A well-built Seiko mod is a precision instrument. Treat it with the same respect you'd give any quality mechanical watch and it will reward you with years — potentially decades — of reliable service. Neglect it, and even the best movement will let you down.
This guide covers everything you need to keep your ZJani Mods piece performing at its best — from daily habits and cleaning routines to gasket care, service intervals, and what to do when something goes wrong.
Understanding What You're Caring For
Before diving into the specifics, it helps to understand what makes a mechanical watch different from most objects you own. A Seiko mod contains a movement with dozens of tiny components — gears, springs, jewels, and levers — all working in precise coordination, lubricated with oils measured in microns. The case around it is engineered to keep water, dust, and pressure out.
Both the movement and the case require periodic attention. Neither is maintenance-free. But the care required is straightforward, and most of it is simply a matter of good habits.
Daily Wear: Habits That Protect Your Watch
The way you wear your watch day-to-day has a bigger impact on its longevity than any single maintenance task. A few habits will extend the life of your watch significantly:
Magnetic Fields
Mechanical movements are susceptible to magnetisation, which disrupts the balance spring and causes erratic timekeeping — often running fast by 30+ seconds per day. Modern life is full of magnetic hazards: speaker magnets, magnetic bag clasps, tablet covers, and even some laptop lids. Keep your watch away from these when possible. If you suspect magnetisation (sudden timekeeping change with no other cause), a watchmaker can demagnetise the movement in minutes.
Crown Discipline
Two rules: don't wind the crown while wearing the watch (remove it first to avoid lateral stress on the stem), and always screw the crown down before any water exposure. A crown left unscrewed — even partially — will allow water ingress regardless of the watch's rated depth. This is the single most common cause of water damage in dive watches.
Impact Awareness
Mechanical movements are shock-resistant to a degree, but a hard knock — dropping the watch on a hard floor, catching it on a door frame — can displace components or damage the balance staff. Seiko movements include Diashock protection, which helps, but it's not a guarantee. If your watch takes a significant impact, check the timekeeping over the following 24 hours.
Temperature Extremes
Avoid prolonged exposure to extreme heat (saunas, direct sunlight on a dashboard) or cold. Heat thins the movement oils; cold thickens them. Both affect timekeeping and accelerate wear. Brief exposure is fine — it's sustained extremes that cause problems.
Cleaning Your Watch
Regular cleaning keeps your watch looking sharp and prevents the build-up of salt, sweat, and grime that can degrade gaskets and corrode metal over time.
After Saltwater or Sweat Exposure
Rinse the watch under fresh running water with the crown screwed down. This is the most important cleaning step and takes 30 seconds. Salt is corrosive — left on the case and bracelet, it will attack the metal and degrade rubber gaskets over time. Don't skip this step after beach days or heavy exercise.
Regular Case and Bracelet Cleaning
Every few weeks, give the watch a more thorough clean:
- Confirm the crown is screwed down.
- Use a soft toothbrush with a small amount of mild soap and warm water.
- Work into the bracelet links, case lugs, and bezel edges where debris accumulates.
- Rinse thoroughly under running water.
- Pat dry with a lint-free cloth, then leave to air dry completely before storing.
Avoid harsh chemicals, solvents, or ultrasonic cleaners unless you're confident the gaskets are in excellent condition. Ultrasonic cleaners can dislodge debris that then enters the movement.
The Crystal
Sapphire crystals are highly scratch-resistant but not scratch-proof — they can be scratched by materials harder than sapphire (silicon carbide, certain ceramics). For everyday cleaning, a soft microfibre cloth is all you need. For minor surface marks, a small amount of watch crystal polish (such as Polywatch, though formulated for acrylic, some watchmakers use specific sapphire compounds) can improve clarity — apply sparingly and buff in circular motions. Deep scratches in sapphire require crystal replacement.
The Dial
Never attempt to clean the dial yourself. It's delicate — the printing, lume plots, and applied indices can all be damaged by contact. If the dial has dust or debris visible through the crystal, it needs to go to a watchmaker for proper cleaning in a controlled environment.
The Strap or Bracelet
Different strap materials need different care:
- Leather straps — avoid prolonged water exposure. Rotate straps regularly to allow drying between wears (sweat degrades leather quickly). Condition occasionally with a leather balm. Replace when the stitching frays or the leather cracks.
- Rubber/silicone straps — rinse after saltwater exposure. Inspect periodically for cracking or stiffness, which indicates the rubber is degrading. Replace every 2–3 years under regular use.
- NATO straps — machine washable. Replace when the hardware shows corrosion or the fabric frays.
- Metal bracelets — clean as described above. Check clasp function periodically. Have a watchmaker tighten any loose pins — a bracelet pin failure can result in losing the watch.
Water Resistance: What It Means and How to Maintain It
Water resistance is not a permanent property — it's a rating that applies to a watch in a specific condition at a specific moment. The gaskets that create the seal compress and degrade over time, reducing the effective water resistance even if the rating on the caseback hasn't changed.
