1. The Internal Combustion Engine (Heat Engine)  This is the most used form of power unit in motor vehicles today. It generates its power by burning fuel inside its cylinders. Burning the fuel is achieved by to main methods depending on what type of fuel is used.  Spark Ignition – the fuel is ignited by the use of a high voltage spark. Type of fuel normally used is Petrol.  Compression Ignition – the fuel is injected at high pressure into the cylinder and is ignited by the very hot air in the cylinder. Type of fuel used is Diesel Oil (DERV)  Only the correct fuel must be used with the correct engine type.  Compression ignition engines are used in light and heavy commercial vehicles, and public service vehicles, e.g. buses etc.  Spark ignition engines are used in cars, motor cycles, small vans, performance vehicles.

2. The Internal Combustion Engine (Heat Engine)  An engine consists of many parts, to help us understand how the engine works, lets look at the main ones  The cylinder – a strong metal tube sealed at one end.  The Piston – a round plug that fits inside the cylinder and ideally would be a good tight fit, yet be able to slide up and down.  The connecting rod – a strong rod which at one end connects to the piston through a special pin (Gudgeon Pin) which allows the connecting rod to swing from side to side.  The Crankshaft – a strong shaft that is supported by bearings and forms the main shaft of the engine, it is housed in the crankcase and is designed to have offset crankpins on which the connecting rod is fitted and able to turn. The crankshaft is free to turn in its bearings.

3. The Engine  The engine converts the energy contained in the fuel into heat and the heat into mechanical energy. The heat is produced by burning the fuel inside the cylinder, the pressure resulting from the combustion pushes the piston down the cylinder and hence turns the crankshaft.  Cylinder Block and Crankcase – these two units are usually made as a single casting and form the main structure of the engine.  Cylinder Head – this is bolted to the top of the cylinder block and usually contains the combustion chambers (where the fuel is burnt) and depending on the valve layout, it may carry the camshaft, rockers and valves.  Valves – these control the entry of the mixture into the cylinders (inlet valves) and allows the exhaust gas, which is burnt fuel to escape (exhaust valves). They are opened in the correct order by the camshaft and are closed by the valve spring. The type of valve used is called a “Poppet Valve”  Sump – this is usually a steel pressing bolted to the bottom of the crankcase/cylinder block. It forms the reservoir for the engine oil.

4.  Piston and Piston Rings – the piston is usually made out of aluminium alloy and is a sliding fit in the cylinder. To achieve a gas tight seal piston rings are fitted in groves in the piston.  Connecting Rod – this connects the piston to the crankshaft. Its small end is connected to the piston by the gudgeon pin and its big end is connected to the crankshaft.  Crankshaft and Flywheel – the crankshaft is supported in the crankcase by the main bearings and converts the reciprocating motion of the piston to a rotary motion. Attached to the rear of the crankshaft is the flywheel, its main purpose is to retain some of the energy given to the crankshaft during the power stroke and then release the energy to keep the crankshaft turning during the idle strokes (non working). The flywheel also forms one driving face of the clutch assembly which is bolted to the flywheel.  Camshaft – this is driven at half crankshaft speed. Machined on the camshaft are a number of cams (one for each valve) which open the valves in the correct order. It is driven by the crankshaft.  Multi Cylinder Engines – by using more than one cylinder an engine can produce a smoother turning motion ( torque).Multi cylinder engines have a better power to weight ratio, and as the reciprocating parts are lighter they can move at higher speeds, various cylinder layouts can be used. The Engine

5. Terminology  Top dead centre (TDC) – the piston is at the top or at its highest position in the cylinder.  Bottom dead centre (BDC) – the piston is at the bottom or lowest position in the cylinder.  Bore – the internal diameter of the cylinder.  Valve timing – ensuring the valves open and close at the correct time in the four stroke cycle.  Stroke – the distance the piston moves between TDC and BDC.  Swept volume (SV) – the volume in each cylinder between BDC and TDC.  The combustion chamber – this is where the fuel is burnt (the clearance volume)  Capacity (displacement) – the number of cylinders multiplied by the swept volume e.g. a four cylinder engine, each cylinder having a swept volume of 500cc. has a total engine capacity of 2000cc (2 litre).  Clearance volume (CV) – the volume (space) above the piston when it is at TDC.  Compression ratio – the total volume of the cylinder compared to just the clearance volume.  SI – spark ignition engine (normally petrol).  CI – compression ignition engine ( normally diesel)  Crankshaft throw – the distance between the main bearing and the crankpin.

