A fake Omega Caliber 8605 is a third-party movement dressed to look like Omega's in-house GMT caliber, built from a Seagull, Hangzhou, or modified ETA clone base rather than Omega's own parts. It copies the engraving, the rotor finish, and the spec sheet. It does not copy the Co-Axial escapement, the silicon balance spring, or the twin-barrel power train that define the real 8605.
Below is a breakdown of what the genuine movement does, what usually sits inside a fake, and the checks you can run in a few minutes with a loupe and a phone.
What the Genuine Omega Caliber 8605 Does
Omega built Caliber 8605 as a self-winding GMT movement for dive watches such as the Seamaster Planet Ocean GMT. It runs at 25,200 vibrations per hour, which equals 7 beats per second, and it stores about 60 hours of power in two barrels linked in series.
The balance spring is silicon, and the balance is free-sprung, so the balance cock carries no regulator index with plus and minus markings. Timing is set during assembly instead.
- Beat rate: 25,200 vph (7 ticks per second)
- Power reserve: about 60 hours from two barrels
- Escapement: Co-Axial, three pallet stones
- Balance spring: silicon (Si14), free-sprung balance
- Functions: hours, minutes, seconds, 24-hour GMT hand
What Movement Sits Inside a Fake Omega 8605?
Three bases cover most of the market. None of them is made by Omega, and none of them has a Co-Axial escapement.
Seagull ST25 or ST21 family
The ST25 is a common host because its rotor and bridge layout sit close to the 8500-series shape. Most versions beat at 21,600 vph, so a timing app picks up the mismatch against the 25,200 vph of a real 8605.
ETA clone (A2824 or A2836) with a GMT module
A 2824 or 2836 clone has no GMT function on its own. Builders stack a module on the dial side or modify the date mechanism to drive a 24-hour hand. The result often feels loose at the crown and can slip when you set the second time zone.
Decorated low-grade clones
Some sellers take a cheap automatic, add perlage, Cotes de Geneve stripes, and gold-tone lettering, then photograph it through a display back. The finish looks flat under a loupe and the engraving sits shallow.
How to Spot a Fake Omega Caliber 8605
Start with the balance. A genuine 8605 has a silicon spring and a free-sprung balance, so a regulator arm with plus and minus marks on the cock points to a clone base. That one detail rules out most fakes before you look at anything else.
Check the beat rate
Install a watch timing app on your phone, hold the microphone near the caseback, and let it read the rate. 25,200 vph points to a genuine-format movement. 21,600 or 28,800 points to a clone. The test takes about a minute and needs no tools.
Read the rotor and bridges
Genuine Omega engraving is cut deep with clean edges. Fakes use laser etching or pad printing, so the text looks pale and sits flat. Watch for wrong fonts, odd letter spacing, and Swiss Made on a movement that never saw Switzerland.
Compare the jewel count
Sellers quote jewel numbers straight from the spec sheet. Open the back and count the visible jewel settings on the bridges and the balance cock. A mismatch means the listed specs are invented.
Inspect the caseback and the papers
A display back with a mismatched movement number, a case number that does not match the model, or a missing pictogram card are all warning signs. Genuine Planet Ocean GMT watches ship with a full card set and a matching serial.
Does a Fake 8605 Keep Good Time?
Some do, for a while. A Seagull ST25 can hold a few seconds a day when new. The weak points show up later: the GMT hand drifts, the rotor bearing gets noisy, and a service costs more than the watch because no watchmaker stocks parts for a no-name clone.
What Does a Fake Omega 8605 Cost?
Most fake 8605 watches sell for a few hundred dollars, while a genuine Planet Ocean GMT runs into the thousands. That gap explains the market, and it also explains why nobody drops a real Co-Axial movement into a 200-dollar case.
Why the Co-Axial Escapement Cannot Be Copied Cheaply
The Co-Axial escapement uses three pallet stones and a coaxial wheel layout set to tolerances that take years of tooling to reach. A cloner would need the same machinery, the same silicon etching, and the same testing, and at that point the cost stops making sense. That is why every fake 8605 uses a standard Swiss lever escapement instead.
Buying Advice If You Want the Look
If the goal is a GMT dive watch on a budget, a Seiko or a microbrand with a real GMT movement gives you parts and service support. If you buy a replica, treat the movement as disposable and check the beat rate before you pay.
Frequently Asked Questions
Can you tell a fake 8605 without opening the case?
Yes, in many cases. A phone timing app reads the beat rate through the caseback, and the GMT hand behavior shows up at the crown. A loupe on the caseback engraving catches shallow or printed text.
Do fake 8605 watches have a working GMT hand?
Sometimes. With a 2836 base and a module, the 24-hour hand moves, but it often jumps or slips when you set it. Watches with no module just slave the hand to the hour hand.
Is the case finish a giveaway too?
Often yes. Sapphire with a weak anti-reflective coat, uneven lume, and a bezel insert with off-center markings show up before you even look at the movement.
Should you service a fake movement?
Seldom worth it. A swap to a fresh clone costs less than a service, and parts for the base movement sit outside the normal supply chain.