Why the CHS GMT movements are failing

[KJ2020]

I can see where the confusion comes from man! Ill have a set of proper (disregarding the gmt hand pinion!) hands over to you as soon as my next piece arrives. Who would of ever thought swapping the order of 2 hands would cause this much hassle!

Ok so a couple days ago I took the final step of adding the datewheel back on (previously I had just added the datewheel driving wheel) and right away I noticed the time setting was skipping. On closer examination, I saw that the intermediate datewheel and the hour wheel joint was slipping.

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I thought maybe this was due to worn teeth on the IDW but the fact that it happened right after adding the DW made me look for another cause. Turns out the 2824 motion works cover I had swapped in was not tall enough for the DW and was causing pressure on the gears to make the GMT wheel sit crooked.

Look at the space between the silver GMT wheel and the gold hour wheel on the left side compared to the right, and how that tilts the IDW up.

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Well, I needed the arm on the motion works cover to hold the date corrector down for the restored quickset date function, so I thought maybe a 2836 motion works cover might solve both issues. I cut one down and shaped it up a bit. It worked! Note how all the gears are straight again.
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It's been running perfectly since 2:20 AM yesterday (almost 36 hours) and the date flipped fine about 12:50AM last night (remember this a slow date change 2824).

Remember these are ICHS hands so the gold GMT hand here is the hour hand, and the silver hour hand is the GMT hand.

2:20AM on the 12th

1:00PM on the 13th

I will be able to regulate this better after I get the dial on, I gave up after a few tweaks because the IDW kept falling off when I turned it upside down to adjust the balance arm. Quite annoying!

So maybe we've got a fix here. I'll let it run for a few more days and post back. It's looking pretty good right now!

OldNavitimer

Essray check out the fried silver & black insert!

 

[Dr Fun Socks]

Ok so a couple days ago I took the final step of adding the datewheel back on (previously I had just added the datewheel driving wheel) and right away I noticed the time setting was skipping. On closer examination, I saw that the intermediate datewheel and the hour wheel joint was slipping.

​
I thought maybe this was due to worn teeth on the IDW but the fact that it happened right after adding the DW made me look for another cause. Turns out the 2824 motion works cover I had swapped in was not tall enough for the DW and was causing pressure on the gears to make the GMT wheel sit crooked.
Look at the space between the silver GMT wheel and the gold hour wheel on the left side compared to the right, and how that tilts the IDW up.

​
Well, I needed the arm on the motion works cover to hold the date corrector down for the restored quickset date function, so I thought maybe a 2836 motion works cover might solve both issues. I cut one down and shaped it up a bit. It worked! Note how all the gears are straight again.
​

​

​
It's been running perfectly since 2:20 PM yesterday and the date flipped fine about 12:50AM last night (remember this a slow date change 2824).
Remember these are ICHS hands so the gold GMT hand here is the hour hand, and the silver hour hand is the GMT hand.
2:20PM on the 12th

1:00PM on the 13th

I will be able to regulate this better after I get the dial on, I gave up after a few tweaks because the IDW kept falling off when I turned it upside down to adjust the balance arm. Quite annoying!

Quality work mate! It drives me nuts when that bloody idw falls out haha! Did you not find the idw gets pushed up without the dial on or is it just my shoddy setup? Every time i manually wound it 24 hours as soon as it got near 12 and the date change wheel was engaging it just popped up away from the gmt and hour hands.

 

[KJ2020]

Quality work mate! It drives me nuts when that bloody idw falls out haha! Did you not find the idw gets pushed up without the dial on or is it just my shoddy setup? Every time i manually wound it 24 hours as soon as it got near 12 and the date change wheel was engaging it just popped up away from the gmt and hour hands.

No, it stayed put during the date change. I'd chalk it up to cheap parts not shoddy work. I still want to do the dial shim mod like yours, that was great and it will be a nice preventive measure.

 

[Dr Fun Socks]

No, it stayed put during the date change. I'd chalk it up to cheap parts not shoddy work. I still want to do the dial shim mod like yours, that was great and it will be a nice preventive measure.

Well yours does does look fantastically straight! I think its a case of belt and braces where possible on this movement, what ever is possible to make it more reliable needs to be implemented! Keep up the good work man

 

[Oascom]

Another victim explorer 2....

 

[KJ2020]

100 + hours still running strong with 4 date flips. Independent GMT hand feature is lost, but an offset to GMT can be set when pressing the hand. Remember these are ICHS hands, the gold GMT hand is the hour hand.

7:50AM on the 16th

Quikset date feature restored

The real Achilles heel in this movement impeding this workaround fix is the modified intermediate datewheel (IDW). It can be cocked up by the datewheel driving wheel, or develop worn teeth due to normal or excess use.

