Omega 1141 with Dubois Depraz 2020 module. Chrono starts and stops after cleaning?

[noirrac1j]

Hello and good day to all,

I’ve had some difficulty with my Omega Speedmaster reduced overhaul, Cal 1141 with the Dubois Depraz 2020 module. I overhauled the ETA 2890-a2 last year but didn’t do the chrono at that time. Recently the pushers were sticky, and I decided to overhaul the module.

*disclosure” I am not new to watch hobby, but still don’t have a sonicator. I used lighter fluid to clean the Dubois module and followed Mark Lovic’s excellent reassembly procedures—No problem with reassembly. The watch runs fine without the chrono engaged. The chrono starts but stops after about 15 seconds of running. I disassembled again and this time cleaned with Kleen strip low-odor paint thinner. I was extra careful during rebuilding, but still managed to lose the second pinion friction spring, (part 471 60.131 in the Omega 1141 technical sheet). That’s right I lost the spring. I looked for it, but I have carpet and so I gave up…moving right along.

I know it’s impossible to get the DD module parts unless you buy a whole module from somewhere, but I discovered that needle threader is a good gauge and thickness to make a spring, so that’s what I did. After cutting and bending it seems to fit quite well. I continued the reassembly, and the watch runs fine, but once again when I engaged the chrono, it starts but stops after about 15 seconds in the same way it did before. I don’t think the homemade spring is the problem. What do you think it is? I suspect I need to clean the movement better as I don’t think the DD module is very forgiving of any drag once the power is transferred into the DD module. I welcome any feedback.

[eccentric59]

Does the watch continue to run when the chrono stops? And does it always stop in the exact same place?

Edited January 29, 2024 by eccentric59

[noirrac1j]

Just now, eccentric59 said:

Does the watch continue to run when the chrono stops? And does it always stop in the exact same place?

Thanks for the reply. The chrono stops and the watch stops, and YES it's in the same place each time. The watch restarts as soon as I stop the chrono.

J

[eccentric59]

If it's stopping at the same point both before and after the rebuild then check for dirt or bent teeth on the wheels with the heart cams. These would be the only ones always in the same orientation. My other thought was that the return hammer wasn't pulling back far enough and touching one of the heart cams.

[JohnR725]

1 hour ago, noirrac1j said:

Mark Lovic’s excellent reassembly procedures—No problem with reassembly.

you didn't mention having technical information? So I've attached some PDFs.  Then I don't know how similar they are but cousins were I got a couple of tech sheets from the suggestion that the 1140 is equal to the 3220 and you can actually see that the filename down below. That means you get way more technical data if you include that including one on the module itself.

Oh and notice number 19 below a reference to why the watch might stop.

 

 

 

No 10 Calibres 1140-1141_Assembling screw E_2004_7113.pdf No 19 Free cannon pinion_Calibre 1138-1140-1141 and 3220 E_2.pdf 226_omega1140.pdf 341_omega1140=3220.pdf 4436_Omega 3220 dubois-depraz-module cousins.pdf

[noirrac1j]

Thank you for the comprehensive technical info @JohnR725. I did not know about the new copper beryllium cannon pinion for the 1140. There's  much info here to improve my level of precision. More to come!

1 hour ago, eccentric59 said:

If it's stopping at the same point both before and after the rebuild then check for dirt or bent teeth on the wheels with the heart cams. These would be the only ones always in the same orientation. My other thought was that the return hammer wasn't pulling back far enough and touching one of the heart cams.

Excellent point @eccentric59. I did check the the engagement action of the yokes and levers (as well as all pivots of course)before securing the cover plate on, but it is definitely worth looking specifically at the teeth of the heart cams. Will also make sure the return hammer isn't hanging somewhere. Thank you.

Edited January 29, 2024 by noirrac1j

[noirrac1j]

UPDATE!

I took the DD 2020 apart and this time I got a small stainless basket and put all the parts in very warm water with a drop of dawn dish detergent. I rinsed everything off with water, pegged all the jewel holes in the module, and did a final rinse with 99% Isopropyl alcohol. Reassembled using  the ETA 2892 A2 video by @Mark and took extra care with the Chronograph driving wheel friction spring-. I painstakingly adjusted the tension on my home-made  second pinion friction spring using the specification sheet that @JohnR725sent me as a guide. I also checked the hour/minute heart cam  wheels--thanks for the tip @eccentric59to my surprise I noticed a slight rust on the edges, nothing crazy, but wasn't expecting that. I cleaned and oiled them, and reassembled everything. The chronograph engages, goes around continuously, and resets fine. The watch is keeping good time (always did) and is back on my wrist! Thank you WRT!

 

J

Edited January 30, 2024 by noirrac1j