You Can Now Fix Your "Dead" Seiko NH Movements with These Spare Parts

Seiko’s NH movements are known for being hardy little machines, but they’re not invincible and actually need delicate handling while it’s still outside of a watch. If you’ve been modding for a while, we’re sure you’ve come across your fair share of “dead” movements, whether you were the culprit or not. But sometimes, the movement isn’t actually irreparable to the point of being just paperweight; it could just be one small part inside that’s worn out, bent, or missing, throwing off everything downstream of it.

The not-so-good news is that most modders have no idea these parts even exist until something starts acting weird. Now, you can sharpen your watchmaking skills even further by fixing movement issues yourself, with the help of new OEM spare parts that’s available in our store.

Here are the seven movement spare parts that you can get, what they do, and when to replace them.

 

NH34 Dial Washer (Parts Ref No.: 0491 333)

The dial washer is a thin cup-spring that sits under the dial, wrapped around the central pinion, right above the hour and 24-hour wheels on the NH34 GMT. Its whole job is to press down on those wheels so they stay properly meshed with the motion works and the GMT gear train. Without that pressure, the wheels can lift or drop out of engagement whenever the watch gets handled or the GMT hand gets corrected.

You'll want to check this washer if you've recently swapped a dial and now notice the GMT or hour hand occasionally stopping, jumping, or losing sync whenever the watch is tapped or set face-down. Pop the dial off and you'll likely see the hour or GMT wheels visibly lifting because the washer's missing or deformed. 

The other giveaway is circular rub marks on the underside of the dial paired with a GMT hand that feels stiff during setting. That's usually a distorted washer no longer holding the correct clearance from the gear stack, and if you leave it, it'll keep chewing into the plastic GMT wheels underneath. 

 

NH35/36 Day-Date Corrector Wheel (Parts Ref No.: 0737 183)

This is the wheel that makes quickset work. When you pull the crown to the first click, the day-date corrector setting transmission wheels drive this corrector wheel, and its fingers alternately grab either the date disc or, through the day train, the day mechanism, depending on which way you turn the crown. Counter-clockwise moves the date on both NH35 and NH36, and clockwise engages the day side on NH36 only.

The telltale sign of a damaged corrector wheel is a crown that spins with little to no resistance when changing the day or date. The date might barely move, snap back into place, or fail to change at all. This happens when the teeth on the corrector wheel or its spring fingers are worn or damaged, often caused by adjusting the movement while the quickset mechanism is engaged (ie: between 9PM-4AM).

You might also see the date only creep halfway into the window, or the day wheel randomly skip two positions instead of one. That's chipped or missing teeth from forcing the crown while the midnight change was already in progress. A new corrector wheel gets you back to clean, positive, one-step changes.

 

NH35/36 Intermediate Date Driving Wheel and Pinion (Parts Ref No.: 0817 300)

This one sits in the automatic midnight date-change train, acting as the go-between that links the motion works to the date indicator driving wheel. Splitting it into a wheel and a pinion lets Seiko control the gear ratio and timing precisely, so the date disc advances exactly once every 24 hours without overloading the motion works.

If your watch keeps accurate time but the date only moves partway at midnight, this wheel is the first place to look. Worn or snapped teeth mean it's no longer fully turning the date indicator driving wheel. You may notice similar problems when using the quickset function. The date could move unevenly, grind, or stop halfway through the change. Again, this is usually damaged when engaging the quickset while it’s in the danger zone (9PM-4AM).

 

NH35/36 Barrel Complete with Mainspring (Parts Ref No.: 0201 083)

You can think of the barrel as the movement's fuel tank: a drum holding the coiled mainspring, with teeth around the outside that drive the entire gear train. Both manual winding through the crown and automatic winding through the rotor feed into this same spring, and it's the torque released from here that keeps everything else turning. A fully wound, healthy NH mainspring should give you around 41 hours of running time.

If you fully wind the watch but only get around 20 to 25 hours of power reserve, the mainspring may be worn, fatigued, or slipping inside the barrel. This is especially likely if the movement has otherwise been checked and the escapement and gear train are working normally. 

You'll sometimes catch this on a timegrapher too, seeing amplitude swing wildly as the reserve runs down, or you'll just feel it directly as an uneven winding feel with the odd slipping sensation. Any of that, plus visible rust or contamination inside the barrel wall, and it's time to go for a full barrel swap which is faster, and more reliable than trying to salvage it.

 

NH Small Screws Pack of 5 (Parts Ref No.: 0012 354)

These are the unglamorous parts that hold everything else together. A Seiko movement will have different screws throughout the entire mechanism, but thankfully for watch repairmen, a few of them actually use the same specs. Our NH small screws can be used in the following parts:

- Date indicator maintaining plate
- Hour wheel guard screw
- Automatic train bridge screw
- Pallet bridge screw
- Lower plate for barrel and train wheel bridge
- Center wheel bridge

The most common way modders end up needing these is simply losing one mid-mod or mid-repair. You’ll know that a screw is missing if the plate ends up sitting loose, or the calendar behaves erratically for no obvious reason. You might also want to replace them if they have been stripped or burred from previous work, or rusted from moisture getting into the case. 

 

NH36 C-Clip – Snap for Day Star with Dial Disk (Parts Ref No.: 0963 300)

This is the retaining clip that keeps the day star wheel seated correctly inside the NH36. It's an easy part to lose track of during teardown, and just as easy to damage if the day mechanism gets pushed past where it wants to go. 

If the day wheel feels loose enough to lift with tweezers, or the day indication drifts and hangs between two days, the C-clip has likely been bent or lost during a previous disassembly. You'll see a related but slightly different symptom if the day changes correctly at midnight or in quickset but then slips out of alignment after a light knock or crown adjustment. A new snap restores the correct friction and stops the day wheel from floating.

 

NH36 Intermediate Wheel for Day Corrector (Parts Ref No.: 0989 070)

The day intermediate wheel sits between the day-date corrector wheel and the day star. Its job is simple: it transfers movement from one part to the other while keeping the correct direction and gear ratio. Without it, the corrector wheel can't properly drive the day star, which means the bidirectional quickset function won't work as it should. 

You’ll know there’s a problem when the crown quicksets the date perfectly fine in one direction but does absolutely nothing to the day wheel in the other. That points straight to a missing, wrongly seated, or defective intermediate wheel. You may also notice a similar issue during the automatic date change at midnight. The date changes normally, but the day sometimes fails to advance. A bent arbor or worn teeth could be the cause, especially if someone previously forced the crown while the automatic day and date change was already in progress between 9 PM and 4 AM.  Replacing the wheel gets the day train back to giving the day star a clean, single push every 24 hours.

 

Wrap Up

We know that taking apart the movement to replace one of its miniscule parts is a tall order especially if you’re newer to the Seiko modding scene, but if you already have a defective movement lying around that is otherwise just gathering rust and dust, why not use it to practice taking apart a caliber and fix it? It’s not guaranteed to work after replacing its components, but you’ll gain an even deeper understanding of watch engineering, more than if you’re just modding the case and other external parts.

Ready to try your hand at it? Head on over to our store and get your movement spare parts, tools and accessories, designed to keep your watch in tip top shape while adding some spice to the build as well. Note that we don’t only have NH movements in our inventory, we also offer Miyota and VK Mecaquartz movements, if you want to tinker with something other than a Seiko automatic build.

Happy modding!