Seiko 7546 swap for NH35 movement in ETA 2824 case (you read that right)

2829 Views 14 Replies 5 Participants Last post by bk_lake, 3 mo ago

shazboy

Discussion Starter · Jun 9, 2022

Upon learning from a reddit post that the 7546 movement is a close fit for NH35 cases, I decided to try to cram a 7546 movement into a 36mm datejust case (fitted ETA 2824s but also fits NH35s) with a dial from an old Seiko quartz. I refuse to put a NH35 movement under a seiko quartz dial out of principle--it feels wrong. Everything went pretty well, until I got to the crown.

So the case in question comes with a 6mm rolex-style crown that is apparently threaded for tap 10 (0.9mm) stems. However, the 7546 stems (part # 354-601) are tap 9 (1.0mm). So I bought a tap 9/10 stem extender to connect the two, and the crown is now attached to the stem.

The problem is that the resulting combination is too long (even after trimming the extension as far as possible) for the crown to screw down onto the case tube. I don't own a pair of calipers to check the exact width, but I'm seeing about 2.5-3.5mm of space in between the crown (with screw-down spring depressed) and the base of the tube threading where it should screw down.

I am not sure whether the best bet is to find a tap 9/10 adapter that can cut down that width, find another crown that will match, or something else. I haven't given up yet, but I do feel like I'm running out of options. It's worth noting that I do not have a lot of tools and am very new to this whole thing, so attempting to re-tap any of these parts is out of the question (for me, at least). Any ideas? I welcome your thoughts and any deserved ridicule

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bk_lake

· #2 · Jun 9, 2022

You are almost there but it isn't going to work. I got one step further than you with a 6309 (same dimensions as 754x) in a NH35 case. The stem height is too different. You won't see it/know it until you try to seat the crown. It needs a spacer between the chapter ring and dial. Then you have to worry about the case back. I forgot what the magic number is but somewhere around .5mm or .8mm, something like that. If making this spacer is within your capabilities, it's just one more step. I found a watchmaker's die plate on ebay and used it to rethread the stem. The stem is the cheapest part. Seiko stems are pretty strong steel. I'm not sure the die is usable any more in that size.

I was able to fit a Ronda 515 to an NH35 case. There is a small difference in stem height but not enough to change anything. If I wanted it to be perfect, I would find a .02mm shim. I used a 2824 spacer and a wavy spring I found on aliexpress. The Chinese watchmakers are pretty resourceful. When I saw watches that came in NH35 or 2824 clone movements, I knew they had a reasonable way of adapting the movements in. I took a chance on the on the parts and seemed to have come up with the right combination.

The Ronda 515 movement is pretty decent movement and cost $10-15. Same stem height and diameter as 2824. Path of least resistance on the case you have.

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Grammarofdesign

· #3 · Jun 9, 2022

@bk_lake that is a great tip. Thanks.

I have learned the 7548 cannot be subbed into a 7S or 4R because of the stem hole distance from top of dial. No go.

bk_lake

· #4 · Jun 9, 2022

My observation was that you would need a spacer between the dial and chapter ring. Or a special chapter ring that extends down. I don't think there is enough length to the hour and minute posts to raise the dial off the movement. It's a bridge too far. Not sure how a spacer would look. I guess one could get artistic and use a different color and size combination to make it step looked. Not that motivated and have no eye for these things.

shazboy

Discussion Starter · #5 · 12 mo ago

bk_lake said:
My observation was that you would need a spacer between the dial and chapter ring. Or a special chapter ring that extends down. I don't think there is enough length to the hour and minute posts to raise the dial off the movement. It's a bridge too far. Not sure how a spacer would look. I guess one could get artistic and use a different color and size combination to make it step looked. Not that motivated and have no eye for these things.

Thanks for the advice. For this attempt, I also had to use dial adhesive to stick the dial to the movement, as the dial came from an 8222 and the feet placement is different between that and the 754x. So I imagine that might cause even further problems with the stem height issue you mentioned. I will look into trying the Ronda movement as that seems like the next best thing, and will see about what else I can do with my 7546 now that this case seems to be off the table. Thank you!

Masman

· #6 · 3 mo ago

bk_lake said:
You are almost there but it isn't going to work. I got one step further than you with a 6309 (same dimensions as 754x) in a NH35 case. The stem height is too different. You won't see it/know it until you try to seat the crown. It needs a spacer between the chapter ring and dial. Then you have to worry about the case back. I forgot what the magic number is but somewhere around .5mm or .8mm, something like that. If making this spacer is within your capabilities, it's just one more step. I found a watchmaker's die plate on ebay and used it to rethread the stem. The stem is the cheapest part. Seiko stems are pretty strong steel. I'm not sure the die is usable any more in that size.

I was able to fit a Ronda 515 to an NH35 case. There is a small difference in stem height but not enough to change anything. If I wanted it to be perfect, I would find a .02mm shim. I used a 2824 spacer and a wavy spring I found on aliexpress. The Chinese watchmakers are pretty resourceful. When I saw watches that came in NH35 or 2824 clone movements, I knew they had a reasonable way of adapting the movements in. I took a chance on the on the parts and seemed to have come up with the right combination.

