Question: When was the largest bell installed?
About the article "Leaning Tower of Pisa", section "Construction".

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At 90 tons, the Mingun Bell reigned as the largest ringing bell in the world until 2000, when it was eclipsed by the 116-ton Bell of Good Luck at the Foquan Temple, Pingdingshan, Henan, China. 
The clock installed in the Rissik Street Post Office in Johannesburg, South Africa in 1905 was purported to be a unique miniature replica.
The largest bell in this clock is an exact replica of the smallest bell in the Elizabeth Tower.
The clock was stolen in 2002 and the building burnt down in 2008. 
The cathedral has eleven church bells, four of which are medieval.
The first was the 3.8-ton "Dreikönigsglocke" ("Bell of the Three Kings"), cast in 1418, installed in 1437, and recast in 1880.
Two of the other bells, the "Pretiosa" (10.5 tons; at that time the largest bell in the Western world) and the "Speciosa" (5.6 tons) were installed in 1448 and remain in place today.
During the 19th century, as the building neared completion, there was a desire to extend the number of bells.
This was facilitated by Kaiser Wilhelm I who gave French bronze cannon, captured in 1870–71, for this purpose.
The 22 pieces of artillery were displayed outside the Cathedral on 11 May 1872.
Andreas Hamm in Frankenthal used them to cast a bell of over 27,000 kilos on 19 August 1873.
The tone was not harmonious and another attempt was made on 13 November 1873.
The Central Cathedral Association, which had agreed to take over the costs, did not want this bell either.
Another attempt took place on 3 October 1874.
The colossal bell was shipped to Cologne and on 13 May 1875, installed in the Cathedral.
This "Kaiserglocke" was eventually dismantled in 1918 to support the German war effort.
The 24-ton "St. Petersglocke" ("Bell of St. Peter", "Dicke Pitter" in the Kölsch dialect), was cast in 1922 and is the largest free-swinging bell in the world.
Bells of the ridge turret:  Vespers Bell (Mettglocke) 0.280 tons  Consecration Bell (Wandlungsglocke) 0.425 tons  Angelus Bell (Angelusglocke) 0.763 tons Bells of the main bell cage in the south spire:  Hail Bell (Aveglocke) 0.830 tons  Chapter Bell (Kapitelsglocke) 1.400 tons  St Joseph's Bell (Josephglocke) 2.200 tons  St Ursula's Bell (Ursulaglocke) 2.550 tons  Bell of the Three Kings (Dreikönigsglocke) 3.800 tons  Speciosa 5.600 tons  Pretiosa 10.500 tons  St Peter's Bell (St. Petersglocke, Great bell of Germany) 24.000 tons  
Within the bell tower is the 17-ton Founder's Bell.
The bell was cast in 1925 under a commission by Rodman Wanamaker to honor his father John Wanamaker, founder of the department store.
Cast in the United Kingdom, the bell is at the rim and high and is one of the largest bells in the world.
The bell was brought in 1926 by the Cunard liner "Ascania" to New York City, from which it was conveyed to Philadelphia by rail.
The bell was carried on a flatcar and had clearance of only in some of the tunnels the train passed through.
Tuned to a low D bass clef, the bell's original home was the Wanamaker Building, a block from One South Broad.
It hung above the street in a specially built tower on the building's roof.
Hung on December 23, 1926, the bell was first rung on New Year's Eve of that year.
The bell is rung every hour, except on Sundays.
The bell was originally intended to swing in the tower on top of One South Broad, but when it was it shook the building.
A hammer driven by a 230-volt electric motor was later installed and currently rings the bell.
The ringing of the bell, which can be heard for , is often mistakenly assumed to come from City Hall's clock tower across the street.
Philadelphia Orchestra conductor Leopold Stokowski wrote in 1962 that the bell had "one of the finest sounds I have heard anywhere in America, Europe or Russia".
In June 2000 the Founder's Bell was added to the Philadelphia Register of Historic Places by the Philadelphia Historical Commission. 
The tower contains an 8-bell carillon which was installed in the 1920s.