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Seiko 4205(A) Stripdown


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I have done a few of these 4205's  now and although I am by no means an expert, I have learned a few things about them that might be helpful should anyone fancy having a go.

This is my first walk through and guide, some of the photos are not as good as I would have liked. I have bought a mini tripod which has helped a lot but the lighting is not the best, something to look into for the future. I will try and explain things as clearly as I can as we go along, if anything is unclear please just ask.

So, here is the little devil. No guesses as to where it came from.  It is a bit tatty but they do scrub up well.  This one is actually trying to run so hopefully all it will need is a clean and service. Keeping my fingers crossed as you never know what you might find once you begin.

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Before I start taking it apart I now check that everything works as it should.  It’s good practice I know, but the first couple I did I was a bit lax and I had to strip the whole thing down again when “faults” appeared. 

In particular, make sure that the winding mechanism feels ok, they have a habit of skipping when trying to wind it up,  you might feel it wind for a turn or two and then will just turn freely without resistance. Next, make sure the date rolls over around midnight and the quickset works ok.  Never had a problem with the quickset yet but sometimes depending on the version of the movement the date change can be problematic. I will make a point of mentioning these problems and what goes wrong as we proceed.

 

This watch is a 4205-0156 and is fitted with the earlier 4205A movement. The 4205B is slightly different. I tell them apart by the fact that the A has two retaining screws in the balance cock whereas the B is single screw.  Now, I can’t swear that there might be versions of the A that have single screw balance cocks or vise versa, sometimes things are never that straightforward it seems.

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The bezel on this one is free so it will come off no problem. I have freed stuck bezels by simply dropping out the movement and dumping the whole case in some releasing oil for a day or so. Then I dry it a bit and lay it bezel side down onto a nice piece of “grippy rubber that I have, lay some weight on it through the heel of your hand and twist it in jerking movements to and fro. The lugs are quite sharp so protect your hand with a glove or something Really stubborn ones can be a pain but you just have to be a bit more brutal in your method. There is a notch in the case to allow you to prise the bezel off.

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With the bezel off you can remove the bezel insert, shim and o ring.

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Hard to tell through the scratches but the dial might be ok. Unless the crystal is cracked I would leave it in the case as there is a dial retaining ring that holds the glass in and they can be awkward to refit and do sometimes crack.

Try as I might I couldn’t get the picture the right way round for some reason.

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Depress the little button and remove the stem.

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There might be screws holding the movement ring but usually they are missing.

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Looks as if someone has fitted a new dial and hands which is a bonus.

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One of the dial feet is a screwhead that needs to be turned until it is clear and the other is a small lever that needs to be swung out. You can see it sticking out near the 28 on the date wheel.

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Take care not to lose the washer that sits behind the dial. Some of the ones I have done , there was no washer. So either someone before me lost it or it was not necessary. All seemed well when there was no washer fitted so I didn’t worry about it.

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Well worth getting is a holder like this. I had difficulty securing the movement in my holder. I was recommended to use these as made by Halo8. He is on the bay and made one specially to fit the 4205 when I asked him about it. I bought a few more of the most popular sizes while I was at it and they are great.

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Here it is in the holder, it does make a big difference. I like to leave the stem in place to check things as it comes apart. The first thing I take out of harms way is the balance, just one of the lessons I learned the hard way.

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It is worth checking that the autowind works ok before taking off the rotor, I just spin it around a few times with a cocktail stick and make sure the ratchet wheel is turning.

Do take the balance out first, as if you do slip while turning the rotor you can bet the first thing that get’s it is the balance. So better safe than sorry.

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In order to let the mainspring down you need to remove the three small screws that secure the rotor bearing assembly, keep an eye on the pawl lever as you lift things away as they can spring off. The pawl lever grips the transmission wheel and you can’t let the spring down until it is removed. The screw that hold the transmission wheel is left hand thread. The mainspring can now be let down. I gently ease the ratchet wheel back slightly with my finger and then carefully hold the click out with my trusty needle and slowly allow the spring to unwind.

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I am pointing out the date wheel finger. If you find that the date will not change as you wind the hands through past midnight this finger can be the culprit.

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If you see the date wheel trying to move but not quite making it, you might find that this is worn. The little finger on the right wears and is then not quite long enough to flick the date ring around. It’s a poor idea if you ask me, there is not much of it to start with.

What I decided to do was just to try and nip the end with a pair of strongish tweezers and tease a bit more length out of the plastic. It did work, but obviously it will fail again sometime. But unless you have the luxury of a spare movement there is little else you can do.

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Remove the screws that hold the date wheel retaining plate and carefully lift it off. Have a good look where it sits and where the locating points are.

With that out of the way I have highlighted two potential flyers, the tiny date jumper and spring.  Be ever so careful as you remove the date ring so as not to disturb them.

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I am pointing out the intermediate date wheel and pinion here. I have found that the 4205A has a metal one which is good, the B has a plastic one which is not so good.

