Short answer
A "fake IW371424" is either a replica built to look like the IWC Portugieser Chronograph, or a genuine watch rebuilt with aftermarket parts. The two problems need different checks. On a replica, the giveaways are proportion and movement behavior: a case that runs 13.5 mm or thicker, subdials pushed out toward the chapter ring, and a rotor that freewheels with a rattle. On a "genuine" watch, the giveaways are a dial that does not match the reference, a caseback with shallow engraving, and papers that do not line up with the serial.
What ref IW371424 actually is
The 3714 family is the steel Portugieser Chronograph: 40.9 mm wide, roughly 12.3 mm thick, sapphire crystal, 30 m water resistance, and a two-register dial with chronograph minutes at 12 and running seconds at 6. The date sits at 3. IWC based these on the Valjoux 7750, reworked as calibre 79350, which runs at 28,800 vph with about 44 hours of power. That detail matters, because the 7750 architecture explains both the dial layout and the feel of the watch on the wrist. The chronograph has a firm start and a snap-back reset, the seconds subdial ticks in eight small steps per second, and the rotor winds in one direction only.
Dial variants inside the 3714 line change color, hands, and numerals, but not the layout. If a listing shows a third subdial or a 9 o'clock register, it is not a 3714.
The tells that decide it
Subdial spacing and dial printing
I measure the gap between the two subdials before anything else. On a real dial they sit close to the center, leaving generous space at the outer edge. Plenty of replicas use a stock movement and a printed plate, so the subdials drift outward and the hands end up too short for the space they occupy. Look at the type as well. Printing on a genuine dial is thin, sharp, and evenly spaced. Replica printing is heavier, and the kerning around "Schaffhausen" is usually off.
Case profile
Thickness is the second check. A 3714 should sit near 12.3 mm and slide under a cuff. Replicas commonly run 13.5 to 14.5 mm because the movement and spacer stack is taller. Run a finger along the case side. Real ones alternate brushed flanks with a polished bezel and polished lug tops, and the transitions are crisp. Fake cases feel soft at the edges, and the bezel is often a hair too wide.
Pushers, crown, and caseback
Pushers should be pump style, with a short, even throw and no side play. The crown is signed and sits flush against the case. Flip the watch over. Engraving on a real caseback is deep and readable under raking light, with the correct reference, serial, and IWC lettering. Lasered or shallow engraving is a warning sign. If the back is a display back, rotor engraving and bridge finishing should look crisp rather than stamped foil.
Movement behavior
Wind it and listen. A 7750 family movement has a distinct rotor whir and a light wobble when you move your wrist. Cheap replicas either rattle, run silent because they are quartz, or use a 21,600 vph movement, so the small seconds sweep looks slower than the real thing. Time it over a day. A healthy 79350 holds within a few seconds.
Checking a listing before you pay
- Ask for a dial macro, a case-side shot, and the caseback, all in daylight.
- Ask for a movement photo or a timegrapher screenshot if the seller claims the watch is genuine.
- Compare the engraving against the reference number, then check the serial against IWC records.
- Weigh it. Steel 3714 examples land in a narrow band, and a light case usually means a hollowed replica.
If a seller refuses those four things, stop there. That refusal tells you more than any photo will.
Bottom line
Fake IW371424 watches fail on proportions and movement feel far more often than on logos. Get the thickness, the subdial spacing, and the caseback engraving fixed in your head, and most listings sort themselves out in a couple of minutes.