ETA 7750-201 Great Wheel

Product Description

This is a genuine ETA 7750-201 great wheel (Article number 16), an original Swiss-made component for the ETA/Valjoux 7750 automatic chronograph movement. As the first wheel in the gear train, the great wheel is mounted on the mainspring barrel and is responsible for transmitting power from the mainspring to the rest of the gear train, ensuring consistent energy delivery to the center wheel and ultimately the escapement .

This brand new original part is essential for watchmakers restoring proper power transmission and timekeeping accuracy when the original great wheel becomes worn or damaged.

Key Features & Functions

• Designed for ETA/Valjoux 7750 movement
• Mounted on mainspring barrel as first gear train wheel
• Transfers power from mainspring to center wheel
• Essential for accurate timekeeping and power transmission
• Swiss Made quality and precision

Usage Instructions

The great wheel is mounted on the mainspring barrel and is the first wheel in the gear train. Its function is to transmit power from the mainspring to the center wheel, which then drives the motion works.

Signs of Great Wheel Wear:

• Reduced power reserve (well below 42 hours)

• Watch runs intermittently despite being fully wound

• Unusual noise during manual or automatic winding

• Visible wear or damage to the wheel teeth

Proper Handling Tips:

• Use non-metallic tweezers when handling the great wheel

• Keep the pivot ends clean and free of old oil

• Inspect the mainspring barrel for wear when replacing the great wheel

• The great wheel works with the ratchet wheel (article 13) and crown wheel in the winding train

Installation Instructions

CRITICAL WARNING: The ETA 7750 is a complex chronograph movement. Great wheel replacement requires partial disassembly of the gear train. Professional installation is strongly recommended.

Tools Required:

• Non-metallic tweezers

• Screwdrivers (1.20mm, 1.40mm, 1.60mm)

• Movement holder

• Loupe or microscope (10x recommended)

• Rodico cleaning putty

• Appropriate watch oils (Moebius HP 1300, 9010)

Step-by-Step Installation:

Step 1: Movement Preparation

• Remove the movement from the watch case

• Remove the hands and dial

• Remove the automatic module to access the gear train

• Remove the oscillating weight (rotor)

Step 2: Remove the Gear Train Bridge

• Locate the barrel and train wheel bridge

• Remove the bridge screws and carefully lift the bridge

• The great wheel is located on the mainspring barrel

Step 3: Remove the Old Great Wheel

• Using non-metallic tweezers, carefully lift the old great wheel from the barrel arbor

• Note the orientation for reinstallation

• Inspect the mainspring barrel for wear or damage

Step 4: Inspect and Clean

• Inspect the center wheel, third wheel, and escape wheel for wear

• Clean the pivot area using Rodico to remove old oil and debris

• Check that all teeth are intact on the new great wheel

Step 5: Install the New Great Wheel

• Position the new genuine ETA 7750-201 great wheel onto the barrel arbor

• Ensure the wheel sits flush and engages properly with the center wheel

• The wheel should rotate freely but with minimal play

Step 6: Lubrication

• Apply Moebius HP 1300 to the great wheel teeth contact points

• Apply Moebius 9010 to the pivot points

• Avoid over-lubrication, which can attract dust

Step 7: Reassembly and Testing

• Reinstall the gear train bridge and tighten screws evenly

• Reinstall the automatic module and oscillating weight

• Test manual winding: turn crown clockwise – should feel smooth with consistent resistance

• Test automatic winding: rotate the rotor – the gear train should advance smoothly

• Test chronograph function: start, stop, reset

Important Notes:

• The great wheel works in conjunction with the center wheel, third wheel, and escape wheel

• Professional installation is strongly recommended for those without movement service experience

• ETA recommends not cleaning certain components if they are very dirty or rusted; they should be replaced instead

Repair Guide

Common Symptoms of Great Wheel Issues:

Diagnostic Process:

1. Power Reserve Test: Fully wind the movement and time how long it runs. If significantly under 42 hours, inspect the great wheel and mainspring.

2. Visual Inspection: Under magnification, examine the great wheel teeth for wear, chipping, or deformation.

3. Gear Train Check: With the gear train bridge removed, test the freedom of the train by giving a gentle puff of air to the great wheel – the entire train should spin freely .

4. Endshake Test: Gently lift the great wheel to check for excessive vertical play.

When Replacement is Necessary:

• Visible tooth damage or wear on the great wheel

• The wheel does not engage properly with the center wheel

• Bent or damaged pivot

• The movement has been in service for 5+ years and power reserve has degraded

Preventive Maintenance:

• Service the movement every 3-5 years

• During service, inspect all gear train components for wear

• Use proper lubrication (Moebius HP 1300 on teeth, 9010 on pivots)

• Replace worn components as a set when necessary

When to Seek Professional Help:

• You lack experience with gear train disassembly

• Multiple components show signs of wear

• The movement has other issues affecting timekeeping

• You do not have a timing machine for verification

Frequently Asked Questions

Q1: What is the function of the great wheel?

A: The great wheel (article 16) is mounted on the mainspring barrel and is the first wheel in the gear train. It transmits power from the mainspring to the center wheel, which then drives the motion works and the rest of the gear train. It is essential for consistent energy delivery to the escapement .

Q2: What other parts should I inspect when replacing the great wheel?

A: Inspect the center wheel, third wheel, escape wheel, and the mainspring barrel for wear. Also check the ratchet wheel and crown wheel in the winding train. The gear train components work together as a system – wear on one component often affects others. The 7750 is known for its robust design, but proper maintenance of the gear train is essential .

Q3: Can I install this part myself?

A: This part requires movement disassembly, including removal of the automatic module and gear train bridge. Professional installation by a qualified watchmaker is strongly recommended. The ETA 7750 is a complex chronograph movement used in many luxury watches, and improper installation can damage the gear train or affect timekeeping accuracy .

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