The teeth are very very tiny on the plastic ones and I have come across some that have been crushed. This is another reason for your datewheel not turning. This has nothing to do with the quickset by the way. Now, maybe I have just got the patience of a saint or something, but I have rescued a couple of these poor crushed wheels by carefully opening up each and every tooth with the tip of a scalpel. It’s not a lot of fun as you can imagine but again, if you don’t have a replacement what are you going to do. I did once bite the bullet and ordered another similar movement from Ramon, but guess what?  Yep, that one was exactly the same!

Deary me, said I on discovering that.

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 Here is the metalwheel removed.

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The minute wheel, hour wheel and date indicator driving wheel are and date corrector finger have been removed. Notice the small plate still attached just below the cannon pinion, there is nothing holding it on other than being a tight fit on the locating pins.

Never had one drop off but I prise it off anyway just in case.

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Next is the setting lever, spring and yoke and the dial side is stripped.

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Well done Davey, and thanks for joining the walkthrough brigade. I hope more folk will make the time and effort share their knowledge as you have.

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Flipping it over and the three train bridge retaining screws are removed. One of them holds a small friction spring in contact with the centre seconds pinion, meant to show that sorry.

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Lift the bridge clear but watch out for the transmission wheel pinion that is left behind. It can stick to the underside of the bridge and drop out when you aren’t looking, the small intermediate wheel next to it in the black box is also free to fall off. I am beginning to think that instead of removing the left handed screw and removing the transmission wheel you could leave it attached and then there would be no danger of losing the pinion below it. Removing the pawl lever as described above would still allow the mainspring to be wound down. In 4205B movements this is one unit anyway so not to worry.

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Barrel,train wheels and the centre seconds pinion are next. Then the pallet bridge and fork.

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At the beginning I mentioned that sometimes the winding mechanism might not feel right, you might get a few turns of the crown and then it goes loose then winds again.

Given the age of these things by now there must be considerable wear and some of the gears in the winding mechanism are well worn

I found that the winding pinion on the stem was not contacting the sliding crown on the winding bridge very well, it was tending to lie to one side and flop about. So what I did was to bend the spring that you can see inside the black box so that it puts more tension on the sliding crown and it seemed to keep things engaged a bit more positively. It’s easier to do this once spring has been removed.

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Take off the winding bridge and it’s almost there.

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Remove the centre wheel bridge and take out the escape wheel.

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Pull off the cannon pinion and remove the centre wheel.

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The barrel and spring.

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And the spring is removed.

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All the parts ready for cleaning.

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And that's it. Once everything is cleaned and ready, reassembly is just the reverse procedure.

I will be quite happy to post the pictures of it going back together if you wish.

Either way I hope it has been of help and that I have made things easy to understand.

It’s difficult to know exactly how much detail to include or omit. If anything is unclear or just plain wrong please let me know and I will try to explain things or make some edits to the post.

 

 

 

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Yes I can do that, but I am gasping for a cuppa right now :)

I imagine you need the height and thickness of the spring. What other dimensions do you need?

 

MS go by height, thickness (strength), and length - for which you use best approximation. Plus barrel I.D. - I don't know why.

Enjoy your well deserved Ale! (if that's what you fancy).

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MS go by height, thickness (strength), and length - for which you use best approximation. Plus barrel I.D. - I don't know why.

Enjoy your well deserved Ale! (if that's what you fancy).

 

No problem, I'll do it tomorrow and let you know.

 

Davey, excellent. Yes do show it going back together.

 

Alright, I'll  do it.

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I have two of these waiting to be fixed... crystal is pretty scratched... have tried a first pass with the Dremel and Cerium oxide but still hazy..

 

Oh and the hour hand broke off on one of them, they seem to be less robust than on the normal divers.. !

 

Anil

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Great walkthrough Davey. It,s a real shame Seiko have started to fit plastic parts.

 

That is a movement from 80s, although it's still being made. There is less plastic on the more current 7S / 4R / 6R, and I think it's used where it ought to be.

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Could you measure mainspring and barrel? Cousins had the barrel complete but the spring alone could help old movements anyway.

 

I have measured the barrel and spring.

The barrel ID is 7.0mm

Spring. H=1.08 / Thickness=0.07 / Length=245mm give or take a few mm.

If you manage to find a replacement for the spring I would be glad to know the part number. Wouldn't mind trying a new spring in future, it's got to help.

 

Many thanks for the kind words everyone. I will put up the pictures of the build when I start. Before I do that I am going to assemble just the winding mechanism. I am wearing one at the moment that I thought I had fixed the winding problem on, it does wind but occasionally the crown still jumps as if something is not engaged. Got a feeling it is simply wear and one or two teeth are not catching, but I will have a good look at this one before final assembly.

 

 

I have two of these waiting to be fixed... crystal is pretty scratched... have tried a first pass with the Dremel and Cerium oxide but still hazy..

 

Oh and the hour hand broke off on one of them, they seem to be less robust than on the normal divers.. !

