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Presentation on
CHAPTER 1
Automotive Engine Parts

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Introduction:
• Energy is used to produce power.
• The chemical energy in fuel is converted to heat
by the burning of the fuel at a controlled rate.
• This process is called combustion. If engine
combustion occurs within the power chamber,
the engine is called an internal combustion
engine.
• I.C. engines are used in marine, locomotive,
aircraft, automobile and other industrial
applications.
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Classification of IC Engines

1.) On the basis of no. of cylinders

Some of them are:
1 cylinder engine such as mopeds and scooters,
2 cylinder engine such as Toyota,
3 cylinder engine such as Maruti Omni van & Maruti
800,
4 cylinder engine such as in cars & jeeps of Indian
made,
5 cylinder engine such as Mercedes Benz E250D,
6 cylinder engine such as Ashok Leyland trucks and
busses,

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8 cylinder engine such as V engine large size

saloon,
10 cylinder engine such as Peugeot 205 racing car,
12 cylinder engine such as Mercedes Benz S600
16 cylinder engine such as in Cadillac car having 2
sets of V8 cylinders inclined at 135 deg to each
other.

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2.) On the basis of fuel used

• Petrol engine such as in Bajaj rear engine
autorikshaw,
• Diesel engines such as Eicher 1070,
• Gas engine such as propane gas, coal gas, CNG
engines, Liquefied petroleum gas (L.P.G.) engine
such as in Ashok Leyland’s Eveko bus.
• Bi-fuel engine such as in military vehicles & hybrid
cars,
• Hydrogen fuel engine such as in Musashi 3rd car
(Japan),

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3.) On the basis of no. of strokes per cycle

• 2 stroke engines such as motor cycles, mopeds,
scooters,
• 4 stroke engine such as in bullet and Hero Honda
motorcycles.

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4.) On the basis of dimensions of stroke L and

bore D
These engines can be named as:
• Over square engine if L > D such as in Maruti 800
• Square engine if L = D such as Bajaj Chetak
• Under square engine L < D such as Hero Honda
CD100SS.

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5.) On the basis of arrangement of cylinders

In line engine:
2-cylinder in-line such as Mahindra 255 DI
tractor
3-cylinder in-line such as Maruti Omni,
4-cylinder in-line such as Tata Sumo
5-cylinder in-line such as Mercedes Benz
E250D
6-cylinder in-line such as Ashok Leyland comet
8-cylinder in-line such as Packard eight car

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V-engine:
V4 such as in Ford explorer
V6 such as in Pajero jeep
V8-900 such as in Ford
V10 such as in Peugeot 205
V12-600 such as in Ferrari
V16 such as in racing cars
• Opposed piston engine such as in Alfa Romeo
Alfasud racing cars
• Radial engine

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Different arrangement of
cylinders

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6.) On the basis of location of valves

These can be
• I-head or over head valve engine such as Maruti
800
• L-head valve engine such as in Dodge/Fargo
89M4 petrol
• F-head valve engine such as in Willeys jeep
• T-head valve engine such as in Ford T model
cars of 1908

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Location of valves in a
cylinder

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7.) On the basis of working cycle

• Constant volume cycle or otto cycle engine
such as petrol and gas engines
• Constant pressure cycle or diesel cycle engine
such as diesel engines
• Constant volume and constant pressure cycle
engine or dual combustion cycle engine

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8.) On the basis of cooling

Air cooled engine such as in mopeds, scooters

Water-cooled engine such as in most cars,

jeeps, busses & trucks

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9.) On the basis of ignition

• Spark Ignition Engines (S.I.E.) such as petrol
and gas engines.
• Compression Ignition Engines (C.I.E) such as
diesel engines.
• Magnetic Pulse Ignition Engines such as
Chervolet Corvette car
• Semi-transistorized ignition engine such as
several 2-wheelers
• Transistorized ignition engine such as Volvo
740 GL car models

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10.) On the basis of fuel supply system

Carburettor mounted petrol engine such as Hero
Honda Splendor
Injector mounted petrol engine such as Lancer
Air-injection type diesel engine such as in older
Detroit engines of general motors
Airless or solid injection type diesel engine such
as in modern diesel engines
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11.) On the basis of engine (crankshaft) speed

Slow speed engine, generally having crankshaft
speed N < 1000 rpm
Medium speed engine, generally having
crankshaft speed 3000 > N > 1000 rpm
Fast speed engine generally having crankshaft
speed N > 3000 rpm

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12.) On the basis of axis orientation of engine

Horizontal engine such as in farm vehicles
Vertical engine such as in Packard eight car
Inclined engine such as in Lambretta Innocenti. It
is inclined at 90 forward from vertical.

