A fake Omega Caliber 8605 is a replica movement dressed to look like Omega's in-house GMT caliber. Most examples start life as a generic Swiss or Asian automatic, often an ETA 2892-A2 or a Chinese clone of the 8500 family, then receive a stamped rotor, laser-etched bridges, and a 24-hour hand. The genuine Caliber 8605 is a twin-barrel co-axial automatic with a silicon Si14 balance spring, a 60-hour power reserve, and a free-sprung balance that carries no regulator index. That missing regulator arm is the fastest tell on the whole watch.
What the 8605 Number Refers To
Omega used the 8605 in the Seamaster Aqua Terra GMT and the Planet Ocean GMT, plus a small number of other GMT references. It belongs to the 8500 movement family: co-axial escapement, two mainspring barrels in series, a 4 Hz beat rate, rhodium-plated bridges with arabesque Cotes de Geneve stripes, and a Si14 silicon balance spring. The GMT hand tracks a second time zone and the date corrects through the crown. A watch sold as an 8605 that lacks those traits is not an 8605, whatever the rotor says.
Before You Look at the Movement
- A 10x loupe or a macro lens with strong, angled light
- A timegrapher, or a timing app and a quiet room
- Reference photos of a genuine 8605 from a service manual or an owner thread
- A caseback opener, or a watchmaker who owns one
- The exact reference number the seller claims
How to Check a Suspected Fake 8605
- Confirm the reference number the case should carry, since the 8605 was never fitted to every Omega GMT.
- Open the caseback or use the display back, then set the movement under 10x magnification.
- Inspect the balance, because a genuine Si14 silicon spring reads dark and matte while replica movements show a blue steel hairspring or a bright spring under a regulator arm.
- Read the engraving on the rotor and bridges, then compare depth and font weight against your reference photos.
- Turn the crown through each position and note the order of hour jump, date correction, GMT setting, and hand winding.
- Run the watch on a timegrapher in four positions and record rate, beat error, and amplitude.
- Feel the winding by hand, since a twin-barrel 8605 loads up with firm resistance instead of a thin, loose spin.
- Hand the watch to an independent watchmaker and ask for a written note on the movement's origin before you pay or resell.
Red Flags That Point to a Replica
- Shallow laser etching that catches light in a flat, uniform way
- Arabesque stripes that stop at the bridge edge instead of running under the screws
- A blue steel hairspring paired with a regulator arm on a movement that should be free-sprung
- A GMT hand that jumps with the hour hand instead of setting on its own
- Rotor engraving that reads 8605 on a reference that shipped with another caliber
- Timegrapher readings that drift more than 15 seconds a day across positions
- Soft, chewed screw slots and jewels seated without chatons
Service and Resale Reality
Replica 8605 movements are built around donor calibers, so spare parts come from the donor, not from Omega. A watchmaker who knows the difference will decline to service it under an Omega part number, and an Omega service center will refuse the watch outright. That matters at resale: a buyer who opens the back spots the missing regulator arm and the wrong finish in seconds. If you collect replicas as a hobby, treat the 8605 as a costume part, not as a movement you can maintain for 20 years. If you want the real caliber, buy from a seller who supplies movement photos, a service history, and a return window long enough for an inspection.