Cooling and lubrication

Conduction : Is the transfer of heat between two metals. Conduction occurs in an engine between the piston and the cylinder wall

Convection : Is the transfer of heat in a liquid by the circulation of the heated parts. Convection occurs inside the radiator of the cooling system, the hot water rises to the top of the radiator and the cooler water sinks to the bottom of the radiator which is then circulated through the engine.

Radiation : Is the heat transfer from a substance into the air. Radiation occurs in the radiator of a cars cooling system, the air travels through the hot radiator and dissipates the heat into the air. Radiation also occurs on the fins outside the combustion chamber of a two stroke engine.

A thermostat maintains the core temperature by regulating the flow of coolant into the radiator. the thermostat operates by using a sealed wax pallet that is solid when it is cold, when the engine heats up the wax melts and expands, opening the thermostat. The thermostat stays closed until the engine reaches optimum operating temperature. when it opens it allows more coolant to flow into the radiator.

Why do engines have coolant in them?
Engines have coolant in them to lower the freezing point of the water in the radiator so it doesnt freeze and crack the block or pop out frost plugs. it also raises the boiling point of the water. Coolant in an engine also prevent corrosion of the aluminium head

When should an oil filter be replaced?
an oil filter should be replaced every time the engine oil is replaced. the engine oil should be changed every ten thousand km

What projects the oil pressure and where is it situated?
The oil pump creates the oil pressure in the engine. the oil pump is connected to the crankshaft which turns the gears inside the oil pump, creating pressure. The oil pump is located on the block of the engine.

4stroke

4 strokes of a petrol 4 stroke engine

A stroke refers to the full travel of the piston from Top Dead Center to Bottom Dead Center

The crankshaft completes its cycle with two revolutions of the crankshaft

Stroke 1- down

            Intake

            Piston travels down the cylinder bore and the intake valve is open. The low atmospheric pressure draws in the air/fuel mixture

Stroke 2- up

            Compression

            Both valves are close and the piston travels up the cylinder bore to TDC, compressing the air/fuel mixture

Stroke 3- down

            Combustion

            When the piston is close to TDC the spark from a spark plug ignites the compressed air/fuel mixture, the resulting explosion forces the piston down the cylinder bore. Creating the power for the other pistons attached to the crankshaft to rotate.

Stroke 4- up

            Exhaust

            The exhaust valve opens and the piston travels from BDC to TDC pushing out the exhaust gas, clearing the chamber so the process can start again

2stroke

2 strokes of a petrol 2 stroke engine

A stroke refers to the full travel of the piston from Top Dead Center to Bottom Dead Center

The 2-stroke engine completes its cycle with one revolution of the crankshaft

stroke 1- up

            Intake

            The air/fuel/oil mixture is drawn into the crankcase from the vacuum created by the piston traveling to TDC The piston is blocking the exhaust and the transfer ports and the intake port is open

            Compression

            The air/fuel mixture that is transferred to the combustion chamber from the pervious stroke is compressed

Stroke 2- down

            Power

            At the top of the stroke the compressed air/fuel mixture is ignited by the spark from the spark plug, the burning fuel expands forcing the piston down the cylinder bore

Exhaust

As the piston travels down it opens the exhaust port and the transfer port and closes the intake port. The fuel/air mixture enters the combustion chamber pushing the burnt gases out

Glow Plugs

Glow plugs

Diesel enignes do not use a spark to ignite the fuel, they rely on the compression to raise the temperature of the air so the diesel will combust when sprayed into the pre chamber. Diesel engines usually have quite large and strong blocks. When starting the vehicle from cold the engine will act as a heat sink and dissipate the heat that is generated by the piston compressing the air. Therefore the engine cannot generate enough heat for the diesel fuel to combust.

Glow plugs are used to pre-heat the cylinder or pre-chamber before cranking the engine. Switching the key to the on position the dashboard will show -------->

This indicator shows that the glow plugs are active and usually lasts between 2-5 seconds
once the light goes out the enigne is ready to crank