Vehicle Engine Principles, Operation, Service and Repair

Unit 44:

Level: 3

Guided learning:  60 hrs


Unit introduction

Although the technology used in modern vehicles is under constant development, the basic principles of the internal combustion engine (ICE) have remained the same for many years. However, advances in design have produced engines that are more efficient, powerful, environmentally friendly and, with the aid of electronics, much more responsive to the needs of the user.

Developments in engine design and materials technology have significantly increased the reliability and durability of engine components and systems and, therefore, minimised failure and the need for subsequent repairs. However, the modern motor vehicle technician still needs to have a working knowledge and understanding of the engine, and associated sub-systems, to enable them to carry out the necessary care, fault diagnosis and repair.

This unit will enable learners to develop an understanding of a range of engines in terms of their operating principles and processes, applications and service/repair. Two and four-stroke cycle spark and compression ignition engines will be considered, together with their related sub-systems – fuel, cooling and lubrication. The unit also examines current and future developments in engine design that make use of alternative fuel and power systems.

Finally, the unit will give learners an opportunity to apply their understanding of engine principles by carrying out engine service and repair work in a vehicle

workshop environment. Learners will gain practical experience of using a range of tools and equipment and will work to industry standards relating to vehicle service and repair.

Note that the use of ‘e.g.’ in the content is to give an indication and illustration of the breadth and depth of the area or topic. As such, not all content that follows an ‘e.g.’ needs to be taught or assessed.


Learning outcomes

On completion of this unit a learner should:

  • Understand the principles of operation of an internal combustion engine
  • Understand the principles of operation of fuel supply systems
  • Understand the principles of operation of engine cooling and lubrication systems
  • Be able to carry out engine service and repair


Unit content


  • Understand the principles of operation of an internal combustion engine

Operating cycles: internal combustion engines (ICE), e.g. four-stroke spark ignition (SI) and compression ignition (CI) cycles, two-stroke cycle, Wankel (rotary); pressure-volume diagrams and engine performance diagrams (torque/power), e.g. the Otto cycle, identification of induction, compression, ignition, exhaust strokes, effects of bore, stroke, swept and clearance volume; engine efficiency, e.g. engine timing, pressure charging, compression ratio

Engine configurations and layout: orientation (longitudinal/transverse); position of engine (front, mid and rear); cylinder arrangement, e.g. single cylinder, multi cylinder; cylinder configuration, e.g. in-line, vee, horizontally opposed arrangements; vehicle design and performance, e.g. space saving, arrangements for power transmission, vehicle function (passenger,

people carrier, off-road, motorsport), cost, environmental issues

Engine assemblies: engine types, e.g. four-stroke SI and CI, two-stroke cycle, Wankel (rotary); components, e.g. cylinder block (piston, connecting rod, crankshaft and bearings), cylinder head (camshaft, inlet/exhaust valves, valve operating mechanisms such as overhead valve (OHV), single overhead cam (SOHC), double overhead cam (DOHC), variable valve timing); flywheel;

inlet and exhaust manifolds


  • Understand the principles of operation of fuel supply systems

Petrol combustion process: fuel principles, e.g. composition of petrol, characteristics of petrol, composition of air, air/fuel ratio, lambda ratio; combustion process, e.g. mixing of fuel/air, flame spread, exhaust emissions; effects of pollutants/causes of undesirable emissions, e.g. weak mixture,

rich mixture, oil control problems; symptoms of incorrect combustion process,

e.g. detonation, pre-ignition; fuel supply method, e.g. fuel injection, mechanical, electrical; fuel system components, e.g. tank, petrol filter, air filter, supply/pressure pump, pressure regulator, injectors

Diesel combustion process: fuel principles, e.g. composition of diesel, characteristics of diesel, air/fuel ratio; combustion process, e.g. phases, delay, combustion/flame spread, spontaneous/direct burning, pressure/crank angle diagrams, diesel knock; exhaust emissions e.g. normal, excess air, excess fuel, effects of pollutants; fuel supply method, e.g. rotary, inline, unit injector;

fuel system components, e.g. low pressure (tank, filter(s), supply pump), high pressure (in-line pump, governor, injector, cold start arrangements)

Alternative fuel/power: systems, e.g. electric, liquefied petroleum gas (LPG), natural gas, hydrogen, hybrid; adapted/additional components, e.g. batteries, fuel tank, additional modifications, cooling system, management control system, performance; legislation, e.g. emissions, tax, health and safety


  • Understand the principles of operation of engine cooling and lubrication systems

Engine cooling systems: types of system, e.g. air-cooled (cylinder construction, fan, shutters, thermostat), water-cooled (radiator, radiator cap, expansion tank, water pump, viscous/electric/mechanical fans, thermostat, hoses, types of coolant, level indication, anti-freeze protection, effects and prevention of corrosion); cooling control systems, e.g. engine temperature sensor, ambient air temperature sensor, thermostatic control valves (mechanical and electrical), cooling air flow control (air flow control via flap for warm up); engine management system (EMS), e.g. overheating, fuel cut-off

Engine lubrication system: system components, e.g. wet/dry sumps, oil pump, pressure relief valve; engine oil types and filtration methods, e.g. viscosity, Society of Automotive Engineers (SAE) International rating, multi-grade oil; filters, e.g. full flow or bypass; lubrication control systems, e.g. sensors, level indicator (mechanical, electrical); pressure sensors, e.g. absolute and gauge or lamp; low pressure safety system, e.g. EMS fuel cut-off


  • Be able to carry out engine service and repair procedures

Routine engine service: procedures, e.g. changing engine lubricant, filters

(air, lubricant, fuel), checking and adjusting engine timing (ignition, camshaft); working to instructions, e.g. manufacturer’s service schedules/data, dealership work schedules/job cards; use of tools and equipment, e.g. hand tools, vehicle lift equipment, oil drainer, on-board service indicators; safe working procedures,

e.g. personal and vehicle protection (personal protective equipment, vehicle covers, mats); Control of Substances Hazardous to Health (COSHH) Regulations 2002; safe disposal of waste products

Major engine repair: procedures, e.g. strip and inspect bore and crankshaft journals for wear, cylinder head for distortion, valves for seating and damage; working to instructions, e.g. manufacturer’s repair manuals, web-based information, dealership work schedules/job cards/supervisor’s instructions;

use of tools and equipment, e.g. engine crane, chains, slings, torque wrenches, micrometers, dial test indicators (DTI), timing tools, locking devices, cleaning equipment; safe working procedures, e.g. personal and vehicle protection (personal protective equipment (PPE), vehicle covers, mats), manual handling, use of lifting and support equipment, use of cleaning solvents; safe disposal of waste products