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13.) On the basis of camshaft position

Overhead camshaft (OHC) engine
i.) Double Overhead Camshaft (DOHC) engine
such as in Cielo
ii.) Single overhead, camshaft (SOHC) engine
such as Lancer
Under head camshaft (UHC) engine

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Over head camshafts

Note: SOHC engines usually require additional components such as a

rocker arm to operate all of the valves. DOHC engines often operate the
valves directly

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14.) On the basis of no of valves per cylinder

Conventional (2 valves/cylinder) engine such as
Ford Escort

Recent (multi-valves/cylinder) engines such as

4/cyl in Nexia, 3/cyl in Hyundai Accent.

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Single cylinder engines

• A single cylinder engine has a power stroke

every 720° of crankshaft rotation for a four -
stroke engine.
• Generally for scooters and motor cycles.
• Maximum size of the single cylinder engine is
restricted to about 500-600cc
• Bcs of higher unbalance forces, -difficult to be
balanced. Further the weight of the flywheel
required becomes excessive for higher engine
sizes.

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Two cylinder engines

• Apart from providing more power, gives more
uniform torque and balancing possible is also
better as compared to single cylinder engines.
• In practice two cylinder engines are rarely
employed for automotive
(a) In-line type cylinders placed side by side. This
type has two single cylinders placed side by side
vertically so that their pistons are in phase. Such an
engine will have a power impulse every 360 degrees
of crankshaft rotation.

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(b) In-line type. cylinders 180° out of phase. In this

the two single cylinders are in effect, placed side by
side vertically, so that their cranks are 180°out of
phase. This type provides good balancing, but the
disadvantage is in unequal firing intervals: the spark
takes place at 0°, 180°, 720°, 900° and so on.

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Four-cylinder engines.
In this type, the torque obtained, as compared to
a single cylinder engine, is much more uniform
because two working strokes per revolution are
obtained. Further, the balancing is also better. Apart
from this, the maintenance is also easier as
compared to the engines with larger number of
cylinders.
(a) In-line vertical type: This is perhaps the most
popular engine for ordinary cars of medium size
(from 0.75to 2.0 liters). It has a power impulse every
180 deg of crankshaft rotation.
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The four cylinders are all in a line. The second and

third cylinders are in phase, while cylinders I and 4
are also in phase, but in the direction opposite to 2
and 3. Thus the reciprocating forces are also nearly
balanced.
• Firing order is 1-3-4-2 or 1-2-4-3. Regarding
crankshaft torsional wind-up and uneven
breathing spacing between adjacent cylinders.
both these firing orders have equal merits and
demerits.

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Merits and Limitations of Single/ Multi Cylinder

Engines
The following major factors are required to be
considered while comparing engines of different
cubic capacity and various numbers of cylinders
• For a given maximum piston speed the shorter
the piston stroke, the higher can be the
crankshaft rotation.
• As the cylinder becomes smaller, the piston
becomes lighter in the proportion to the cylinder
size, accordingly causing higher piston speed

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• For the same engine cylinder capacity and

maximum piston speed, multi cylinder engine
develops more power than a single cylinder.
• A single cylinder engine with the same piston
cross-sectional area as a multi-cylinder engine
produces a greater torque output.
• The smaller the cylinder size, the higher is its
surface-to-volume ratio and hence higher is the
compression-ratio with an improvement in
engine thermal efficiency

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• For a given total volume, acceleration response

improves with the number of cylinders, because of
lighter reciprocating components and the smaller
flywheel.
• As the number of cylinders and the engine length
increases tensional vibration becomes a problem.

