Expert: Martin Meyer - 11/29/2008

Question
Brought mechanism to local clock shop. Inspection revealed stretched chain links that he said may not be available. Also saw the stems that mount into the back clock brass plate have wear & elongated holes. repair cost over $599. I am mechanically inclined & wonder if i could fix & how to get parts.

Answer
Hi Frank,

Replacement chains are available in many sizes from clock repair supply houses. Unless the ones on your clock are a very unusual size, they should be replaceable.

Your local clockmaker was referring to the pivots, which are the tips of the gear shafts, and turn in holes in the two brass main plates. These holes serve as simple bearings. When they are worn, they must be drilled out and replaced with bushings.

Rebushing is one of the essential skills of a clockmaker, and it is not quickly or easily learned. Additionally, special tools are required, including cutting and centering reamers, cutting broaches and polishing broaches. There are no general shop tools which will substitute, such as drills or ordinary reamers. When the original holes wear into elongated egg-shaped holes, the center is lost and must be reestablished very accurately or the gear shafts will be crooked, or cocked. The reamers must cut holes about .001" smaller than the O.D. or the bushing, so that the bushings can be press-fitted in. Then the holes in the new bushings must be hand cut and polished to establish a clearance of about .002" larger than the pivot. The holes must be absolutely perpendicular to the plate, or the pivots will bind. The pivots also must be refinished, as wear creates rough grooves in them. Pivot polishing is accomplished on a watchmaker's lathe with various grades of very fine abrasive and pivot polishing tools.

Aside from the actual bearing repairs, the movement must be completely disassembled. Reassembly and setup is complicated, as many of the gears must be precisely indexed to each other, and many other adjustments must be made. The operation of the chime, strike and time trains must be fully understood, as must the chime and strike warning processes and the chime correction assembly, or proper reassembly will be impossible. Finally, the pallet faces must be adjusted to contact the escape wheel teeth at exactly the correct point for proper pallet drop and locking.

For these reasons, such repairs are extremely labor intensive and knowledge intensive, and so, expensive. I could not recommend that anyone but an experienced clockmaker attempt such work, especially on a very high grade clock such as a Herschede.  http://www.clockmasteronline.com