New Watch Rebuild – Stunning 70's Seiko Bullhead – Dual Register Chronograph – OSA Owned – Tons Of Pics

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
Hello OSA. It's been a little bit but we're back with another OSA owned watch rebuild thread. This one is a really stunning Seiko 6138-0040 (a.k.a Bullhead) made in June of 1977. They don't come much cooler (for me at least) than this folks!! For those of you who've read some of the previous rebuild threads and their comments, you may already know who owns this watch. If not, I'll leave it to him to chime in if he chooses to do so.

A little history on this watch. Seiko is credited with making the first production automatic chronograph movement. There were other prototypes around at the time of Seiko's release, but they were the first ones to bring them to full production. While this is impressive enough, these 6138 and 6139 movements (dual register and single register) they created are very well made column wheel (more on that later) chronograph movements. There was really only one weak point on the 6138 movement (which is fixed now on this watch), but otherwise they are well designed, machined, and excellent timekeepers. The line of chronographs that Seiko put out in the 70's are just so eye catching, that nothing today really compares. They'd probably make a killing if they would start remaking them again.

The owner of this watch bought it in a PX, and if I remember correctly, he wore it daily until it stopped working in the late 80's or early 90's. He had sent it off to repair, but it quickly failed on him again. It has sat in his drawer since that time, untouched for 30 years or more. This made a lot of sense to me, as the outside of the watch shows that it was definitely loved and worn, but the inside of the watch was a time capsule. Once I got the movement out of the case and out from behind the scratched up crystal, the dial and hands were flawless. Where you normally see wear around the edges of the bridge plates on the back side of the watch, (from the bearing on the rotor getting worn and rubbing the bridge plates), this had absolutely none of that. It tells us that this watch has sat for a long period of it's life. This is something you just don't see, and what collectors kill for.

Now, on to the rebuild. FYI, this will be VERY pic heavy, and will require multiple follow up posts to get everything in. Sit back, relax, and make sure you have some time to read before moving forward to the next post, there is 11 more of them!!
 
Last edited:

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
When I got the watch in, it showed it's age. Here's a few pics of where it was before starting on it.

51.JPG

52.JPG

55.JPG


There was also a significant bend in the clasp of the original bracelet that would not allow it to latch shut.

The case had years of dirt and DNA in it the typical spots, as one would expect from a watch of this age.

3.JPG

4.JPG

53.JPG

54.JPG
 

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
57.JPG


At first I tried to get a reading on the timegrapher. I could get the watch to start running, but it would not produce any results on my machine, so unfortunately I do not have a starting reading to share. Just know that it would start up with a little persuasion, but wouldn't produce a signal strong enough for the machine to pick up on.

After I got the movement out, this is when the watch really showed how good shape it was in. First and foremost, the dial is what everyone sees on the watch, and this one was just perfect. I checked the date code on the back of the dial and it was original to the watch, not that it was ever in question, but Seiko fans like myself just love this type of stuff.

56.JPG


In an effort to save a little room on the OSA server, I won't upload every single pic of the jewels that I took before the service, but this one shows a clear example of the condition that basically all of them were in. This is a picture of the rear chronograph wheel jewel. If the balance is the beating heart of the watch, the chronograph wheel (on these Seiko movements) is it's brain, and just as fragile. They cannot be repaired, and they are no longer being produced. NOS replacements sell for hundreds of dollars themselves, for just the single part. Luckily this one was in working order, and able to be re-used after cleaning and a bit of special lubrication.

9.JPG


Here's some photos of the back side of the movement before starting on anything. As you can see it looks really good. I added some arrows to the side of the bridge plates to show the lack of wear marks as detailed earlier. This is one of the very first things I look for when inspecting these movements. If there was significant wear marks, it can still be repaired, but looking at this tells you a lot about the condition of the rest of the movement.

5.JPG

6.JPG
 
Last edited:

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
Here's a few closer pictures of the rear of the watch before beginning. In this first pic it shows a good example of the column wheel. You can see it in the center upper-half of the photo. It has levers from the chronograph start/stop, reset, and hammer all interacting with it. When you interact with the chronograph, this wheel engages and disengages all of those different levers in the proper order to make the mechanism function.

7.JPG


Pic of the lower half of the rear side before starting.

8.JPG


The movement disassembly on this 6138 model begins on the dial side. At the very front is the calendar works, which is what controls the day and date wheels shown at the 6 o'clock position on the dial. Here are a few pics showing the disassembly in sequence.

