Friday, May 6, 2011

The Engine Assemblies

This is an introductory chapter on engines.  It reviews the various engine components and sub-assemblies and looks at some representative engine arrangements.  The things will be introduced in this chapter and will be covered in more detail in the chapters that follow.  Rotary engines are not included here, but they are covered later in a separate chapter.
The engine assembly
The complete and engine assembly consists of the mechanical components than make up the engine itself and also a number of associated systems.  These are the systems that are needed to start the engine and also to control it and keep it running.

The mechanical Parts of the engine assembly can be broken down into the number of sub-assemblies, or groups of associated components, although these are usually referred to merely as assemblies – for example Cylinder-Head assembly and piston assembly.

There are two side views a of 4 Cylinder engine which has two over head camshafts.  Some parts of an Engine are there internal and other parts.  This illustration identifies a number of external parts.
Modern engines often have top covers that are also used as sound barriers to reduce engine noise. With the engine installed in the vehicle, it is not easy to identify the components as many are partly hidden by covers or shields.
In both views of the engine, there are components that can be identified at the front of the engine and also at each side the engine.  The flywheel at the rear side all the engine is the only major part that is not shown.

Front of the Engine
Front of the engine

The following parts are located at the front of the engine:
1. Crankshaft pulley.   
This is attached to the end of the crankshaft. It drives the ribbed belt of the alternator.

2.  Timing cover.  
This is attached to the front of the cylinder block and covers the toothed timing belt.

3.  Oil Pump. 
The pump is mounted on the front of the crankshaft.

Right hand side of the engine
Right Side of Engine
Parts to be seen on the right hand side of the engine are:
1Intake manifold

There are upper and lower parts of the assembly. They are designed to facilitate the air flow into the engine. 

2.  Throttle body assembly
This is the part of the electronic fuel injection system.

3.  Fuel Rail
This carries the injectors.  The fuel rail has pressurised fuel and the injectors are timed to spray it into the engine.

4.  Engine Electronic Control Unit (ECU).

This controls the electronic the fuel injection system and also many other engine functions.
Top of ECU
Bottom of ECU
Left hand side of the Engine
Left Side of Engine
Parts to be seen on the left hand side of the engine are:

1.  Exhaust Manifold
The manifold is covered by a metal heat shield that prevents heat from radiating to other parts of the engine compartment.

2.  Oil Pan
Located on the underside of the engine, it encloses the crankcase and holds the engine oil.

3. Oil Filter
This is at the rear of the crankcase.

4. Oil dipstick
This is also located at the rear of the crank case.

Other Parts of the engine

1. Top cover
This fits over the top of the engine and also helps with the sound deadening.
2. Flywheel
This cannot be seen but is is mounted at the rear of the crankshaft.

3. Mounting flange
A mounting flange is provided at the rear of the crankcase for the transmission.
Engine Components

The various components of the engine are assembled together during manufacture and most of these are secured by means
of bolts, nuts and other types of fasteners. Some parts are internal and others are attached to the outside of the engine
The following are the main parts of an engine.
Cylinder block
Cylinder Block (Top)
The Cylinder block is the largest part of an engine; the other parts are either fitted into the block or attached to it. As its name suggests, it is basically a block of cast metal, usually cast iron, but it can be aluminum alloy with cast iron or steel liners. Aluminum is used to reduce the weight.

The cylinder block has accurately bored cylinders to take the pistons, the lower part of the block is known as the crankcase and this has bearings that carry the crankshaft. The water-jackets that surround the cylinders are filled with water or coolant.
The top of the cylinder block has the machined surface for the cylinder head and the bottom of the cylinder block is machined to provide the mountings for the oil pan, or sump.
The cylinders can be arranged in the block so that they are in line or they can be set at an angle (V-type engine).

The crankshaft is mounted in bearings in the lower part of the cylinder block (the crankcase). The connecting rods connect the pistons to the crankshaft, which is rotated by the power strokes of the pistons when the engine is running. the up and down or reciprocating, motion of the pistons is changed to rotatory motion by the combined action of the connecting rods and the cranks of the crankshaft, the term crankshaft came from the word cranked which also means bent. It is a shaft with a number of cranks and bends.
  • With in-line engines, there is a crank for each cylinder but, with some V-type engines, there
is one crank for each pair of cylinders.
Engine Flywhee


A ring gear is fitted to the rim of the flywheel so that the engine can be rotated by the starter pinion when starting the engine.
With automatic transmissions, a drive plate and torque converter takes the place of the flywheel and performs the same functions as a flywheel, as far as the running of the engine is concerned.

