Movement review - ETA 7750 with running seconds at 6

[onzenuub 307]

Originally posted by Ziggyzumba at RWG.

 

Well finally, a review of the Mystery Swiss 7750 modified with running seconds at 6 oclock movement in the new Daytona.

 

Lets get right into the details on this highly modified 7750.

 

First point, why use a genuine Swiss Valjoux movement when there are plenty of copies available?? Why not use an Asian 7750 as a base movement?

 

Probably for one reason and one reason only, the tolerances, quality, finish precision, etc, on the real one all add up to give you one thing - POWER. Once you see all the extra gears (and there are lots of them) then youll see that using anything but the real movement is useless. Add all this to the Asian model, and it probably wont start or run at all.

 

Update

 

This article was written before the latest version of the Asian 7750 was produced. The newest version on the Asian 7750, is as good as the ETA one, and has corrected all of the defects with the older version. I have reviewed the newest Asian 7750, so if you need details on it, please read my review. My comparison is with the old Asian 7750, not the new one

 

I remember stating that I figured it was impossible to modify this movement to the new layout. Well it has been done, and probably in a way that was not thought of (at least not by me). Kind of like the new inventions on Infomercials, once you see it, it seems so simple, Why didnt I think to re-label spray paint cans and sell it as instant hair replacement(got to give Ron Popeill credit where credit is due).

 

The movement was only disassembled to a certain level; there are a few reasons for this as youll see. As much as it would have been even more informative to have a complete teardown, remember that the added parts are all replica parts, and therefore dont have the same quality or tolerances of the real product. Total disassembly was far too risky, and also an unknown area, not sure what would be found and exactly how it was put together.

 

Please understand that this is a very complex movement, and the pictures and drawings are intended to clarify the layout, although at first glance they may seem confusing, I think if you review the text and compare it to the drawings, you can figure it out at least I hope so

 

Background

 

Some background info is required if everyone is to understand how these modifications were accomplished, why they were needed, and what the end results are.

 

Until 2000, Rolex used Zenith El-Primero movements in their Daytona models. This movement has running seconds at the 9 position, 12-hour counter at the 6 position, and the 30-minute counter at the 3 position on the dial. Funny that Rolex is supposed to be setting the standard in movements, yet it took them 26 years to come up with their own in-house movement for the Daytona.

 

Post 2000 Daytonas (which is what this latest model is trying to replicate) are a problem to copy because of the sub-dial locations. The new models have running seconds at the 6 position, 12 hour counter at the 9 position, and 30-minute counter at the 3 position.

 

The big problem is trying to find a movement that has this layout, there isnt one (apart from the real Rolex one). So this modified 7750 is trying to replicate the new dial layout; and it does do it; although as youll see there are some drawbacks and possible problems down the road.

 

What is needed to get the right sub-dial layout?

 

So a standard 7750 has the following sub-dial layout:

 

 

The new Daytona has this layout:

 

 

How to go from an original 7750 to the new layout, is to add lots of gears to move the outputs across the dial face to the new locations.

 

 

New movement

 

 

 

 

 

12 position on the 7750

 

So lets work our way around the dial starting at the 12 position in a CCW direction. The 12 position is where the output from the 30-minute counter comes through from the back of the movement. The output is a small shaft on which the sub dial hand would normally be fixed.

 

On this modified movement, a new gear is pressed onto the shaft, where the sub-dial hand would normally be placed. The piece of the shaft left sticking up is cut off flush with the gear. To get the motion from the 12 position to the 3 position requires 2 more gears as you see here.

 

 

 

9 position

 

The 9 position has the running seconds. This is a shaft extension from the 2nd wheel on the other side of the movement, to which a sub-dial hand would normally be attached. The modified model needs to have running seconds at the 6-position. This is done with some clever thinking, and some special gears.

 

 

 

First off, a new gear is pressed onto the shaft as was done to the 30-minute counter, and the remaining shaft is cut off. Two more new gears are added to take the motion first towards the right and upper part of the movement, then a gear with a large hollow center part is placed over the hour hand shaft, taking the motion down, and 2 more gears are added to finally get the motion on the 6 Oclock position.

 

So how well does this work? Not bad - but not great either. There is a fair amount of slack in the gear teeth, and the result is that the seconds hand jerks as it moves around the dial. The other possible long term problem is the friction of the big hollow gear on the hour hand shaft, any bit of old oil or dirt in this critical area will bring the movement to a halt. Look at any movement, there are jewels and tiny pivots at all rotating points throughout the gear train to reduce friction to a minimum. The friction from the new gear here

 

 

 

Must be very high (certainly if we compare it to a pivot set into a jewel) so I wonder how that will affect the accuracy and life of the movement.

 

The one area that will cause problems is beyond belief (at least to me it is).

 

Question: What sub-dial is running all the time and has the most potential for wear and should be jeweled to reduce wear???

 

If you answered the Running seconds at 6 sub dial then your right!

 

So then why in the world would you choose this one to NOT put a jewel into??? Any of the other ones, not a problem, no jewel = not a big deal. But the one that is running all the time, and you have brass on metal for a pivot point?? The only other location where there is metal on metal is the mainspring barrel, and it moves a complete rotation every 8 hours or so, not once every minute.

 

This is the pivot for the running seconds gear:

 

 

Its not a question of will it fail, I think its a question of when will it fail And when it does, or the drag gets too high for the movement to be able to swing out really well, then the watch will stop working. Biggest design flaw in an otherwise well made modification (the large gear on the center post is not a design flaw, simply a point of extra drag).

