Omega 18SPB Pocket Watch

[Endeavor]

Hello All;

I received an Omega 18SPB gold-plated pocket watch, allegedly a non-runner. It was a heirloom item and had to be passed on to the younger generation.

Luckily it wasn't a total "non-runner"; after a full wound it ran for 7 hrs. The small seconds-hand was missing and there were visible signs of dirt inside the case & movement. According to bidfun-db ( http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&&2ustu&1095006620), it is a "Gents Omega Hunter", from the 1924 era and the 18SPB movement has 15-jewels, a bi-metallic screw balance with a Breguet hairspring.

Here are some pictures of the watch in the condition I received it;

Front cover and dial;

Notice the dirt on dial and on the inside of the bottom edge glass ...

Rear covers and movement;

The 18SPB movement seems pretty straight forwards and judging the case marks / movement-screws-heads; not very often "messed" with. The case numbers did match-up and the gold-plating wear on the case & the chain seem to match up as well. Also the tapered chain seems the original & authentic one; a great bonus !

Before removing the winding stem, remove the residual power in the main-spring; in this case there wasn't any residual power left (?). To pull the winding stem, the set lever screw has to be undone by 1-1/2 to 2 turns;

After removing the winding stem, there are two case-screws which have to be taken out. It's a "front loader", the movement is placed inside the casing  through the front. Flipped the case over and carefully remove the glass & bezel ...... both the glass and bezel are of very thin material ......

Carefully remove the movement. There is a thin ring around the movement, between the bottom of the movement and the watch case; not shown in the picture. The hands are a straight pull up. The dial is attached to the movement by three (3x) dial-screws, each with a roughly 120 degrees spacing in between;

Stripping the keyless works, minute and hour wheel revealed some excessive lubrication;

Note; the winding pinion didn't come out at this stage. Pulled the canon-pinion but left both keyless-springs (left and right) in place. Keep an close eye on the minute pinion, which protrude above the main-plate !!

Flipped the movement over and removed the balance.

Thereafter removed the pallet-bridge, the pallet and the wheel bridge. Note that the crown wheel screw is left-handed, but hasn't got the triple markings some left-hand screws have; 

Removed ratchet wheel and the crown wheel, also note there is an additional washer underneath the crown wheel;

Removed the wheel train, barrel-bridge, spring-barrel, winding pinion and the set lever screw.

All items collected in a tray;

Opened up the main-spring barrel;

Took the old spring out and I have to say that the old spring wasn't eager to get its freedom back !

Before I started on the watch, I asked under the "Watch repairs Help & Advice" the forum for some help. A very educative discussion followed;

Luckily I received some excellent help from JohnR725 and StuartBaker104. Both noticed that a wrong main-spring was fitted. The spring fitted had a "normal-bridle", whereas the barrel needed a "DBH" special bridle. This meant that the old spring was not a good reference for a new spring

With the help of both forum members above, and the "Spring calculator" on David Boettchers website; http://www.vintagewatchstraps.com/mainsprings.php, we were able to guesstimate which spring was needed. The internal barrel diameter was 14.4mm. Feeding this number in the "Reverse engineering calculator" yielded the follow answer:  Spring thickness = 0.177, length = 450, turns = 6.4, area = 55%. From measuring the barrel, the maximum allowable height of the spring was 1.9mm.

Scrolling through CousinsUK list for 1.9mm high DBH springs, the closed match was spring GR5617DBH which dimensions were 1.9x0.18x440x14.5 (Height x thickness x length x washer ID). That was the spring which was ordered, pictured below;

Even though the spring fitted from the washer inside the barrel, I couldn't engage the hook, so the spring had to be unwound. Note the difference in the amount of "un-cloiling" between the old tired spring and the eager spring. No wonder there was no residual power in the old spring left after 7 hrs running !

Fitted the new spring and it was a perfect fit

While this all with the spring was going on, StuartBaker104 made me aware of an eBay auction for a lot of small fusee seconds-hands. The auction ended late in the evening and I throw in a bid, never thought to win it. Lo and behold, I did win !! Whether they fitted had to be seen, but judging the sellers pictures, they had to be close. Thanks again for the tip Stuart !

 

While the hands were on their way, I thoroughly cleaned and de-magnatized the movement parts.

To be continued in part II since I nearly lost all my work above; about 2 hrs of work !!

This program doesn't allow intermediate saving, which isn't so good ! @Mark: can that be changed ?

 

 

 

 

Edited December 19, 2017 by Endeavor

[Endeavor]

Part II: Assembly and the end result.

After cleaning all the jewels, I wasn't able to undo the balance cap-stones. Lubrication was therefor difficult and not optimal.

Before placing the barrel bridge,  next to the spring barrel, remember to lubricate & place the winding-pinion and the set lever screw;

Assembling is the reverse of disassembling;

Barrel-bridge, click and crown-wheel lubricated & installed ;

The wheel train;

Train bridge, pallet fork & bridge

Keyless works and winding stem;

Installed the balance wheel and ........... a healthy "tick" !!

Did some initial checks on the time-grapher and all looked good enough to go ahead and to install the dial and hands. The tubing of the one of the eBay small seconds hand had to be squeezed / pinched with a pin-vice. Luckily I managed to get a nice fit and the hand doesn't look "off"  

Cleaned the case. It was decided to leave the gold-plating wear of the case and chain as is; the watch was allowed to show its age & previous usage in all its glory

To conclude; here are some of the time-graphs. I later adjusted the daily-rate a bit. As for the Beat Error; I decided to leave it as is, too little and not worth the risk. Besides, the watch won't be worn daily, but more to be worn on special occasions. The bench-test showed that the watch ran indeed as accurate as the graphs suggest .......

Dial Down;

Dial Up;

For some unknown reasons the CU & CD parameters weren't copied to the USB stick, but the amplitude & BE were about the same as dial up & dial down; around 300+ degrees and 2m/s.

Crown Up;

Crown Down;

to me; not too scabby for a nearly 100 years old movement !

I hope the next owner will enjoy & proudly wear this nice watch. For sure, it was for me a privilege to work on it. Thank you Solveig for giving me this opportunity !

Hope that you will enjoy this walk through and that it is of some use to somebody, someday;

Roland.

 

 

Edited December 19, 2017 by Endeavor

[Chopin]

Very nice. I always enjoy such walkthroughs. Do you have a setup for photographing your work or did you just snap a pic every stage of the process ?

Also, is that warm light that you use ? Ever used cold light ? I wonder if it's better as I just ordered a LED lamp that has both modes apparently and I'm curious to see what it'll feel like.

[Endeavor]

@Chopin Glad you like the walk through. No, I don't have a setup for taking the pictures. I use a tripod which I "drag-in" at every stage. The light is just a fluorescent lamp and to be honest, I don't change the white-balance on the camera either ... as long as the pictures are clear, I'm happy ........ it is what it is. This was different at a certain stage and there is a thread on this forum about photography; https://www.watchrepairtalk.com/topic/3985-horology-photography-thread/

But we now digress from the topic in this thread .......

 

[dadistic]

Great walk through! Thanks so much. I sympathize with the lack of ability to save a post as a draft, makes doing these elaborate posts quite a chore.

Hope you're up for doing more,  they are so helpful.