Introduction
A mechanical clock that runs too fast or too slow is almost always suffering from pendulum length issues, friction, or escapement problems. This guide explains the most common causes and how to diagnose each one safely and accurately.
Check the Pendulum Length
Verify pendulum length matches the movement
If the pendulum is too short, the clock will run fast. If it’s too long, the clock will run slow.
Inspect the rating nut
Turning the rating nut to lower the bob slows the clock; raising the bob speeds it up.
Check for missing components
A missing suspension spring, top hook, or pendulum leader can change the effective length.
Check for Friction or Drag
Inspect the crutch loop
If the crutch loop is too tight on the pendulum rod, friction will slow the clock.
Look for pendulum rub
If the pendulum touches the case, backboard, or chime rods, the clock will run slow or stop.
Check for dirt or dried oil
Dirty pivots or gummy oil reduce power and slow the timekeeping rate.
Check the Escapement
Verify pallet lock and drop
Uneven lock or excessive drop can cause the clock to run fast or slow depending on the imbalance.
Inspect pallet wear
Worn pallet faces change the impulse and can alter the rate.
Check escape wheel tooth condition
Bent or worn teeth can cause inconsistent timekeeping.
Check for Power Issues
Weak mainspring
A tired or gummy mainspring may not deliver consistent power, causing slow running.
Worn bushings
Excessive pivot play reduces power and slows the clock.
Bent pivots
A pivot that runs out of true causes drag and inconsistent rate.
Check the Beat
Uneven beat affects timekeeping
A clock out of beat may run fast or slow depending on how the pendulum interacts with the crutch.
Level the movement
Ensure the movement is level side-to-side and front-to-back for accurate beat and rate.
Recommended Internal Links
FAQs
Why does my clock run fast?
The pendulum is too short or the bob is raised too high.
Why does my clock run slow?
The pendulum is too long, rubbing, or the movement has friction issues.
Can worn bushings affect timekeeping?
Yes. Worn bushings reduce power and cause slow or inconsistent running.
Does beat affect the rate?
Yes. A clock out of beat may run fast or slow depending on crutch interaction.
How much should I turn the rating nut?
Small adjustments—typically one full turn equals several minutes per day depending on the movement.
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