Four Stroke Internal Combustion (IC) Engine


This 3D model shows a four stroke diesel internal combustion engine. The engine is for trucks, vans and lorries etc. and not for small passenger vehicles. All major components associated with a typical four stroke combustion engine of this size are shown on the model. A summary of each engine part is given below followed by a detailed description.


Engine Parts Explained

A four-stroke combustion engine consists of the following main parts:

  • Rocker Arm – presses down upon the valve bridge or valve stem.
  • Tappet Clearance – space between valve tip and rocker arm. 
  • Valve Spring – returns valves to closed position when rocker arm not applying force.
  • Fuel Injector- injects fuel.
  • Fuel Inlet Pipe – transfers fuel to the fuel injector.
  • Suction Valve – allows air into the combustion space.
  • Exhaust Valve – allows exhaust gas to exit the combustion space.
  • Fuel Injector Nozzle – sprays atomised fuel into the combustion space.
  • Clearance Volume – the volume calculated between top dead centre and the top of the cylinder.
  • Swept Volume – the volume based upon the stroke of the piston and area of the cylinder bore.
  • Cylinder Volume – the total volume within the cylinder.
  • Cylinder Bore – the internal diameter of the cylinder.
  • Compression Ratio – a calculation based upon the volume ratios within the cylinder. Petrol/gasoline engines have a low compression ratio (6-9:1) whilst diesel engines have higher compression ratios (14-20:1).
  • Top Dead Centre (TDC) – a piston’s furthest point of transit towards the inlet and exhaust valves.
  • Pushrod (push rod) – transfers force from the cam lobe to the rocker arm.
  • Piston Crown – the top of the piston.
  • Piston Ring Grooves – where the piston rings locate within the piston.
  • Piston Rings - used to seal the space between the piston and cylinder liner.
  • Stroke – the distance the piston travels from bottom dead centre (BDC) to top dead centre (TDC).
  • Piston – the piston.
  • Piston Skirt – the piston skirt (may be short or long).
  • Piston Pin / Gudgeon Pin / Wrist Pin – the connection between the piston and connecting rod.
  • Cylinder Wall – the boundary of the combustion space (also sometimes called the cylinder liner).
  • Cylinder Liner – the internal surface of the cylinder.
  • Camshaft – used for controlling engine timing such as fuel injection and valve timing; driven by the crankshaft.
  • Cam / Cam Lobe – presses against the tappets to actuate the rocker arm(s).
  • Cam Follower – is pushed by the cam and transfers the movement to the push rod.
  • Bottom Dead Centre (BDC) – the closest point a piston reaches to the crankshaft.
  • Cooling water system air bleed.
  • Fuel Filter
  • Belt Tensioner
  • Cooling Water Pump
  • Crankcase Breather Filter
  • Air Cooler
  • Turbocharger
  • Starter Motor
  • Engine Sump
  • Rocker Arm Cover


Engine Components (Detailed)

Cooling Water Air Bleed Valve

The air bleed valve is used to vent air to atmosphere. It is necessary to vent the air after refilling the jacket water system. Air in the system will lead to reduced heat transfer and possible cavitation of the jacket water pump.

Lubrication Oil Filter

Lubrication oil is continuously filtered in order to prevent metal particles damaging engine parts (cylinder liners, piston rings etc.).

Fuel Filter

Fuel is filtered in order to prevent incombustible particles entering the combustion space; these particles can corrode engine parts and block fuel injector spray holes (changing the spray pattern and causing a reduction in engine efficiency).

Belt Tensioner

The belt tensioner ensures that the belt does not become slack as it stretches due to age; it also makes it easier to replace the belt (remove the tensioner and the belt is also easy to remove).

Cooling/Jacket Water Pump

The cooling water (or ‘jacket water’) pump circulates jacket water through the engine and has two purposes. It ensures heat is dissipated through the engine uniformly and the circulation of jacket water allows the removal of heat generated by the engine.

Main Belt

The main belt drive is used to transfer energy via the means of a belt. The main drive allows a small amount of the engine’s overall power to be used for driving ancillaries such as the jacket water pump and alternator etc.

Belt Tensioner

The belt tensioner ensures that the belt does not become slack as it stretches due to age; it also makes it easier to replace the belt (remove the tensioner and the belt is also easy to remove).

Charge Air Cooler / Intercooler

Charge air (compressed air) is cooled in order to increase the density of the air. The increase in density means that there is more oxygen available for combustion per volumetric space.

The air density must not be too high otherwise moisture will form.

Crankcase Breather Filter

Air/Oil vapour is vented from the crankcase. Oil from the vapour is separated and drained back to the crankcase, the air is expelled. Separation of the oil reduces oil losses and reduces overall running costs.

Turbocharger Compressed Air Discharge

Compressed air is often referred to as ‘charge air’.

Compressing the air allows the oxygen density per volumetric space to be increased. More oxygen per ignition cycle is available for combustion and thus more energy per combustion cycle can be released.

Turbocharger Air Inlet

Ambient air is drawn into the turbocharger compressor due to the pressure differential created by the compressor when it is in motion.

Turbocharger Air Compressor

Ambient air is compressed by the turbocharger air compressor in order to increase the air density used for combustion.

Increased air density gives an increased oxygen density and this allows more energy to be released per combustion cycle.

Center Hub Rotating Assembly (CHRA)

The shaft and bearings connecting the exhaust gas turbocharger turbine and turbocharger air compressor are housed within the centre hub rotating assembly (CHRA).

Turbocharger Exhaust Gas Turbine

Exhaust gases from the combustion chamber drive an exhaust gas turbine. The exhaust gas turbine is connected on a common shaft to the air compressor.

Exhaust Discharge

After the exhaust gas turbine, the exhaust gas is discharged and expelled to atmosphere.

Note: A pipe would connect the turbocharger exhaust to atmosphere (not shown here). A muffler may also be used for noise reduction.

Drive Shaft

The drive shaft connects the engine with the intended power recipient. Normally, a gearbox or clutch will be installed as an intermediary; this allows greater control of how the engine power is utilised.


A flywheel stores rotational energy and resists changes to rotational speed. Essentially a flywheel is a heavy metal disc that smooths the engine combustion cycles. The amount of energy stored in the flywheel is the square root of its rotational speed.

Engine Block / Cylinder Block

The engine block houses the internals of the engine. Channels within the block are used to distribute jacket water for cooling.

Starter Motor Solenoid

A solenoid engages the starter motor gear tooth with the fly wheel upon receiving a start signal. A spring disengages the gear tooth again in order that it is not damaged when the engine is rotating at higher revolutions.

Starter Motor

The starter motor is an electrical motor used to rotate the engine upon receiving a start signal. It is not possible to start the engine without the starter motor as the engine must be in motion prior to fuel injection.

Engine Sump Drain Plug

Lubrication oil from the engine can be drained here. The oil will at some point need to be exchanged, this becomes evident due to colour change (clear to dark brown). Oil exchanges are regulated by service hours or a specified time interval.

Lubrication Oil Sump/Reservoir

Lubrication oil is stored in the oil sump/reservoir.

Lubrication Oil Suction Pipe

The suction pipe connects the sump and lubrication oil pump (suction side).

Exhaust Discharge Manifold

Exhaust gas from the combustion cylinders is discharged into the exhaust gas manifold. Sometimes a common exhaust manifold is used for all cylinders, but not always.

Rocker Arm Cover

The rocker arm cover encases the rocker arms. It is necessary to encase them as they are splash lubricated and operate at relative high speeds.


Additional Resources