Watch Rebuild – OSA Member Owned – U.S. Contract Pilot's Watch Issued In Vietnam – LONG POST - PIC HEAVY

thor447

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Hey OSA,

I got another one to bring you today. This is by far the longest write-up I've done yet. This will be a total of 6 posts and 30 pictures. Fair warning!

This watch was an absolute honor to work on. It is an OSA member owned watch which he received while in Vietnam. I will not call him out by name, but he is more than welcome to let the group know who's watch this is if he chooses to do so.

This is a Benrus military issue Pilot's watch, manufactured in July of 1971.

0 - Full Watch - Before.JPG

0 - Close Up Before.JPG


A little history on this one first. Since the Vietnam war, they had issued military watches, made under GG-W-113 specification, to their pilots. These watches were manufactured under government contract by various American watch companies such as Benrus, Hamilton, and Waltham. The GG-W-113 watches had striking resemblances to military field watches (made under MIL-W-46374 specification) that were issued to soldiers on the ground. Same case, same hands were used, along with the usual 24 hour markings on a black dial. Both GG-W-113 and MIL-W-46374 watches were equipped with manual-wind movements. The GG-W-113 watches, however, differed in the following aspects (data pulled from a website):

1. Equipped with a 17 jewel manual-wind movement, it had the desirable hack feature, allowing precise synchronization of watches to a known source of time. MIL-W-46374 did not have the hack feature until the mid-eighties.

2. H3 and propeller shaped radiation marks were omitted from the dial to make the dials more legible.

3. Watches were normally issued with black (instead of olive drab) nylon band, although some were issued with olive drab band in Vietnam.

When I first learned that this model was specifically a pilot's watch, I pm'd the OSA member and asked if he was a pilot during his time in Vietnam. In his reply he told me a bit about his service history. One part of his response, telling me how he came into the watch, made me chuckle: “I acquired the watch mid or late 1972 from a crusty old lifer Army supply sergeant. …..old supply sergeants are known to be scroungers so there is no telling how he came to have them but he had three and with me needing a watch that I wouldn't have to baby I gave him a few dollars, signed a fictitious name to get it off his books and wore it daily till I returned from VN.”

The watch looked to be in really great shape when I received it. The OSA member had mentioned to me that he was planning on giving it to his son, and would like to make sure that it is in good running order. He initially thought that the watch had never been worked on, but we found out later that wasn't the case (will explain later on). During the initial inspection while testing the basic functions (before doing any disassembly), everything appeared to work except the hacking feature. While doing my research on this watch, everything I read pointed me to this watch having a hacking seconds feature, but it just wouldn't work. I spoke with the OSA owner of this watch, and he told me that he never remembered it having the seconds hand stop when the crown was pulled out to set the time. After the initial inspection, and him agreeing to let me do a complete overhaul, he told me that if it was there, and was fixable, to go ahead and get it working, but it had never worked to his memory so it wasn't a big deal if the hack didn't function. The crystal looked to be in good shape when I first received it. Once put under magnification I found several smaller scratches. These aren't even noticeable when you're wearing/looking at the watch, but now that I saw them they needed to be addressed!

Since the watch would run when it was first received, before doing any work it I put a full wind in the watch, and put it on the timegrapher to get some base-line readings.

1 - Before Service.JPG


You can see from these readings that the watch in the dial up position is running quite slow at 71 seconds per day. It had very low amplitude (degree of rotation of the balance wheel in each direction) of 184 degrees. This is considered very low on a full wind for a movement of this type. The amplitude gives you an idea of how efficiently power is transferring from the mainspring, through the mechanics of the watch and into the balance. The less power getting to the balance, the lower the amplitude you'll have (also must take into account the pivots on the balance itself – which are critical). It had a beat error of 2.8 milliseconds. The beat error is the difference in time between the clockwise swing and the counterclockwise swing of the balance. That isn't really all that bad for a vintage watch, and would be considered acceptable in some standards. If the watch was keeping good time, but still had a beat error of 2.8m/s, many watchmaker's wouldn't even bother with it. I suppose my OCD is a good thing when it comes to watchmaking. I knew that if it was 2.8 to start out before any service work that I could get it closer to 0 m/s, which is the ideal. Technically speaking, anything at 1.0 m/s or lower would make no difference in the watches ability to keep time accurately.

Here's a few pics of the initial tear down:

5 - Rear.JPG

6 - Front.JPG


Continued on next post.
 
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thor447

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Disassembly & inspection continued.

9 - Pallet Fork Engagement.JPG

11 - Pallet Fork Inspection.JPG


When everything had been disassembled, I inspected the jewels. This was also done during the initial inspection, where I found (as expected) pretty much all of the lubricant had gummed up. Inspecting them while the movement is disassembled can give you views to the underside of each jewel, and provides a much clearer picture of their current state.