I will add a shim to the underside of the dial, like Dr Fun Socks did on his.





​​​​​​​Gluing the two halves of the GMT wheel together should not increase or change any stress points on gears in this movement. We are just forcing the hour jumping spring (which no longer even needs to be present) to remain in its stationary state, a condition it is in 99% of the time if the CHS time setting rules are followed.

Success of this workaround fix is therefore largely dependent on an IDW with good teeth that will stay engaged with the hour wheel. This part is unique to this movement and cannot be sourced other than from a Chinese factory which isn't going to happen.

Special thanks to Tickleshoes for the original idea for this fix, and Dr Fun Socks for continuing support of parts and ideas.

 

[Dr Fun Socks]

100 + hours still running strong with 4 date flips. Independent GMT hand feature is lost, but an offset to GMT can be set when pressing the hand. Remember these are ICHS hands, the gold GMT hand is the hour hand.

7:50AM on the 16th

Quikset date feature restored

The real Achilles heel in this movement impeding this workaround fix is the modified intermediate datewheel (IDW). It can be cocked up by the datewheel driving wheel, or develop worn teeth due to normal or excess use.

I will add a shim to the underside of the dial, like Dr Fun Socks did on his.





Gluing the two halves of the GMT wheel together should not increase or change any stress points on gears in this movement. We are just forcing the hour jumping spring (which no longer even needs to be present) to remain in its stationary state, a condition it is in 99% of the time if the CHS time setting rules are followed.

Success of this workaround fix is therefore largely dependent on an IDW with good teeth that will stay engaged with the hour wheel. This part is unique to this movement and cannot be sourced other than from a Chinese factory which isn't going to happen.

Special thanks to Tickleshoes for the original idea for this fix, and Dr Fun Socks for continuing support of parts and ideas.

I agree about the idw. There seems to be no way to get a spare one which is a pain in the ass! Great idea about putting the quickset date in though man, proper stroke of genius. Lets be honest no one ever uses the jumping hour hand anyway, i bet people with the gen probably only use it once a year tops if they go away. Its just nice to have a 24 hand and a splash more colour than the usual submariner.

I know this is a hell of a long shot, but the idw is made up of several gears pressed onto a spindle. If its somehow possible to get the worn gear off, maybe that one flat gear would be easier to replace than the unit as a whole? Theres so many little gears in watch movements, one of them has to be close? I know im dreaming a bit but it may be possible.

 

[KJ2020]

I agree about the idw. There seems to be no way to get a spare one which is a pain in the ass! Great idea about putting the quickset date in though man, proper stroke of genius. Lets be honest no one ever uses the jumping hour hand anyway, i bet people with the gen probably only use it once a year tops if they go away. Its just nice to have a 24 hand and a splash more colour than the usual submariner.

I know this is a hell of a long shot, but the idw is made up of several gears pressed onto a spindle. If its somehow possible to get the worn gear off, maybe that one flat gear would be easier to replace than the unit as a whole? Theres so many little gears in watch movements, one of them has to be close? I know im dreaming a bit but it may be possible.

Had contemplated that myself bro. In fact the IDW from the 2836 ICHS movement has the exact same gear on it. It's situated below a smaller gear that turns the GMT wheel, which is above the hour wheel on that model. Essentially the top two IDW gears, and the two hour wheels have swapped positions to allow for the hands to be swapped. So we have a ready made gear to use as a replacement. I compared the two closely, and they are for all intents and purposes identical. The sample ICHS gear I looked at had nice better teeth, same 24 in number as the CHS one. I was thinking about how to separate one from the column and install the other when I saw that the motion works cover switch was going to work, so I abandoned that pursuit. But I think it is definitely an ace in the hole to pull out next if all else fails. In a brute force approach, I think even grinding/sanding the CHS gear off and carefully epoxying the ICHS one on would work, though certainly a more elegant solution would be preferred.

 

[Dr Fun Socks]

My thinking is they are interference fitted together on the spindle, so in theory something like this would work to get the top one off, which seems to be the one that wears:

Gives me something fun to make on the lathe haha! Im thinking just put an m5 thread on the punch and it will work in a crystal press or something similar. Getting them back together, i guess just bung it in a vice?

 

[KJ2020]

Just what I needed, the toolmaker's touch! Could just get a new hollow tube and re-stack the gears then punch the ends larger. Looks like that's how it was done originally. I may talk to a local jeweler.

 

[Dr Fun Socks]

Just what I needed, the toolmaker's touch! Could just get a new hollow tube and re-stack the gears then punch the ends larger. Looks like that's how it was done originally. I may talk to a local jeweler.

