Omega Seamaster PRO 300 GMT

I am interested in watches. I like tinkering with them. I have a growing pile of parts that I hope to reuse at some distant time in the future. There is this fascination I have with Omega. At first I dismissed them out of hand. I thought they were ugly and pointless, especially the Seamasters. But then they grew on me. They are not particularly blingy (at least not the generation I am interested in) and they do not carry an insane price tag. Genuine Seamasters can be bought for about 2000 EUR, used, but not abused. That does not really break the bank in the world of horology. I have no idea how popular they are in replica form. I know that people are really interested in the bond versions (oh yes James Bond now wears an omega. I think he switched from Rolex in 1995 – Pierce Brosnan was the first Bond to wear exactly the watch we are discussing, in Golden eye). It is not that I am such a huge fan of Bond flicks, but I do like the Seamaster. It has to be blue, though. I have enough black watches.


Through time, I owned four Seamaster divers’ reps. They all broke at some time, or I destroyed them inadvertently. I started with the barebones, Seamaster PRO 300 with a blue wavy dial. It looked like this:

Omega Seamaster PRO 300 (SMP)

It was not horribly expensive and was reasonably like the genuine. The little cap (the Helium Evacuation Valve) on the upper left side is in the right position (above the 10th hour), the crown is long enough and the crown guards are ok. The dial is pretty crap, but you could buy a used genuine dial for not very much. The bezel is duller and the dot is not exactly right. The bezel ring is misaligned – the pointy bits should be aligned with the bezel triangle at 12 and with the crown. The red part on the seconds hand is too short, and for this model, the date wheel should actually be white. But I like it black, so there. Also, the crystal has one-sided anti-reflective coating and the genuine SMP does not have AR.

It was still a nice watch. It broke in three weeks. It would stop suddenly. And if I wound it, it would start again. The problem was not power retention. I changed movements, same shit. I later  realised it was the ring that holds the movement inside the case. It was too tight and it was bending the ebauchement. My initial reaction was to get rid of the ring, and put in a plastic one. That works if you don’t need to wind the watch. There is an ISA (1198) quartz movement that has the same hands dimensions as ETA 28xx / 29xx. So I bought it (it costs about $10) and put it in. IT was working just fine. At that time, I did not have the Water Resistance testing equipment, or the timegrapher. I assumed it was safe to swim with – I greased the seals and thought I was fine. I took it to the swimming pool and it was ok. I then went on a holiday on another continent and the first day wore it in a jacuzzi. The inside of the glass misted over, which means that some moisture came in. When I came back, I changed the quartz movement and sealed the HEV which was not sealed before.

After a year or so, I bought myself a WR tester. A that time I had two SMP’s, one with an ETA clone and one quartz. Both crowns broke. One would free spin unless held in a specific way (which was not too bad for the quartz and the other was eventually destroyed by me – I wanted to shorten the stem so I cut it to the correct length but when I screwed it back into the crown, it broke right where at the point where none of it was left. I read about it online and realised I could use a weak acid solution which would dissolve the stem (iron) but not the crown (steel). This takes about 12 days of constant immersion. What I didn’t realise was that the pusher into which the stem screws was also iron, so I dissolved that too :(. Wah wah. Then the other crown stopped working altogether. I first bought generic crowns that are shorter than the SMP ones. And they don’t have the spring needed to screw-in. They work on the quartz although it is clearly the wrong crown.

So, I figured, I’ll buy another SMP. And this time the GMT version, because I like GMT watches. I found a genuine Omega prototype GMT dial on eBay and won an auction. So, I had the dial. I then asked a dealer to source me a Seamaster GMT. They sent this photo for my approval:

There are issues with this too. The dial is crap (the 12 markers are misaligned, the shade of blue is wrong, and the logo has the so called happy feet) , but I had another, genuine, dial. The GMT hand is wrong, but I thought I could source another. The datewheel is white, which is actually correct, but I wanted to change it to black. The bezel ring is misaligned and the HeV seems to be sticking out a bit. But, generally, I could work with this. It has the correct crown, at least.

When I got the watch, I attempted to wind it and the whole dial started swimming. WTF. Something was rattling inside. Also, the crown did not screw in. DoH! I opened it up and one of the case washers was kicking around inside. The two that were supposed to hold the movement in, were still there. Three washers? it turns out that one was wedged between the ring and the case in order to keep it in place. Now, I had a problem. Regardless of what I would do, this one would not be Water Resistant, probably. I changed the movement and attempted to secure it. IT worked up to a point, but I figured I would rather shave the ring with a dremel and secure it with fasteners as it should be. I proceeded to just slightly distort the ring when I put it into a vise to shave bits of it off. Well ok, I thought, I’ll leave this for later and put in a regular movement, with another (non – GMT) genuine dial I had. I used this for a bit and it was working fine, however it was emphatically not water resistant (I have blown out crystals and broke one of them from the force of ejection). I felt this to be a total letdown – what good is a divers watch that will get destroyed if I took a shower?

