Grandfather clocks are highly sensitive to changes in their environment. A minor move will offset the delicate balance of the clock's pendulum. The pendulum is the sole regulator of the clock's internal movement. Each tick of the pendulum advances the clock's gears slightly further. Grandfather clock maintenance involves watching over the visible portions of the clock---the pendulum and weights---and their connections to the interior clock movement.
Adjusting the Pendulum
Pendulums work by gravity. The weight at the base of the pendulum causes it to fall toward the earth. However, as the top of the pendulum is attached to the pendulum bob, it cannot actually fall. Instead, it swings from side to side in rhythmic strokes that are determined by the relative length of the pendulum. The longer the pendulum, the longer the period of time that pendulum takes to complete one movement from side to side. Pendulums cause problems when they are the incorrect length, or if they stop moving altogether. Pendulums that are too short will cause the clock's movement to run too rapidly. The clock movement consists of the various gears and wheels inside the clock. It is the movement that ultimately turns the hands on the clock face and moves any additional dials, such as a moon dial or calendar dial.
To modify the swing of the pendulum, adjust the grandfather clock's pendulum bob either up or down. Keep track of the time. Continue making adjustments until the grandfather clock is accurate to within 3 minutes a week. If, on the other hand, the pendulum has stopped, it is most likely because the clock has been thrown off balance. Move the clock slightly in different directions, swinging the pendulum at each point. When the ticking of the pendulum appears regular, stop moving the clock and secure it in that specific position. Either build up the height of the clock with wedges underneath, or attach it to the wall with a brace.
Adjusting the Weights
Although the 3 weights on a grandfather clock may appear identical from the outside, they are indeed different on the inside. The brass casing of each weight contains a steel or lead filling. These steel or lead rods reach different heights, thus producing weights that weigh varying amounts. The top of each weight is connected by a chain to a particular part of the grandfather clock's movement. One controls the time, a second the striking of the bell, and a third, the sounding of the clock's chimes. Each of these parts requires a somewhat different weight to move the gears inside its part of the clock. In general, the heaviest weight belongs to the chimes, because the chimes themselves are the heaviest part of the grandfather clock.
If the clock is not working properly, try rearranging the chimes. Many modern grandfather clocks---those made within the past half century---feature weights with small letters on the bottom. The weight marked "L" goes on the left, the one marked "R" on the right, and the one marked "C" in the center. If there are no markings and the clock has a wooden pendulum or small lyre pendulum, the heaviest weight usually goes on the right; that is, the right-hand side of the person working on the clock. The other 2 weights can simply be attached to either of the left-hand positions. However, if the grandfather clock has a lyre-shaped pendulum that is at least 6 1/2 inches in diameter, the lightest weight will go on the left, with the heavier 2 at either point on the right.