Antique mantel clocks are small, tabletop clocks. The name comes from the fact that they were originally intended to sit on the shelves, or mantels, atop fireplaces. Antique mantel clocks are mechanical clocks. A spring supplies powers to internal gears. Located in the back of the clock is a pendulum that regulates the time. The pendulum swings back and forth, slowly advancing a toothed wheel that controls the gears. Fixing antique mantel clocks can be as simple as adjusting the pendulum.
Open the back of the antique mantel clock. Use your hand to stop the pendulum.
Find the nut at the bottom of the pendulum bob. The pendulum bob is the weight at the bottom of the pendulum.
Turn the nut to the left if the clock is fast. Turning the nut to the left lowers the pendulum bob. Lowering the pendulum bob "lengthens" the pendulum. The longer the pendulum, the slower it will move.
Note the time on the antique mantel clock. Check the time again 24 hours later. If the clock is still fast, lower the pendulum bob again.
Turn the nut at the bottom of the pendulum bob to the right, if the clock is slow. Turning the nut to the right will raise the bob on the antique mantel clock. The higher the pendulum bob, the "shorter" the pendulum. A short pendulum runs faster.
Check the time again 24 hours later. Adjust the pendulum bob up or down as necessary. Keep checking the time every day for a week. Antique mantel clocks should be accurate to within 1 minute a week. Close up the back of the clock after completing the adjustments.
The pendulum cannot hit anything while it is swinging. Try leaning the antique mantel clock slightly to one side, to the back or to the front. Use a piece of cardboard to raise the clock at the appropriate point. Clocks that have been moved will have to be rebalanced.
Check the size of the pendulum bob if the pendulum still hits part of the clock during its swing. The pendulum bob may have been replaced and might be too large for the clock.