So I had three cases, one working crown, two crystals, two destroyed case rings (oh yeah, I tried to modify another one), but I did have two genuine dials and six genuine seconds hands that I procured a year or two ago. I seriously contemplated buying a replica of the new ceramic SMP, which is very very good, but the new ceramic SMP does not have the wavy dial. And I think that that wave dial is actually pretty awesome. And I have a genuine one. Well, I could buy the ceramic one and swap the dial. I was about to do that, when a sale came up on a forum I visit often. It was for a high end SMP GMT rep and the price was reasonable. Because I got burned before, I contacted the seller and asked whether the crown screwed in (IT DID) and what kind of movement was in it (Asian ETA clone with the GMT module). I figured the movement will need replacing (but I have a mint one in my spare parts drawer) anyway. And the GMT hand looked right, so I could reuse that or buy another. I have the dial, already. I went and bought genuine hour and minute hands. The genuine seconds hand, I already have. I knew there would be some work to do, but I might actually end up with a water-resistant divers watch :).

The seller was in UK and delivered the watch in less than 48 hours. Very cool.

Here it is:


It has the correct display case-back.

I figured I would first put it onto a timegrapher, to see how bad it was. IF the amplitude was low and it was very slow or very fast, I would know that it was badly in need of a service. Boy, was I surprised.

Face up, +0 s/d, amplitude 284
crown right, +5 s/d, amplitude 274


Face down, +3 s/d, amplitude 273
crown left, -2 s/d, amplitude 261


WOW. This would pass official Swiss COSC certfication. It is almost as if it was not a clone. Wait. It is not a clone, almost certainly. It has the ETA stamp and the numbers would also support the claim that this is a genuine ETA movement. Cool. Excellent. I am not swapping it. The winding was slightly rough, I’ll clean and oil the winding bridge and the winding mechanism.

I need to work on two bigger things. The (1) the insides and (2) the case

Genuine seconds, minutes and hours hands + genuine dial next to the unsuspecting victim.


(1) The insides

out of the case.


I took the hands and dial off. I replaced the date wheel for the white text on black background. I so don’t care that this is not right for this model. I dislike the the white date wheels on dark dials.

Black DW already on.



Here is a comparison shot of the two dials:

Genuine on the right (on the movement), rep on the left.


The lume is uncomparable, the dots are different, even the GMT color is brighter on the gen. I then attempted to fit the hands and encountered a snag. The dial hole is not big enough for the rep GMT hand. And for some reason, I we are not allowed to buy the genuine hand. I mean this one looks identical to the genuine anyway. Well. Luckily I have a dremel and a dremel rig.



After several incremental drillings, the GMT hand finally fit. Then I attempted to fit the genuine hands and was totally unable to get the minute hand on. I suppose it is possible that I inadvertently bought the wrong set (but it is very unlikely as the hour would not fit either then. The eta dimensions for quartz are 120/70/20 for mechanical 150/90/25). Well, whatever. I put the rep minutes hand in and the genuine seconds. If I can be bothered at some time, I’ll fix that. For now, it’s fine.

The movement has hands on.

I left the movement outside of the case overnight, to see whether everything is fine and started focusing on the case.

I mixed marine epoxy to epoxy the HeV shut.




I left the epoxy to dry overnight and proceeded next morning.

Next morning, I took the clasp off and prepared the case for WR testing (greased the seals and gaskets). The movement was working fine, by the way, so it is ready to be put into the case.

First attempt










DAMN. The crsytal blows. But not the front. The back. The front is fine.


I add silicone grease, and try again. No luck, it blows again. I glue the crystal into place. Wait for an hour, and re-do. I know that I could have used the sapphire crystal glue (which I have), but gorilla glue dries more slowly and gives you some time to adjust everything before it sets.

Third attempt at WR.










Yep! Passed this time. 6ATM. I then spent about an hour removing the excess glue from the back crystal. I used pegwood.

I dried off the case, and put the movement back in. Now, only the last bit remains. Cleaning the winding mechanism and oiling the winding parts. I won’t do the whole service, because there is so much I could screw up and I don’t have the cleaning machinery, so I would need to clean by hand and while I’ve done it before, it is long and painful and the watch does not seem to need it yet.

Movement cased.
About to clean and oil


And the last few shots of the watch.


