Short answer
A counterfeit Omega caliber 8605 almost never copies the actual movement. It is a decorated Asian or Swiss ebauche (usually a 2836 or 2893 family base) hidden under a bridge plate engraved to look like an Omega. You identify the fake by four things: the escapement is a standard lever instead of co-axial, the beat rate is wrong, the twin barrels are absent, and the GMT setting logic does not match. Everything else, including the rotor text, is cosmetic and easy to fake.
omega caliber 8605 counterfeit
What a genuine 8605 should show
The 8605 is a self-winding co-axial GMT with two mainspring barrels in series, a 60-hour power reserve, a free-sprung balance, and a silicon hairspring. It runs at 25,200 vibrations per hour (3.5 Hz). Omega fits it to Planet Ocean GMT and Aqua Terra GMT models, so most fakes you meet will be sold as one of those two.
- Co-axial escapement with a three-pallet layout, not a two-pallet lever fork
- Free-sprung balance with no regulator index and no curb pins
- Two visible barrels under the bridges, rhodium finish, blackened screws
- Laser-engraved "Omega 8605" and "Co-Axial" on the bridge, crisp under a loupe
Step-by-step check
- Ask the seller for a sharp macro photo of the movement through the display back, taken at an angle in daylight. Refuse stock images.
- Confirm the beat rate on a timegrapher or a phone timing app. Genuine 8605 sits at 25,200 vph. Fakes usually read 21,600 or 28,800.
- Examine the escapement under 10x magnification. A co-axial has three pallet stones and a distinct two-level escape wheel. A fake shows a standard lever fork with two pallets.
- Look at the balance cock. The genuine part carries no regulator arm. If you see a moveable index with curb pins, the movement is a conventional lever caliber.
- Check the hairspring color. Silicon reads gray and matte, not bright blued steel. Blued steel is the standard fake tell.
- Count the barrels. Two large barrels sit side by side under the train bridges. One barrel means the base is a 2893 or similar.
- Test the crown logic. The GMT hand and the date must set independently of the running time, with distinct detents at each position. Fakes bind, skip, or move the date with the GMT hand.
- Inspect the engraving quality on the rotor and bridges. Genuine Omega text is laser-cut with sharp edges. Fake plates use shallow pad printing that fades at the edges.
Red flags that settle it
- Seller will not provide a movement photo or asks you to trust "Swiss made" printing on the dial
- Caseback crystal is cloudy or the movement looks flat and printed rather than machined
- Price is far under the current secondary market for the reference
- Serial on the case and the movement do not fall in the correct production range for the reference
Before you buy
Have an independent watchmaker pull the back and time the movement. A five-minute check on the escapement and the beat rate is enough to separate a real 8605 from a decorated fake, and no seller with a genuine watch will object to it.