FARM TRACTORThe history of tractor development is to lang to relate here .Landmarks along the road include the fires use of an internall combustion engine in a tractor in the United States in 1890;the Iveltractor of 1901; the American Ford of 1917 , and the International Farmall of 1923 . During the 1930s , the use of low-pressure pneumatic tyres soon became popular , and the first Ferguson system tracrors incorporating three-point linkage with hydraulic draught control were introduced .Classification of tractor types.Tractors as now manufactured can be classified as follows:A. According to method of securing traction and self-propulsion:1. Wheel tractorsa. Three tractorsb. Four wheels 2. Track-type tractorsB. According to utility :1. General-purpose or utility2. All-purpose or row-crop type Wheel tractors. The wheel-type tractor is the predomingating type,particularly for agricultural purposes.Wheel tractors are made either with three wheels or with four wheels .The usual arrangement consists of two rear-drive wheels and one or two front steering members. Track-type tractors. The traction mechanism in the track-type tractorconsists essentially of two heavy,endless,metal-linked devices known as tracks themselves by reducing the movement of one track below the speed of the other. General-purpose or utility tractor.A general-purpose tractor is one ofmore or less conventinal design such as an ordinary four-wheel machine or a track-type machine.This type is also referred to as autility troctor. It is made to perform only the usual tractor jops,including both field and belt work such as plowing ,harrowing,road grading ,combining,feed grinding,and the like.All-purpose tractors.An all-purpose or row-crop type is a tractor designed to handle practically all the field and belt jops on the average farm,including the planting and intertillage of row crops.The conventional tractor consists basically of two engine-driwen wheels,usually at the rear, and two support wheels st the front . The type of the engine used to power the heart of the tractor; it is here that the fuel,the chemical potential energy , is converted into the mechanical emergy which causes the wheels to turn.The difference between n internal and external combustion engine is simply that in an internal combustion engine ,the conversion of potential energy into mechanical energy takes place wholly in the cylinder,whereas with external combustion the fuel is burnt outside the cylinder .A steam engine or a gas turbine is a good example of the latter.How can liquid fuel be changed into rotational mechaanical energy? This is achieved by accurately mixing the fuel with air and then burning it in controlled condition.When this mixture burns ,it expands and pressure builds up ,forcing the piston to move down the cylinder in a straight line. It is said to rotary motion .This linear motion is converted into rotary motion by a connecting rod and crank arrangement joined to the piston.To be able to use this energy effectively, the burning and combustion proce and the force of expansion have to be controlled. To do this , the enginemust have :1. A tube or cylinder closed at one end ,in which the mixture of fuel and air can be compressed and burnt .2. A piston , which slides freely and yet fits closely in the cylinder ,so that the expanding gas force it down the cylinder ,and do not escape past it .3. Two passages or ports in the cylinder . One for the mixture of fuel and air to enter the cylinder , the inlet prot , and the other to allow the used gases to escape , the exhaust port.4. Two valves , the inlet valve to control the the movement of the mixture to the cylinder , and the exhaust valve to control the escape of the used gases . By carefully timing the ignition of the mixture in relation of the opening and closing of the valves and the position of the piston , it is possible to make the piston move up and down the cylinder continuously .The working of an internal combusition engine , once it is started , involves a sequence or cycle of operations in each cycle and the two-stroke cycle . In the four-stroke cycle , the crankshaft completes two revolutions and the piston four strokes , a stroke being the movement of the piston from one end of the cylinder to the other . In the two-stroke cycle , the crankshaft makes one revolution and the piston two strokes in each cycle .Your tractor probably has a complete electric system which provides electicuty for the self-starter , for igniting the fuel , and for lights . Insome designs electricity is also used for certain other accessory circuits.Such complete systems comprise several circuits : (1)generator circuit, (2) starting motor circuit , (3) lighing circuit , (4) ignition circuit . The storage battery may well be considered the basis of the complete system bacause it is connected to and works with all four of these principal circuits .We must re