Addendum 09/10/2017

There are always things that bug you about reps. Some are solvable, some not so much. Once I’ve done everything I had to do, the watch worked fine for a few days and then I noticed that the GMT hand would get stuck every once in a while. I attributed that to the uneven hole in the dial and resolved that I would fix it. I had an additional pet peeve, because the seconds hand was a rep one, although I have four genuine ones stashed away in my watch drawer. I couldn’t use the genuine ones, because the seconds wheel pillar was too low, or the seconds hand tube was to short, take your pick. Since I would be opening the watch up, I would try to solve this, I figured. The rep seconds hand is too stocky, the back is too long and the red part in front is too short, compared to gen.

Once I opened the watch up, I took the hands off, and managed to break the tube of the rep seconds hand. Doh. So, now I needed another solution. I had a Planet ocean seconds hand, with long enough tube to fit, but that hand does not have a dot but an arrow at the end. It would work temporarily. I could not find any rep seconds hands for an Omega, and gen ones would be useless. I figured I could buy a rep silver Rolex submariner hand, with an extra long tube and then paint the end red. The back in the rolex has a dot and in the Omega it has a square, but still better than an arrow instead of the dot in front. I ordered the hand and the correct enamel paint.

Planet Ocean seconds hand

In the meantime, I enlarged the hole in the dial, but it seems that I borked the GMT hand that now just spun on the GMT wheel without traction (for obvious reasons – it got stuck on the dial, but the wheel was still turning, which meant that the GMT hand was enlarged just enough to lose traction on the wheel). OK, I thought. Since this is the old version of the GMT wheel, where it does not click by an hour every time you set it, posing difficulties if you are not setting the GMT hand on the hour, I figured I could try and replace this one for the GMT wheels I have in my spares drawer. This worked, because the movement is the same in both cases (modified ETA 2836). I replaced the four pieces that need replacing (the calendar wheel, the calendar cover, the day wheel and the GMT wheel – this has been extensively documented here, and here for example). And then I found something else out – the old GMT wheel has a 2 millimetre diameter, and the usual ETA dimensions are 1.8mm. So, this is why the dial did not fit initially. Also the GMT hand is now absolutely too big, I’ll need to replace it. Also, I now have a hole in the dial, that is too big. Not unsolvable, the hand covers it, but I can now push it too far in, which means the outer diameter would now get stuck in the dial opening. So a bit of tenderness is required. I don’t have any Seamaster PRO GMT hands. I have any number of other GMT hands but they all look distinctly different from the original. The closest one I have is the rose gold Omega Aqua Terra GMT hand. Which is roughly the right dimensions and correct shape, but is not completely red as the genuine. I fitted that and I like it enough that I’ll keep it for now. I could always repaint it if I wanted since I have ordered the red enamel paint in the first place (for the seconds hand). I had to also replace the hour and minute wheels, because the original GMT wheel was a different height (lower) than the ones I have, which meant that replacing the GMT wheel necessitated replacing the hour wheel, otherwise the hour hand had no purchase. Which necessitated changing the minute wheel because now the minute hand had no purchase (and the seconds pillar was deep in the movement anyway…). That also meant that I could not use the genuine minutes hand, as it has to much of a lip and would not stay on, or would, but would immediately fall off, when I attempted to press the seconds hand into position. So I put in a rep minutes hand (which has the wrong colour lume, but hey, best I could do).



I set everything up, aligned the hands, put in the Omega Planet Ocean seconds hand, and wore the watch like that for a while, but the solution kept nagging me (I would always know that the seconds hand is not correct even when I switched it for the Rolex one. I kept thinking about this and it occurred to me that it is possible to buy a higher seconds central wheel with pillar (ETA part number 2801). Apparently the one I had had H1 (height 1: 4.80 mm) and there are six more heights to go (all the way to H6: 6.05mm). That could work – I could use the genuine seconds hand! I ordered two H6 and two H5 seconds wheels and waited for arrival. I know how this is replaced, it is incredibly fiddly if you do not have a microscope – you need to catch four little spindles in the correct jewel openings on the brige and all of them are eminently breakable. If you screw in the bridge without proper alignment, you will break them off, only later realising you did this, because the movement would not work. I have screwed at least three escape wheels this way. However, the good thing is that you do not need to touch the calendar side at all, except for removing the seconds hand, of course). When the seconds wheels arrived, I first test replaced one of them in another movement, just to get my hand in and when this worked, I went to the Seamaster and manged to replace the wheel in question without screwing up the movement. I did need to re-seat the bridge a few times, but I did not bend or break anything. One note for budding watchsmiths – you absolutely need to remove the winding wheel on the barrel, because the seconds wheel goes under it! It is also smart to remove the whole winding bridge with the barrel, plus if you are up for it, the balance too. If you remove the escapement lever, it makes it even easier, but I have managed to screw this up a few times, with the lever never again seating correctly (lack of a microscope FTW), so I tend to avoid this. You do not need to do any of this (except removing the barrel winding wheel), but it makes it a lot easier to set the drive train. Also, while you are at it, you could oil everything up, and clean it too, if there is a need. You have everything out on the top side of the movement, anyway.

