Buying a fake IW371640 comes down to one decision: choose a build that uses a true Valjoux 7750 architecture inside a 40.9 mm case, and skip anything running a 21,600 vph automatic or a quartz hybrid. The beat rate, the subdial layout (running seconds at 6 o'clock, chronograph minutes at 12), and the case profile are the three checks that separate a convincing replica from a disposable one. Strap, box, and paperwork can be swapped later. The movement and the case cannot.
Why This Reference Attracts Replica Makers
The IW371640 sits inside the Portugieser Chronograph family, which means it shares the traits that make the line easy to copy: a plain round case, a printed dial with no stacked complications, leaf-shaped hands, and a bi-compax layout. There is no module bolted on top of the base movement, no unusual crystal shape, and no exotic material to fake. A workshop that already produces a decent 7750 chronograph can turn out this dial in a few weeks.
The same simplicity works against buyers. Because so little of the watch is visually complex, the small differences carry all the weight. Subdial spacing, hand length, whether a date aperture appears at all, and the crown profile are what tell you which tier you are holding.
What to Look For
Movement and beat rate
Ask for the beat rate and the winding feel. A 7750-based movement runs at 28,800 vph, sweeps with a faint stutter, and has a rotor that spins with a light metallic ring. Cheap substitutes run at 21,600 vph, which makes the running seconds hand tick in visible steps, and some drive the 6 o'clock subdial through a transfer gear that adds drag and noise.
Power reserve should land between 40 and 48 hours on a full wind. If the seller quotes 20 hours or cannot answer, treat the movement as unknown.
Case and crystal
Measure the diameter across the bezel. It should read roughly 40.5 to 41 mm, with a thickness near 12.5 mm. Anything past 14 mm is a thicker generic case with a spacer inside. Lug width is 20 mm, tapering to an 18 mm buckle. The crystal should be slightly domed sapphire with coating on both faces. A flat mineral crystal with a heavy blue tint is a downgrade you will notice in daylight.
Dial and hands
Check the printed numerals for even line weight, the track for clean concentric rings, and the leaf hands for a proper taper. On a strong replica the hands reach into the minute track without touching the numerals. On a weak one they are short, flat, and painted instead of polished. Many Portugieser Chronograph references have no date, so any date window is an immediate tell.
Caseback and engraving
This reference uses an exhibition back, so the movement is on display. Engraving depth and font matter more than the numbers themselves. Look for crisp serial text, a centered reference, and rotor finishing that shows Geneva stripes rather than flat paint. A solid caseback on a watch that should have a display back means you are looking at the wrong build.
Parameter Bands Worth Knowing
- Case diameter: 40.5 to 41 mm. Below 39 mm or above 42 mm, the proportions read wrong on the wrist.
- Case thickness: 12 to 13 mm. Budget builds often reach 14 mm or more.
- Lug width: 20 mm, tapering to an 18 mm buckle.
- Movement: 28,800 vph automatic with a 40 to 48 hour power reserve.
- Water resistance: the original is rated to 3 bar. Treat any replica as splash resistant at best, regardless of what the caseback claims.
- Strap: alligator grain leather with a signed deployant or pin buckle.
Pitfalls to Avoid
- Buying from photos alone. Dial print quality, hand polishing, and crystal clarity do not survive a phone camera.
- Confusing a 7750 copy with a real 7750. Both exist, and the gap shows up in how the chronograph resets.
- Accepting a quartz chronograph. The pushers feel instant and hollow, and the seconds hand ticks.
- Paying a premium for a box and papers that carry no resale value on a replica.
- Ignoring the strap. A correct 20 mm strap changes the look more than any other single upgrade.
FAQ
How can I tell a fake IW371640 from the real thing?
Start with the movement. The original uses IWC Calibre 79350, a modified Valjoux 7750 running at 28,800 vph. Top-tier replicas copy that layout and the middle tier does not. Then check case thickness, crystal material, and the sharpness of the dial print under a loupe.
Does the subdial layout matter?
It matters more than almost anything else. Running seconds belong at 6 o'clock and chronograph minutes at 12. A swapped layout is an immediate tell to anyone who knows the line, and it cannot be fixed after purchase.
Is a 21,600 vph movement always a bad sign here?
Yes, for this reference. The original never ran at that rate, so the running seconds hand will step rather than sweep and the chronograph sweep will look slow.
What should I check when the watch arrives?
Wind it fully, start the chronograph, and let it run past 30 minutes to confirm the minute counter advances. Time it over 24 hours to see how far it drifts. Check the pushers for a firm return and the crown for smooth winding. Any grinding or stiffness is a reason to send it back.