The replica Omega caliber 8605 is a non-Omega movement built to imitate the look and layout of the genuine Omega 8605, a self-winding bi-compax chronograph caliber with a co-axial escapement. In replica watches, the "8605" label almost always describes a decorated Asian chronograph base, most often an ETA 7750 style automatic or a Seagull ST19 hand-wound caliber, rather than a true copy of Omega's internal architecture. No replica version carries Omega's METAS certification or its silicon balance spring.
What the genuine Omega 8605 does
Omega designed the 8605 as part of its co-axial movement family, so the real unit combines a chronograph with an escapement that separates the impulse and locking functions of the balance wheel. The features people are paying for when they buy the genuine article include:
- Automatic winding with a two-counter layout, meaning running seconds and a 60-minute chronograph totalizer
- A co-axial escapement rather than the traditional lever escapement
- A free-sprung balance, with a silicon balance spring on newer production
- A power reserve in the region of 60 hours
- High magnetic resistance, well beyond what a standard mechanical watch tolerates
Those specifications are documented by Omega itself, which is why the gaps between a genuine caliber and a replica movement show up quickly once you test winding, pushers, and timing.
What actually sits inside a replica "8605"
Replica makers rarely reverse engineer a movement. They buy an existing caliber and add cosmetic work: a rotor engraved with Omega markings, rhodium or gold-toned plates, and bridge shapes that echo the original. Through a display back the result can look convincing, while the behavior is nothing like the real caliber. The common bases are:
- ETA 7750 or 7753 style automatic. The 7753 is the bi-compax variant, so it fits a two-subdial dial naturally. This is the base most often found in automatic replica chronographs, and it has the widest parts support.
- Seagull ST19. A hand-wound, column-wheel chronograph. Pusher feel is often better than the price suggests, but there is no automatic winding module and the beat rate is lower.
- Thin modified Asian automatics. Slimmer cases are usually the reason these appear, and they tend to have the shortest service life of the group.
A watch advertised as automatic that only runs when you wind it by hand is a good sign the seller is describing the dial, not the movement.
How to check the movement before you buy
- Count the subdials. A genuine 8605 chronograph uses two counters. Three subdials point to a different architecture entirely.
- Test the rotor. Tilt the watch side to side. An automatic rotor should spin and the watch should wind without hand winding.
- Feel the pushers. Start, stop, and reset should feel distinct and consistent. Mushy or gritty pushers suggest a low-grade cam mechanism.
- Listen to the beat. The 7750 family runs at 28,800 vibrations per hour. An ST19 runs at 21,600, so the tick sounds noticeably slower.
- Run a power reserve test. Wind it fully, set it down, and check it the next day. Big losses overnight are common on inexpensive replica movements.
- Inspect the caseback decoration. Engraving and plating are cosmetic and tell you nothing about the base caliber underneath.
Accuracy, servicing, and parts
Replica movements typically keep time within a broad range rather than a tight one. Independent watchmakers may or may not agree to service them, and parts availability depends entirely on the base caliber, not the label on the rotor. ETA 7750 derivatives have broad parts support in the United States, while Seagull parts are harder to source and often require a replacement movement instead of a repair. That matters over a few years of ownership, because a movement that cannot be serviced turns a wearable watch into a static object.
Legal and value notes
Omega and the Swiss watch industry treat replica watches as trademark infringing goods, and US Customs and Border Protection can seize imported shipments. Resale value on a replica is effectively nil, and the movement is the main reason why: buyers who know watches check the caliber first. If the appeal is the look of a bi-compax co-axial chronograph, it helps to go in knowing that the "8605" inside is a stand-in for the real thing, with different winding, different timing behavior, and different long-term costs.