H1 on the left, H6 on the right (sorry for the bad closeup – it’s iPhone’s fault)

So, I replaced the H6 pillar for the H1 pillar without issue and put in the genuine seconds hand. Yay!

This is the whole process (I took photos of different movements I have lying around. I hope you don’t mind me not opening up the movement that is currently beating in the SMP GMT. They are all ETA 2836 derivatives. Before you start you need to unwind, or (if you don’t know how to unwind) let the power go out of the spring. If you don’t do that you will be breaking the teeth off some of the wheels and the rest will go flying around once you remove bridges.

Fully assembled movement. Auto-winder module needs to be removed. Two black screws there.


Auto-winder needs to be removed pretty much always. Note. When you wind your watch and hear a whirring sound as if your winder weight is freely spinning, that means that this bridge is broken. Once you have removed the auto-winder module, the bridges and the balance are exposed.

You need to remove the winding wheel! See how the seconds wheel is underneath it? If you remove the hand-wind wheel, be aware of two things: (a) it unscrews clockwise! and (b) there is a spring underneath which is prone to go flying at high speed. They cost 6 pounds a pop. Just saying. You will notice in the next picture that I removed it, but for this you do not need to. I removed it from a non-working movement, because I needed the spring that flew somewhere on a working one.


The bridge removed, but barrel still in place.


You could remove the balance wheel before or after you remove the drive train bridge. Or leave it in place. Up to you.


Once you’ve lifted up the seconds wheel, put the other in place and follow the same steps in reverse. Balance goes in last. Be careful to seat the the four spindles into their respective sockets. If you have removed the escapement lever (under the balance) then once you have seated the wheels and reattached the train bridge, they should all spin, if you move the seconds wheel. If you haven’t removed the escapement lever, then they should all move together. If there is resistance, you need to see which wheel isn’t sitting right. That is why it is smart, although not required, to remove the barrel at least, so you can check whether the wheels are seated correctly. If you don’t remove the barrel, then you need to reassemble everything, wind it up and if the balance doesn’t spin, unwind, and remove the winding and train bridges and re-seat. Repeat until it works.

While I was working on the movement, I removed excess oil (it was swimming in it. I do not know who works on these watches when they are preparing them, but they should seriously cut down on the amount of oiling. There seem to be only two extremes available in reps – (1) bone dry, no oil whatsoever or (2) over-oiling everything, to the point where wheels are literally covered with oil. Literally. Seriously dudes, get a grip. both (1) and (2) are bad for the movement long term – one results in excessive wear and the other in gumming up the works once it starts degrading. The correct amount of oil is invisible to the naked eye.

There were still two or three things bothering me.

  • The crown is slightly wonky. It winds, but it will go at some point in time. Omega rep crowns really suck. I sourced a genuine crown, but it does not fit the rep tube. I have yet to find a tube that fits (I’ve tried several). Also, on most Omega reps, the crown tube is pushed into the case, but on this one, it seems to be screwed in. I bought the genuine tube for this model, which is also screw in, but it does not seem to work with the genuine crown I have. I know, this is all confusing. Simply put, the crown will go at some point and then, I’ll have a problem :). It won’t be unsolvable – I have another SMP GMT case available, that has a crown that does not screw in, which makes it not watertight at all. However, I have recently acquired a crown press and I have a rep crown that screws onto the tube, but does not screw into the case. This might work as a replacement case if the one I have fails. I would need to swap the bezel insert (because the current one is a lot more accurate than the other one) and I would have to see whether the display case-back fits (on the genuine and the case I am using there is a display back) on the other case, there isn’t. I also have another SMP case, but there is one distinct difference between the GMT and non-GMT cases – the crown guards.
  • The GMT hand is not correct, but I kind of like it, anyway. So, I might let this stay as it is, or repaint it at some point. For now, I am fine.
  • I am worried about waterproofing – the dodgy crown, etc. So, I took the movement out and retested it, this time properly – left the case under 6 atm of pressure for at least ten minutes, before lowering it into the water. It passed! So now, at least I am reasonably sure that there won’t be an issue there (I started marking the insides of the case when and what pressure they pass the WR test. Otherwise I keep forgetting which watches I can swim with, and which ones, I cannot).

Well, everything back to normal. The movement oiled, the hands seated correctly and waterproofing done. The date flips between 00:00 and 00:01. Here are two more  wrist shots:








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