Dr. Ito's thorough analysis of mechanical watches!! Vol.11 - What is the difference between an overhaul and a partial service?

Hello everyone!

This column, which discusses mechanical watches from an engineer's perspective, is now in its 11th installment.

"The difference between an overhaul and a partial service"

We will be discussing this topic.

A mechanical watch is an assembly of dozens, or even hundreds, of parts. Even a minor issue can lead to a malfunction, necessitating regular maintenance.

This is where "overhauls (complete repair)" and "partial services (partial repair)" come in.

This time, we will explain questions such as "What is an overhaul?" and "What is the difference between an overhaul and partial maintenance (partial service)?" Please read to the end!

"What is an Overhaul?"

"Overhaul" comes from the English word "OVERHAUL," meaning disassembly and repair, or thorough inspection. It refers to "the process of disassembling a mechanical product down to its component parts, cleaning and adjusting them, reassembling them, and then performing inspections to restore them to their as-new performance." Incidentally, this term is also used in industries other than watches, such as for cars and musical instruments.

It is also often abbreviated as OH, and even those not particularly familiar with watches may have come across it.

During a watch overhaul, the movement is disassembled, thoroughly cleaned, and adjusted. The main steps are as follows:

1. Remove the movement from the case, and remove the hands and dial.

2. Disassemble each part, and replace any damaged parts.

3. Clean all parts in a dedicated ultrasonic cleaner.

4. Reassemble and adjust, lubricating gears and other components.

5. Perform accuracy and water resistance tests.

Most of the overhaul process is done manually by technicians. It's clear that it requires skilled craftsmanship and a lot of time.

Why an overhaul is necessary

The purpose of an overhaul is to prevent major breakdowns by replacing worn-out parts inside the watch.

Just like humans, mechanical watches require regular check-ups to detect problems early.

If a problem is caught in its early stages, the watch can be restored to good health through adjustments or the replacement of small parts. However, if a problem is neglected and the entire movement is damaged, it may be necessary to replace the main plate, also known as the base plate, or the entire mechanism.

For this reason, an overhaul is recommended for many mechanical watches every 5 to 10 years.

If an overhaul is neglected for many years, what kind of condition will the watch be in?

・Wear and damage to parts due to lubricant deterioration

・Loss of water resistance and rust due to rubber gasket deterioration

・Decrease in accuracy

・Decrease in power reserve

These problems will occur.

Deterioration of lubricant is a particular issue. The various gears in a mechanical watch move smoothly when lubricated with oil, but prolonged use can cause the oil to dry up, leading to wear on the gears.

In this state, the gear shafts or bearings may be worn down, or the gear teeth may chip, potentially leading to expensive parts replacement.

Difference from Partial Service

Are you aware that there is a term "partial service" in contrast to "overhaul"?

Some manufacturers call an overhaul a "complete service," implying "complete" and "thorough."

On the other hand, "partial service" means performing "partial" or "some" maintenance.

For example, if a watch is only a year old since its last overhaul and is experiencing symptoms such as "the watch is running slow" or "the calendar gets slightly stuck when changing," a partial repair, or partial service, can restore the watch to good condition.

However, if more than five years have passed since the last overhaul and there are symptoms such as "significantly poor accuracy" or "the calendar is not changing," then an overhaul is necessary. (*Some workshops may not offer partial service and only provide overhaul.)

As you might have guessed, overhauls are more expensive than partial services because they involve more labor. However, from the perspective of how challenging the work is, partial services can actually be more difficult.

For a technician, an "overhaul" is a somewhat "standardized" task, but for a partial service, the technician must identify the cause based on the watch's condition and the nature of the malfunction, and then determine the necessary work.

In other words, it is difficult to perform a partial service without a technician who has years of experience with overhauls and has accumulated a certain level of expertise.

Furthermore, if any defect arises within the warranty period, it is likely that experienced technicians are assigned to repair it, as each manufacturer must identify the cause of the defect and provide feedback to their headquarters. Considering these factors, a "partial service" could be considered a more luxurious form of maintenance than an "overhaul."

Incidentally, it's often thought that a watch can continue to be used with just partial services. However, partial services only repair the faulty parts, and other areas are not lubricated. Therefore, regular overhauls are still absolutely essential.

Summary

How was it?

Overhaul (complete repair) and partial service (partial repair). Just hearing the words, it might seem like an overhaul is more difficult, but I hope you now understand that a partial service has its own unique challenges and that the technician's experience is crucial.

Even if you request a partial service, some manufacturers' policies or the watch's condition might only allow for an overhaul. However, I believe understanding the differences between the two is important for enjoying your wristwatch life to the fullest.

I hope this article was helpful to everyone and that it sparked even a little more interest in luxury watches! Also, if you have any questions, please feel free to ask, and we will answer them thoroughly. We look forward to your visit and inquiries.

Stay tuned for the next installment! See you then!