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This project started out as another attempted investigation into whether or not the rep Rolex GMT CHS movement could be repaired once the hour jumping spring has broken. That investigation is still on-going but as a corollary to it, I was also interested in seeing if the rep CHS cases would take either of the common ICHS movements, the 2836 ICHS or the DG2813/3804 ICHS movements (hereafter simply referred to as ‘3804’). For those interested in following the repair efforts, please see this thread:
https://forum.replica-watch.info/for...-failing/page7
Surely someone has discovered this before, but it was news to me and I haven’t seen it posted elsewhere so guess what? BOTH the 2836 and the 3804 GMT ICHS movements fit and function properly in the CHS case I had to work with. No mods to the case, rotor or caseback are needed.
At this point I’d like to thank OldNavitimer whose posts I had seen indicating multiple CHS movement issues. I contacted him and he generously sent me three watches, a 2824 CHS, a 2386 ICHS and a DG2813 ICHS. Without his pieces to work on, I could not have made these tests and conclusions. Thanks bro!
Both the ETA watches were BP factory, but I think it’s safe to assume we can apply the same results to other factory watches. Please post back with your own findings on other factory watches!
I started off by taking some key measurements and doing some visual comparisons of the ETA ICHS vs CHS. Here is what I found. All measurements are in mm
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I did not see a need to measure everything about the 3804 case, but it’s stem height is 2.5mm and its dial spacer was .67mm, dial thickness 0.5mm
So you can see the important elements of the two ETA cases are similar enough to be negligible, and adding up the stem height of the movement, dial, and dial spacers we get:
2824 CHS: 3.80mm
2836 ICHS: 3.75mm
3804 ICHS: 3.67mm
After reviewing the measurements and examining the cases, it’s apparent that BP just used a 2836 case to house the 2824 CHS movement. They used a thicker dial spacer to make up the height difference, and raised up the datewheel to help offset overmagnified dates. The extra space created by the thicker dial spacer on the 2824 CHS allows room for the modified intermediate date wheel, which we will see a photo of later. This modified intermediate wheel is considerably taller than its 2836 counterpart, and would have made using a 2836 as a base impractical.
Here are some shots of the cases, crowns, dials, datewheels and dial spacers.
Datewheels and dial spacers
As ingenious as the design of the 2824 CHS is, I am struck by how cheap the parts are. It is a real shame that the time and money spent on pretty decorations and engravings for the backside bridges wasn’t better allocated to the movement parts that matter. The CHS movement looks marvelous when you open the back. Take the dial off and it’s a different story altogether.
Here’s a shot of the two movements together. You can see in this pic that the CHS date corrector is missing. The hole for it to fit into the CHS movement is not a slot like a normal 2824, meaning it can’t move to the right with the crown in position 2. This disables the quickset date feature usually provided by this gear.
Here you can see an additional intermediate wheel was added to the CHS to allow the date corrector gear to interact with the GMT wheel. This is where the hour jumping spring comes into play, supposedly freezing the GMT wheel while jumping the hour wheel (in gold color).
In the next few pics you can see the intermediate date wheels and how much taller the modified CHS one is. The gears are reversed vertically to drive the reversed wheels on the CHS, all necessary to have the GMT and hour hand positions swapped. The third tiny gear on these wheels is to power the datewheel driving wheel to change the date.
Here you can see just how little there really is to the CHS movement.
Here’s pics of the 2 ICHS movements installed in the CHS case
Things you will need to replace your CHS movement
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This freshly serviced 2836 ICHS movement is happy in its new CHS case home.
I hope this will be the first of many and we can start returning our paperweights to their former glory!
A new DG3804 movement is about $40, hands about $20. Easily found on ebay or Startime.
A new 2836 ICHS can be gotten for around $110, hands about $30. Look on ebay or ask your TD.
https://forum.replica-watch.info/for...-failing/page7
Surely someone has discovered this before, but it was news to me and I haven’t seen it posted elsewhere so guess what? BOTH the 2836 and the 3804 GMT ICHS movements fit and function properly in the CHS case I had to work with. No mods to the case, rotor or caseback are needed.
At this point I’d like to thank OldNavitimer whose posts I had seen indicating multiple CHS movement issues. I contacted him and he generously sent me three watches, a 2824 CHS, a 2386 ICHS and a DG2813 ICHS. Without his pieces to work on, I could not have made these tests and conclusions. Thanks bro!