6. Engine Operation Reciprocating motion converted to rotary movement. Petrol/Diesel burns in combustion chamber. Expansion forces piston and connecting rod down. Crankshaft converts to rotary motion. Rotary motion drives wheels via gearing. Next >

7. Aluminium piston for light weight and strength. Piston Construction Skirt – below gudgeon pin. Connecting rod connects the piston to crankshaft. Rapid changes of speed and direction. Gudgeon pin connects piston to connecting rod. Connecting rod Next > Piston Crown (top of piston) Piston ring grooves

8. Gudgeon Pin Construction Press-fit gudgeon pin. Pressed into connecting rod. Floating gudgeon pin. Circlips in grooves. Bronze bushing in small end. Some with pin offset, front of piston marked for assembly. Next >

9. Connecting Rod Construction Connecting rod has a small end and a big end. Big end has bearing inserts. Small end may have a bush for the gudgeon pin. There may be an oil hole in the small end. Each rod and cap must be numbered for identification. Next >

10. Piston Assembly Oil ring Piston Connecting rod Bush Compression rings Circlip Gudgeon pin Bearing shells Cap Next >

11. ( Main Bearing) The Crankshaft throw is equal in length to half the Stroke Single Cylinder Engine A journal is part of a shaft which rotates (turns) in a bearing

12. Crankshaft Crankshaft bearing surface is called a journal. Offset determines stroke (or travel) of piston. Counterweights prevent vibrations. Oil passages lead to rod and main bearings. Offset Journal Oil passages Counterweights Next >

13. The engines valves control the entry and exit of the alr/fuel mixture into the cylinders

14. Valve Spring Assembly The Valve Spring Holds The Valve Closed Cotters and spring retainer. Outer spring. Inner spring. Oil seal. Spring seat. Next >

15. The Camshaft – Which Is Driven By The Crankshaft At Half Engine Speed Made from forged steel. Belt or chain driven. Consists of a number of cams (lobes) and journals. Controls opening and closing of valves. Cams Journals Next >

16. Solid follower. Hydraulic follower. Roller follower. Bucket type follower. Cam Follower Types Next >

17. Overhead Valve (OHV) Cam-in-Block. Common in earlier engines. Uses Valve follower, push rod and rocker arm. Push rod Rocker arm Valve follower Next >

18. Overhead Cam (OHC) Camshaft in cylinder head. Uses cup type follower. May have separate camshafts for intake and exhaust valves. Next >

19. Engine valve arrangements

20. Cylinder Block Bottom End View Cast iron (strong) or aluminium (light). Underside view Cylinders, providing “walls” for pistons. Plain bearings for crankshaft. Mountings for starter motor, water pump and alternator. Next >

21. Core plugs seal water jacket. Cylinder Block Top View Deck surface for mounting cylinder head. Numerous machined and tapped holes. Next >

22. Wet and Dry Sleeves Dry sleeve presses into cylinder block. Not in contact with coolant. Wet sleeve is in contact with coolant. Thicker to withstand combustion pressure. Seals prevent coolant leaks. Next >

23. 3 A) Wet type B) Dry type Which type of cylinder sleeve is represented by the diagram? Question

24. Cylinder Head Components Valve mounts. Bare cylinder head holds many parts. Valve openers. Valves. Cotters Retainers Seals Springs Bare cylinder head Valves Rocker arms Pivots Push rods Next >

25. Cylinder Head (2 Valve) Water jacket holes match Cylinder Block. Combustion chamber for each cylinder. Intake valves. Exhaust valves slightly smaller. Next >

26. Engine configurations (how the cylinders are arranged) Most engine have four cylinders arranged in-line with each other some have up to six. Horizontally opposed engines have the cylinders laying flat down on both sides of the crankshaft. “V” engines have the cylinders arranged in a “V” formation. All engines have a firing order i.e. the order in which the power strokes take place, this helps reduce engine vibration and stress e.g. a four cylinder in-line would have a firing order of either 1342 or 1243, an in-line straight six has a firing order of 153624.

27. Four-Stroke Cycle - Stroke One - Induction Inlet valve opens. Piston moves down. Low pressure in cylinder. Air/fuel mixture drawn in. Next >

28. Stroke Two - Compression Inlet valve closes. Piston moves up. Air/fuel mixture compressed in cylinder. Next >

29. Stroke Three - Power Near TDC spark plug fires. Burning fuel mixture forces piston down. Next > Air/fuel mixture ignites.

30. Stroke Four - Exhaust Exhaust valve opens. Piston moves up. Exhaust gases expelled. Exhaust valve closes. Cycle repeats. Next >

36. The Two Stroke S.I. Engine. The 2 stroke engine uses both the top and bottom of the piston to control the air/fuel mixture entering and leaving the cylinder, as the piston slides up and down in the cylinder, it covers and uncovers the inlet port, exhaust port and transfer port. The cycle of operations is completed in one revolution of the crankshaft (2 strokes), there is a power stroke every 360 degrees. Compared to the 4 stroke engine, the 2 stroke has twice the number of power strokes, however due to poor cylinder charging, its power output is not double. Simple construction and smoothness make the engine suitable for small applications

37. Piston going up, compressing the air/mixture above the piston, fresh air/fuel mixture drawn in below the piston into the crankcase. Exhaust and transfer port closed, inlet port open. Mixture ignited by the sparkplug, the piston is forced down, the exhaust port and transfer port are opened, inlet is closed the fresh mixture is forced to the top of the cylinder. Lubrication of the engine is proved by premixing a small of oil with the petrol. (20:1)