41 - 4th Wheel Lower Jewel.JPG

42 - Center Wheel Bridge Jewel.JPG

43 - Escape Wheel Bridge Jewel.JPG

44 - Pallet Fork Lower Main Plate Jewel.JPG



Continued on next post.
 

thor447

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45 - Thrid Wheel Bridge Jewel.JPG

46 - Wheel Bridge Jewels - Underside.JPG


As you can see, all of the lubricant left in the watch was gummed up. None of the gears in the wheel train or escapement would run well in this state, and definitely contributed to the low amplitude numbers we were seeing. What isn't pictured (among several) is the condition of the upper and lower balance jewels, but they were basically in the same state as these. The condition of the balance settings and cap jewels play a critical role in the watches ability to run efficiently, as much or more than any other part of the watch.

While doing the tear down I found a watchmaker's mark on the inside of the case-back dating to 1997. I found this during my initial inspection and let the OSA member know about it. They never remembered taking it in, but he told me that he and his wife read my initial inspection message to him together, and she remembered him taking it in during the 90's because it quit working on a camping/hunting trip.

99 - Watchmaker's Mark - 1997.JPG


During tear down, I found out that indeed this watch did have a hacking seconds feature, but it was unfortunately broken. On this watch it is very simply designed as a flat plate with a stud mounted at 90 degrees on it, and under tension to rotate from a small spring. When the crown is pulled out, that plate is free to rotate towards the balance wheel and the stud would make contact with the balance, thus stopping it. On this watch, that stud is broken off of the plate, and nowhere to be found in the watch. It's possible the previous person who worked on this in the 90's didn't assemble it correctly. You have to have the hack installed first, then when mounting the balance, you'd have to manually pull the stud out of the way while the balance is seated. If this process was reversed, I could see how the stud could break off. I informed the OSA owner about this. They weren't concerned with the hacking feature, so I didn't bother trying to find a replacement part.

10 - Broken Hacking Lever.jpg


Here's a pic of the watch fully disassembled.

80 - Disassembled.JPG


At this point in the photo, I had already cleaned all of the parts by hand to get most of the major stuff taken care of. After this photo everything went into the cleaning machine which will get into every nook and cranny to make this thing as clean as the day it was made.

The only thing not visible are the hands (and the strap of course), which I keep in a little storage box with a silicon membrane. It just keeps the hands straight, and keeps them from getting damaged in case I send a part flying towards them! They are very delicate so once I remove them, I safely store them away until the watch is rebuilt and ready to have the them re-installed.

Continued on next post.
 
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thor447

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Assembly went really well. I'm sorry for the lack of photos for this part, but once I get going putting one of these back together I just get hyper-focused on what I'm doing and taking photos slips my mind.
I did take 1 single photo during the assembly process however! After cleaning, the very first step I do when assembling the watch is to put the mainspring, barrel, and arbor back together. With the initial low amplitude ratings we were seeing, and the age of the watch, I was somewhat anticipating needing to replace the mainspring. During disassembly I found that this watch had the mainspring replaced already, no doubt from the watchmaker in 1997. The mainspring in this watch was of a newer type than what would've come originally in this watch. Once removed from the barrel it had no kinks in it, and sat level, which is what you want to see. After disassembly I told the owner of the watch that I'd like to try re-using the existing mainspring first to see what kind of numbers we can get out of it. These newer types have a much better temper in them, and will last decades longer if properly serviced. When I first took the barrel apart during disassembly I found that it had about 5x too much grease in it, which had gummed up.
Here's the pic of the mainspring and arbor cleaned, lubricated, and re-installed into the barrel (before I installed the top piece of the barrel). It gives you a great view of how a non-automatic mainspring sits in a step on the inside of the barrel wall. When you wind a manual watch, when you reach full wind you feel resistance when trying to turn the crown. This resistance comes from the barrel being at full wind (spring moves inward toward the arbor), and the catch you see the spring sitting in on the inside edge of the barrel engages and prevents you from going further. This is why they tell you to NEVER over-wind or muscle through when winding a manual watch. This is a breaking point if you put too much force on it.

15 - Mainspring - Cleaned Lubricated & Reassembled.JPG


The other issue I found is that the barrel had too much side shake when the bridge is mounted (no pics). This will happen over time because the pivot on the barrel arbor will wear out the bearing walls of the bridge when it rotates. Along with the dirty jewels, and gummed up mainspring, this was absolutely contributing to the poor amplitude numbers we saw during the initial testing. I used a staking set on the bridge and closed that arbor pivot point, and then used a smoothing broach to open it back up to the correct diameter, it also burnishes the inside walls of that bearing race to make it less resistant to wear in the future.

After the initial assembly was complete, it put a full wind in it, let it run for about an hour, and then put it on the timegrapher for initial regulation. After about 10 minutes of adjustments, here's where you find out if all the work being put in to the watch was worth it.

