Seiko’s OEM movements as well as their ‘generic’ NH calibers are known as reliable workhorse movements that can power a watch for years before needing a replacement. That said, they are not exactly immune to sudden breakage, especially when handled improperly.

When operating on something as fragile as watch movements, so many things can go wrong. As a bundle of thin and small mechanical parts, there are a hundred ways you can break your movement and make it unusable for watch builds. Once the caliber stops tracking time accurately or loses one of its complications, it becomes nothing more than a paperweight, which is why you should always practice some safety precautions when working with one.



In this article, we tackle the top 5 things to avoid when working with NH calibers and other watch movements, and hopefully by the end of this read, you’ll know the proper care and safety needed to handle them.


Do not place it near magnets

This one is more of an obvious warning, and probably something you have heard before (or learned the hard way). Magnets are bad for movements, not because they damage them outright, but because it affects accuracy. What’s a watch that tells the wrong time? The part of the movement most affected by magnets is the balance spring which contracts and expands in a steady tick to regulate your watch. Placing movements near magnets will make your watch run faster, slower, and in some cases, can even cause it to stop completely.



There may be more magnets in your home than you may realize. In your modding workspace, you may have magnetic clips to organize documents, or magnetic cabinet latches to keep drawers closed. Wireless phone chargers also use a strong magnet that can affect a watch movement when placed closely together. Screwdrivers can also be magnetized, which is not advisable to use if you’re swapping out your watch rotor.


Do not expose it to open air

‘Is Oxygen bad for movements?’ You might be asking. It is not the air that’s bad for watch movements though, but the dust and particles that are present in it. Small particles can easily interfere with the movement’s functions, and while it may not be obvious at the start, too much dust and debris on a movement will cause it to wear out much earlier than normal.



Be in the habit of keeping your modding area clean with regular vacuum cleaning. When wiping surfaces, use a damp cloth or sponge to make sure the dirt sticks instead of just being spread into the air. Proper airflow helps reduce dust accumulation, so keep a window open and make sure that the HVAC filter is changed regularly.

And even if you make sure that your workspace is clean, it is still best practice to keep your movement in a sealed storage until the time comes when you’re about to use it for a mod. Use a dust blower before casing your movement to get as much debris off it as possible.


Do not drop it

While today’s watch movements often have some degree of shock-proofing, it’s safe to say (or perhaps, not safe) that dropping a movement or applying sharp and sudden force can cause it to malfunction. Mechanical movements like the NH calibers have moving parts that are under constant torque, and a sudden shock can cause these to dislocate, or worse, to break.



Seiko movements often arrive in tight and padded containers to protect them during shipping, and it’s wise to just keep the movement in this packaging for safety until it’s time to use it for a mod. That said, these containers do not offer 100% protection and the dangers of transit can still affect the movement, so always make sure to double check that all the functions of your movement are working as normal before using it for your Seiko mod.


Do not over-tighten screws

This advice is more specific to our modfam who have decided to spice up their movements with a beautifully designed rotor like our new Asanoha or Cloud rotors. It’s a simple mod to do, but you can still mess up your movement if you’re not careful!



First, make sure that you’re using the correct screwdriver to remove the rotor screw. You’ll need a 2.5mm wide screwdriver with the correct thinness or else you won’t be able to safely remove the screw. Second, make sure that you are applying just the right amount of force when reinstalling the rotor screw, as too little force will cause the rotor to rattle and make noise when you move, while too much force may cause it to lock up and possible even break the movement.


Do not let it dry up

Watches should be serviced every three to five years. Mechanical parts naturally generate friction, and proper lubrication at regular intervals will extend the lifespan of your movement, and by extension, your watch.

To know more about which oils to use, parts you’ll need, and best practices for oiling your movement, check out our in-depth article here.


Wrap up

In the world of watchmaking, your timepiece's beating heart deserves some tender loving care. NH calibres and other movements keep your watches ticking with precision, but they can be delicate so remember to always handle your movements gently and to keep your workplace clean and organized. With these general guiding principles, your Seiko mods will serve you well for years to come.

And now that you’re aware of how to properly work on watch movements, be sure to check out our catalog for your movement needs! We have a wide selection from the GMT NH34 movement to the skeleton NH71, and we have accessories as well like rotors and replacement day / date wheel discs to make your watch calibre look even better.

Happy modding!

October 22, 2023 — Jeremiah A

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