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As the number of cylinders increases

• The power consumed in overcoming rotational
and reciprocating drag also increases,
• Mixture distribution for carburetted engines
becomes more difficult,
• The cost of replacement of components becomes
proportionally higher and
• The frequency of power impulses increases, due
to which the power output becomes more
consistent.

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Components of An Engine

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Components of An Engine
Size- small, big
Material- Metallic, Non Metallic..
Process- Casting, Forging..

Mainly
Structure forming component-Stationary
Mechanism forming components- Moving

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Cylinder head block and crankshaft assembly

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Cylinder Block
• Basic structure of an engine.
• Other parts are either assembled, or are attached
to it.
• Generally a single piece casting having
intricacies and complexities, and is made of grey
cast iron or aluminum alloy.
• Complexities - block contains water jackets in its
surrounding, passageways to accommodate
valve mechanisms, openings for inlet and outlet
valves, and other provisions + cylinders.

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• The inlet valve seat in some engines, especially in

L-head engines, is an integral part of the cylinder
block. Main bearings, which support the engine
crankshaft, are located in lower position of the
cylinder block.

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Other items mounted or supported in the cylinder

block are as follows:
1. A camshaft and its supporting bearings in the lower
portion
2. An oil pan attached to the lower part which serves
as a reservoir and allows cooling of the lubricating oil
3. The inlet and outlet manifolds attached to the block
on opposite sides
4. A water pump which is driven through a belt-pulley
arrangement and whose pulley is mounted on the
crankshaft,
5. Cover for timing gears, or sprockets and chain
mounted on front of the block
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6. Housing for the flywheel and the clutch attached

to the rear end of the block
7. Ignition distributor, generally, mounted on the
side of the cylinder block
8. Lubricating oil pump mounted in the lower part
of the block
9. Fuel pump mounted on the side of the block,
10. Cylinder head attached on top of the block to
enclose the valves and pistons.

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Cylinder block materials

Cylinder blocks are commonly made of the following

materials:
1. Grey cast iron.
2. Alloyed cast iron (Ni or Cr as alloying materials).
3. Aluminum alloy.

Cylinder block

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Cylinder Head
• Single piece casting mounted on a cylinder block
and provides protection to the valves and pistons
by enclosing them.
• Depending on its shape the cylinder head can be
of the following types
1. I head type
2. L head type
• Both -contain cooling water jackets, spark plug
opening for valves and the combustion chamber.
• Pockets are curved - so that the air fuel mixture
entering through the inlet valve is subjected to
turbulence (or whirling) in the combustion
chamber.
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Cylinder Head

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The turbulence of mixture is a desired

phenomenon as it
a. Assures uniform mixing of air and fuel.
b. Improves the process of combustion,
c. Helps in preventing local zones of high
pressures and high temperatures
d. Avoids detonation (or knocking) in the
engine.

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Gaskets
A gasket is a sealing agent between two stationary
parts such as
1. Cylinder block and cylinder head
2. Cylinder block and oil pan
3. Cylinder block and the manifolds.
• It provides a tight joint between these parts and
prevents leakage of water, oil or gas.
• Gaskets are made up of materials like copper,
zinc, asbestos metal, copper plated steel, steel
asbestos, crimped steel stainless steel, fiber
composites etc.
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Gaskets

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Cylinder liner or sleeve

The cylinder liners are cylindrical components that fit
inside the cylinder’s bore,
The piston rings press upon these liners and always
remain in contact with them, and rub on them during
their motion.
A cylinder liner serves two purposes.
a. It provides a suitable wear resistant surface for
the cylinder bore of Al alloy engines and
b. It simplifies the production of cast iron engines
by allowing open deck form of cylinder block.
The liners are made of Cast iron and are
centrifugally casted.
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Cylinder liner or sleeve

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Types of liners
1. Dry liner Dry liner maintains metal to metal
contact between its outer wall and the cylinder
block. It is known as dry liner because its outer wall
is not exposed to the coolant.
2.Wet liner- In case of wet liner its outer wall is
exposed to the cooling water circulating within the
cylinder jacket.
• Both the liners can be detachable from or casted
integrally with the cylinder block.
• It is casted integrally with Aluminum alloy cylinder
block as shown in figure below

