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The Water Cooler
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Another OSA Owned Watch Rebuild – 1961 Bulova Type A17A Military Issue Navigation Watch
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<blockquote data-quote="thor447" data-source="post: 3915186" data-attributes="member: 24867"><p>This photo shows wear on the barrel bridge from the crown wheel. There is a gear (winding pinon) that the crown/stem attaches to. When it is turned, it interacts with the crown wheel, which in turn rotates the ratchet wheel, which is attached to the top of the mainspring barrel – thus winding the watch.</p><p></p><p>[ATTACH=full]326516[/ATTACH]</p><p></p><p>Here's a photo of the dial side of the movement before disassembly. It wasn't bad at all. Once I got in close there was dried up lubricant of course, but all in all everything was in great shape. This is about as simple as it gets with the dial side of a watch. Bulova very cleverly designed this movement and didn't over complicate anything. It is reminiscent of Seiko. Seiko uses as few parts as possible to achieve the desired task. Many times combining multiple functions into a single part. Springs and cover plates are engineered into the same part, etc. On this watch, there is only 10 total parts and 1 screw on the front side, not counting the balance jewel assembly.</p><p></p><p>[ATTACH=full]326515[/ATTACH]</p><p></p><p>As stated earlier, this watch was born as an A17A Navigation watch, which had the hacking seconds feature. I created the video below to show how this hacking feature works in this watch. When the crown is pushed fully in, it engages a clever set of levers and a spring that keep the hacking lever held back and away from the balance wheel. When the crown is pulled out, it releases this hold on the spring and the levers move outward and touch the rim of the balance wheel, thus immediately stopping the watch. It's a pretty cool way of doing it I think!</p><p></p><p>[MEDIA=youtube]b3Ndc0pC77k[/MEDIA]</p><p></p><p>After everything was fully disassembled and cleaned, I took the obligatory parts photo:</p><p></p><p>[ATTACH=full]326513[/ATTACH]</p><p></p><p>Before assembly could begin, a couple of things needed to be addressed. The main thing I found wrong during disassembly was that there was too much side shake between the mainspring barrel and the barrel bridge. Having too much play will cause a loss of power, lower amplitude, and just makes the watch not run as well as it would otherwise. After everything was cleaned I got out my staking set (thanks again to [USER=43697]@Nic D.[/USER] and his family), and using a domed punch and a domed anvil I reduced the size of the arbor hole in the bridge plate.</p><p></p><p>[ATTACH=full]326514[/ATTACH]</p><p></p><p>After the diameter of the hole was reduced down to a point where it was too small for arbor of the mainspring barrel to fit in, I used a smoothing broach to slowly open it back up until it had the correct amount of side shake. This requires opening the hole slightly, mounting the barrel and bridge back on the watch to test, disassembling, adjusting again, remounting, etc. until the correct side shake is achieved. I once read a very seasoned watchmaker talk about the proper amount of side shake. He said, “You want as little as possible, but some”. In the beginning I questioned how much was too much, and would routinely post up short videos on a watchmakers forum to get their suggestions. I'm now at a point where I can tell by sight and feel when it's right and when it's not.</p><p></p><p>Here's a before and after video (I've been playing around with a free video editor I downloaded, so be thankful I'm not putting flashes of [USER=8854]@RickN[/USER]'s posts in these videos!).</p><p></p><p>[MEDIA=youtube]HwPASXEM-ik[/MEDIA]</p><p></p><p>You'll notice in the video that the 'before' was taken during disassembly, while the watch was still dirty. In the 'after', you see some wear marks on the bridge plate. This wasn't really noticeable in the first part of the video because it was covered in old gunk and grease.</p><p></p><p>Another issue I found was that there was a slight horizontal bend in the mainspring. It wasn't that bad at all, but you want your mainspring to sit perfectly flat when it is out of the watch. If it is bent up or down by any amount, it will cause it to wear excessively against the floor or roof inside the barrel, and lowers the power output of the spring. I very gently massaged the spring level again and it was good to go for installation. Any kinks in the mainspring are grounds for replacement, but very slight adjustments to it's flatness can be worked out carefully.</p><p></p><p></p><p>Continued on next page.</p></blockquote><p></p>
