Omega stem shaft pivot hole problem

[AdamC]

I have been working on a lovely old 1924 Omega 23.7 S.T2 gents' wristwatch and have had some limited success in stripping down, servicing and reassembly in that the movement now works and keeps good time. However, on inspecting the parts as I went, I realised that the crown and stem weren't original, explaining why it kept falling out. So I ordered a replacement Omega stem for the exact calibre from Cousins, which arrived today. However, thinking this would be the issue resolved, I was disappointed to find after closer examination of the keyless works, that the pivot shaft end of the stem will not slide home through the pivot shaft hole. I have included photos the best I can to illustrate the problem with some additional photos of the watch for reference.

I have been watchmaking as a hobby for about 8 months and this looks like a pretty advanced problem to solve. If anyone has any ideas how I can get the stem engaged in the pivot hole or any other suggestions, and really appreciate hearing from you.

[Chopin]

I noticed that, sometimes, Cousins offers more than one stem for a movement and I once ordered a stem for a Seiko (one of those mass produced and popular caliber movements) and it was the wrong length...

So maybe the stem isn't really the right one ?

[AdamC]

I noticed that, sometimes, Cousins offers more than one stem for a movement and I once ordered a stem for a Seiko (one of those mass produced and popular caliber movements) and it was the wrong length...
So maybe the stem isn't really the right one ?

Thanks Chopin. I’ve taken your advice and ordered a NOS item on eBay from France. Fingers crossed.


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[Chopin]

That one will most likely be the right one!

[rodabod]

Omega did did change some stems on earlier calibers during their lifespan, but I’m only aware of them changing the threaded diameter. Not sure why they did that. 

If the stem is “correct” then you could get someone to turn down the end section on a lathe. Good luck with the other part. 

[jnash]

I would also check that there is actually not something in the hole blocking it. You never know

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[AdamC]

I would also check that there is actually not something in the hole blocking it. You never know

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That was one of my initial thoughts. However, the movement was stripped down fully and ultrasonically cleaned. When investigating yesterday, I double-checked that the hole was not obstructed under high magnification. Thanks for your interest, appreciated.


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[Tudor]

I was going to say the hole in the main plate may have been damaged and a brass sleeve was made and installed, but sized for the smaller pilot diameter of the replacement stem...

if the NOS one has the same problem, I’d broach the main plate hole enough for the stem.

Note the correct stem may be larger diameter threads and you may need the correct crown, if you haven’t considered that already. 

PS: I always try to get at least two stems in case I cut it short... also, thread it through a die plate before cutting, and then bring it through the plate to perfect the threads after cutting. I like to square the end with a file and slightly relieve the first thread as well. 

[AdamC]

I was going to say the hole in the main plate may have been damaged and a brass sleeve was made and installed, but sized for the smaller pilot diameter of the replacement stem...
if the NOS one has the same problem, I’d broach the main plate hole enough for the stem.
Note the correct stem may be larger diameter threads and you may need the correct crown, if you haven’t considered that already. 
PS: I always try to get at least two stems in case I cut it short... also, thread it through a die plate before cutting, and then bring it through the plate to perfect the threads after cutting. I like to square the end with a file and slightly relieve the first thread as well. 

Thanks for your response. I noticed that the NOS stem I’ve ordered is tap 11 rather than the tap 9 sent from Cousins, and the crown and stem that came with the watch is also tap 11 but the stem was not even long enough to engage the pivot hole, hence the replacement. I generally allow about 2-3mm over on stems that I cut and then finish trimming to size and deburring with a carborundum stone. Great idea about the die plate, thanks.

Though I’m developing my skills and getting a good set of tools together, I don’t have any broaching tools and I’m not sure I’d have the confidence to tackle that yet. Perhaps something I could attempt on a scrap plate first once I have purchased the tools. Hopefully it won’t come to that but really appreciate your thoughts on this.


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[rodabod]

Regarding the broach suggestion, it might work, but I think I'd prefer to drill a hole with parallel walls for a snug fit if you were to go that route (ie. you were positive that the base plate was modified with a smaller hole). Do not use carbide bits for these jobs as they snap too easily. HSS is a far better choice.

[Tudor]

I guess we can never know the level of skill experience and tooling one may have on the other end. 

If the bore looks really sloppy, by all means, re-bore it. I’d even go so far as to say use an endmill, if it can get in without fouling on the opening for the clutch. Jig the plate on a 1-2-3 block, and indicate the large opening in the plate within 0.0005”. Place a Precision pin in the existing hole and indicate that without moving anything to see how close it is to center. If good, drill  if not, mill. 

A drill will want to follow the existing hole; a mill will remove material while staying on centerline. Plus it will make a flat bottom hole...

 brass can be tricky regardless of low hardness- flood with plenty of oil while boring.

thats what I’d do anyway.  

[AdamC]

Very interesting discussion. In my case I’ll take note for potential future repairs as all these tasks requiring more advanced technical expertise is what I aspire achieve in the future but unfortunately I’m not ready yet at my current skill level.


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[AdamC]

I noticed that, sometimes, Cousins offers more than one stem for a movement. Maybe the stem isn't really the right one ?

Chopin, thank you so much for the advice you gave me a few days ago. The replacement stem arrived from France and it fits perfectly. Cousins have even agreed to a refund! I have now been able to complete my restoration of this old gem and it’s now being enjoyed on my wrist


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[Chopin]

No problems Adam. I wish my watch problems were so straightforward. I just ordered the wrong type of crystal from Cousins...

It's good to always try to check the information (dimensions, models, etc.) on all possible websites before ordering so that such things will not happen in the future.

Out of curiosity did you tell them that the part might not be working as intended ?

Truth be told they make stems for movements, not cases, since a movement can fit many types of cases and that's the case of vintage Omegas... I guess the stem might have been for a different case ?

[AdamC]

Out of curiosity did you tell them that the part might not be working as intended ?

Cousins did quibble a little to start with, saying my order matched the part supplied. They said their supplier, Bestfit state that there’s no difference in stems between the Omega 23.7 caliber variations. They requested photographic evidence of the movement showing the caliber reference and a side by side photo of the stems to compare. After sending, they agreed that there was a problem and offered the refund on return of the stem at my expense. Oh well, £2.11 to return it for a £20 refund. I shall definitely check the market in future for my more obscure parts. Thanks again.


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[Nucejoe]

What is wrong with getting the right stem.

Broaching the stem hole in the mainplate is destruction of mainplate, at best.

If it came down to makiing alteration , all alterations are to be done on stem.

1. Cut a piece of sandpapre, shape it like V. Place the V in your tweezers.

2.install the stem in your stem holder.

You can turn manually or turn stem holder with drill.

[Nucejoe]

All  round profiles of the stem can be reduced this way. Even the groove, the square part requires different method.

Regards joe

[AdamC]

Nucejoe, that’s a great common sense approach to this problem and a valuable tip to readers. Thank you.


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[Nucejoe]

2 hours ago, AdamC said:

Nucejoe, that’s a great common sense approach to this problem and a valuable tip to readers. Thank you.


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You are welcome Sir. Lets say the most to loose is a stem.

The stem hole in the mainplate often gets worn due general use, especially if manual wind, so with this method if the diameter of the hole is worn down to non standard size, the watch can receive a fit stem yet.

In some cases the hole is busted open, that where one pretty well is to mess with the mainplate.

Don,t forget to grease the stem pivot upon assembly, lots of side friction there. The gold or chrome plating in the hole is the first to go upon use of the watch anyway.

Regards joe