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Comparison between Dry and Wet Liner:

Description Dry Liners Wet Liners

Contribution of rigidity of cylinder

More rigidity Less rigidity
block

Cooling Inferior Better

Comparatively
Renewal after wear Easy
difficult

Chances of coolant leakage Less More

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Crank Case
• Main body of the engine
which contain crankshaft,
crankshaft bearing.
• Holds other parts aligned
• Part of lubricating system
• Protective cover for
crankshaft

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Oil Pan
• Stores oil for engine
lubrication
• Collecting drained oil
• Container for impurities
• Cooling sump for
lubricating oil

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Inlet Manifold

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Inlet Manifold
Casting attached to the cylinder head
in - overhead valve engine; or to the
cylinder block in - side valve engine.

Passage through fresh charge enters

the cylinder. Petrol engine – fresh
charge- air fuel mixture; Diesel engine
- atmospheric air.

Even distribution of charges to all the

cylinders
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Exhaust Manifold

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Exhaust Manifold
• Casting attached to the cylinder head -overhead
valve engine or to the cylinder block of a side
valve engine.
• Through the exhaust manifold, the products of
combustion escapes from the engine cylinders
to the atmosphere.
• The size shape and orientation - will cause quick
and complete discharge of the combustion
product from cylinder.
• The gases let out by one cylinder should never
enter into another cylinder.

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Piston

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Piston
• The gas force produced
during power stroke acts
on the piston.
• It is designed as a metal
cup.
• Its parts are crown, head
with grooves (some time
called ring belt) for rings,
skirt and piston pin
bosses and ribs.

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• The piston crown must be thick enough to with

stand the gas forces and also to transmit the heat
transferred to it during combustion to the ring
belt.
• The gas load gets transferred to the piston pin
bosses through the ribs.
• The heat gets transferred to the cylinder walls
through the ring belt and the rings.

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Piston Heads (Crown)

• Domed
• Flat Top
• Recessed (valve reliefs)
• Dished

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A domed piston with valve

reliefs or valve pockets.

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A Flat Top piston

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A Flat Top piston with valve
reliefs or valve pockets.

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A Dished piston with valve

reliefs or valve pockets.

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Piston Material
• Alloy steel, alloy cast iron or aluminum alloy.
• Different aluminum alloys used for pistons are
SAE300, Y alloy, SAE 301, Low expansion alloy- HG
413, Low expansion alloy- HG 416.
• In these Al alloys, various metallic compounds are
added to improve their properties.
– Magnesium improves bearing properties.
– Nickel and copper increase thermal stability and
improve to some extent mechanical properties at
high temperatures.

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- Alloys with silicon have lower coefficient of

thermal expansion.

At present Al alloy piston is more popular since its

heat conductivity is higher and inertia forces are
lesser.

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Types of Piston

1. Cutaway piston. In this type of piston the piston

skirt is cut uniformly. This arrangement permits a
lower and more compact engine construction. Eg.
Maruti Engine

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2. Solid skirt piston. To encounter high

combustion loads, the solid skirt piston of rigid
construction are favored now a days. The piston
skirt is machined oval in contour and taper in
profile to compensate for the thermal expansion.

• When - cold, the minor axis of skirt ovality is disposed in

the direction of gudgeon pin
• When - hot, the skirt takes on to circular shape on
account of greater expansion. The top of the skirt
expands more than the comparatively cooler lower
portion. Its consequence is that the ovality diminishes or
vanishes.
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3. Cam ground piston. The ovality in solid skirt

pistons is obtained on grinding them by a cam. The
cam is a highly accurate object having such a
contour which is similar to the desired profile on a
piston.
• So the pistons of oval section are made by cam
grinding process.
• Such pistons are called cam ground pistons.
Oval tapered pistons have been provided in Fiat
1100.

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4. Split skirt piston. An alternative to solid skirt

piston is a split skirt piston which incorporates a T
type compensatory slot.
• Nearly vertical part of the T slot extends down to
the base of the skirts and thus splits the skirt.