 

Anil

 

Hi Anil

I found it was taking forever removing the scratches with the powder, so now I use a small disc of "wet and dry" rubbing down paper in the Dremel tool. Starting with something co**BLEEP** like 320 grit, it really takes the scratches down and then I use progressively finer grades like 600 1000 and 1200. I need to find some good quality discs somewhere as the stuff they use for car body repairs does not last two minutes on the Dremel. I did get some good ones included in a kit and they were nice and heavy with a backing to them, but they are worn out now and I need some more. I then finish it off with some Autosol metal polish. Before I got the Dremel tool I used to lay a piece of the rubbing down paper on a nice flat surface and rub the watch, crystal down, on the paper with a little water splashed on now and again. That worked too but took a good while. It's satisfying though when you look at the finished article compared to the mess it was in at first.

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The nearest spring I could find was GR2524X which measures

1.05 x 0.075 x 260 x 6.5 dia

 

Might work but barrel complete is even cheaper at £6.60+VAT. P/N 201.420

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Davey, I have no words, excellent walk through and simple, to the point narrative pointing to what matters! I would provide for you the drink you craved if I were in your neighborhood! All I can say is excellent! I've done a couple of them too but I'm yet in my baby steps with this movement. This is a great help!

 

By the way, I suppose -- even if the mainspring is more expensive -- you would probably are interested in experimenting a bit with the one suggested. I know I would, just for the sake of it....it is a hobby anyway and maybe I get better mileage out of the new one. Still, whatever choice you make it would be perfect! -- I know the new barrel complete is tempting, including price. Just let us know how it turns up. Any reason you are not reusing the old one?

 

Cheers,

 

Bob

 

PS. Yes, please, put it back together to give closure to this excellent walkthrough, and please, don't forget the cleaning and lubrication for points of interest. Thank you in advance!

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Looking at the scoring on the inside of the original barrel I would do the same.

 

I know it looks rough in the picture CB but in "real life" it doesn't look that bad actually. I imagine the sort of age this one is now it would be good policy to fit a new one anyway. But if everything looked ok would you just put it back in cleaned and oiled?  I'm just looking for some guidance as to what's ok and what is not as I am still learning as I go along.

 

Davey, I have no words, excellent walk through and simple, to the point narrative pointing to what matters! I would provide for you the drink you craved if I were in your neighborhood! All I can say is excellent! I've done a couple of them too but I'm yet in my baby steps with this movement. This is a great help!

 

By the way, I suppose -- even if the mainspring is more expensive -- you would probably are interested in experimenting a bit with the one suggested. I know I would, just for the sake of it....it is a hobby anyway and maybe I get better mileage out of the new one. Still, whatever choice you make it would be perfect! -- I know the new barrel complete is tempting, including price. Just let us know how it turns up. Any reason you are not reusing the old one?

 

Cheers,

 

Bob

 

PS. Yes, please, put it back together to give closure to this excellent walkthrough, and please, don't forget the cleaning and lubrication for points of interest. Thank you in advance!

 

Well thank you Bob, that is most kind, the drink would not have cost you too much as it only amounted to a tea bag and some hot water. Mind you, I have got a nice bottle of Larhroaig scotch that comes out once in a while to sooth the shredded nerves.

Like I was saying to CB above, I was going to put that spring back in, I already have has it happens because I wanted to build the winding mechanism and see what might be going on there. I have come to the conclusion that it must be down to wear in the various wheels and they are not fully engaging with each other. Best I can do is flex both of the springs a bit when it goes back together so they apply a bit more tension and hopefully keep things together a bit more tightly.

Getting back to the spring, the cost of just the mainspring is more than half of what I paid for the watch. And judging by the amount of skin and nail that is left behind after feeding the spring back in I am not sure that it might be doing more harm than good this way. So I am still not sure, would one replace the barrel complete as a matter of course if the watch was performing ok or as CB pointed out above, if there were signs of scoring and wear just swap the thing out for a new one and be done with it.

 

When it comes to the cleaning, I'm afraid it is the part I hate most after oiling. I just use an ultrasonic some Priory cleaner and lighter fuel, but it is such a faff. And as for the oiling I am completely hopeless, I need a much better loupe and lots of practice getting the right amount of oil on the oiler. Sometimes I have to completely reclean this bit or that because oil has gone where it wasn't supposed to. So I hope you don't mind but can we take it as read that I have cleaned and oiled it in some fashion as it goes back together. Even just thinking about it I can almost hear the sound of bottle against glass as the golden liquid is being poured. And with that.............

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 LOL. No worries, Davey, I am just as enthusiastic with your walkthrough as if I was working on the watch myself! Just do what you had planned, no pressure, only friendly encouragement! :D

BTW, I just got some crystal I had ordered from borel for my project 4205's, if you are curious about those, -- and they fit perfectly, -- they are part number: 280W45KA00 in their site, just like the Seiko number. For all I know they are the real thing for about US12.

 

Cheers,

 

Bob

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That's a good price for a new crystal Bob. I looked on the Borel site but they don't seem to reveal much unless you login and it looks as if you need to be in business to register, or am I not looking properly?

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