Seiko 6139-7100 ‘Helmet’ Chronograph

I have been getting a lot of requests lately for Seiko servicing and restoration. Traditionally, it wasn’t something that I did as I stuck to Swiss movements but the more I have been doing the Seiko 6139 the more enjoy them. I think they are going to be something that I start taking in a lot more of. I know that many people collect them but there aren’t many watchmakers who take them on.

Vintage Seiko’s can be had for not much money in today’s insane vintage market. They are an incredibly reliable movement and having been designed in 1969 they still stand up today. They share a lot of similar architecture with the Rolex 4130 movement which was developed several decades later.

Here is the Seiko 6139-7100 ‘Helmet’ chronograph. Such a great design in my opinion.

Here is the movement in the case.

The case with movement removed.

The movement with dial and hands.

The dial and hands removed.

The automatic weight has been removed.

Slowly dismantling the movement.

The dial side disassembled.

The barrel with the cover removed. Note the dirty mainspring.

With the movement disassembled, it is ready for the cleaning machine. Once cleaned it is ready for assembly.

Once cleaned I adjust the balance spring to make sure it is flat and centered.

I then assemble the base movement, and then the chronograph. The one downside of this movement is that you can’t check the timekeeping and performance until the whole movement is pretty much assembled.

I then install the rest of the movement.

Now I install the automatic module.

I can then install the dial side of the movement.

I then assemble all the dial side which includes the calendar work.

Seiko 6139-7100 'Bullhead'

Once the dial and hands are installed the movement is put in the case. It loads through the back but we can’t fit the crystal yet.

Seiko 6139-7100 'Bullhead'

First, the bezel needs to be put in place, then the securing ring and gasket.

Seiko 6139-7100 'Bullhead'

I then loosely sit the crystal on top and place the white nylon gasket around the crystal.

Seiko 6139-7100 'Bullhead'

I can then fit the bezel over the crystal assembly and it secures the whole thing together. Quite a cool design.

Seiko 6139-7100 'Bullhead'

The overhaul is now complete and ready for testing.

Seiko 6139-7100 'Bullhead'

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