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Methods for controlling piston expansion

• Unequal thermal expansion of Al piston within a Cast
iron cylinder is a drawback as Al expands more than
cast iron, the chances of engine slap cannot be ruled
out.
• Therefore control of the piston expansion is
essentially required. This is accomplished by one of
the following methods.
1. Incorporation of compensating slots
2. Provision of controlling inserts.
3. Arrangement of heat dam
4. Wire wound piston
5. Piston of low expanding materials
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Incorporation of compensating slots:

The compensatory slots are usually made in the
circumferential direction beneath the oil control
groove

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Arrangement of heat dam:

• A groove is cut below the piston crown as
shown.
• The path of heat travel from piston crown to the
skirt is reduced by this arrangement.
• The skirt therefore remains cooler and so the
expansion is reduced

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Wire wound piston:

The thermal expansion of piston skirt may also be
prevented by using a mechanical force on it.
In this case, a low expansion steel wire is wrapped
around the piston between gudgeon pin and the
lowest oil control ring.

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Provision of controlling inserts:

• Alloy steel inserts having lower coefficient of
thermal expansion than that of the piston material
are used to restrict the expansion of the skirt
along the skirt axis.
• Depending the arrangement of inserts the inserted
pistons can be of two types. i. Autothermic piston
and ii. Bimetallic piston. In autothermic insert
piston the steel insert has a mechanical bond with
the aluminum body whereas it is casted in case of
bimetallic piston.

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Piston Clearance
The gap between piston and cylinder liner

• If it is too small there will be loss in power due

to excessive friction, severe wear and possible
seizure of the piston in the cylinder- Complete
engine failure.
• If the gap is excessive, piston slap will occur.

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Piston Slap
• Caused by the sudden tilting
of the piston in the cylinder as
the piston starts moving down
in the power stroke.
• The piston shifts from minor
thrust side of the cylinder to
the other side major thrust
side with sufficient force.
• This hitting of piston surface
on the cylinder wall produces
a distinct noise (metallic
noise) called piston slap.

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Piston Slap
• The shifting of the piston from the compression
thrust face to the expansion thrust face which
causes piston slap

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Piston Slap

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Engine rotation and rod angle during the power stroke

causes the engine to press harder against one side of the
cylinder, creating a major thrust surface.
In this CW rotating engine, as viewed from the front of the
engine, the major thrust surface is on the left side.

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Special purpose piston to control slap, heat, wear etc.

1. Offset piston
2. Inserted ring carrier piston
3. Oil cooled piston
4. Heat shielded piston
5. Two piece piston
6. Cast steel piston
7. Anodised piston
8. Tinned piston
9. Low expansion alloy piston

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Offset Piston
• Its design is such that the center line of piston does
not coincide with the cylinder and remains at an
offset.
• The offset is given towards the major thrust side.
The gudgeon pin is also provided with slight offset.
• The effect of providing offset in the piston is felt
during compression stroke when the piston tilts
slightly while approaching the top dead center.
• After completion of the compression stroke, the
piston moves down smoothly, remains in contact
with the cylinder wall and avoids piston slap.
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Inserted ring carrier piston

• In this design the

austenitic cast iron ring
inserts are tightly fitted
beneath the aluminium
crown as shown .
• The ring inserts are
properly machined and
perfectly bonded with the
carrier piston such
pistons are suitable for
HCV’S.
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Oil cooled piston

• In heavy duty vehicle where
piston get more heated and
require additional cooling - oil
cooled piston are used.
• An oil cavity is produced in them
into which the oil is directed from
the c-rod small through open or
closed galleries.
• During reciprocating motion of the
piston the movement of oil inside
the oil cavity takes heat from the
crown and keeps it cool.
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Two piece piston

• Such pistons are made of

Al skirt and steel crown
both bolted together.
• The skirt and the crown are
generally forged and
secured by means of
inclined bolts.
• Such pistons find use in
those engines whose
temperature is higher than
the working temperature
range of aluminum.

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Piston rings
Piston rings in an I.C. engine are provided to serve
the following purposes.
• To act as
– 1. Seal to prevent leakage of combustion
gasses into the crank cases.
– 2. Passage of heat flow from piston crown to
the wall of the cylinder.
– 3. Lubricating oil controller on the cylinder wall
so as to minimize wear.