Yeah that makes sense but why rebuild the whole stack if its only the top one that needs changing? If the new gear is a loose fit you could just get a tiny center punch or something similar and give it a little tap in the spindle to tighten it up?

 

[KJ2020]

Yeah that makes sense but why rebuild the whole stack if its only the top one that needs changing? If the new gear is a loose fit you could just get a tiny center punch or something similar and give it a little tap in the spindle to tighten it up?

Sure, I was just thinking if it got damaged punching it out. I watched a guy completely make a new center wheel from scratch on you tube, teeth, spokes, pinion leaves, pinion properly tapered, wow. So swapping one gear should be pretty easy really. Maybe I should send you an ICHS gear, you are better equipped to try this. Only problem is if you muck it up you've lost an irreplaceable part. So yeah I think you should do it, haha.

 

[Dr Fun Socks]

Sure, I was just thinking if it got damaged punching it out. I watched a guy completely make a new center wheel from scratch on you tube, teeth, spokes, pinion leaves, pinion properly tapered, wow. So swapping one gear should be pretty easy really. Maybe I should send you an ICHS gear, you are better equipped to try this. Only problem is if you muck it up you've lost an irreplaceable part. So yeah I think you should do it, haha.

Haha you have much faith in my little ability! Ive got a bit of time spare tomorrow, i might have a little play around with some bits ive got in my parts bin and see how feasible it actually is. In theory it should be doable, in reality... we’ll see!
i looked into those gear making machines (begins with a b but i forget the name) when i was looking for replacement idw’s. At £6k a pop, not the most practical solution haha

 

[Dr Fun Socks]

KJ2020 Its actually really easy mate. Took me all of 5 minutes. Im assuming this is as similar a wheel as you can find in a miyota, albeit the piece the brass wheel is pressed onto has a slightly larger diameter. I just found the size of the second largest wheel in the stack, in this case about 2mm, and the depth of the stack minus the brass wheel (im removing the brass wheel obviously) which was 1.8mm. Used a 2.5mm center drill (its just the start of a 10mm/2.5mm center drill) and took it 3mm deep. Is it worth doing a through bore just incase your bit gets stuck? Probably. But mine didn’t. it got stuck on the tooth pick as you can see. Press down with a tooth pick or peg wood or whatever you have, boom its apart. Chucked it in my mini vice (hold it vertically or alignment will be a bitch) and boom its back together again. Should be a doddle.

 

[KJ2020]

KJ2020 Its actually really easy mate. Took me all of 5 minutes. Im assuming this is as similar a wheel as you can find in a miyota, albeit the piece the brass wheel is pressed onto has a slightly larger diameter. I just found the size of the second largest wheel in the stack, in this case about 2mm, and the depth of the stack minus the brass wheel (im removing the brass wheel obviously) which was 1.8mm. Used a 2.5mm center drill (its just the start of a 10mm/2.5mm center drill) and took it 3mm deep. Is it worth doing a through bore just incase your bit gets stuck? Probably. But mine didn’t. it got stuck on the tooth pick as you can see. Press down with a tooth pick or wood or whatever you have, boom its apart. Chucked it in my mini vice (hold it vertically or alignment will be a bitch) and boom its back together again. Should be a doddle.

Very nice bro, I knew you had it in you!

 

[Dr Fun Socks]

Very nice bro, I knew you had it in you!

You happy giving it a go or do you want me to test pilot the unobtainable piece?

 

[KJ2020]

You happy giving it a go or do you want me to test pilot the unobtainable piece?

Need to think about this carefully. I'm not sure we need to do it as a preventive measure if the movement is running well, as mine is. It may come to needing to do it on yours. I'll see where we are when it arrives. It's a nice extra workaround to have in the bag o tricks, though. The 2836 gear we would use for the mod is not available separately but would have to come off a dead ICHS. So they are scarce too but I have a few.

 

[Dr Fun Socks]

Need to think about this carefully. I'm not sure we need to do it as a preventive measure if the movement is running well, as mine is. It may come to needing to do it on yours. I'll see where we are when it arrives. It's a nice extra workaround to have in the bag o tricks, though. The 2836 gear we would use for the mod is not available separately but would have to come off a dead ICHS. So they are scarce too but I have a few.

That works for me mate i wasn’t particularly looking forward to trying it on a non disposable part haha! Good to have in the bag though as you say

 

[AussieWatcher]

Awesome work here.. fascinating insight into a fix!

 

[Vvvlllooo]

Would anyone happen have a spare of this spring, broken or not? I am interested to take stab at drafting it and seeing what it would cost to tool replacements out of a higher quality material.

This, have you made one or gotten a hold of something