The Ronda 515 movement is pretty decent movement and cost $10-15. Same stem height and diameter as 2824. Path of least resistance on the case you have.

bk_lake said:
You are almost there but it isn't going to work. I got one step further than you with a 6309 (same dimensions as 754x) in a NH35 case. The stem height is too different. You won't see it/know it until you try to seat the crown. It needs a spacer between the chapter ring and dial. Then you have to worry about the case back. I forgot what the magic number is but somewhere around .5mm or .8mm, something like that. If making this spacer is within your capabilities, it's just one more step. I found a watchmaker's die plate on ebay and used it to rethread the stem. The stem is the cheapest part. Seiko stems are pretty strong steel. I'm not sure the die is usable any more in that size.

I was able to fit a Ronda 515 to an NH35 case. There is a small difference in stem height but not enough to change anything. If I wanted it to be perfect, I would find a .02mm shim. I used a 2824 spacer and a wavy spring I found on aliexpress. The Chinese watchmakers are pretty resourceful. When I saw watches that came in NH35 or 2824 clone movements, I knew they had a reasonable way of adapting the movements in. I took a chance on the on the parts and seemed to have come up with the right combination.

The Ronda 515 movement is pretty decent movement and cost $10-15. Same stem height and diameter as 2824. Path of least resistance on the case you have.

I know this is an older thread but figured i'd give it a shot... I am looking to build two watches with Ronda 515 movements in NH35 cases. Do you by chance have the links for the spacer and wavy spring you used to make it work? Any help is greatly appreciated!

bk_lake

· #7 · 3 mo ago

I'll look at my old orders but the parts were from Aliexpress. Give me a few hours to get to a real computer.

Grammarofdesign

· #8 · 3 mo ago (Edited)

Update I just built a mod using a 7546 in a case designed for the 4R36. Managed to get the stem hole lined up to the crown tube hole exactly using a standard 7546 dress watch style spacer. Got a vintage NOS 354601 stem to adapt the movement to the crown same tap.

Bumper Automotive exterior Auto part Household hardware Strap

Overcame the "true 4 o'clock stem location" issue simply by using a no-date dial. Otherwise a date window overlay and taking apart and re-staking the day wheel would have been necessary.

Can be done !!

Calling @vincentg !!

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vincentg

· #9 · 3 mo ago

Grammarofdesign said:
Update I just built a mod using a 7546 in a case designed for the 4R36. Managed to get the stem hole lined up to the crown tube hole exactly using a standard 7546 dress watch style spacer. Got a vintage NOS 354601 stem to adapt the movement to the crown same tap.

View attachment 512515

Overcame the "true 4 o'clock stem location" issue simply by using a no-date dial. Otherwise a date window overlay and taking apart and re-staking the day wheel would have been necessary.

Can be done !!

Calling @vincentg !!

The case is taking longer than I thought to fit fat bars and an EO MN, plus I had to drill out the spring bar holes for the fat bars, using a #57 to good success

I should have the case done tomorrow and I will take some pics this weekend. The titanium case was from AliX and idk how they expected a strap to be mounted.

Automotive lighting Audio equipment Rim Output device Gadget

Awesome build Jon, I can't wait to get a wrist shot, or see my Son when he opens the present. Far exceeds my expectations thank you again!

Watch Analog watch Watch accessory Clock Font

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2

Masman

· #10 · 3 mo ago

bk_lake said:
I'll look at my old orders but the parts were from Aliexpress. Give me a few hours to get to a real computer.

Any luck finding the orders? Thanks for checking!

bk_lake

· #11 · 3 mo ago

I think it was this one: https://www.aliexpress.us/item/3256...tewayAdapt=glo2usa4itemAdapt&_randl_shipto=US
Also used one of these 29.2mmx25.5mm: https://www.aliexpress.us/item/3256...tewayAdapt=glo2usa4itemAdapt&_randl_shipto=US This store that has the plastic ring has a bad rating now. I would shop another store.

And, this one: https://www.aliexpress.us/item/3256...!sea!US!1782742677&curPageLogUid=m0bniWF7jNSw

bk_lake

· #12 · 3 mo ago

Grammarofdesign said:
Update I just built a mod using a 7546 in a case designed for the 4R36. Managed to get the stem hole lined up to the crown tube hole exactly using a standard 7546 dress watch style spacer. Got a vintage NOS 354601 stem to adapt the movement to the crown same tap.

View attachment 512515

Overcame the "true 4 o'clock stem location" issue simply by using a no-date dial. Otherwise a date window overlay and taking apart and re-staking the day wheel would have been necessary.

Can be done !!

Calling @vincentg !!

Any idea what the part number on that spacer is? Or, what model it came out of?

This may revive a crazy idea I had but abandoned because of stem height.

bk_lake

· #13 · 3 mo ago

There are 3 part numbers listed in the 7546 tech guide and parts list. Trying to narrow down the possibilities.

Grammarofdesign

· #14 · 3 mo ago

bk_lake said:
Any idea what the part number on that spacer is? Or, what model it came out of?

This may revive a crazy idea I had but abandoned because of stem height.

bk_lake said:
There are 3 part numbers listed in the 7546 tech guide and parts list. Trying to narrow down the possibilities.

Part Number 884750 used in a whole bunch of 6309s, 7546s and Y513s

bk_lake

· #15 · 3 mo ago

Thanks. Need to go digging through my Ramon stash to see what I have.

Reactions: 1

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