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Sealing Surface

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The piston rings are of two types according to the

purpose served by them.
1. Compression or gas rings
2. Oil control rings or oil scraper rings.

The compression rings generally of 2 or 5 in number,

are placed in combustion chamber for,
i.) Sealing of the combustion gas
ii.) Heat transfer from piston crown to the cylinder
wall.

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• The oil control rings, generally 1 to 2 in number

prevent excessive oil from passing
a.) Through the end gap of the rings
b.) Between the cylinder wall and the ring face.
• They avoid undesired burning of the lubricating
oil. –Smoke- Pollution
• The oil control rings scrapes off excess
lubricating oil from the cylinder walls during the
downward movement of the piston.
• The oil scraped and collected from the cylinder
walls
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Piston pin or Gudgeon pin

• It connects the piston and the connecting rod.

• The piston pin is a hollow cylinder made of case
hardened steel. It makes the joint between the
boss of the piston and the small end of
connecting rod.
• Based on the anchoring arrangement of
gudgeon pin and oscillation of connecting rod in
it, there are 3 types of piston pins employed on
different I.C. engines.

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a. Fully floating piston pin

• Employs separate bushes -pressed
between the pin and piston, and b/w
the pin and small end eye of the
connecting rod.
• Since the gudgeon pin almost remains
floating in the bush, the assembly is
known as fully floating. The lateral
motion of the gudgeon pin is
prevented by circlips on both the ends.
• Bearing in this arrangement is highly
stressed and difficult to lubricate
effectively.
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b. Semi floating gudgeon pin

• Gudgeon pin floats in the

bush located between it and
the connecting rod eye.
• The pin is anchored between
the piston and the gudgeon
pin.
• Due to this, the gudgeon pin
oscillates only in the
connecting rod.

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c. Three fourth floating piston pin

• a clamped connection exists

between the gudgeon pin and the
small end of the connecting rod
• while the pin oscillates over the
bush in the piston.
• Thus the assembly is neither fully
floating type nor semi floating type.

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Connecting Rod

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Connecting Rod
• Small end is connected to the piston and the big end
is connected to the crank shaft through the crank pin.
• During operation- subjected to combined axial and
bending stress. The combustion gas pressure and the
inertia forces due to reciprocation produce axial stress
while the bending stresses are developed due to the
centrifugal action.
• The cross-section -“I” type to provide improved rigidity
and to reduce the weight.
• Manufactured by either drop forging process or by
casting. Alloy steel and aluminum alloy are used.
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Crankshaft

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Crankshaft

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Crankshaft
• Crank shaft - rotating component to which crank is
connected. It receives the power produced in the
engine for transmission- transmission system.
• Power comes from the connecting rod and is then
transferred to the clutch through a flywheel, which is
mounted on it.
• Crank pins are eccentrically located with the axis of
crank shaft. The eccentricity is called throw of the
crank.
• Provision of crank web- Avoid the tendency of
bending of the crank shaft due to centrifugal action
during engine operation.
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• The crank shaft is of either built in type or a single

piece type.
• A single piece construction is more common.
• The crankshafts are generally made by forging of
medium carbon alloy steels. They are then induction
hardened to ensure uniform hardness and checked
for balancing dynamic balancing machine.
Materials
 Carbon steel
 Alloy of nickel, chromium & molybdenum
 Specially alloyed grey cast steel.
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Various forms and details of crank shaft

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Engine Valve
• Mechanical control elements
needed to admit fresh charge
and allow the burnt gasses to
escape out of the cylinder.
• Two valves, an inlet and the
other exhaust are used.
• Fresh mixture of fuel and air
enters the inlet valve through the
inlet manifold, and the burnt
gases pass through the exit
valve and go to the exhaust
manifold
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Types of valves

1. Poppet valve or mushroom

valve such as in Ambassador
Diesel Nova.
2. Sleeve valve
3. Rotary valve such as in
KB125 motorcycle, Bajaj 3
wheeler etc.
4. Cooled hollow valve such a
sodium cooled valve used in Alfa
Romeo 2000 spider veloce car.