Both the ETA watches were BP factory, but I think it’s safe to assume we can apply the same results to other factory watches. Please post back with your own findings on other factory watches!
I started off by taking some key measurements and doing some visual comparisons of the ETA ICHS vs CHS. Here is what I found. All measurements are in mm
_
| 2836 ICHS | 2824 CHS | |
| Max dial diameter | 28.0 | 28.2 |
| Rehaut aperture | 26.8 | 26.8 |
| Distance from bottom of rehaut to center tube | 3.9 | 3.95 |
| Distance from bottom of rehaut to underside of crystal | 2.8 | 2.8 |
| Movement holder outside diameter | 28.2 | 29.2 |
| Movement stem height | 2.25 | 1.8 |
| Dial thickness | 0.5 | 0.5 |
| Dial spacer | 1.0 | 1.5 |
| Datewheel tooth ring height | 0.75 | 0.9 |
| Hands H/M/S (GMT) | 1.5/1.0/.25 (2.0) | 2.0/1.0/.25 (1.5) |
I did not see a need to measure everything about the 3804 case, but it’s stem height is 2.5mm and its dial spacer was .67mm, dial thickness 0.5mm
So you can see the important elements of the two ETA cases are similar enough to be negligible, and adding up the stem height of the movement, dial, and dial spacers we get:
2824 CHS: 3.80mm
2836 ICHS: 3.75mm
3804 ICHS: 3.67mm
After reviewing the measurements and examining the cases, it’s apparent that BP just used a 2836 case to house the 2824 CHS movement. They used a thicker dial spacer to make up the height difference, and raised up the datewheel to help offset overmagnified dates. The extra space created by the thicker dial spacer on the 2824 CHS allows room for the modified intermediate date wheel, which we will see a photo of later. This modified intermediate wheel is considerably taller than its 2836 counterpart, and would have made using a 2836 as a base impractical.
Here are some shots of the cases, crowns, dials, datewheels and dial spacers.
Datewheels and dial spacers
As ingenious as the design of the 2824 CHS is, I am struck by how cheap the parts are. It is a real shame that the time and money spent on pretty decorations and engravings for the backside bridges wasn’t better allocated to the movement parts that matter. The CHS movement looks marvelous when you open the back. Take the dial off and it’s a different story altogether.
Here’s a shot of the two movements together. You can see in this pic that the CHS date corrector is missing. The hole for it to fit into the CHS movement is not a slot like a normal 2824, meaning it can’t move to the right with the crown in position 2. This disables the quickset date feature usually provided by this gear.
Here you can see an additional intermediate wheel was added to the CHS to allow the date corrector gear to interact with the GMT wheel. This is where the hour jumping spring comes into play, supposedly freezing the GMT wheel while jumping the hour wheel (in gold color).
In the next few pics you can see the intermediate date wheels and how much taller the modified CHS one is. The gears are reversed vertically to drive the reversed wheels on the CHS, all necessary to have the GMT and hour hand positions swapped. The third tiny gear on these wheels is to power the datewheel driving wheel to change the date.
Here you can see just how little there really is to the CHS movement.
Here’s pics of the 2 ICHS movements installed in the CHS case
Things you will need to replace your CHS movement
_
| Replacement ICHS | What you need |
| 2836 ICHS | CHS case crown CHS case movement holder CHS or ICHS dial ICHS datewheel with DWO (or CHS DWO cut off and swapped to 2836 DW) 2836 ICHS Movement 2836 ICHS dial spacer Hour and GMT hands (or whole new set) |
| DG 2813/3804 ICHS | CHS case crown CHS case movement holder CHS or ICHS dial (3804 dial must fit and have gen-spec date window position or CHS dial needs feet cut and redone) ICHS datewheel with DWO (or CHS DWO cut off and swapped to 3804 DW) 3804 ICHS Movement 3804 ICHS dial spacer Whole new hands set |
This freshly serviced 2836 ICHS movement is happy in its new CHS case home.
I hope this will be the first of many and we can start returning our paperweights to their former glory!
A new DG3804 movement is about $40, hands about $20. Easily found on ebay or Startime.
A new 2836 ICHS can be gotten for around $110, hands about $30. Look on ebay or ask your TD.
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