After the Seiko 11A watch, I went to a bit larger sized watch. I was given a Benrus watch that had a DR-25 movement in it. The DR-25 (if I remember correctly) is based off of the ETA-2370 line.
At first, when I took a look at the watch, I figured it was going to be a screwed caseback, but when I took a look at it, it didn’t have any groove where you would expect to see threads or a place to slip a case knife.
With this watch, in order to get at the movement, you need to first remove the crystal. Once you remove the crystal, you need to separate the crown from the stem and then the movement will come out with no problem. This is the first time that I have had a two piece crown, and unfortunately I don’t have a non-blurry picture of the two piece stem, so here is another fabulous computer drawing I whipped up.
As you can see, the crown has a bulbous portion that friction fits into the stem portion. The stem is cut just enough that it will open up to allow the crown to slide in then it will close down a bit to keep the crown in place when it is in the watch. I’m not a big fan of this design if only for the fact that working with it when it is out of the case (letting down the power/winding it up) is kind of a pain. The work around I used to wind the watch was to use a screwdriver in the slot, and to unwind it, I put the free end of the stem into a pin vise to hold allow me to let the power down without the mainspring zipping down and potentially breaking.
With this watch, the first issue I needed to fix was the hands getting caught on each other and stopping the watch The hands were an easy fix. I just needed to check the clearance of the hands and adjust the minute and second hand to ensure that they weren’t rubbing as they went around.
The second issue that the watch was having difficulty winding. Once I got the movement out, I saw why. The click spring was deformed.
If you take a look at the picture, you will see that the spring is crimped together fairly tightly which meant that the click wasn’t able to spring back and together with the ratchet wheel, prevent the mainspring from unwinding. Again, an easy enough fix. All I needed to do was to spread it apart with some pliers (I used some round nose pliers to hold the spring at the curved bend) and a bamboo peg. Perfect fit. The click now springs back smoothly. I want to point out that I really like this style of click. I can’t say for sure if this is mechanically superior to the other kind of click that you typically see (the screw down kind), but it definitely is very easy to work with. I feel like the lack of the screw (as well as the lack of a screw hole) will help eliminate a potential weak area that could fail over time.
As with the other movements I have worked on, there was also a lack of kickback. For this, a quick tightening of the innermost coil of the mainspring around the arbor did the trick.
After that, I got the movement cleaned up, reassembled and oiled. I put the watch on the timing machine and was getting some weird rate results. I wasn’t happy with the beat error, so I got it tightened up to about .2, but it was still testing kind of weird. I took it up to Mr. Poye to look at and he mentioned that it was a bit out of round and flat, as well as having some issues at the collet. I decided to address the out of round/flat errors first before adjusting the collet (one small mistake at the collet can cause a lot more issues than a simple bend off the stud).
Well, as luck would have it, when working at the stud to correct a small hockey-stick bend, the hairspring broke. Great. After talking with Mr. Poye, he said to take this time to work on the collet and then re-pin the stud, and we would adjust the increase in rate after that. To tell if the hairspring is loose at the collet, you watch the hairspring while it is in motion. If it is properly level and round, the hairspring will look level and the expansion and contraction of the spring will look even. If it is loose, it will look something like this
Go ahead and change the resolution to HQ (1o80) and full screen. Watch the spring about 2 or 3 coils out from the collet and you will see it wobble/wiggle. Once the hairspring was centered properly, it was looking great. I put the stud back on, the spring back in the watch and the rate jumped from 18000 bpm to 18,500. I got the beat down to .1 ms before taking it to be checked out. Mr. Poye recommended moving the regulator to maximum slow. Unfortunately, it only moved the rate down to 18,300 and was about 150 seconds fast. Since there aren’t any screws on the balance to add timing washers to, it was stuck at that rate. At this point, I was left with two options:
- Vibrate a new hairspring (which I haven’t learned yet)
- Replace the part
There was only one replacement part left that Mr. Poye was able to find on short notice (he had a line of students that needed help), but sadly upon close inspection, one of the timing screw heads was broken and there was a crack in the rivet of the balance staff. Mr. Poye let me know that the watch was pretty much finished at this point. This was my first (and hopefully last) watch that I had to write “Not Working” on the sixteen point check sheet. 😦
As much as that sucks, I’m glad that I got to experience that while in school as opposed to out in the real world.
Prior Entries in the 16-Point Check Project
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Value of the watch