Why the Fly and Warning Wheel Setup Matters
The fly and warning wheel control the speed, timing, and safety of the strike train. Without proper setup, the strike may run too fast, fail to enter warning, or release at the wrong moment. As explained in our guide on testing a clock train during reassembly, the strike train must run freely before these adjustments can be made.
Understanding the Fly’s Role
The fly acts as a governor, regulating the speed of the strike train. It also prevents the train from slamming into motion when the warning wheel releases. Proper installation ensures smooth, controlled striking.
Preparing the Strike Train for Adjustment
Confirm wheel freedom
Spin S1 and ensure all wheels rotate without hesitation.
Check pivot seating
Verify that S1, S2, and S3 pivots are fully seated in their bushings.
Ensure the plates are snug but not tight
The plates should be held together with nuts but still loose enough to allow minor pivot adjustments.
Installing the Warning Wheel (S3)
Position S3 correctly
The warning wheel must be oriented so its warning pin will contact the stop lever at the correct moment.
Verify pin clearance
Rotate S3 slowly and ensure the warning pin clears the stop lever when the train is at rest.
Check for smooth rotation
S3 should rotate freely without rubbing the plates or neighboring wheels.
Installing the Fly
Seat the fly arbor
Insert the fly arbor into its pivot holes, ensuring the long arbor is fully seated.
Check fly blade clearance
The fly blades must not touch the plates or any levers.
Verify free rotation
Spin the fly lightly. It should rotate smoothly and coast briefly before stopping.
Setting the Warning Run
Bring the train into warning
Manually lift the strike release lever until the warning wheel begins to move.
Stop the train at the warning position
The warning pin should stop against the stop lever with minimal backlash.
Check the warning distance
The warning wheel should rotate a small amount—typically less than one full tooth—before stopping.
Setting the Strike Release
Simulate the hour lift
Lift the hour lever to simulate the clock reaching the hour.
Verify clean release
The warning pin should release cleanly, allowing the train to run.
Check fly engagement
The fly should immediately regulate the speed of the strike train.
Testing the Complete Strike Sequence
Run the strike train manually
Rotate the great wheel to simulate a full strike sequence.
Observe the fly behavior
The fly should regulate speed consistently throughout the strike.
Confirm proper stop
The train should stop cleanly when the stop lever engages the warning pin at the end of the sequence.
Common Mistakes
Incorrect fly seating, misaligned warning pin, insufficient warning run, over-tightened plates, or fly blades rubbing the plates.
Troubleshooting
Strike runs too fast
Check that the fly is fully seated and not slipping on its arbor.
Strike fails to enter warning
Adjust the warning pin position so it contacts the stop lever correctly.
Strike releases too early
Reduce the warning run by repositioning the warning wheel.
Fly does not spin freely
Ensure the fly blades are not rubbing the plates or levers.
FAQs
What does the fly do in a clock movement?
The fly regulates the speed of the strike train and prevents sudden acceleration.
How much warning run should there be?
Typically less than one full tooth of rotation before the warning pin stops.
Why does the strike run too fast?
A loose or improperly seated fly can cause excessive speed.
Why won’t the strike enter warning?
The warning pin may be misaligned or the stop lever may not be positioned correctly.
Why does the strike release early?
The warning run is too long and must be reduced.
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