The quickest way to expose a fake IWC Portugieser Chronograph IW371631 is to turn it over. A genuine example runs IWC calibre 69355, an in-house column-wheel chronograph with a 46-hour power reserve, and the movement sits under a sapphire display back with crisp Geneva stripes and a signed rotor. Most replicas hide a Seagull ST19 or a cloned Valjoux 7750 behind coarse decoration, and that mismatch is visible in seconds.
What is the IW371631?
The IW371631 belongs to the current Portugieser Chronograph family, a 41 mm stainless steel watch with a 30-minute counter at 12 o'clock, running seconds at 6, and a date window at 3. It is a time-only chronograph, not a perpetual calendar, so anything complicated on a claimed IW371631 is a red flag. Case thickness sits around 13 mm and lug width is 20 mm.
How do you tell a fake IW371631 from a genuine one?
Work through the watch in a fixed order: dial, hands, case, movement, then paperwork. Fakes fall apart at the movement stage almost every time, so never buy without seeing the caseback.
Dial and printing
- Genuine dial text is applied or pad-printed with razor-sharp edges; replicas show soft or doubled lettering under a loupe.
- The subdials have fine concentric snailing; fakes often use flat discs or a printed pattern.
- The date window cut is crisp and beveled, and the date font matches IWC's block numerals.
- Applied numerals sit flush with a polished bevel; on replicas they look thick or slightly rotated.
Hands and crystal
Feuille hands should reach the minute track exactly and show a mirror polish with no tool marks. Genuine sapphire has anti-reflective coating on both faces, which gives a faint blue tint at angles; replicas usually coat one side or use mineral glass that scratches.
Case and crown
The bezel is polished, the case flanks are brushed, and the transition between the two is sharp and even. The crown carries a clean IWC engraving and turns with light, positive clicks. Soft edges, uneven brushing, or a wobbly crown point to a replica case.
Caseback and movement
The reference number, case serial, and model name are laser-engraved between the lugs, and the engraving is deep and even rather than dotted. Under the sapphire back, calibre 69355 shows a column wheel, Geneva stripes, blued screws, and a rotor engraved with the Probus Scafusia seal. Fake movements show stamped bridges, painted stripes, and a rattling unidirectional rotor.
What movement should a genuine IW371631 have?
Calibre 69355, a self-winding integrated chronograph with a column wheel and vertical clutch, beating at 28,800 vibrations per hour. Earlier Portugieser Chronograph references used the 79350, a modified Valjoux 7750, so confirm the generation before you judge. A quick listen helps: the 69355 winds smoothly and the chronograph pushers feel crisp with no grinding.
How heavy should it feel?
A steel IW371631 on a leather strap weighs roughly 80 to 90 grams, and the head alone reads close to 60 grams on a kitchen scale. Replicas often come in lighter because of thinner case walls or a base-metal midcase. Always weigh the watch without the strap for a fair comparison.
What should you check on the box and papers?
- Warranty card with matching reference, serial, and dealer stamp.
- Instruction booklet and a guarantee booklet printed on heavy stock.
- Outer and inner box with correct IWC typography and no glue residue.
- Serial number on the card matching the engraving on the caseback exactly.
Fake paperwork is common, so treat documents as supporting evidence only. The watch itself decides authenticity.
Frequently asked questions
Can a good replica fool a watchmaker?
Not once the caseback comes off. Dial-side fakes can look convincing in photos, but movement finishing and the column wheel are hard to replicate at low cost.
Is a quartz IW371631 always fake?
Yes. The Portugieser Chronograph has never been produced as a quartz watch, so a ticking seconds hand at 6 o'clock confirms a counterfeit.
Where is the serial number on an IW371631?
Engraved on the caseback between the lugs, usually at 6 o'clock, alongside the reference number. Compare it against the warranty card before buying.