Pistons and Connecting Rods
The piston has grooves that carry piston rings and these provide a seal between the piston and cylinder wall. Compression rings are used as gas seal and the oil ring is used to prevent excess oil from finding its way to the combustion Chamber. The connecting rod has a removable cap and a split bearing as its lower end where it is connected to the crankshaft. Its upper end has a piston pin that provides a wrist type of action with the piston.

Connecting Rods
§  Because of its action, the piston pin is sometimes referred as a
 wrist pin.                 

Cylinder Head
The cylinder head is made of cast aluminum alloy. It is bolted to the top of the cylinder block so that it encloses the cylinders. It has combustion chamber above the cylinders in which the air fuel mixture is burnt.
Cylinder-head Top
Cylinder head can be made of cast iron, which is more resistant to corrosion, but aluminum alloy is used for the petrol engines because it has advantages of better heat transfer and lighter in weight.
Cylinder head has intake ports and exhaust ports. The intake valves open the intake ports to enter the fuel charge into the cylinder during the intake stroke; the exhaust valves open the exhaust port to discharge the burnt gases through muffler (Silencer) also referred as tail pipe.
*Note: The combustion chamber is given in the cylinder head only for the petrol engines while the combustion chamber is given in the pistons only for the diesel engines (Petrol engines has the piston’s top surface flat while the diesel engines pistons have specific design on the top of the pistons). If you see carefully then you can see the combustion chamber is given in cylinder-head .

Camshafts and Valves

Camshafts of DOHC Engine
The camshaft and the valves mechanism are used to open and close the valves at correct time. The camshaft is driven from the crankshaft at half of the crankshaft speed (Camshaft gear is twice in diameter of the crankshaft gear).
Intake & Exhaust Valves
Intake (Small) Exhaust (Big)

The camshaft could even be one or two in the cylinder head sometimes to operate the intake and exhaust valves separately (One camshaft for the intake side and the other shaft for the exhaust side). Engines having one and two camshaft are known as SOHC (Single overhead camshaft) and DOHC (Double/Dual overhead camshaft) consecutively. QOHC (Quad overhead camshaft is used in v-type diesel engines)  

Valve cover, also called cylinder head cover, is fitted to the top of the cylinder head. This encloses the valve mechanism. An additional cover on the top of the engine covers the ignition coils.

The cylinder head arrangement, for a four-cylinder engine, has two camshafts (DOHC) and sixteen valves. Other four-cylinder engines can have two camshaft and twelve valves or one camshaft (SOHC) and eight valves. (Mentioned on the engine top cover or sticker pasted on the back windshield).
Timing Belts, Pulleys and

Timing Belt and Pulleys
The timing belt and pulleys drive the camshaft at half of the crankshaft speed (engine speed). A toothed drive belt or the chains and gears also used - in some instances belts or chains are both used.
On some engines, the timing chain is used to drive the oil pump. On diesel engines a timing chain or a timing gear is used to drive the injection pump as well as the camshaft.
Oil Pan /Oil Sump
Oil Pan/Sump
The oil pan, or sump, holds the oil for the engine lubricating system. The oil pan or sump is made of steel that has been pressed to shape. Other oil pans are made of aluminum alloy that has been cast to shape. The oil pan is bolted the underside of the engine so that it closes off the crankcase. Only the ends of the crankshaft that extend beyond the cylinder block are exposed.                                                                                                          
Gaskets, seals and small parts
Various forms of gaskets and seals are used between the surfaces where the parts are bolted together. Some of these are used to seal against oil, some against coolant and some against heat and pressure. Some provide a seal on flat surfaces, others seals against rotating shafts.
As well as the larger parts of an engine, there are numerous small parts. These include bolts, nuts, washers, retainers, springs and brackets which go to make up the mechanical components of the engine.
V-type Engine assembly
The parts covered previously are the main mechanical parts that are needed for a bare engine. However, for s V-type engine assembly, such as there are parts that are attached externally, parts that can be identified in the illustration are:

Crankshaft balancer
At the front of the engine (this is the part of crankshaft pulley).

At the rear of the engine.

Oil Pan and Oil Filter 
At the underside if the engine.
Exhaust Manifold
On the left side of the engine.

Intake Manifold
located in the valley between the cylinders.

Throttle body assembly
At the front of the intake manifold.

Water pump and pulley
At the front of the engine.

Fuel rails
on each side of intake manifold.

Ignition coils
on top of the valve cover (there are four coils on each side).

Spark plugs
at the side of each bank of cylinders.

                                                                                                                                  See Engine systems>>>>>>>>>>

1 comment:

  1. This is just perfect type of blog as well as tutorial to fully help in understanding the whole mechanism of a vehicle engine. It beautifully specify the every part of the engine with its functions.