Gasket Maintenance Schedule
- Regular swimmers and divers: Have gaskets inspected and replaced every 2–3 years. Have the watch pressure-tested annually.
- Occasional water exposure: Have gaskets inspected every 3–4 years.
- Primarily land wear: Have gaskets inspected every 4–5 years or at each service.
After any caseback opening — for battery replacement, service, or inspection — always have the watch pressure-tested before water exposure. The act of opening and closing the caseback can disturb the gasket.
Signs of Water Ingress
If you see any of the following, stop wearing the watch near water immediately and take it to a watchmaker:
- Condensation or fogging inside the crystal
- Water droplets visible inside the case
- Rust-coloured marks on the dial or movement visible through the crystal
- Sudden timekeeping changes after water exposure
Water damage to a movement is serious and expensive to repair. Caught early, it can often be remedied with a full service and movement clean. Left untreated, it causes corrosion that can destroy the movement entirely.
Service Intervals: When and Why
A mechanical movement requires periodic servicing — disassembly, cleaning, lubrication, and adjustment by a qualified watchmaker. This is not optional maintenance; it's essential to the long-term health of the movement. The oils that lubricate the gear train and escapement dry out and congeal over time, increasing friction and wear on the components.
Recommended Intervals
For NH35A and NH36A movements under normal use: every 5–7 years. Watches worn in demanding conditions (saltwater, extreme temperatures, heavy physical activity) may benefit from more frequent servicing.
Signs a Service Is Overdue
- Timekeeping accuracy has deteriorated significantly (more than 30 seconds per day)
- The rotor feels rough, gritty, or catches when the watch is moved
- The watch stops unexpectedly despite a full power reserve
- The crown feels stiff or gritty when winding
- Visible moisture or condensation inside the crystal
- The watch hasn't been serviced in over 7 years
What a Service Includes
A full service of an NH35A movement typically includes: complete disassembly, ultrasonic cleaning of all components, inspection for wear or damage, replacement of worn parts (mainspring, keyless works components if needed), lubrication with the correct oils for each component, reassembly, regulation on a timing machine, and pressure testing of the case. Expect to pay €80–€150 for a quality service from an independent watchmaker.
Storage: Protecting Your Watch When Not Worn
How you store your watch matters, particularly for pieces not worn daily:
- Away from direct sunlight — UV exposure fades dials and degrades rubber straps and gaskets over time.
- Cool and dry — humidity accelerates gasket degradation and can cause condensation inside the case. Avoid bathrooms and kitchens for long-term storage.
- In a watch box or roll — protects the crystal and case from contact scratches and keeps dust out. A simple watch cushion is sufficient; you don't need an expensive case.
- Watch winders — for automatic watches not worn daily, a winder keeps the movement running and the lubricants distributed. Use a quality winder with the correct turns-per-day setting for the NH35A (approximately 650–800 TPD). Alternatively, simply wind the watch manually before wearing — about 20–30 turns of the crown is sufficient.
When to See a Watchmaker
Some situations always require professional attention — don't attempt to address these yourself:
- Any moisture or condensation inside the case
- A damaged, loose, or difficult-to-operate crown
- Significant impact (dropping the watch on a hard surface)
- Timekeeping suddenly off by more than 30 seconds per day
- Any caseback opening — always pressure-test afterwards
- A rotor that rattles, catches, or feels wrong
- Any visible damage to the crystal, case, or bracelet that affects function
Frequently Asked Questions
How often should I service my Seiko mod?
Every 5–7 years under normal use for NH35A/NH36A movements. If you swim or dive with the watch regularly, have the gaskets inspected every 2–3 years regardless of the service interval.
Can I shower with my Seiko mod?
Technically yes, if the watch is rated to 100m or more and the crown is screwed down. However, soap and shampoo can degrade gaskets over time, and the steam in a hot shower is more penetrating than cold water. It's better practice to remove the watch before showering.
How do I know if my watch has been magnetised?
The most common symptom is a sudden increase in rate — the watch runs fast by 30 seconds or more per day with no other obvious cause. A watchmaker can confirm magnetisation with a simple test and demagnetise the movement quickly and inexpensively.
Can I replace the strap myself?
Yes — strap changes are one of the few things you can safely do yourself with a spring bar tool. Be careful not to scratch the case lugs. If the spring bars are tight, don't force them — a watchmaker can change a strap in minutes without risk of damage.
Built to Last
Every watch from ZJani Mods is assembled with quality gaskets, pressure-tested before shipping, and built to be worn. Follow this guide and your piece will serve you well for years to come. Whether you own the Custom Vintage Green Milsub Mod Watch or the Custom Blue Speed Seiko Mod Watch, the care principles are the same. If you have questions about caring for your specific build, don't hesitate to get in touch.
