nice to share it here.

I started by completely stripping down the watch. Details of removing bezel and crystal retainer ring can be read in the links on the right side panels of this blog. I compiled them from various sources under the category "SEIKO Diver Technical Resources". Below is how it looks after complete dismantling.

▲ Dismantled SEIKO 6309-7040.

I found out that the naked cushion case is full of dirt. It is no surprise for a 31 year-old dive watch. So I decided to clean the case first before I proceed with the new crystal. I used my old Victorinox Swiss Army multi-tools to do most of the work. I purchased this Swiss Army almost 10 years ago and it has been serving me very well. Notice the dirt on the edge of the blade. Be careful not to scratch the internal stepped wall around the crystal gasket. If it is scratched, the case will most likely lose its watertight properties.

▲ Cleaning the case.

After lightly scratching out dirt with Swiss Army blade, I used WD-40 to clean the external and internal surface of the case. The same process was applied to the crystal retainer ring. Be careful when you dismantle or clean the retainer ring because it is one of the most fragile parts of the 6309-704x diver. Also be careful not to cut your fingers once the retainer ring comes of.

▲ Cleaned case and crystal retainer ring.

Before we go on with the assembly, here is a comparison shot of the old original crystal (left) and the new domed sapphire crystal. Looking at the clarity of the sapphire makes me smile and forget all the waiting... and the price I must pay for it.

▲ Comparison of original crystal (left) and new domed sapphire crystal.

Next, put all the parts back into the case. Don't forget to apply some grease on the new crystal gasket. I use the original SEIKO Silicon Grease. Make sure the crystal and gasket sits properly in the center and lies flat. Take your time and do the best in this phase because it is very important.

▲ Assembling the parts.

Ensure all parts sits properly inside the case and then bring the assembly under the press. Again, make sure the assembly sits properly on the press. Use a cone-type press head with the same outer diameter as the crystal retainer ring.

▲ Using press to fit the crystal retainer ring.

After fitting the crystal retainer ring, check again to make sure the crystal is centered and lying flat. The best way to do this is by fitting the bezel and running your fingertip along the gap between crystal and bezel insert. If everything is OK, clean the inside of the crystal and case with dust remover and dust blower. Now we can slip the movement back into the case and close the caseback. It is almost finish now.

▲ Fully assembled 6309-7040.

Since the domed sapphire gives a very classic look, put on a fitting flat vent Z22 rubber or, if possible, an original GL831. Now sit back, have a cup of coffee, and enjoy the beauty of the domed sapphire crystal. :-)