Seiko 7040 crown gasket replacement.

lexacat · September 6, 2023

Hi all, have bought an old 6309-7040 for restoration, and will be replacing the crown gasket. It appears as though the gasket is already missing, but I'm not sure. I've dug around with the dental tools to see if I can fish anything out, but can't seem to find anything in there.

That's actually a bit irritating, as I was going to use the location of the old gasket to figure out how/where to install the new one.

Is there meant to be a channel inside the crown, or does the gasket just sit around the pole where the stem screws in?

Any advice would be much appreciated!

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lexacat · September 23, 2023

For anyone searching for the same answer in the future, I figured it out. The crown gasket is located in a groove just below the threads. The old one was still in my crown, but was rock hard and difficult to see.

I've highlighted the groove in this image.
image.png.7d9436db6ab4e4e9821786a75164d2d5.png

And here's the old gasket next to the new replacement. The part number for the gasket is 0k0240b0a but my local supplier had it as OkO24ObOa

lexacat · September 25, 2023

If you've never done it before and can't find any good resources, replacing this gasket is a real pain in the arse. I tried a lot of different methods and spent probably a good 45 minutes on this, but the gasket would just fold up into the bottom of the crown and (due to it being covered in gasket grease) would just spin around when I tried to coax it back up.

To prevent the gasket from bunching up in the bottom, I tried to install it with the full crown stem installed, but there wasn't enough room to get the gasket past the spring on the lower half. Then I tried using just the lower half of the stem with the spring removed.

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This allowed enough room to slide the gasket past, and to use a thin piece of pegwood to get it down past the thread. The wide end of the stem was enough to prevent the gasket from bunching up at the bottom, and was actually useful by unscrewing the stem and using the end to "pull up" any parts of the gasket that got too low. Within a couple of seconds I had it in place.