What a fake IW371740 is
A fake IW371740 is a replica of the IWC Portugieser Chronograph, the bicompax model with a 30-minute counter at 12 and running seconds at 6. The decent ones come from a handful of factories, use a modified 7750 or a decorated clone, and sell for somewhere between $350 and $700. The cheap ones cost under $150 and give themselves away the second you look at the subdials or the case profile. What follows is the order I check things in, and it doubles as an authentication pass if someone offers you a "genuine" one.
Start with the subdial layout
This is the fastest tell and the one buyers miss most. A stock Valjoux 7750 has running seconds at 9 o'clock. The Portugieser Chronograph does not. IWC reworked the 7750 into the caliber 79350 to push running seconds to 6, and the newer references run an in-house 69355 with the same 12 and 6 arrangement. So a watch with small seconds at 9 is not copying anything, it is a plain 7750 dropped into a Portugieser-shaped case.
When the seconds do sit at 6, look at how they got there. Relocating them takes a transfer gear, which adds height and drag. On cheap reps the small seconds hand stutters, the chrono counter drifts past zero when you reset it, and the subdial rings crowd the center. On a good rep the layout is right, but the rings are flat printed instead of snailed.
Case size, thickness, and profile
- Ask for caliper photos rather than trusting the listing. Diameter on this reference family lands near 41mm, thickness in the 12 to 13mm range depending on which version the factory copied.
- Most 7750-based reps run 1 to 1.5mm thick, because the movement plus transfer gear needs the space. You feel it as a slab-sided case and a caseback that stands proud on the wrist.
- Look at the flank finish. Genuine cases are brushed on the sides with a polished bezel edge. Reps often polish the sides or brush them in the wrong direction.
- Pushers should be pump-style with a short, crisp throw. Wobbly pushers and a mushy click point to a cheap movement and cheap case tubes.
- Weigh it if you can. A steel replica frequently comes in light for its size, and the strap hardware feels thin.
Dial and hands
Applied Arabic numerals should have polished bevels that catch light along the edges. On reps they are often flat, or the bevel is there but shallow. The printed rail track should be fine and even, not fuzzy under a loupe. Compare the weight of the "IWC" and "Schaffhausen" text to reference photos, since replicas tend to print slightly heavy or slightly small.
Leaf hands matter more than people expect. Genuine ones have a crease down the middle with polished facets on either side, so they read dark from one angle and bright from another. Flat stamped hands read the same from every angle. Anti-reflective coating is another giveaway: genuine dials go near-black and shift blue at an angle, while many reps have no inner coating or a tinted one that washes the dial out.
Caseback, engraving, and hardware
Engraving depth is easy to judge in a photo. Genuine casebacks have crisp, deep lettering with clean edges. Reps look shallow and slightly soft, and the reference number font is often wrong. On a display back, check the rotor engraving and the bridge finishing. IWC rotors carry the Probus Scafusia motto, and blued screws should be blued, not painted blue. The crown engraving should be sharp, and the strap release hardware should work with one hand without rattle.
Movement check in hand
- Wind it slowly and feel the resistance. A 7750 feels coarse and gritty. A column-wheel caliber feels lighter and more defined.
- Listen to the rotor. Loud spinning and a metallic whir on the wrist is characteristic of an unmodified 7750.
- Hack it and watch the seconds hand. A stutter or a jump is a bad sign. Power reserve should land near 44 to 46 hours on a healthy movement.
- Run the chronograph. Start, stop, reset a few times and watch whether the minute counter returns to zero cleanly.
Price and paperwork
A steel Portugieser Chronograph on the used market trades in the mid four figures, so a $300 watch described as genuine tells you everything. If you are buying real, ask for movement photos, service records, and matching numbers on the caseback and movement. If you are buying the replica, know what it is and price it accordingly. Buying or importing a counterfeit is illegal in the US, and that is a customs risk worth weighing before you order.
Quick checklist
- Running seconds at 6, not 9
- Case thickness measured with calipers
- Snailed subdial rings, not flat print
- Faceted leaf hands with a center crease
- Deep, correctly spelled caseback engraving
- Blue screws that are actually blued
- Clean chrono reset with no counter creep
Bottom line
A fake IW371740 lives or dies on the movement layout and the case thickness. Get those two right and the watch wears like the thing it copies. Get them wrong and no amount of dial printing will save it. Verify the exact reference specs against official sources before you compare, because this family has changed size and movement more than once.