Introduction
Sessions movements are known for reliable performance, but age, wear, and dried lubrication can cause the escape wheel to stick or hesitate. When the escape wheel fails to advance smoothly, the clock may stop, flutter, or lose power. This guide explains how to diagnose a sticking escape wheel on a Sessions movement, how to inspect the pivots and bushings, and how to restore proper escapement action.
Understanding the Sessions Escapement
Escape wheel function
The escape wheel releases power to the pendulum in controlled increments. Any friction or misalignment disrupts this rhythm.
Pallet interaction
The verge pallets must lock and drop cleanly. Worn pallet faces or incorrect depth cause hesitation.
Power flow
The escape wheel depends on smooth power from the entire train. Wear in lower wheels reduces impulse strength.
Sessions movement characteristics
Sessions clocks often use thinner plates and smaller pivots, making them sensitive to wear and dirt.
Effect on timekeeping
A sticking escape wheel causes erratic beat, weak amplitude, and frequent stoppage.
Diagnosing a Sticking Escape Wheel
Check pivot wear
Oval pivot holes or grooved pivots cause the escape wheel to lean, binding against the verge.
Inspect the verge depth
If the verge is too deep, the escape wheel teeth drag. If too shallow, the escapement flutters.
Check for bent teeth
Even a slightly bent escape wheel tooth can cause intermittent sticking.
Test wheel freedom
With power let down, spin the escape wheel lightly. It should rotate freely without catching.
Check for dirt and dried oil
Old oil hardens into varnish, increasing friction at the pivots.
Correcting the Problem
Polish the pivots
Use a fine abrasive or pivot polisher to restore smooth pivot surfaces. Rough pivots cause drag.
Install bushings where needed
Oval pivot holes must be bushed to restore proper depthing and alignment.
Adjust verge depth
Move the verge slightly until the escape wheel locks cleanly and drops evenly.
Check pendulum spring alignment
A twisted or bent suspension spring causes uneven beat, making the escape wheel appear to stick.
Verify pendulum rod clearance
Ensure the rod does not rub the case or crutch, which reduces amplitude and power.
Lubrication and Final Setup
Oiling the pivots
Apply a small drop of oil to each pivot hole. Sessions movements are sensitive to dry pivots.
Do not oil the pallets
The verge pallets must run dry. Oil causes skipping and erratic lock.
Check beat symmetry
Adjust the crutch so the tick and tock are even. Proper beat ensures stable escapement action.
Test under full power
Wind the movement and observe the escape wheel. It should advance smoothly with consistent amplitude.
Verify long-term running
Let the clock run for several hours to confirm the issue is resolved.
Troubleshooting Flowcharts
If the escape wheel sticks intermittently
Check pivot wear → Check verge depth → Check bent teeth → Clean pivots → Check beat
If the escape wheel flutters
Shallow verge → Check pallet faces → Check pendulum spring → Check crutch pressure
If the clock stops after a few minutes
Check power train → Check pivot lubrication → Check pendulum clearance → Check escapement lock
If the escape wheel runs weakly
Polish pivots → Install bushings → Clean movement → Check pendulum amplitude
If the escapement is noisy
Check verge depth → Check pallet wear → Check escape wheel tooth shape → Verify beat
Common Mistakes to Avoid
Oiling the pallets
This causes skipping and inconsistent lock.
Ignoring pivot wear
Sessions movements often require multiple bushings due to thin plates.
Over-adjusting the verge
Small movements make big changes. Adjust in tiny increments.
Forcing the pendulum rod
Bending the rod affects beat and amplitude.
Skipping cleaning
Dirt and dried oil are major causes of sticking escape wheels.
Checklist for Final Verification
• Escape wheel rotates freely
• Pivots polished and lubricated
• Verge depth correct
• Pendulum spring straight and aligned
• Sessions paper dial reinstalled without interference
• Clock runs a full 24 hours without stopping
FAQs
Why does the escape wheel stick on a Sessions movement?
Usually due to pivot wear, dried oil, or incorrect verge depth.
Should I oil the escapement?
No. Only the pivots receive oil—never the pallets.
Can a bent escape wheel tooth cause sticking?
Yes. Even slight bends cause intermittent hesitation.
Does the pendulum spring affect the escapement?
Yes. A twisted or damaged spring causes uneven beat and weak impulse.
Do Sessions movements commonly need bushings?
Yes. Their thin plates wear quickly, especially around the escape wheel.
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