Short answer
A fake IW371717 is a replica of the IWC Portofino Chronograph ref. IW3717. The genuine watch has a steel case of 42 mm, a calibre 79320 chronograph movement, two subdials and a date window at 3. Copies reproduce the outside and save money on the inside. Four checks catch most of them: movement type, subdial spacing, caseback engraving and weight.
What the reference is
- Case: steel, 42 mm across, sapphire crystal, 30 m water resistance.
- Movement: calibre 79320, a Valjoux 7750 base, 25 jewels, 28,800 vph, about 44 hours of power reserve.
- Layout: running seconds at 6, 30-minute counter at 12, date at 3.
- Strap: leather with a steel pin buckle on most variants.
IWC lists several dial and strap variants in the IW3717 family. Confirm the exact variant code on IWC's site before you compare a watch to photos.
Where copies fail
- Movement. Many replicas run a quartz module or a low-grade Asian 7750 copy. A quartz small seconds hand jumps once per second. A mechanical one sweeps.
- Subdial spacing. On a 7750 the 6 and 12 subdials sit on a vertical line through the center. A different base movement pushes them off that line.
- Date. Check the font, the crispness of the print and the magnification under the cyclops, if fitted.
- Caseback. Engraved text has depth and clean edges on the original. Laser printing looks flat.
- Weight. A steel case with a 7750 inside weighs more than a thin brass or pot-metal shell.
- Pushers. Start and stop should give a firm click. Reset should snap back with no grind.
Bench checks
- Measure the case across the bezel with calipers. Compare to the published figure.
- Weigh the watch head with the strap removed.
- Start the chronograph and watch the 30-minute counter step.
- Set the time and watch the date change. A crisp flip near midnight is correct. A slow creep over 40 minutes is not.
- Inspect the crown logo and the caseback text under a 10x loupe.
Papers and serials
Ask for the warranty card, the booklet and the sales receipt. Serial numbers on replicas repeat across batches. A serial that shows up on many listings points to a copy. Genuine IWC papers carry a dealer stamp and a date that matches the serial range.
Price and law
Used IW3717 examples trade in the low thousands of US dollars. An offer far below that range is a copy. In the US, trafficking in counterfeit goods is a federal crime under 18 U.S.C. 2320, and Customs can seize shipments. A replica also resells for close to zero.