Introduction
The Sessions 8-day two-train chime movement is known for its unusual design and its reputation for being challenging to service. Unlike typical three-train Westminster clocks, this movement combines chime and strike functions into a single train powered by one main wheel. With proper setup and understanding of its sequencing, the movement becomes predictable and reliable. This guide explains the core operating principles, servicing considerations, and how to protect the Sessions pendulum rod and spring during work.
Understanding the Sessions Two‑Train System
How the combined chime/strike train works
The movement uses a single train to perform both chiming and striking. A player drum with multiple disks advances according to rack counts, producing quarter-hour chimes and the hour strike.
The role of the star wheel
A four-arm star wheel on the center shaft lifts the control lever at each quarter, releasing the appropriate rack for chime or strike sequencing.
The twin racks
The movement uses two racks: a small auxiliary rack for chime counts and a larger rack for hour strike counts. Their combined tooth totals determine how far the drum advances.
The shifting drum
The player drum shifts outward for chiming and inward for striking. A cam on the back of the movement controls this shift.
Importance of power delivery
Because one train handles both chime and strike, the main wheel must deliver consistent power for the entire sequence.
Servicing Considerations
Inspecting pivots and bushings
Sessions movements are known for soft pivots and worn pivot holes, especially on the second wheel and gathering pallet arbor.
Checking gathering pallet alignment
Worn pallet pivot holes cause misalignment with rack teeth, leading to incomplete gathering or jamming.
Handling variations in production
Some movements have solid front plates; others have cutouts. Some main wheels use click shields; others do not. These differences affect disassembly and reassembly.
Protecting the pendulum assembly
The Sessions pendulum rod and spring must be removed before servicing to prevent bending or twisting during movement handling.
Cleaning considerations
Do not clean the aluminum player drum in the same solution as brass parts to avoid chemical reaction and staining.
Disassembly Overview
Step 1: Restrain and let down the springs
Use spring retainers or wire to secure both mainsprings before letting them down.
Step 2: Remove pendulum components
Remove the pendulum, suspension spring, and rate adjustment assembly before accessing the movement.
Step 3: Remove hammer assembly
Lift the hammer bank off the movement and note the order of levers and spacers.
Step 4: Remove the player drum
Remove the drive arm, coil spring, and drum disks. The outer disk comes off separately; the inner four come off together.
Step 5: Remove racks and snails
Unhook rack return springs and remove both racks and snails from the hour pipe.
Main Wheel and Power Delivery
Main wheel variations
Some Sessions movements use a brass sleeve on the main wheel arbor to increase diameter and reduce stress on the inner spring coils.
Click and click-spring issues
Sessions clocks are known for click failures. Later models added a thin shield over the click to prevent slipping.
Spring sizing concerns
Original springs varied. Replacement springs should not be thinner than 0.018" or shorter than 96".
Overpowering risks
Too strong a mainspring can cause excessive pendulum swing and interference with the chime lever assembly.
Ensuring smooth power flow
Proper bushing work on the second wheel and gathering pallet arbor is essential for consistent chime and strike performance.
Reassembly and Adjustment
Check center shaft and cam
The cam on the back of the movement must be tight and properly aligned to shift the drum at the correct time.
Install racks and snails
Ensure both racks move freely and return springs provide proper tension.
Set gathering pallet depth
The pallets must gather teeth smoothly without skipping or binding.
Verify drum shift timing
The drum must shift outward at the first quarter and return inward at the hour.
Test full chime/strike cycle
Run through all four quarters and the hour to confirm correct sequencing.
Troubleshooting
If the clock does not chime
Check drum shift, rack release, and gathering pallet alignment.
If the clock chimes incorrectly
Verify auxiliary rack position and star wheel timing.
If the strike count is wrong
Check hour rack position and ensure the drum locks correctly at the hour.
If the train stalls
Inspect main wheel power, pivot wear, and spring condition.
If the pendulum motion is weak
Check the Sessions pendulum rod and spring for bending or twist.
FAQs
Why is the Sessions two-train movement considered difficult?
Its combined chime/strike system requires precise alignment and consistent power.
Why does the drum shift outward?
To engage all five disks for chiming.
Why does the drum shift inward?
To isolate the outer disk for hour striking.
Why does the movement lose synchronization?
Worn pivots or misaligned racks can cause incorrect drum advancement.
How often should this movement be oiled?
Sessions recommended annual oiling due to high pivot loading.
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