TRACTOR SYSTEMS

1. Electrical system

The electrical system in tractors consists of the ignition circuit generator (dynamo) circuit,

starter motor circuit and lighting circuit. Each of these circuits operates independently except

that they rely on tractor battery. The battery stores electrical energy supplied by the charging

system. The electrical energy produced by the running engine which is driven by a generator

charges the battery.

At charging time chemical change takes place in the battery allowing the electrical energy to

be stored.

Lead acid battery showing battery cells

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The battery has two sets of plates, a positive and negative where the terminals are attached.

Electrical system of a tractor

Care and maintenance of a tractor battery

i) The level of electrolyte should be kept just above the place by topping with distilled water

ii) Corroded terminals should be scrapped clean and smeared with grease

iii) The battery should be tightly fixed in a box to avoid spillage and damage

iv) The battery should be fitted correctly on the tractor

v) The battery should be charged regularly and periodically

vi) In case of long storage the battery contents should be emptied and the battery be kept upside down

vii) The generator fan belt should always be functional to ensure the battery is always charged

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2. Ignition system

The ignition system of petrol engine consists of ignition coil, the distributor, contact breaker and the condenser.

In spark ignition system, the battery or generator supplies the sparks required for ignition.

Tractor ignition system

i) Ignition coil

The ignition converts the battery voltage from 12 volts to about 6000 volts. It provides a spark at the sparking plugs located in the engine cylinders.

ii) The distributor

This causes the spark to occur at each cylinder in the required firing order of sequence.

iii) Contact breaker

The function of contact breaker is to interrupt the normal flow of current in the primary circuits. This results in the generation of high voltage from the coil that produces the required spark in the sparking plugs.

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iv) Condenser

The condenser absorbs the self induced current in the primary circuit therefore preventing the contact breaker points from excessive heating.

Common faults of ignition system

1. Sudden stopping

This could be caused by the following:

Poor terminal connections

Faulty ignition system

The measures that can be taken to correct these faults are:

Proper tightening of the terminals

Proper cleaning and readjustment of the terminals

2. Continuous engine running

This could be caused by the following:

Broken leads

Poor terminal connections

Faulty contact breaker

The measures that can be taken to correct these faults are:

The broken leads should be replaced

The leads should be cleaned and tightened regularly

Maintenance of ignition system

i) The carbon deposits on the spark plug electrodes should be removed.

ii) The spark plugs whose electrodes are worn out should be replaced.

iii) The contact breaker points should be cleaned.

iv) The breaker points should be adjusted so that they lie between 0.30mm and 0.50mm.

v) The condenser should be replaced regularly. (vii) The ignition system should always be kept dry. (viii) Ignition wires with poor insulation should be replaced.

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3. Cooling system

Power production process in the tractor engine gives a lot of heat. This heat should be reduced and kept at safe limits. Too much heat within the engine may lead to overheating and hence expansion of engine components.

Expansion of the engine components distorts its shape causing gas leakage, valve burning, loss of engine power and even cracking of the cylinder or its head.

Cooling system therefore aims at preventing the engine from overheating which would otherwise cause piston seizure in the cylinder. Some tractor engines are cooled by air while others are cooled by water.

Type of cooling systems.

i) Air cooled system.

This cooling system is commonly used in light weights farm machine such as mowers, motor-bikes and landmasters.

Characteristics of air cooled engines

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Characteristics of Air Cooled Engines.

They are simple in construction

They have fins and fan blade which assist the circulation

They are light in weight for they have no radiators and water jackets

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Problems of air cooled engines

They get hot quickly and use heavy lubricating oils

The cooling is not adequate under all conditions especially when carrying heavy loads

ii) Water cooled system

In this system water is used to absorb heat from the engine block at a reasonable rate.

The major components of water cooled engine are the radiator, water jackets, water hoses, water pump, thermostat and fanning mechanism.

Water cooling system

Cool water is sucked from the bottom part of the radiator with help of water pump. It is pushed through the water jackets and circulates within the engine block and the cylinder head. A thermostat is used to regulate the temperature of water in the engine at 800C-900 C.

When the water becomes too hot it is forced back to the radiator for further cooling.

Care and maintenance of water cooling system6

i) The water pump should be lubricated regularly

ii) Clean water should be used in the radiator and trash removed from the fins

iii) All pipes should be fitted tightly to avoid leakage

iv) The radiator should be filled with clean water before starting day’s work

v) Fan belt tension should be checked regularly and if too tight or too loose should be adjusted accordingly.

4. Lubrication system

This system is aimed at supplying oil to all parts of the engine where friction is likely to occur.

Importance of lubrication system in tractors

i) It helps to increase the efficiency of the machine and reduces the rate of wear and tear of moving parts

ii) It reduces the heat created by the rubbing surfaces and act as a seal between them

iii) It acts as a cleaning agent because it washes off all the dust, dirt, soot and metal chippings from the oil paths to the sump

iv) Oiling prevent rusting of stationary machines.

Types of lubrication systems

There are three types of lubrication systems used in tractors for efficiency production. These are splash feed, force feed and the oil type.

i) Splash feed type

This is the type of lubrication systems where the cranks of the crank shaft are dipped in the oil and splashed up as they move. This is not a good type of lubrication.

ii) Force feed type

This is the most common and modern method in a four stroke cycle engine. The components of this type are the oil sump, pump, filters and oil ways (galleries) around the cylinder block, pistons, connecting rods, camshaft, crankshaft and the valves.

The oil in this case circulates around the engine and drips back to the oil sump. A dip stick is used as indicator of how much oil is in the oil sump.

iii) Oil mist type

This is common with two stroke cycle engines. The oil is mixed with fuel mainly petrol in the tank at the rate of 0.25 litre of oil to 6 litres of petrol.

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DrivingGetting Started

1) Sit in the driving seat. The five primary controls of tractor driving are easily and comfortably accessible to hands and foot.

Steering Wheel

Hand Throttle

Gear Lever

Clutch Foot brake Accelerator

Ensure you have maximum vision to the front, sides and rear for a distance of at least 100 meters.

2) Grab and hold firmly the steering wheel.

The two front wheels of the tractor move whenever the steering wheel is turned. The steering wheel must therefore be held firmly (¼ to 4) and moved only on purpose.

Clutch

3) Clutch is always on the left foot. The clutch is a coupling between engine and transmission. When the clutch- pedal pressed down the power is not transmitted from the engine to the gear-box and road-wheels. The clutch allows selection of gears.

The brakes

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4) The brakes stops the road wheels from moving. It should be used in the absolute minimum, because the driver should allow the engine to go slow and stop the moving tractor before the brakes are applied. The foot-brake is always between the two pedals clutch and accelerator and is applied first before the hand brakes are engaged.

Ignition

5. With the gear neutral and brakes firm, put the ignition key in the key hole and turn it to crank the engine. Give a little time to allow engine oil to flow through the engine.

Gear-up

6. With the foot firm on the clutch pedal, engage the first or reverse gear using the gear lever, depending on the direction you want to take.

7. Release the clutch pedal slowly and the vehicle will start moving. Use the steering wheel to direct the tractor to the direction where you want to take it.

Drive

8. While on motion, clutch down to engage higher gears as you proportionally increase the fuel by the throttle/ accelerator.

9. To slow down, reduce the fuel feed, clutch and engage the heavy gears down to gear one.

10. To stop, step on the foot-brake firmly then apply the handbrake.

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