[QUOTE="thor447, post: 3915186, member: 24867"] This photo shows wear on the barrel bridge from the crown wheel. There is a gear (winding pinon) that the crown/stem attaches to. When it is turned, it interacts with the crown wheel, which in turn rotates the ratchet wheel, which is attached to the top of the mainspring barrel – thus winding the watch. [ATTACH type="full" alt="36.JPG"]326516[/ATTACH] Here's a photo of the dial side of the movement before disassembly. It wasn't bad at all. Once I got in close there was dried up lubricant of course, but all in all everything was in great shape. This is about as simple as it gets with the dial side of a watch. Bulova very cleverly designed this movement and didn't over complicate anything. It is reminiscent of Seiko. Seiko uses as few parts as possible to achieve the desired task. Many times combining multiple functions into a single part. Springs and cover plates are engineered into the same part, etc. On this watch, there is only 10 total parts and 1 screw on the front side, not counting the balance jewel assembly. [ATTACH type="full" alt="35.JPG"]326515[/ATTACH] As stated earlier, this watch was born as an A17A Navigation watch, which had the hacking seconds feature. I created the video below to show how this hacking feature works in this watch. When the crown is pushed fully in, it engages a clever set of levers and a spring that keep the hacking lever held back and away from the balance wheel. When the crown is pulled out, it releases this hold on the spring and the levers move outward and touch the rim of the balance wheel, thus immediately stopping the watch. It's a pretty cool way of doing it I think! [MEDIA=youtube]b3Ndc0pC77k[/MEDIA] After everything was fully disassembled and cleaned, I took the obligatory parts photo: [ATTACH type="full" alt="20.JPG"]326513[/ATTACH] Before assembly could begin, a couple of things needed to be addressed. The main thing I found wrong during disassembly was that there was too much side shake between the mainspring barrel and the barrel bridge. Having too much play will cause a loss of power, lower amplitude, and just makes the watch not run as well as it would otherwise. After everything was cleaned I got out my staking set (thanks again to [USER=43697]@Nic D.[/USER] and his family), and using a domed punch and a domed anvil I reduced the size of the arbor hole in the bridge plate. [ATTACH type="full" alt="21.JPG"]326514[/ATTACH] After the diameter of the hole was reduced down to a point where it was too small for arbor of the mainspring barrel to fit in, I used a smoothing broach to slowly open it back up until it had the correct amount of side shake. This requires opening the hole slightly, mounting the barrel and bridge back on the watch to test, disassembling, adjusting again, remounting, etc. until the correct side shake is achieved. I once read a very seasoned watchmaker talk about the proper amount of side shake. He said, “You want as little as possible, but some”. In the beginning I questioned how much was too much, and would routinely post up short videos on a watchmakers forum to get their suggestions. I'm now at a point where I can tell by sight and feel when it's right and when it's not. Here's a before and after video (I've been playing around with a free video editor I downloaded, so be thankful I'm not putting flashes of [USER=8854]@RickN[/USER]'s posts in these videos!). [MEDIA=youtube]HwPASXEM-ik[/MEDIA] You'll notice in the video that the 'before' was taken during disassembly, while the watch was still dirty. In the 'after', you see some wear marks on the bridge plate. This wasn't really noticeable in the first part of the video because it was covered in old gunk and grease. Another issue I found was that there was a slight horizontal bend in the mainspring. It wasn't that bad at all, but you want your mainspring to sit perfectly flat when it is out of the watch. If it is bent up or down by any amount, it will cause it to wear excessively against the floor or roof inside the barrel, and lowers the power output of the spring. I very gently massaged the spring level again and it was good to go for installation. Any kinks in the mainspring are grounds for replacement, but very slight adjustments to it's flatness can be worked out carefully. Continued on next page. [/QUOTE]
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Another OSA Owned Watch Rebuild – 1961 Bulova Type A17A Military Issue Navigation Watch
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