A replica Omega Caliber 8605 is not a copy of the Omega movement. It is a Chinese-assembled automatic chronograph built on an Asia Valjoux 7750 base, often with a bolt-on GMT module, then finished so it resembles the original when the case back comes off. It will run, it will time, and it will hold reasonable accuracy. The co-axial escapement, silicon balance spring, twin barrels, and 60-hour reserve of the genuine caliber are not present. Treat every listing that says "clone 8605" as a decorated 7750 until you can prove otherwise.
What the Genuine Caliber 8605 Is
Caliber 8605 belongs to Omega's in-house 8500 family. It is a self-winding bi-compax chronograph with a central GMT hand, a co-axial escapement, a free-sprung balance, and two mainspring barrels. Omega rates the 8500 family for a 15,000-gauss magnetic field and a 60-hour power reserve. The 8605 shows up in Seamaster Planet Ocean chronograph GMT references and in some Aqua Terra GMT chronograph models. Omega publishes the spec sheet for the caliber on its own site. That sheet is the benchmark you compare any replica against.
What a Replica 8605 Contains
Sellers describe these movements in tiers, and the tiers are cosmetic.
- Base tier: an Asia 7750 with a GMT module bolted to the dial side. Roughly 44 hours of reserve, standard lever escapement, no co-axial parts.
- Mid tier: the same base with decoration. Cotes de Geneve stripes, an engraved rotor, and a shaped bridge that imitates the co-axial layout.
- Top tier: a better-finished 7750 with a genuine-style rotor and a printed plate. The architecture underneath is still a 7750.
How to Check One Before You Buy
- Ask the seller for a macro photo of the movement with the case back removed, not a stock catalog image.
- Count the jewels on the bridges and compare the number to the figure Omega publishes for the 8605.
- Inspect the escapement under 10x magnification. A co-axial movement has a two-level escape wheel and three points of pallet contact. A 7750 has a single standard pallet fork.
- Check the balance spring. Genuine uses a dark matte silicon spring. Replicas use blued or white metal.
- Test the GMT hand. Pull the crown to the setting position and rotate. The genuine hand jumps in one-hour steps on its own. Replicas often drag the main hour hand with it.
- Time the power reserve. Wind it fully, rest it dial up, and check it every six hours. Expect 44 hours at best.
- Run it on a timegrapher and record rate, beat error, and amplitude. Compare the beat rate to the published spec. A mismatch identifies the base movement.
- Cycle the chronograph 20 times. The pushers should feel the same on every push, and the counter should snap back to zero without drift.
- Examine the rotor text and case back engraving under a loupe. Laser etching on replicas is flat and shallow. Genuine engraving has clean edges and depth.
What to Expect in Daily Use
Expect the watch to gain or lose 10 to 30 seconds a day after regulation, and expect the GMT module to be the first part to fail. Omega will not service a counterfeit, and most independent watchmakers will refuse to source parts for a modified 7750. When the movement stops, the common fix is a full movement swap, which costs close to what you paid for the watch.
Legal Notes for US Buyers
Counterfeit watches are illegal to import into the United States. US Customs and Border Protection seizes them at the border, and the shipment can be destroyed with no refund and no notice to you. Under 19 U.S.C. Section 1526, the trademark owner can also pursue damages. Buying one for personal use does not make the import lawful.