Chronostop amateur service

Tinkering with an 865 Chronostop which I've owned for best part of a year and never worn as it is like a hailstorm on the timegrapher. These are half an 861 so parts are not cheap and am not willing to risk damaging it.

De-cased, hands and dial off and this is what the dial side looks like:

The 'ring' about half way out on the lower right is just oil and there is a neat spray of oil across the Incabloc. Why does no-one tell you that this is the correct way to oil a movement. Spread it about and hope some if it goes where it's needed. Have been out to my garage and picked up one of these:

Now I'm sorted (And have plenty of GTX available with my cars....)

The bridge was very oily/dirty too especially under the crown wheel on the left.


After cleaning, came up nicely but they don't use a crown wheel seat (read washer between the crown wheel and the bridge) on these so, the wear happens directly to the bridge. Some wear around the barrel area which is not good news either.


Plate has cleaned up nicely.

Cheers, Chris

Thought I’d modify this thread as the Chronostop is the first Omega chronograph I’ve worked on. It is just about the simplest as well with just a central second hand register (no minute or hour totalisers). I’m an amateur and am working through some simple chronograph services to build up to a 3 register caliber. It was oily and dirty but cleaned up nicely so here are some pictures:

Here is the gear train for an 861/865/1861 looking from the back of the watch just placed in position. You can see the long staff on the fourth wheel which will come through the bridge to power the chronograph part.



Here with bridges and cocks mounted and the fourth wheel staff can be seen on this side of the big bridge. This is just a basic watch movement, there is no chronograph part here and it is very similar to many other mechanical watches. It’s quite a clean movement but there is some marking of the big bridge where the chronograph parts have rubbed and some damage to the screw heads. I thought this was better preserved but looking back to when I bought this watch, my memory has been deceiving me. I’ve also realised it has taken me nine months to get around to looking at it….


With the balance mounted and having run for a day, the movement looks fine but I have a large beat error so need to fix that before assembling anything else. This is at 24H so, amplitude is pretty good.


Here’s the complete balance assembly which needs adjustment to solve the beat error.

In very simple terms, what you’re basically trying to do here is align the ruby pin of the balance wheel with an imaginary line between the balance jewel and the pallet fork jewel. The error can be either way and the timegrapher doesn’t give an indication of which way it needs to be rotated. Luckily, having been well advised (thanks, @Archer) I had mounted the balance in the plate before assembling anything to review the hairspring concentricity/flatness etc and at that point, it was easy to see that the jewel appeared to rest a few degrees towards the middle of the movement so, the balance needed to rotate anti-clockwise in this view. This is easy when the top end of the spring (mounted on the balance cock) has an adjustable stud carrier as you can move it around with the movement running and mounted in the timegrapher.

But this is a fixed carrier and this means running in the timegrapher, removing the balance assembly, adjusting, replacing the balance and then iterating until you get the value you want. The top end of the spring is fixed so the balance needs rotating versus the spring at the point where the lower end of the spring is attached to the balance - this is the collet. This is not the easiest thing to move the right amount and one slip here and the hairspring is ruined (new balance at 600 GBP from Cousins!) so am nervous. A couple of iterations and the beat error is down to spec in this orientation but 0.1 or 0.2 above in other orientations. Will leave it to run like that as it might settle a little more (it does).


Here are the chronograph parts in the orientation they will mount on the movement.


A few more photos showing this lot back together for later.

Cheers, Chris

Thanks Al. I decided that the stud carrier was fixed but just opened the watch and it is clearly adjustable😟 I learnt a bit more in the classic style, as you said, but would have been happier on a much cheaper balance....

Omega mount the driving wheel before the clutch. I suppose to stop you accidentally pressing the driving wheel on and damaging the wheels if they are not correctly meshed. I used my Horia and pressed it a little high, then mounted the clutch before final height adjustment. The Horia really works well for me in these situations - good advice previously, thanks.

And yes, I stripped it and cleaned the pivots and bushes. As I'm new to chronographs, I take these quick pics with the phone as I strip parts on the dirty mat. Mainly in case I get the screws mixed up but I've realised this doesn't happen as these calibres are correctly designed and the screws go back in obvious places.

These really are a nice movement and I'm very pleased with the result. So much so that I've just ordered a 22 mm mesh to go with the watch. Bit of a pain lining up the tachymetre ring when pressing on the new crystal but the watch looks very smart with it on.

Cheers, Chris

You're catching me up Chris. I must get back onto the 1040 this weekend as I have got my chrono goal as an incoming.

Great work. 👍

Thanks for the encouragement Guys. First time for me following a tech guide by the book and it's good and bad. The bad part is that you can think less if you want. Part of this hobby that appeals to me is opening up a different movement and working out how each part is acting on the others. Al's right by the way, I am very cautious as have little experience and don't want to damage things.

I'm pleased to hear that Al puts the keyless works in after the barrel and crown wheel. I've generally been working that way but have never seen it recommended so have not been admitting it here.... I couldn't see any disadvantages. I will view these tech guides as a guide only from now on.. Stem first, hmmm.😉

I have just cleaned my wife's Slava 1601 (mid seventies Sekonda) and looking on Cousins for a mainspring noticed the cost of a balance complete. Not £600, not £60 but £6 plus VAT! How many of those do you need to make to get the cost down to the price of a couple of beers?

Of interest to some, here are a couple more pics with those chrono parts loosely mounted to show how this simple chrono works. Here with the main parts loosely mounted in chronograph off position. The driving wheel on the lower left will be pressed on to the fourth wheel staff (with the Horia) and permanently drives the clutch wheel that is on the curved plate. The central second gear has a ‘heart’ that is held by the hammer (the large kinked plate). Wherever the hammer strikes this heart, it will always end up in this position - this is how it resets the second hand to zero.


Here the clutch wheel plate has rotated about its lower end and is now in contact with the gear that drives the second hand so, it is in chronograph running position (I moved the hammer out of the way for clarity).

These really are great movements and this one easily exceeded it's 48 hour power reserve, making better than 53 and runs within a third of its rate variation average over 24 hours.

Cheers, Chris

Flipping heck! Leaving the setting parts on the plate is just laziness but cleaning the balance like that.. I can't believe it wouldn't have a damaged hairspring especially as there is another piece in the same basket. Maybe fixing hairsprings is his hobby😁

Mistakes happen I suppose. I have a 354 or 501 which ran terribly. The centre seconds friction spring had been bent to fit on the wrong side of the gear so it was both pushing in the wrong direction and catching the driving gear as that rotated. Well, I've made some schoolboy errors myself (see "fixed" stud above!) but am feeling better about those now😀

Cheers, Chris

I've not seen a blue sunburst on these. Sounds interesting. Here it is on it's original deployant and black strap but I think the dial doesn't show off well. Tried it on a 20 mm mesh and it lifts the whole watch so, have ordered one in 22mm...
https://omegaforums.net/threads/wruw-today.567/page-1238#post-279658

Anyway, it's running really well and very pleased so have opened up a different watch and will post that one in another thread.

I see you're looking for the expansion ring. I don't have one but can take mine off and make an Engineering drawing for someone to make one, if that's of help.

Cheers, Chris