 

6 position, the biggest mystery of them all solved!

 

If you remember my comments on first seeing this movement, I asked how the 12 hour counter could be moved from the 6 position to the 9 position. My biggest issue was the overlapping of the gears (moving motion from the 9 to the 6 dial position, and from the 6 to the 9 position), which as we saw was solved by taking the running seconds and sending it across the dial face, through the middle of the movement, and to the 6 Oclock position. With those gears out of the way, the space is now cleared to get the 12-hour sub-dial into the new location.

 

 

 

The original 12 hour counter works as follows: the gear is actually two pieces, the bottom half is connected directly to the bottom of the mainspring barrel and it turns ALL the time, even with the chrono stopped. The top half of the gear is driven through a clutch. In the chrono stopped position, there is a small brake lever that rests on the side of the top half of the gear and holds it locked. The gear also has a heart piece cam on it, which serves to center the gear when its reset.

 

Its simple to take the top half of the 12-hour gear, add two more gears, and reposition the 12-hour counter to the 9 position on the dial.

 

The problem of having the brake and reset to zero levers moved across the dial face is solved by retaining the original ones, since the top gear is connected to the new gears, then resetting the chrono will in turn reset the new gear as well (pretty clever).

 

Some have reported problems with the 12-hour sub dial; from not resetting to 12, to running all the time. Not resetting to 12 is probably due to a loose hand (not uncommon on chronos), or the gear slippage from the original gear to the new ones. Because I did not have a chance to disassemble the movement, I can only assume that a new gear was installed over the old one, not sure if that is the case, but if you look at the teeth on the gear here,

 

 

they are not really gear teeth, but notches for the brake to rub against and stop the gear from moving. They may have substituted a new gear for this one with the clutch built in etc, no way to know until its opened further (which was not done with this one).

 

As for the people with this model and it has the 12-hour running all the time, that is simply the brake lever being out of place on the arm from the bottom pusher. See the picture here to see how it sits in the notch, easy to assemble the watch with it out of place.

 

 

Why not disassemble completely??

 

If your following along, you note that new gears have to be press fitted on the original posts to carry the motion to a new location on the dial. These new gears and the shafts they go over are small, the shaft diameter is 0.18mm, or about the size of the period at the end of this sentence. Unless the watch was broken, then in my view, it is too risky to press the gears off the stems when you dont know the quality of the gear material. It looks like brass, which is very soft, whereas most Valjoux gears are made from Glucydur, an extremely hard and stable material.

 

Conclusions

 

So now that we know how they did it, what is the final verdict?

 

No question on the movement origin, its a real Valjoux 7750. The basic movement is very well made, fantastic finish on all the parts, and runs really well. Its a strong runner and by itself should last a lifetime if serviced correctly and maintained over the years. The additions made to the top of the movement, are well-done, good quality on the bridges and gears etc. Most of the pivots are jeweled, except for the one that should be jeweled but isnt (running 6 seconds).

 

So overall a great piece of engineering, how well will it hold out in the long run is anyones guess. What will fail first is the running seconds, simply because of the extra drag from 5 new gears, non-jeweled pivot, the drag from that big gear in the center of the movement. All added together – it certainly exceeds the design limits that the movement was originally intended to power. Proof of this is to simply look at the design drawings of the variants (7753, 7765 etc) of this model, every added gear is mounted to have the least possible resistance on the movement.

 

How to make it last.

 

Good chance that the chrono large seconds hand will slip on the shaft and stop resetting to zero. Common chrono flaw. Fix = dont reset any further than +- 10 seconds from the 12 position.

 

Have the movement serviced, so the new bridge and gears are offering the least resistance to the movement.

 

Is it worth it??

 

If youre a Daytona fan, and must have the post-2000 model, then I guess it is.

 

On this particular model, one of the movement hold down clamps was out of place and not attached to the case side grove, the top pusher was sticking and needed to be lubricated, and the 12 hour counter reset to the 4 position. A bit of a let down for the price paid.

 

These are small details, but unless you can open the case, remove the movement and remove and reposition the 12 hour sub dial hand, reattach the movement clamp, and lube the pusher, then your left with a watch that the chrono doesnt work, and possible problems because the movement is loose in the case.

 

UPDATE

 

Since doing this review, I have had a few of these Swiss powered Daytonas in house for repair and servicing. Some of the problems have been the 12 hour subdial not resetting as it should, on these I had to freeze the subdial as I could not fix it. On others there have been problems with the jerkiness of the running seconds hand, simply due to the culmination of clearances between the 5 new gears. And also I have had to disable the running seconds on some models, as the friction of the new gears was too high, and the movement would not work.

 

I have also ventured all the way into the movement and disassembled totally the new bridge and new transfer gears. It was not as scary as it appeared to be initially, but as with any new movement, and with no reference drawings, its very risky to take something apart, not knowing how they put it together.

Thanks for reading.

[greg_r 81]

Cool! Thanks again, Onze!

[taokexun 0]

Nice post.

[bananakid0 0]

Nice post.

 

How does this guy have 0 posts

[RUSH2112 11]

I think this question is an excellent reason to bump a thread that is 7 years old.

[bananakid0 0]

I think this question is an excellent reason to bump a thread that is 7 years old.

Thank you