I started working on a Hamilton 992b. The watch had very poor balance motion and ran very slow. It would slow down to a stop dial up. When disassembled I found a dial washer bent in half under the balance cock. Obviously, it was put their to prevent stopping the motion of the balance staff.

I gave it a good cleaning and oiling and found the balance jewels to be very dirty. Once re-assembled without the extra dial washer, the balance had no endshake and would not give any motion with the balance cock screw tightened.

My first thought was to check the balance cock itself to see if it was bent. It looks fine. The jewels also look good and the cap jewels appear fine. There is not interference with the hairsping or balance wheel.

Using process of elimination, I could conclude that the balance is too long or the shoulders on one or both pivots are too wide. Also the pivots could be too short. Checking out the balance standing up in the jewel hole, It appears fine. The pivots measure a perfect .11mm.

Lastly, I would shorten the top pivot, considering that the roller jewel seems to be setting perfectly in relation to the pallet fork.
My concern about doing this is that the total lenght of the balance is 5.67mm. The length should be 5.7mm.

Any advice would be great.
Thanks

It could have been rejewelled with improper jewels or the jewels might not be fully seated. The 992B uses press-in jewels so I would try that.

Don't rule out a bent balance cock either. It doesn't ake much to bend them and you might not detect it visually.

A over-long staff MIGHT be a problem but there aren't thst many friction staffs around and the most common are probably for the 992B. Even a butcher would have no problem buying a 992B staff and there would be little incentive to improvise.

But.... I would look at the jewels again first and whether the cock itself it bent.

Take a close inspection of the cap jewels upper and lower to insure they are not seated below the plate they are seated in. Peter brings up a good point with the re-jeweling for if the hole jewels are not proper for the movement the step may be the wrong dimension altering the final seat depth. As far as the balance cock goes to check if its bent indicate the balance cock at the screw area and work towards the jewel setting on a surface plate....any deviation will show on the dial as you tram the cock.
Hope this helps...if nothing shows up from the above checks altering the top pivot would be acceptable for you have done your homework with the roller relationship to the pallet fork....nice work.
dave

I would suggest that you find a correct balance staff for your 992B and go from there.

Bravo to friend Fure! Remove the endstones and examine a correct staff in place without balance using a 10 power loupe. This will give you your diagnosis. You can measure over the plate and cock carefully with a micrometer if you are one of those rare watchmakers without a surface plate (heh,heh).

Thanks to all who commented on my post. I am happy to say the watch was repaired and fine.

Lawrence, you take the prize on this one. Although the measurements in length were correct of the 992b staff and the pivot sizes were correct, the staff did not have the oil sink of the 992B. So it was the wrong staff after all.

I searched through my Hamilton stuff and had a number of 992B staffs, and fit a new one. Sadly, the roller table was too large to fit the hub. So I was left with three choices, 1, make new staff, 2, attempt to close hole in table with a punch, or 3, resort to glue.

Well, the watch works great and keeps time in all the positions.

Thanks again for all the help. Sometimes you really need to get a fresh perspective on some of these watches.

The hole was probably enlarged in order to fit the wrong staff. Did you measure roller seats to see if there was a difference? If that was true I would have used a round faced punch to close the hole,or find another roller.

Roller tables are nearly dead hard. It will most likely crack when you attempt closing the hole. You could bush it, make a new one-but 992 B parts are pretty easy to find.


M