On July 28, 2011, about 1200 eastern daylight time, a Cessna 172M, N1443U, was substantially damaged during a forced landing in Lake Okeechobee, near Pahokee, Florida. The certificated flight instructor was not injured and the certificated student pilot incurred minor injuries. Visual meteorological conditions prevailed. No flight plan had been filed for the flight, between Palm Beach County Glades Airport (PHK), Pahokee, Florida, and Fort Lauderdale Executive Airport (FXE), Fort Lauderdale, Florida. The instructional flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. According to the flight instructor, the accident flight was part of a series of cross country and student solo flights that day. Upon arrival at PHK, three practice landings were completed before a full stop landing. During a subsequent takeoff for FXE from runway 17, with winds from 100 degrees magnetic at 10 knots, the student pilot was at the controls. All of the gauges were "in the green," and the fuel tanks were half full. After the takeoff and a straight-out departure, as the airplane reached 500 feet, the engine started shaking, sputtering, and making "alarming" noises. The flight instructor immediately took control of the airplane, and quickly glanced at the mixture, fuel selectors, engine instruments, and fuel, without noting anything abnormal. The flight instructor then turned the airplane back toward runway 35, and transmitted via radio an engine failure, but saw that the engine did not completely quit. Instead, it was not producing any thrust, and the airplane could not maintain altitude. The flight instructor also stated that after turning the airplane back toward runway 35, she realized that it was too high and too fast. She pulled out the throttle; however, she did not use flaps or attempt to slip the airplane. The airplane then overflew the entire length of the runway, and the flight instructor had to consider other options. In front of her was a house, to the right was a road lined with power lines, and to the left was the lake. The flight instructor then turned the airplane over the lake, and "floated" it as long as possible before it touched down and nosed over. The flight instructor and student pilot exited the airplane and waited on its belly until rescue. After its removal from the lake, Federal Aviation Administration (FAA) inspectors and flight school maintenance personnel examined the airplane and the Lycoming 0-320-E2D engine, and found that the No. 3 cylinder exhaust valve head had sheared off the stem. The stem, spring and rocker arm were still intact, and the No. 3 piston exhibited signs of mechanical damage from the sheared head inside the combustion chamber. The airplane's engine was last inspected during a 100-hour inspection on July 21, 2011. According to the logbook entry, at that time, the engine had accrued 2,211.8 hours of operation since major overhaul. At the time of the accident, hours of engine operation since major overhaul were 2,229.5. According to Lycoming Service Instruction 1009AU, dated November 18, 2009, recommended time between overhauls of the O-320-E engine is 2,000 hours.