Before you begin servicing an American time-and-strike movement, you need a small set of reliable tools and a clear understanding of how to safely contain and release mainspring power. This guide walks you through the essential tools, how to select the correct mainspring clamps, and the complete let-down procedure. These steps form the foundation of safe and successful clock repair.
If you are new to mechanical clock restoration, you may also find it helpful to review full movement tear-downs such as the Gilbert 8-Day diagnostic guide or the Sessions 8-Day movement diagnosis before continuing.
Basic tools you likely already have
General-purpose screwdriver
A standard 4 mm flat-blade screwdriver will handle most screws found in American clock movements. This size fits the majority of plate screws, dial screws, and motion-work screws.
Long-shaft screwdriver
Many American clocks have deep cases, making it impossible to reach movement mounting screws with a short driver. A long-shaft screwdriver allows you to reach inside the case and remove the upper mounting screws cleanly.
Screw-holding screwdriver
This specialty driver has a blade that closes around the screw when you slide the collar down. It is extremely useful when inserting screws deep inside a movement where your fingers cannot reach.
Pliers and cutters
Long-nose pliers
Extra-long pliers, such as those available from Timesavers, allow you to reach deep inside a movement. They are especially helpful for tightening the inner coil of a mainspring when it slips on the arbor.
Square-nose pliers
Square-nose pliers are useful for bending levers, adjusting wire springs, and handling small components without slipping.
Wire cutters
A simple pair of wire cutters is essential for trimming springs, wires, and other small components during repair work.
Supporting the movement during repair
PVC pipe support
A simple 4-inch PVC pipe section, cut to about 5 cm (2 inches) high, makes an excellent movement stand. The plates rest flat on top while the arbors hang freely over the edges, giving you full access to both sides.
Brass movement stands
Commercial brass stands clamp onto the movement’s mounting legs and hold the plates well above the bench. These provide excellent stability and clearance for arbors and levers.
DIY dowel supports
Four pieces of dowel, each 2.5 inches long with a small hole drilled in the top, can be used as inexpensive movement supports. The movement’s mounting legs screw into the dowels, raising the plates safely off the bench.
Mainspring clamps: an essential purchase
Mainspring clamps are absolutely required when working on spring-driven clocks. Without them, a mainspring can explode open during disassembly, damaging wheels, bending arbors, or breaking teeth. Clamps typically come in sets of four, and you will use them constantly.
Selecting the correct clamp size
Most American clock mainsprings use clamp size 6, but always test the fit. In this example, size 7 was too large, size 6 was still too big, and size 5 was the correct fit. The clamp should sit securely around the spring without excessive looseness.
Let-down tool collets
A standard let-down tool includes three double-ended collets: 10/12, 7/8, and 5/6. Choose the collet that fits snugly on the winding arbor before beginning the let-down process.
How to safely let down a mainspring
Letting down a mainspring is one of the most important safety procedures in clock repair. Until you own a mainspring winder, this is the method you will use to release power for cleaning and lubrication.
Understanding the click and click spring
The click is the small pivoting piece that locks into the ratchet wheel. The click spring pushes the click into engagement. To let down the spring, you must temporarily hold the click out of the ratchet while controlling the arbor with the let-down tool.
Let-down procedure
1. Turn the movement over and slide the clamp onto the mainspring so it rests loosely around the coil.
2. Fit the correct collet onto the winding arbor and tighten the let-down tool about a quarter turn.
3. Insert a screwdriver under the click spring and hold the click out of engagement.
4. Allow the let-down tool to rotate slowly in your hand, releasing tension into the clamp.
5. Adjust the clamp so it sits centered on the spring, not off to one side.
6. Continue letting down until all tension is held by the clamp.
Letting down the second mainspring
If the spring is too wide for the clamp to fit, wind the spring slightly to reduce its diameter, then slide the clamp on. Repeat the let-down procedure until the spring is fully contained.
Beginning movement disassembly
With both mainsprings safely clamped, you can begin removing wheels and levers from the movement.
Escape wheel and motion works
The escape wheel is always at the top of the time train and is easy to identify by its pointed teeth. Remove it first. Then remove the motion works, including the cannon arbor, which carries the hour hand.
Removing levers
Remove the lift lever, count lever, the maintenance cam lever, and the warning lever. The hammer lever remains attached until its wire spring is removed. The wire spring wraps around the plate and applies positive pressure to the hammer lever.
Removing the time train
The time train wheels are removed in order: T3, T2, T1. Keep all time-side components together in a tray. The great wheel is left in place temporarily for later steps.
Removing the strike train
Fly and count wheel
The fly sits at the top of the strike train and is removed first. The count wheel, with its deep slots, sits above the strike great wheel.
Strike wheels S1, S2, S3
S3 is the warning wheel and is identified by its pin. Any wheel with a pin belongs to the strike or chime side. S2 is the maintenance cam, with two pins that lift the hammer. S1 is the first wheel on the strike side.
Preparing the time-side mainspring for cleaning
With the strike side disassembled, the next step is to let down the time-side mainspring. Since beginners typically do not yet own a mainspring winder, this manual let-down method allows you to safely clean, grease, and reinstall the spring.
0 comments