WWII 4992B Pocket Watch - Overhaul

During World War II, Hamilton produced a variety of time pieces to support the war effort.  In fact, all of Hamilton's production was dedicated to defense purposes.  However, they did still produce some wrist watches using excess movements produced in the 1920's.

One of the war-related watches was a pocket watch with a central sweep second hand.  The movement was based on the 21 jewel, 16 size 992B movement.  However, an extra jewel was added to support the second hand pinion, so the movement got 22 jewels and was called the 4992B.

The 4992B is known as a "Navigator's Watch" as it was used by aviators to aid in navigation.  In fact, the watch above was carried through the Pacific by my wife's grandfather while in the US Navy during the war.

Here's a couple of advertisements from WWII-era Life Magazines that featured the 4992B.

You'll often see 4992B's in a case or a box that was intended to isolate it and protect it from shocks or accidental damage.

If you look closely at the dial, you'll see that it's a 24 hour dial so it takes a full day for the hour hand to make a full rotation.  12:00 noon on a 24 hour dial looks like 6:00 on a 12-hour dial.  The minute hand still makes it around the dial in one hour, so the ratio of the minute hand to the hour hand is modified using a different minute wheel and hour wheel ratio.

Another interesting aspect to the 4992B is it "hacks" or stops when you pull out the crown to set the time.  This allows you to set a very precise time... the old, "synchronize your watches" phrase comes to mind.

I recently purchased a 4992B pocket watch with a somewhat unusual 12-hour dial set up.   I have seen them before but they're not as common as the 24 hour black dialed variety.  Oddly enough, this one does not hack.

I actually purchased it a few months ago but other than seeing if it ran, I haven't done anything with it.  If you don't know the service history of a vintage watch you really shouldn't run it very long without getting it serviced.  Watches need to have oil in the crucial spots or they will potentially wear themselves out.  They may run - but are slowly damaging themselves if the oil has evaporated out.

I finally got around to servicing this watch so I will show you what it takes.

The first step is to remove the hands.  That prevents any damage when you pull the watch from the case.  The movement comes out the front so once you unscrew the front bezel you can open up the back and prepare to pull the movement.

On the opposite side, you can see there are two case screws holding the movement into the case.  They are located along the edge, at about the 11 and 5 o'clock positions.  In addition to the case screws, you need to remove the stem and crown.  A few turns of the set lever screw will allow you to pull it out... just like a wrist watch movement.

In fact, the 4992B is a lot like a giant 987S movement... or specifically, the 2987 which has an extra jewel for the second hand.

With the movement out of the case, there are three dial foot screws on the side of the movement.  Loosen them up and the dial comes right off.

As you can see on the dial-side of the main plate, the watch looks a lot like a 6/0 sized 987S movement.  It's "positive set", meaning when you pull the crown out you move the keyless works into the winding position against the force of springs.  Pushing the crown back in releases the springs and puts the keyless works back into the winding position.  A "negative set" movement does the opposite... you effectively push the stem in against the force of springs to get to the winding position.   I know, that's confusing... my point is that prior to WWII, many Hamilton pocket watches were negative set, and they look a lot different on the dial side.

Anyway, removing the hour wheel from the center of the movement exposes the cannon pinion and the minute wheel just to the right of it.  Those come off next, as does the set bridge (with two screws) and the cap jewels on the upper left of the movement.

Working on the reverse... first all the mainspring tension is let off.  Then it's disassembled just like a conventional wrist watch movement.

The bridge for the second hand pinion and the pinion is removed.  Also removed is the main spring ratchet wheel.  Three screws hold the barrel bridge on... once they're removed the barrel bridge can be taken off.

In the shot below, you might be able to see that the larger seconds wheel on the top of the barrel bridge is on the same axle as the 3rd wheel below the bridge.  The pivot of the 3rd wheel is extra long and extends into the seconds wheel.  So, as the 3rd wheel turns it turns the seconds wheel, which then turns the seconds pivot and the seconds hand on the front.

I find removing the larger seconds wheel from the axle of the 3rd wheel to be a challenge.  The same is true on the 987S.  Eventually it comes loose after some gentle persuasion.  In the shot below you can see the mainspring barrel is still in the movement but the other wheels are off to the right.

The next to come out is the train bridge and the 4th wheel and Escape wheel that it supports.  That then leaves the balance assembly and the pallet fork underneath it.

With the balance out you can see the pallet bridge, also known as the anchor bridge, that holds the pallet fork in place.

Now everything is disassembled and ready to be cleaned.  The main plate is too large for my usual cleaning set up - which is one reason why it didn't service it until now.  I'll clean it separately from the the smaller parts - to protect them from accidental damage during cleaning.

With everything cleaned and dried, all the parts seem to sparkle now.  It's time to re-oil everything and put it back together.

I always put the cap jewels back on first and the keyless works since the main plate is on that side.

With the back side up, the parts go back in the reverse order from which they came off.  So the pallet fork and anchor bridge are the first things on.  Care is taken to make sure the pivots for the pallet fork go into their jewels before the bridge is tightened.

Next the Escape wheel and the 4th wheel go on.  In a 992B the 4th wheel has a longer pivot to support the second hand at the 6 o'clock position.  The pivot on the 4th wheel of the 4992B is a little shorter and doesn't pass through the main plate.

Then the barrel, 3rd wheel and center wheel go on.  In this shot you can see the serial number, 4C97207, that dates the watch to 1944.

With the barrel bridge installed and the mainspring ratchet wheel installed this movement is just like a 992B at this point.

The seconds wheel and seconds pivot are installed.  Then the little bridge for the seconds pivot goes on to secure it all in place.

Finally, the balance assembly is ready to go on.  The trick here is to re-oil the pivot jewel under the hair spring.  You need to thread the oiler through the hairspring to get to the jewel without getting any oil on the hairspring.  Even a tiny amount of oil on the hairspring will throw the timing off.

With the balance reinstalled and the watch running, the cannon pinion, minute wheel and hour wheel are installed.  The keyless works gets a fresh dose of microgliss lubricant.

I didn't like the corrosion along the perimeter of the original dial and I was lucky enough to find a loose 4992B dial, so I'll make the dial swap now.

With everything reinstalled the watch goes on the timer... running 3 seconds fast per day... good enough for my tastes.

And here it is all spiffed up and ready to be used daily for years to come.

UPDATE -

A friend of mine pointed out that there were some 4992B hack springs on eBay so I snagged a pair of them so that I could restore this watch's hacking function.

Here's how it went.

You may recall from above that the hack spring is used to stop the watch when the crown is pulled out to set the time.  In order to get to it I had to remove the movement from the case and then pull the sweep second wheel, pinion and barrel bridge.

In the shot below the parts have been removed.  Turns out I needed to remove the dial and hands too, as well as the cannon pinion and hour wheel so I could get the center wheel out of the way.

Here's a close of the the hack spring bridge and mechanism, sans-spring.  The stem has a point on the end of it and when the stem is pull out (to the right in the shot below) a spring moves the hack mechanism.  When the stem is pushed back in, the point of the stem will move the hack spring back to it's original position.

Here's a close up of the new hack spring on the right and it's bridge is in the above right.  The old hack mechanism lost it's j-shaped wire

In this shot the new hack spring is installed and the stem is pulled out to the time setting position.  Note how the j-shaped wire is resting against the balance wheel (my tweezers are pointing to it).

Here the stem is pushed back in and the wire has been moved away from the balance wheel - so now the watch will run.

Swapping out this part was an easy operation and it's rewarding to return this fine time piece to it's correct hacking form.