Pendulum suspension from a Smith of Derby clock. If you look very closely, you will see that the minute hand doesn’t move smoothly but it sits still most of the time, only moving on each tick by 1.5cm. The swinging pendulum releases the “escapement” every two seconds which then turns the hands on the clock’s four faces.

The pendulum suspension spring is especially critical because it holds up the huge pendulum bob which weighs 321kg.

If any of these weights falls out of control (as in the 1976 incident), they could do a lot of damage. Two other weights that ring the bells are each over a tonne. The “drive train” that keeps the pendulum swinging and that turns the hands is driven by a weight of about 100kg. The weights that drive the clock are, like the bells and hammers, unimaginably huge. Big Ben’s clock has had only one major breakdown, in 1976. The resulting damage took months to repair.

In 1976 the speed regulator for the chimes broke and the mechanism sped up to destruction. In its 162-year history it has only had one major breakdown. The clock mechanism itself is remarkable. There are plumbing and electrical works to be done for a lift to be installed in one of the ventilation shafts, toilet facilities and the fitting of low-energy lighting.

There is water damage to the masonry and condensation problems will be addressed, too. There is corrosion damage to the cast iron roof and to the belfry structure which keeps the bells in place. But a clock just doesn’t stop – especially not a clock as iconic as the Great Clock at the Palace of Westminster. It is convenient to choose a day when we’re out of the house to paint the doors, or when we don’t need the car to repair the brakes. The Illustrated News of the World December 4 1858Īny building or machine needs regular maintenance – we paint our doors and windows when they need it and we repair or replace our cars quite routinely. Instead, it is the Elizabeth Tower (1859) and the clock mechanism (1854), designed by Denison and Airy, that need attention.

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