21 - After Service & Initial Regulation.JPG


As you can see, it's running SO much better. I got it down to 0 to 3 seconds per day in the dial up position, amplitude is excellent at 278 degrees (which tells me that we don't need a replacement mainspring), and the beat error I got down 0.0 – 0.1.

I couldn't have asked for better results, but this isn't the end of the work needing to be done to a watch movement after it's serviced. The watch needs to be put on a full wind and ran in for at least 24 hours. This allows the lubricants to settle in the jewels/pivots, for the barrel to unwind and distribute the lubricant, etc.

I finished the assembly in the evening, put it on the timegrapher, and left it alone for 26 hours. The s/d reading will always change after it's initial run-in, and the amplitude will drop as the mainspring unwinds over that 24 hour period. The rule of thumb for this type of manual movement is that you want to see amplitude drop to no less than 210 degrees (general rule of 190 degrees on automatics – not counting Japanese movements which are designed to run on lower amplitudes). Although I didn't get a picture of the initial readouts after 24 hours, the s/d had dropped (as expected) to about 9 s/d in dial up, and had been holding steady at that level for quite some time. The amplitude had only dropped to 255, which is fantastic.

Now that the movement had been run in, I did a full regulation (in multiple positions). Here's a photo of the same dial up position after everything was said and done, and the watch had been fully reassembled back into the case.

22 - Fully Assembled - Final Timekeeping.JPG


I think you've seen enough of these timegrapher readouts to know what looks good and what doesn't. I'll let you be the judge! I'll just say that my hat is off to these old Benrus movements. The readout in the dial down position is very close. Crown left, right, etc. positions saw a drop in amplitude, but everything was working great. FYI – a drop in amplitude from dial up/down to any other position will happen because the watch is on it's side. All of the points of friction on the balance, wheels train, etc. are no longer on the tips of the pivots, but now on the side of the pivots which have a much larger surface area. This creates more friction, which equates to lower amplitude. Even the best watches in the world see this same drop. This why to properly regulate a watch, you have to test it in multiple positions. Dial Up, Dial Down, and Crown Down (position when standing with your arm hanging) are the 3 most used positions a watch well ever be in. The smaller you can make that variance between those positions, the more accurate the watch will keep time while going through the motions of being worn throughout the day.

Continued on next post.
 
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thor447

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This is the final post (thank goodness)!
The watch had been fully assembled, but the case still needed some attention. It was in really good shape, but just needed to be cleaned. I absolutely wasn't going to restore/polish the finish in any way. We were going to keep it original, but just give it a thorough cleaning to remove dirt, spot rust, and gunk (and honestly it was hardly any at all). I just made some simple before and after pics:

23 - Case Rear - Before & After.jpg

24 - Case Front - Before & After.jpg



Regarding the crystal, I had mentioned earlier that it had several very small scratches on it. Honestly, these weren't even noticeable when you weren't looking through magnification, but here's a before and after on the crystal, just using a little elbow grease. It isn't absolutely perfect, but it's light-years better than it was, and makes this original crystal just look great.

8 - Crystal Scratches - Before & After.JPG


Well here it is fully finished. Again, thank you to the OSA member for allowing me to bring this amazing watch back into working order. I was honored that you trusted me with this, and thanks again.

25 - Finished.JPG


One thing of note, I had another watch owned by another OSA member. I had worked on his before I began work on this Benrus. I won't call him out by name either, but he knows who he is. This one was an interesting project. It wasn't starting up very easily, and wasn't keeping the best of time. It's a totally cool looking watch though. After a bunch of trial and error, I finally nailed down why this watch wouldn't kick in when winding. When it would start, it would keep time pretty well, and then all of the sudden start to run fast for a few minutes then come back down to normal.

I tracked the problem down and it would only do it off and on in the dial up position. The hairspring was not aligned properly and engaging the regulating pins in an irregular manner. When the watch was dial up, gravity is pushing down on the hairspring, and it would routinely engage the base of the regulator, throwing the watch out of whack. When it was in the dial down position, gravity is pushing the hairspring away from the base of the regulator and the watch would run fine.

The movement in this watch wasn't something I had worked on before, and I got LUCKY and found replacement 'balance complete', which is the pre-assembled balance wheel, hairspring, balance staff, and roller table. The watch had been cleaned and lubricated, and when the part arrived I disassembled the balance assembly from it's bridge, installed the new one, re-cleaned and oiled the balance jewels, and did a full regulation on the watch. This one was a challenge, but we got it figured out! Here's both OSA member owned watches together.

50 - Two OSA watches.JPG


The Benrus was returned to it's owner this morning. The second watch mentioned is being returned to it's OSA owner this afternoon/evening sometime. It was a privilege to get to work on some OSA owned watches, and thanks to both members for entrusting me with these.

OK, I'm done! If you actually read all of this and made it to the end, my hat's off to you.
 

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