Expert: Martin Meyer - 2/12/2008

Question
I purchased a Pearl grandfather clock (new) in 1984. Model No. 413-2150. Single chime - chain/weight driven - moon phase dial.
This clock has always demonstrated this problem ever sense I've owned it.
Here's the problem. The clock keeps good time for months at a time and then gains or looses time. This seems to occur with the changing seasons from summer to winter. Could changes in humidity cause this? If not, what could it be? If so, what can be done to rectify this problem?
I have performed maintenance on the movement (cleaning / lubricating) over the years and this never seems to change or remedy the problem.
Any comment or advise will be greatly appreciated!!
Thank you,
Tom

Answer
Hi Tom,
    The rate of clocks does change with both and temperature and humidity, but the change should be small, perhaps a couple minutes per week. The change due to humidity is even smaller. If your clock is changing its rate to a greater degree, the problem lies elsewhere, and I would be unable to offer suggestions on this.
    The change due to temperature will be greater if you have a metal "lyre" pendulum than if you have a wood stick pendulum. In warmer temperatures the metal of the pendulum expands, and the pendulum effectively becomes slighter longer, and the longer the pendulum the slower the rate of the clock.
    There is such a thing as "temperature compensating" pendulums, which use a row of pendulum rods of alternating metal content to overcome the expansion effect. On modern clocks, however, the rods of alternating color are merely decorative, and not temperature compensating.
    Unfortunately there is no remedy for this; it is simply a characteristic of pendulum clocks.