Machinery
Section 1 - Major Systems and Key Components of the Tractor

The internal combustion engine is a form of heat engine and the name “heat engine” is given because heat energy produced by the burning of fuel within the engine is changed into mechanical energy.

The piston moves down, inlet valve open, exhaust valve closed. The downward movement of the piston creates a partial vacuum in the cylinder and air only rushes in through the inlet valve passage. At the bottom at the stroke the inlet valve closes trapping the air within the cylinder.

The piston moves up, the inlet valve is closed, the exhaust valve is closed. The upward movement of the piston compresses the air to very high temperature, about 1000°F. This temperature is reached because the volume within the cylinder is reduced to approximately 16 times its original volume.

When the piston is at the top of the compression stroke, a spray of fuel is injected into the cylinder. This fuel ignites immediately when it comes in contact with the hot air.
The burning fuel/air mixture expands and thrusts the piston down the cylinder.

The piston moves up the cylinder, the inlet valve is closed, the exhaust valve is open.
The upward movement of the piston pushes the burnt gases out through the exhaust valve passage out to the atmosphere.

Several operating controls and adjustments are available to drivers of tractors and the driver should understand the response characteristics of each control and the purpose of each adjustment.

One key element for the efficient use of all tractors is that they are regularly maintained according to the manufacturer’s instructions.

When you use the tractor, correct gear selection to fit the task will have a significant effect on the efficiency of the operation.

Most tractor field speeds are determined by the implement and not by the power ability of the tractor although considerable savings may be possible depending on how you arrive at the speed.

Slopes: Inclines

In order to maintain the revs, you may need to make gear shift adjustments to meet changes in ground conditions or changes in inclines.

Travelling on rough ground requires a reduction in travelling speed while maintaining tractor revs, this is achieved by moving down to a lower gear.

When operating in areas of the fields where the ground conditions may be wetter, again adjustments will be needed to compensate for the loss of traction and possible decrease in engine revs.

In some field work the tractor may have changing demands from the attachment e.g. when side loading from a forage harvester.

In most tractors the fuel setting is set by the manufacturer and is usually adjusted by the dealer.

Exhaust smoke is a good indicator of the operating condition of your engine.

The operating temperature of an engine, as indicated by coolant temperature, can also affect power and efficiency.

Tyres deteriorate with use and exposure.

The air cleaner is necessary especially when you consider how filthy the air can get when carrying out certain field work e.g. harvesting.

There are two types of air cleaners:

This contains a replaceable element made of wax-paper material which must be changed when it becomes partly clogged with dirt.

A good guide to a partially blocked air cleaner is black smoke from the exhaust.

This is a type of blower, hot exhaust gases from the engine drive a fan which in turn drives another fan which draws air from the air cleaner forcing more air into the cylinders.

The pump is operated by a cam on the engine camshaft so that it pumps continually as long as the engine is running.

Two types of fuel injection pumps are in general use, a plunger type or a distributor type pump.

A Governor is a mechanical device used to govern the speed of machines like engines.

The heat produced on the power stroke of a diesel engine can be as high as 1600°C and this is greater than the melting point of the engine parts that come in contact with the heat, thus it is essential to have an efficient cooling system.

Assuming the heat value of the fuel used to be 100% then probably 30% is used to produce power, 40% is passed to the atmosphere via the exhaust and 30% is dissipated by the cooling system.

It is very important that the engine does not over heat or “boil the water”, but it is equally important that the engine does not run too cool or the fuel will not vaporize properly, again causing damage and rapid wear.

A radiator is constructed to provide the largest surface area possible with fan assisted air flow.

The tubes are also in contact with numerous thin metal plates and this provides a further increase in surface area. The whole radiator looks like honeycomb through which air can flow.

The lubricating system is designed to prevent damage to moving parts on the tractor.

When two surfaces rub together they produce heat (friction) and if the heat generated was high enough then it is possible that these surfaces could melt and weld together.

The main aim of lubrication is to put a film of oil between the working surfaces of the metal parts to cool the effect of friction and therefore protect the surfaces.

There are two main types of lubrication in tractor engines:

Oil filters are fitted within the system to prevent most of the contaminants reaching the working parts of the engine.

A strainer is fitted around the oil pump intake to prevent large particles entering the pump.

There are two main types of filters:

All tractors have a battery.

The battery consists of a number of cells, each cell having an approximate electrical pressure of 2V.

The whole assembly is contained in a battery case with a vent cap on top to allow the battery to be checked for electrolyte level and permit gases to escape.

The function of the dynamo is to:

The principle of the starter motor is based on magnetism and is constructed very much like a dynamo.

The dynamo is driven by the engine and it produces current which flows to the battery.

The starter motor is heavily constructed to enable it to carry the heavy current required to give it good turning power, for it must have enough power to move the engine.

The starter motor shaft around which the armature coils are built extends out of the yoke or casing.

A solenoid switch is installed to open or close the circuit and this solenoid can be operated by a light duty switch as can be found on the control panel of a modern tractor.

The solenoid consists of a soft-iron core which is free to move, placed at one end of a coil of wire, both the coil and the core assume a similar polarity, therefore if a current is passed through the coil the core is drawn into the centre of the coil because adjacent poles are of different polarity.

The electric switch uses the movement created by the solenoid to close, at high speed, the two contacts of the heavy-duty cable.

In the dry, single clutch, the clutch is attached to the engine flywheel so that it rotates with it.

The end of the input shaft is fitted into a bearing in the centre of the flywheel and the plate is positioned between the face of the flywheel and a spring–loaded pressure plate.

In order to transmit the drive from the engine flywheel to the clutch shaft which goes directly to the gearbox, it is only necessary to allow the clutch plate to be gripped between faces of the flywheel and the pressure plate.

The heavy spring pressure is sufficient to do this and form a solid drive to the shaft.

The main purpose of the gearbox is to reduce the speed of the drive from the engine crankshaft before the drive is applied to rear wheels of the tractor. It will also change the speed ration as required.

The differential achieves the following:

Its main use is in the operating of field machinery for either above or below surface implements.

In the tractor hydraulic system the pump supplying oil to the ram cylinder is usually a gear pump driven by the engine or some part of the transmission system and pressures of up to 910 kg (2000Ib approx.) are provided.

It is necessary in such systems to have control over the flow of oil so that excessive pressures are not built up, therefore safety valves are incorporated as protection.

The three-point linkage shown consists of two lower links pivoted beneath the tractor’s back axle, and a top link pivoted at the top of the back axle housing.

Valves in the system which may be arranged to operate automatically or by hand lever control.

The tractor’s hydraulic system also provides a useful source of hydraulic power for the operation of implements or parts of implements remotely connected to the tractor.

Nearly all modern tractors are provided with outlet points where flexible pipes can be fitted to convey oil from the hydraulic pump to an external ram and cylinder fitted to an implement.

In the tipping trailer a flexible pipe is connected between a self- sealing outlet union on the tractor, to a ram and cylinder beneath the trailer body.

Tractor will be either two-wheel or four-wheel drive.

There is a need for increased stability if you are operating on inclines and for a larger footprint when operating on soft surfaces.

On two-wheel drive tractors the tyre treads of the front wheel tend to be ribbed following the circumference of the tyre.

The four-wheel drive tractor will have the same tread on both sets of wheels.

There are two types of tyre available:

The ply-rating refers to the number of layers e.g. four ply/six ply.

Standard tyre – 13.6/12-38

The rotating brake disc is gripped on both sides by pads mounted in one or two fixed brake callipers.