berlintime

Registered User
Jan 11, 2022
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Hello there dear Watch bangers!

I recently got an old Citizen watch with a Miyota 6628 skeleton movement from an Ebay purchase and fixed it up in a video for youtube. I just wanted to have the whole step by step process in writing aswell so thats why im sharing my journey with you!

General Overview:
. Here we have the "out of the box" watch:
DSC04689.JPG



The one thing that we immediatly realize is that the watch hands have come loose and are free in the case, that the case and case back is a bit roughed up, that there are small stains on the skeletal window of the dial and that the both watch glases could use a refurbishing.
Upon closer inspection of the back side of the movement after opening it up, we have a clear culprit of why the watch is not running. The balance spring is totally demolished! That will definetly have to be replaced.
broken mainspring pic.jpg




Now I did some researching before I started working on this movement just to see what my chances are with sourcing replacement parts and the results were pretty bleak. I had only seen 2 or 3 of these models being sold in the last years. Luckily, I had recently only worked on a few Miyota 6658 movements and I had noticed the similarity. It turns out that the 6628 was later replaced with the 6658 and then 6T58 calibers so I used those movements as a potetial doner source. I assume that the difference between the 6628 and the 6658 line is that the 6628 is sekeletonized and doesnt have a day/date complication aside from smaller technical/mechanical changes ( such as center pinion sizes and etc. I assumed that the basics (balance and mainspring, all the bigger parts) ) would be just the right fit.

Here starts the actual repair process:
1.
Removing the watch movement from the case by pressing on the stem clasp and removing it. Taking the movement out of the case and removing the movement spacer. Taking of the hands, in this case just a matter of picking them up since there where loose, removing the dial by unscrewing the dial feet screws on the side of the movement and revealing the setting system.
DSC04698.JPG DSC04699.JPG

DSC04700.JPG

2. Removing the setting system in this order: Canon pinion, minute wheel, hour wheel cover and wheel, intermediate wheel, setiing cover/ bridge, spring, yoke, clutch mechanism and optionally the setting lever ( it was kinda hard to remove in this movement haha) giving you a stripped front side:
DSC04701.JPG

Next we flip the watch to work on the backside
3. Removing the rotor ( be carefull, citizen has a specialized screwhead for the rotor, conventional screwdrivers wont work, I opted for the Aliexpress version which has worked fine but im afraid its usage is slowly dwindeling)

DSC04702.JPG DSC04703.JPG

4. Remove powel wheel bridge, powel wheel and clickspring.


DSC04704.JPG DSC04705.JPG


5. Remove mainbridge and all the 2 gearworks, 2 reduction wheels next to the mains spring and the mainspring itself. And ofcourse the escapement wheel ( which is still on the picture haha).

DSC04708.JPG DSC04709.JPG


6. Remove the balance wheel ( and in our case get the replacement ready).
DSC04710.JPG


DSC04711.JPG
7. Remove the pallet bridge and fork.
DSC04714.JPG

8. And lastly we remove the sweep second pinion and its spring, the center cock/bridge and the center wheel.

DSC04715.JPG

Now before you slap this bad boy into the cleaning process aswell, dont forget to take out the shock jewel on the front side of the movement. Its the big red jewel, you cant miss it. Here are all the parts sorted:
DSC04720.JPG

Cleaning

I use a lighter fluid- isopopropanol cleaning method because its cheap and effective and it worked for me up until now. Of couse there are much better methods. Just leave the parts in the lighterfluid for 5 minutes or so and shake them in isopropanol alocohol afterwards so that the benzin gets washed off properly.

Optional processes which I can post about which I did in this service but didnt want to write down because of space:
  • Mainspring maintenance (hand cleaning and lubrication)
  • Shock jewel maintenance (lubrication and cleaning)

Reassembly:
1.
Center wheel, bridge and sweep second pinion with spring.
DSC04733.JPG

2. Gear train, mainspring, reduction wheel,escapement.
DSC04734.JPG

3. Mainbridge and clickspring. Then balance and pallet fork and bridge. It works!! Sorry for not having a picture, the data got blurry sadly :( Dont forget to oil the Balance Jewel here!
4. The powel wheel and the powel wheel bridge. It should in the end look like this:

DSC04738.JPG


I sadly forgot to take pictures of the Front side reassembly so you will just have to look up above at the disassembly.
This is literally just the reverse order of the dissasembly pictures, for more details check those out again. However here is a list of things to watch out for.
Lubrication:
  • I used 8200 on Mainspring and 8217 for breaking grease.
  • 9010 for the all jewel bearings and shock jewels.
  • Hp 1300 for lubricaton on mainplate friction points and a bit in the setting system.
  • 9415 on the escapement.

Tipps:
Beware that the due to the thin strip of metal which makes the sketon effect of this movement possible, makes the reassembly of the pallet fork and escapement wheel very difficult and tedious. It took me quite a while!

Exterior appearance:
I did not end up replacing the glas because of time management but managed to clean up the small stains on the window cirle on the dial and went over the case with a jewelers cloth to give it a bit of a new shine.

5. Now after putting on the rotor, recasing, redialing and putting the hands back on it was time for the timegrapher.:

Timegrapher values:
  • Preliminary Results: +78/ 178amp./ 8.9be
  • After regulation: +4/230amp/0.2be

This improvement took a few hours actually, I virtually tried every combination of the stud and regulator and had some countles micro adjustments but I had some boring Uni Lecture at the same time so it was a good investment of time :)

Finally I closed up the back with the watch press and here are the final results:


DSC04746.JPG

Screenshot 2022-01-27 185909.jpg


Sadly you cant post gifs or videos here because the moving watch looks so much better! Questions, comments, criticism and tipps are always welcome! I hope that I have helped you!

Till the next time watch bangers!
 

Skutt50

Registered User
Mar 14, 2008
4,194
399
83
Gothenburg
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Welcome to the forum.

This can't be your first service. Good job and congratulations to a nice watch.
Any chanse of a picture of the timer screen.......

PS. Replacing the hairspring? The original only needed some minor adjustments.....lol. DS
 

berlintime

Registered User
Jan 11, 2022
7
13
3
23
Country
Welcome to the forum.

This can't be your first service. Good job and congratulations to a nice watch.
Any chanse of a picture of the timer screen.......

PS. Replacing the hairspring? The original only needed some minor adjustments.....lol. DS
Ive of course tinkered with a few other movements before but this is my first full service! Thanks! It also took around 20 hours haha skipped way too many meals for the watch! And youre right! I shoud have just bent the hairspring back with my fingers a bit! It would have fixed everything ;)

As a disclaimer, I wrote the post during work since I was very impatient to share so I got some of the numbers wrong. The amp is slightly lower and the initial rate and BE is better (Im pretty sure the rate jumped to +2 after I stopped recording though)! Heres the requested of course: timegrapher.jpg
 

Skutt50

Registered User
Mar 14, 2008
4,194
399
83
Gothenburg
Country
That screen looks like that of a well functioning watch....
 

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