Servicing a Sinn U1 Automatic Watch
The German brand Sinn Spezialuhren is renowned for its “form follows function” philosophy, producing some of the most robust tool watches in the industry. Founded in Frankfurt am Main in 1961, Sinn originally focused on pilot chronographs and navigation clocks. However, it is their diving range—specifically the Sinn U1—that has become a modern icon. Built from high-strength, seawater-resistant German Submarine Steel, the U1 is designed for extreme durability.
While the exterior is engineered to withstand the pressures of the deep, the heart of the watch requires precision care. On the bench today, we have a Sinn U1 in for a full service.
The Movement: Sellita SW200-1
The Sinn U1 is powered by the Sellita SW200-1, a high-quality Swiss automatic movement. This calibre is a respected industry workhorse, found in many high-end timepieces. For instance, TAG Heuer utilizes this architecture for their Calibre 5 movements, and it is also a staple for brands like Oris and MeisterSinger.
As a BHI accredited workshop and an accredited service centre for TAG Heuer, our watchmakers are intimately familiar with the SW200-1. While it is a robust movement, its longevity depends entirely on the condition of its lubricants and the integrity of its components.
The Service Process: Disassembly and Repair
Our client’s Sinn U1 arrived showing signs of poor power reserve and erratic timekeeping. Upon initial inspection, we identified that the movement was running “dry,” meaning the specialized oils had evaporated or thickened over time.
To restore this timepiece to its factory specifications, we followed a rigorous service protocol:
- Disassembly & Inspection: The movement was completely stripped down. We found notable wear on the reversing wheels—a common point of friction in automatic winding systems.
- Cleaning: Every component underwent a multi-stage cleaning process in our Elma Solvex machine. The submarine steel case and bezel were cleaned separately in an ultrasonic bath to remove any built up dirt and debris.
- Reassembly & Lubrication: The movement was rebuilt using a brand-new mainspring and fresh reversers. We applied specific Moebius lubricants to the escapement, gear train, and winding mechanism, strictly following the technical guides for this calibre.
Ensuring Water Resistance
A Sinn U1 is nothing without its diving credentials. After the movement was cased, the watch underwent a pressure test to confirm its water resistance. Given the U1’s significant depth rating, ensuring the gaskets are seated perfectly and the crown seals are intact is a critical final step before the watch leaves the bench.
“We strongly recommend having professional tool watches like the Sinn U1 serviced every 3-5 years to maintain both movement health and the integrity of the water-resistant seals.”
Summary
This Sinn U1 is now back to its best. By replacing the worn reversers and mainspring and performing a full clean and lubrication, the movement is once again ticking with the precision expected of high-grade Swiss and German engineering.
It is always a pleasure to work on Sinn watches. If you have a Sinn watch, or any timepiece featuring an SW200-1 movement that is due for maintenance, please do get in touch with our team.
At W.E. Watch Repairs, we specialise in servicing both modern and vintage timepieces. If your Sinn or Sellita-based timepiece needs repairs, movement servicing, or precision tuning, our skilled watchmakers are here to help.
Take advantage of our Royal Mail Special Delivery FREEPOST service—your watch is fully insured for up to £20,000 throughout its journey, ensuring peace of mind from the moment it leaves your hands until it is safely returned.