Seiko 'Gen 2' RAF Military watch 7T27B - 7A20 requires new movement

[AndyGSi]

2 hours ago, tIB said:

Good spot! I dug mine out and, if it's even the correct one, it definitely isn't the 7t27 version. 

Just realised that the YM57 (351584) is 0.9mm and 7T27 (351580) is 0.8mm so probably best you got away with the old stem and crown. 

[Matt77]

22 hours ago, AndyGSi said:

So there's no signs of even a twitch from the seconds hand?

Have you tried the Chronograph?

Interesting that they appear to have the 7T27 stem.

Sorry for my naivety but what is the ‘Chronograph’ and what do I need to do to it. There is no twitching or movement in any of the dials when the new battery is seated. 

[Matt77]

I have tried pressing all the buttons to try for any movement but to no avail. When I pull the crown I am able to change the minute and hour hand by rotation which seem fee. When doing this however, the 24hr dial (small dial on the left at 9 o’clock) seems to also rotate at hour intervals in relation to the actual hour hand. Should it do this?

[tomh207]

4 minutes ago, Matt77 said:

I have tried pressing all the buttons to try for any movement but to no avail. When I pull the crown I am able to change the minute and hour hand by rotation which seem fee. When doing this however, the 24hr dial (small dial on the left at 9 o’clock) seems to also rotate at hour intervals in relation to the actual hour hand. Should it do this?

I would think so, often quartz chronograph will have a 24 hour subdial linked to the main 12 hour time. I was working on a Miyota one like that yesterday funnily enough.

 

Tom

[AndyGSi]

Here's the instructions.

[tIB]

2 hours ago, AndyGSi said:

Here's the instructions.

Curious about the hands on these - were there two types? I see them all the time with silver hands but the hands that appear in the picture seem to be butand the silver/white... I've never actually seen those on one. We're there two hand types or did they change their mind? Or maybe the civilian one has different hands?

 

Edit: answered my own question: there was a non-lume navy version with the silver/white hands which is pictured there - note the lack of the P showing the lume type. Top geeking!

Edited February 10 by tIB

[hofnerpres]

I did this swop a few years ago using a YM57. Used the original stem and no other issues. A long search found one in Sri Lanka for £40. The eBay ones are in the UK and the £100 price is a splendid example of supply and demand. It was a budget plastic based unit and they will die electronically at some point - 25 years is a result - How old is that one? An issued version is valuable and probably worth the new engine.

[Matt77]

On 2/9/2025 at 2:17 PM, AndyGSi said:

So there's no signs of even a twitch from the seconds hand?

Have you tried the Chronograph?

Interesting that they appear to have the 7T27 stem.

No, there has been no twitching or anything from the watch. I’ve just received a YM57 movement so I’ll ask my local watch repairer if he is willing to have a go. I’ll let you know how it goes. If asked should I advise him on anything specific? I know the obvious of date dial but shall he fit the new stem or keep the old one? 

[AndyGSi]

1 hour ago, Matt77 said:

No, there has been no twitching or anything from the watch. I’ve just received a YM57 movement so I’ll ask my local watch repairer if he is willing to have a go. I’ll let you know how it goes. If asked should I advise him on anything specific? I know the obvious of date dial but shall he fit the new stem or keep the old one? 

I think he'll have to fit the old one as they're different tap sizes so the old crown won't
fit on the new stem (that's based on it being a YM57 stem with the new movement)

[Matt77]

1 hour ago, AndyGSi said:

I think he'll have to fit the old one as they're different tap sizes so the old crown won't
fit on the new stem (that's based on it being a YM57 stem with the new movement)

Sorry, do you mean fit the ‘new’ stem to the YM57 ‘new’ movement?

[AndyGSi]

1 hour ago, Matt77 said:

Sorry, do you mean fit the ‘new’ stem to the YM57 ‘new’ movement?

No I think he'll have to use the old 7T27 stem with crown on the new YM57 movement.

Can you measure the diameter of original 7T27 stem and compare it to the stem that came with the YM57