10.JPG

11.JPG

12.JPG


The mechanisms for the keyless works (parts for setting crown in multiple positions and winding), motion works (setting time) and the hour recording wheel for the chronograph are also on the front side of the movement. These are separated from the calendar works as shown in the photos above by the chronograph plate.

After the calendar works components were removed, the next step would've been to take off the chronograph plate. When I first got the watch and was inspecting it, I could not get hour or minute recording wheels to reset to the zero position. In the photo below you can see part of the hour recording wheel mechanism. The wheel is driven directly by a gear and clutch assembly on the lower barrel arbor itself. It is puts constant pressure on the hour recording wheel to turn (very light amount), but if the chronograph is not turned on, there is a brake that rests against the edge of the wheel. When this break is engaged, it creates enough resistance on the hour recording wheel that it engages the clutch on the barrel arbor. When the chronograph is turned on, the brake is released, it disengages the clutch, and the hour recording wheel begins to rotate. In the photo below, there is a cutout on the chronograph plate that allows you to inspect the interaction of the brake and hour recording wheel. On this watch, the brake was sitting underneath the wheel, and not on it's edge, thus throwing everything out of whack, and is why the wheel would not reset.

13.JPG


This was a few of the issues I found during disassembly which unfortunately shows that this watch wasn't assembled and adjusted correctly when it was previously worked on by the last person 30 or so years ago.
 
Last edited:

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
As much as inspection is done before starting work, even more so is done during disassembly. I was able to get the brake set correctly against the hour recording wheel. After that was done I removed the chronograph plate and continued disassembly.

Here is a photo of the parts (most of them) comprising the hour recording mechanism of the chronograph.

14.JPG


In the photo above, notice the position of the eccentric pin (labeled accordingly) on the left side of the photo. For those who don't do their homework on these movements this would appear to be a screw. Someone in the past had turned this eccentric pin, and it wasn't putting the correct amount of tension on the brake and intermediate wheels (probably what caused the brake to slip underneath the wheel in the first place). I readjusted the eccentric pin to the correct orientation.

15.JPG


There are 3 of these pins within the assembly of chronograph mechanism, 2 on the dial side and one on the rear. All three were severely out of position.

With this issue resolved I began to disassemble the rest of the components of the hour recording mechanism on the dial side of the movement.

16.JPG


During that disassembly the 2nd eccentric pin, which adjusts the travel movement of the hour fly-back lever (this is what is depressed on the dial side of the watch to reset the hour to the zero position). I had removed the lever by the time the photos were taken, but here is the before and after.

17.JPG

18.JPG


I had already rebuilt one of these movements in one of my own watches and had done my research beforehand. Seiko has very detailed technical documents detailing how these eccentric pins should be set. Unfortunately the previous person who worked on this watch was unaware that these are critical adjustments, but thankfully none of them caused permanent damage, it only caused the watch not to function correctly. Simply referencing the technical docs on this movement allowed for an easy fix to this issue.

200.jpg
 

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
After the above was completed, all that was left for the dial side of the watch was to disassemble the keyless works and motion works components. These are pretty straight forward, so no real surprises during their disassembly. Here's a pic of the keyless works before being disassembled.

19.JPG


After this was done the rest of the disassembly work to be done is on the rear of the movement. The first thing I did was to remove the balance assembly and set it aside to protect it from any accidental damage.

20.JPG


After the chronograph bridge was removed (top plate shown in the previous photo), the rest of the chronograph parts were removed. After the chronograph parts were gone, the only remaining items were the barrel, gear train, and pallet fork. Here's a few photos showing that disassembly in a few stages.

21.JPG

22.JPG

23.JPG

24.JPG


25.JPG
 
Last edited:

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
After disassembly I opened up the mainspring barrel. The spring was quite dirty, but it wasn't too bad. It looks worse than it is because the factory lubricant used by Seiko at the time was a black grease.

27.JPG


Another issue causing poor running, so much so that my machine couldn't get a good signal, was that the fact of the stones on the pallet fork were dirty. Even the smallest amount of contaminants on these jewel faces will drastically affect the ability of a watch movement to keep good time.

26.JPG


After all of this was done, everything (including the case) was fully disassembled, all gaskets were removed, etc. Everything (except for the bracelet) went through a few rounds of cleaning. The bracelet was left alone because it was damaged and the owner got a NOS bracelet with this watch at the end of it. He got the original back as well, but I just left it alone since it was going to be fitted with a new one.

Pics below are of all parts on the watch, minus all of the screws. There are tons of different types of screws in this movement and I keep those meticulously organized throughout the rebuild process. I just did not want to take the chance on getting them mixed up by placing them with the parts for the purposes of this picture.

