YN55 vs NH35/NH36: Why I'm Testing Epson's Movement for No-Date Pilot Watches
If you've built or bought a modded watch in the last few years, there's a good chance a Seiko NH35 or NH36 is ticking inside it. It's the workhorse of the modding world, and it powers almost every SQND CITY automatic I've built. But over the past year, the NH35 has roughly doubled in price for me. That pushed me to start testing an alternative: the YN55.
Who makes the NH35, NH36, and YN55?
The NH35 (date) and NH36 (day-date) are made by Seiko's Time Module (TMI) division and sold to modders and microbrands worldwide. The YN55 is made by Epson, which is also part of the Seiko family and the company behind Orient's movements. So this isn't a knockoff. It's a Japanese-made automatic from the same corporate family, just from a different factory. Its sibling, the YN56, adds a day-date.
Close-up of the EPSON YN55A
YN55 vs NH35/NH36: the specs side by side
Beat rate: both run at 21,600 beats per hour (6 ticks per second)
Power reserve: NH35/NH36 about 41 hours; YN55 40+ hours
Jewels: NH35 24; YN55 22
Factory accuracy: NH35 -20 to +40 seconds per day; YN55 -25 to +35 seconds per day
Hacking and hand-winding: both
Size: both 27.4mm wide and 5.32mm thick
Cost: the YN55 and YN56 are about a third cheaper than the NH35 (date) and NH36 (day-date)
On paper they're nearly twins. The power reserve is practically the same, the accuracy window is actually a little tighter on the YN55, and the YN55 and YN56 come in about a third cheaper than their NH counterparts. That's not a huge gap, but with prices rising the way they are, every bit counts.
Are NH35 parts compatible with the YN55?
Mostly, and that's what makes it interesting for a modder. Because the dimensions match, the YN55 fits in NH35 cases, which is exactly what I'm seeing on my bench. The hour and minute hands use the same sizes, so NH35 hands go right on. The seconds hand post is a hair different on paper (0.20mm vs 0.21mm), but in my test builds the NH35 seconds hand fits and runs without issue.
It's not a 100% parts swap, though. The rotors aren't interchangeable, and the date setup is different, so plan around the movement you're actually using.
Where the YN55 wins: no-date watches
This is where the YN55 really earns its spot. In my testing, the way its date wheel is positioned makes it a cleaner choice for no-date dials, which is exactly what you usually see on pilot watches. I've also noticed the seconds hand sweep looks a touch smoother on the YN55. Both beat at the same rate, so that's my observation from the bench rather than a spec-sheet number, but it's something you notice when you watch the hand go around.
A stand-in, not a full replacement
I'm not replacing the NH35 and NH36 across the board. For day-date builds and divers, the Seiko movements are still my go-to: parts are everywhere, service is easy, and buyers know them. The YN55 is a smart stand-in for one specific job: clean, no-date watches.
That's why I'm testing it in my upcoming Meigs line, a future SQND CITY pilot series. So far the YN55s are holding up well, keeping good time, and dropping right into NH35 cases. I'll keep tracking accuracy and power reserve as they wear in before anything goes up for sale.
The bottom line
If you build no-date watches, the YN55 is worth a look: Japanese-made, NH35-case compatible, and about a third cheaper. And no matter which movement is inside, every SQND CITY listing will always tell you exactly what's powering your watch.
Have questions about either movement, or want a no-date build of your own? Send me a message. I'm always happy to talk movements.
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