Bridge straightening and bushing in a 1950s Omega cal 351.

I received this Omega bumper, running poorly and with low amplitude. It has an issue with the hand lume which I deal with here but it is a nice watch.

Omega Seamaster calibre 351

Possibly in an attempt to compensate for the ovalled bearing hole in the bridge, the centre bridge has been deformed at some point in the past and is no longer flat, leading to virtually no end shake of the centre wheel.

Watchmaker showing damaged bridge on Omega calibre 351 watch

This gets straightened.

Watchmaker showing repaired bridge on Omega calibre 351 watch

Additionally, the centre wheel bearing in the bridge was very worn (as was the wheel pivot) and as these don’t have a bush or jewel as in a more modern calibre, I’m showing one way to re-bush a bridge and fit a new wheel. The difficult part here is to ensure that the new hole and bush are exactly aligned so that the wheel is not canted over.

To do that, it’s necessary to collect the centre of the wheel and then bush to the correct location and one way to do this is to use my lathe in non-running mode. This face plate attachment on the lathe with its associated mandrel enables the plate to be mounted and any existing hole collected by the mandrel so that it’s on the lathe centreline. You can see the mandrel in the centre hole of the plate.

Watchmaker showing bridge bushing on Omega calibre 351 watch

Next, the damaged bridge is fitted to the plate and the lathe tailstock with centering attachment brought up to check that the assembly is centered.

Watchmaker showing bridge bushing on Omega calibre 351 watch

As the centreline of the lathe is now aligned with the wheel centreline, I use a set of Bergeon reamers to open out the hole. A typical reamer is shown at the lower left and just above it the reamer tool. Above that is the same tool turned down so that it is a sliding fit in the Boley lathe tailstock shown.

Watchmaker showing bridge bushing on Omega calibre 351 watch

The reamers are fitted to the tool and the hole can then be opened out to the diameter required in stages with the mandrel withdrawn and the lathe locked.

Watchmaker showing bridge bushing on Omega calibre 351 watch

The finished hole in the bridge.

Watchmaker showing bridge bushing on Omega calibre 351 watch

The bridge is removed and a Horia tool is used to press in the new bush which has already been reduced in thickness to that required.

Watchmaker showing bridge bushing on Omega calibre 351 watch

The bush is final reamed to the correct size for the wheel in a similar way to the bridge and the assembly checked.

Watchmaker showing bridge bushing on Omega calibre 351 watch

The third wheel and barrel are fitted to check the depthing (gear engagement) and after building the movement and adjusting, it is running with good amplitude and smoothly. After a few days running, it would be expected to pick up another 15-20 degrees in amplitude so, a good result for a sixty year old watch.

 Watchmaker showing bridge bushing on Omega calibre 351 watch