58.JPG

59.JPG

60.JPG

61.JPG

62.JPG
 

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
Before reassembly could begin, there was an upgrade that needed to be done. I had mentioned in the beginning of this saga that there was one weak point in this movement. The weak point is that the barrel arbor port on the rear bridge of this watch is known to wear. On this particular movement, the barrel arbor port on the rear bridge plate is a steel bushing. On 99.9% of all watch movements, the other barrel arbor port towards the front side of the watch is in the main plate. On this watch, there is just a big hole in that position because the barrel arbor extends further out towards the dial side of the watch. This is because of that gear and clutch assembly I spoke of earlier that drives the chronograph hour recording wheel. Because of this, the other barrel arbor port is in the front chronograph plate. Seiko put a jewel in for that bearing, but left the rear bridge barrel arbor port as a steel bushing. Now this watch hadn't run for multiple decades, so the wear on the rear arbor port wasn't really too bad yet, but it is something that happens to all of these movements. As that steel bushing wears out, it causes additional side shake in the barrel. As it gets worse, the barrel sits at an angle, requiring more force to interact with the gear train, lowering the power reserve. Another issue is that the ratchet wheel is attached to the top of the barrel arbor. When the barrel tilts, the ratchet wheel subsequently tilts and eventually starts touching the bridge plate, causing more friction. You can see this on several old watches when you take them apart, and you'll see wear marks underneath the ratchet wheel or crown wheel. This is due to excessive side shake, causing the wheels to rub the plates. I removed that steel bushing for the rear barrel arbor and pressed in a new jewel. After adjusting end shake of the barrel by raising and lowering the jewel (sets how much free play up/down there is when assembled), this fixed what slight issues there were in that watch, and ensures that it will not happen in the future. With regular maintenance once every 6-10 years, it pretty much eliminates that one weak point from surfacing again.

Pics of the bushing before being removed.

28.JPG

29.JPG


Pressing out bushing

30.JPG


Removed

31.JPG


Pressing in the jewel

32.jpg


Installed

33.JPG

34.JPG
 
Last edited:

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
With the barrel arbor upgrade done, the part was cleaned again and assembly could begin. The first thing I like to do is to address the upper and lower balance shock settings and jewels, and assemble the mainspring, arbor, & barrel assembly.

Unfortunately working on those jewel and shock settings is incredibly delicate work and they are extremely small. I do not have photos of that portion, but getting this work done is good (for me at least) because once the balance is ready to be installed, all of that jewel cleaning and lubrication has been done and you don't have to disassemble those shock settings while the watch is running.

The watch got a new mainspring. Here is a couple of photos showing that spring and the assembly installed before closing up the barrel. The newer synthetic lubrication is quite a bit nicer looking than the old black grease they used to use.

400.JPG


36.JPG


Assembly on this movement does not go in the reverse order. Since the front chronograph plate of this watch has the port of the barrel arbor (and not the main plate), that needs to be in place before building the rear side of the watch. With this in mind, I went ahead and assembled the all of the parts that go underneath that chronograph plate.

37.JPG


Front chronograph plate installed, covering those parts:

38.JPG


With this done I went to work on the rear of the movement. Everything went back in just like it came out, so these are basically the same photos as before, only with clean parts.

39.JPG
 
Last edited:

thor447

Sharpshooter
Supporting Member
Special Hen Supporter
Joined
Sep 1, 2012
Messages
4,921
Reaction score
11,961
Location
Newcastle
In this next photo, if you look at the column wheel on the top of the picture, you'll see some blue grease. This is placed strategically along that column wheel. As the chrono is engaged, disengaged, and reset, the grease works itself around the wheel as needed. It is much better to do it this way than to drench that wheel in grease, but every column face needs to be lubricated. I like doing it this way rather than over-lubricating which can have bad consequences. In the later photos you'll see that grease has worked itself around the wheel nicely.

40.JPG


Remaining rear assembly photos taken in stages

41.JPG

42.JPG

43.JPG


Here's pic of the pallet for stones after thorough cleaning. Notice that there is none of the residue as shown in the earlier disassembly photo.

44.JPG


After the rear of the watch was assembled, it was put on the timegrapher and initial readings were taken. The watch was keeping good time, but the amplitude readings really weren't where I'd like them to be (sorry, no pics). Seiko states that the minimum amplitude is 180 degrees. It is well known that most Seiko movements are designed to run at a lower amplitude than their Swiss counterparts. This isn't a bad thing, it is by design. While I was getting readings within spec, they were too low for my taste. Something, somewhere, was stealing power from this watch.
 

Latest posts

Top Bottom