Omega Bumper Automatic 344 Movement Walkthrough

[Geo]

Here is an insight into the rebuilding of an Omega Seamaster bumper automatic 344 calibre movement from 1952.

I am not going to give a step by step dismantling procedure. Apart from the auto-wind mechanism, the dismantling is fairly standard. I will however give a couple of tips on how to safely remove the auto-wind mechanism, before showing assembly of the cleaned movement.

The Omega bumper mechanism has three clicks A, B & C.

The first A is mounted on the ratchet lever and transmits force to the ratchet gear during winding. It also allows the ratchet gear it to index in one direction only. The driving force is produced by the oscillating weight and transmits force to the lever via a curved rack on the end of the lever.

The second B is mounted on the Train Bridge and ensures the ratchet gear is held stationary when the ratchet lever moves anti-clockwise to the starting position of its clockwise winding stroke. Click B is holding the force of the mainspring during normal use.

The third C is the barrel ratchet click. This is only really required to hold mainspring pressure when the auto mechanism is removed during disassembly.

Disassembly Procedure

When dismantling the watch movement the mainspring pressure must first be removed from the auto mechanism. Once this is done the auto bridge can be safely removed. To do this release both click A and click B to remove all mainspring force from the auto mechanism. This is done by pulling the clicks clear of engagement in the direction of the red arrows. The mainspring pressure will now be held by click C.

Once this has been done the auto-wind bridge can safely be removed. This reveals the lever and ratchet assembly that can now be lifted from the movement.

At this stage the mainspring pressure can now be completely released in the normal way. Use a screwdriver to control the rate of barrel rotation while holding click C clear of the ratchet wheel. Dismantling from here on is much the same as any other manual wind watch.

Reassembly

Attach the Bumper Spring Retaining Plate (at bottom of picture).

Fit barrel and Barrel Bridge.

Fit the Gear Train and Bridge. Blow the perifery of the escape wheel toensure free running of gear train.

Fit the Crown Wheel & Ratchet Wheel.

Fit the Escapement lever and Bridge

Fit Bumper Springs and Retaining Bridge.

Fit Keyless Work.

Fit Auto-wind Mechanism. Ensure that the automatic lever is engaged to allow full travel of the rotor. The rotor should bounce of each spring at the end of its travel. If it doesn't, damage will result.

Finally fit Auto-wind Bridge and Balance Assembly

That’s all folks!

PS. The new LED light from Cousins has greatly improved my pictures. Now shooing at handheld at 200ASA instead of 800ASA.

[WillFly]

Excellent stuff - very impressive!

[bobm12]

Amazing pictures Geo and excellent walkthrough!

 

Cheers,

 

Bob

[mwilkes]

Excellent, excellent post. Thanks. Jealous of your photos - lovely & consistent 

[Mark]

Great stuff Geo.

 

What a coincidence - I was just working on a bumper!

 

[Maurice]

Great pics Geo and Mark can now see how his goes back together!! :D

[Geo]

What a coincidence - I was just working on a bumper!

It must be the year of the bumper. I have an Omega 351 in bits waiting for a sweep second hand pinion coming from Australia, and tomorrow I'm about to service an Alpina President with a 584c bumper movement I recently acquired.

[Geo]

I received the part from Austalia today and now have the 351 up and running. :)

I had an interesting thing happen though. The 351 still had an original style spring with separate bridle, so it was duly cleaned lubed and reassembled, using braking grease between the bridle and barrel wall, and a thin coat of normal grease on the spring. When I wound it by hand, it did not keep winding as per normal automatic, but reached a pint where it would wind no more. Realising there was a problem, I removed the barrel from the movement and took out the spring and bridle, cleaned it in lighter fuel and re-lubed spring and wall of the barrel with normal grease. Once reassembled, everything is working well.

[Lawson]

What a gorgeous movement, and in the safe hands of skilled man.

 

Top write-up with lots of excellent pics too.

Thanks for sharing it Geo

[craynerd]

Hi, sorry for digging up an old thread but I joined this forum just to say thanks.

I've been practicing on watches for years. I actually moved into clock making and haven't focuses as much as I should but my lovely bumper 344 has been sat dead in the draw for a few years. With a young family, I couldn't afford to get it fixed based on the prices I was quoted.

I made a video to log what I did in case I fell into any trouble getting it back together... Thanks fully I fixed it!!

I'm all for constructive criticism, so let me know if you can see anything I've done wrong.

[Geo]

Welcome to the forum Craynerd.

I'm glad that the forum has helped you on the way to getting your bumper Seamaster operational again. I do hope you completely stripped it and gave it a good clean before assembly and lubrication, if not the remnants of old oil may give you problems in the not too distant future.

[craynerd]

Hi Geo

I will be totally honest and tell you that I was nervous enough just dismantling it.

I am however, now very confident that I could dismantle again. What I do need to do now, is learn how to clean and oil it. I expect that you are correct and without a clean I could run into issues.

Thanks again Geo for your original post.

[bobm12]

And welcome from me too!

[rodabod]

 

I had an interesting thing happen though. The 351 still had an original style spring with separate bridle, so it was duly cleaned lubed and reassembled, using braking grease between the bridle and barrel wall, and a thin coat of normal grease on the spring. When I wound it by hand, it did not keep winding as per normal automatic, but reached a pint where it would wind no more. Realising there was a problem, I removed the barrel from the movement and took out the spring and bridle, cleaned it in lighter fuel and re-lubed spring and wall of the barrel with normal grease. Once reassembled, everything is working well.

Hi,

I'm working on a cal 30.10 at the moment which also has the original mainspring with separate slipping bridle. However, the conventional mainspring which sits inside looks fairly "set".

The replacement at Cousins is a conventional automatic mainspring, ie. one piece including bridle. I'm not sure if I'd be best leaving the original, or going for the replacement option which is not as per original, bit at least not set, and probably unbreakable.

Edited June 26, 2017 by rodabod

[rodabod]

Here's a photo of the spring:

[Geo]

If the replacement from Cousins is designed for this movement, I think I would change it.  Keep the old spring and bridle just in case there is an issue.

[rodabod]

The Cousins replacement spring works well, but dial-up, I get over 310 degrees amplitude on full wind and it does occasionally start to bank if left in this position. I think it may be ok in use though, as it will unlikely be left perfectly dial-up and fully wound like that. I shall check this in practice by wearing it for a few days.