Introduction
Hermle movements use a compact click and click spring system inside the sprocket wheel to control winding and prevent reverse rotation. When the click spring breaks or weakens, the clock may slip during winding or fail to hold tension. Replacing the click spring requires careful handling of the Hermle wheel and attention to spring barrel safety. This guide explains how to replace the click spring in a Hermle sprocket wheel correctly.
Understanding the Hermle Click System
How the click works
The click prevents the sprocket wheel from rotating backward when the clock is wound. It engages the ratchet teeth and holds the mainspring tension.
The role of the click spring
The click spring pushes the click into the ratchet teeth. If the spring breaks, the click cannot hold tension.
Hermle sprocket wheel design
Hermle sprocket wheels are crimped together, making access to the click spring more challenging than in older American movements.
Common failure points
Click springs fatigue over time, especially if the clock is overwound or the spring barrel binds.
Safety considerations
Always ensure the mainspring is fully let down before working on the click or spring barrel.
Preparing for Click Spring Replacement
Let down the mainspring
Release all tension from the mainspring before removing the Hermle wheel assembly.
Remove the sprocket wheel
Disassemble the movement enough to access and remove the sprocket wheel containing the click.
Inspect the click and ratchet
Check for wear, rounding, or damage to the click or ratchet teeth.
Identify the spring attachment points
Hermle click springs typically anchor into a small hole or notch inside the sprocket wheel.
Prepare the replacement spring
Ensure the new spring matches the original in length, tension, and shape.
How to Replace the Click Spring
Step 1: Open the sprocket wheel
Carefully pry open the crimped edge of the Hermle wheel just enough to access the click spring. Avoid deforming the wheel.
Step 2: Remove the old spring
Lift the broken or weakened spring from its anchor point and remove it from the wheel.
Step 3: Install the new spring
Hook the new spring into the anchor hole or notch and position it so it applies proper tension to the click.
Step 4: Verify click engagement
Manually rotate the ratchet to ensure the click snaps firmly into each tooth.
Step 5: Re‑crimp the wheel
Close the crimped edge carefully, restoring the wheel’s original shape without binding the click.
Reassembling the Movement
Reinstall the sprocket wheel
Place the Hermle wheel back into the movement, ensuring proper pivot seating.
Check spring barrel alignment
Ensure the spring barrel and sprocket wheel mesh smoothly with the rest of the train.
Wind slightly to test
Apply minimal winding pressure to confirm the click holds securely.
Verify smooth operation
Rotate the train by hand to ensure no binding or slipping occurs.
Complete reassembly
Reinstall plates, levers, and motion works as required.
Troubleshooting Flowcharts
If the click slips under load
Check spring tension → Check click wear → Check ratchet teeth → Check wheel crimp
If the wheel binds after reassembly
Check crimp distortion → Check click clearance → Check pivot seating
If the mainspring unwinds suddenly
Check click engagement → Check spring anchor → Check ratchet alignment
Common Mistakes to Avoid
Opening the wheel too far
Excessive prying distorts the Hermle wheel and causes binding.
Using an incorrect spring
Wrong tension leads to slipping or excessive wear.
Failing to check ratchet teeth
Worn teeth cause slipping even with a new spring.
Reassembling with mainspring tension
Always let down the mainspring fully before working.
Over‑crimping the wheel
Too much pressure restricts click movement.
Checklist for Final Verification
• Click engages firmly
• Spring tension correct
• Hermle wheel runs true
• No binding after re‑crimping
• Spring barrel meshes smoothly
• Click holds under winding pressure
FAQs
Why does my Hermle clock slip when winding?
The click spring is likely broken or weak.
Why won’t the click engage?
The spring may not be seated correctly or the click may be worn.
Why does the wheel bind after repair?
The Hermle wheel may be distorted from over‑crimping.
Why does the mainspring release suddenly?
The click is not holding due to spring or ratchet issues.
Why is the repair difficult on Hermle movements?
Hermle sprocket wheels are crimped, making access to the click spring more restricted.
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