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Rotary Valve Engine

Sleeve Valve Engine

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Types of Valves
• Poppet Valve: The poppet
valve derives its name from
its motion of popping up and
down.
• Also "mushroom valve“ - of
its shape which is similar to
a mushroom.
• Exhaust valves are smaller
than the inlet valves.

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Sodium Cooled Valve

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• Sodium cooled valve: Exhaust valves attain a high

temperature of about 600 – 700°C in normal course.
In heavy duty engines and the racing car engines,
this temperature is still higher.
• It has a hollow stem whose about 50% volume is
filled with liquid sodium. It remains in liquid state at
the operation temperatures of exhaust valve.
Sodium is used due to its higher thermal
conductivity and lower melting point (105°C).
• The liquid sodium moves up and down in the hollow
stem. - absorbs heat from the hot cylinder head
when it moves up and gives the same to the stem
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on downward movement. From valve stem the

heat goes to valve guide, then to cylinder block
and finally to cooling water circulating in the
water jacket.

• This arrangement helps in lowering the valve

temperature by 80-100°C

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• Tulip valve: These are

light weight and small
sized valves.
• They allow the gases to
come in or go out
easily.
• They also provide
sealing of combustion
chamber.
• Such valves are used
on aircrafts and racing
car engines.

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Valve Seat

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Valve Spring

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Valve Stem Guide

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Overhead valve (Under head cam shaft engine)

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Valve operating mechanism for overhead

valve
(Under head cam shaft engine)

• The cam on the cam shaft lifts the tappet during its
rotation. The tappet actuates the push rod which in
turn operates the rocker arm about its fulcrum.
• The rocker arm exerts pressure on the valve stem
against the spring to move the valve stem in the
guide

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• In doing so the valve comes down from the valve

seat and makes space for fuel air mixture to
enter the cylinder.
• With more rotation of the cam shaft, the valve
spring pushes back the valve on its seat when
non-eccentric portion of the cam comes in
contact with tappet. Now the valve is closed

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Valve mechanism for overhead cam

shaft engine
• High volumetric efficiency and high
compression ratio. But its use requires higher
initial cost and a complicated combustion
chamber.
• Daimler Benz, Ford Escort, Lancer having
such

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Valve Mechanism for Side Valve Engine

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Valve Mechanism for Side Valve Engine

• L- Head Engine

• Advantages
– Low height> no parts above cylinder head
– Easy lubrication
– Less complicated
– Less Volumetric Efficiency, Compression
ratio
– Complicated Shape of combustion chamber
– Restricted space for inlet valve
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Theoretical Valve timing diagrams of 4

Stroke SI Engines

Valve opening and closing instantaneously at TDC and

BDC

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Valve timing diagrams of 4 Stroke SI

Engines

Valves open/close before and after the dead centres

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Inlet Valve Opening and Closing

Before TDC Open and After BDC Close

• To get maximum charge inside cylinder.
• It takes time to gain inlet velocity for the
charge, in order to get max inlet velocity at
earliest, valve opens before TDC.
• Kinetic energy of the moving charge used at
the end of intake stroke to produce ramming
effect by closing valve after BDC

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Exhaust Valve Opening and Closing

Before BDC Open and After TDC Close

• For efficient exhaust of combustion products.
Excess pressure - some amout of gas leaves
the cylinder before Exhaust stroke. Exhaust
starts before BDC
• Closing after TDC - kinetic energy of outgoing
gases can be utilized

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• Valve Overlap - Time during which both the

valves (inlet and exhaust) remain open at the
same instant.
• High Speed Engines - Higher Values of
Angles - Short time interval
• Angle values vary from engine to engine

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Firing Order of Cylinders

• Cylinder firing order improves the distribution of the
fresh charge in the manifold to the cylinders and
helps the release of exhaust gases
• Successive cylinders firing allows a recovery of
charge in the manifold and minimizes interference
between adjacent or near by cylinders.
• Normally cylinders from the opposite end of the
manifold are chosen from alternate cylinder banks in
V Engines to draw alternatively. This arrangement
becomes difficult as the number of cylinders
decreases.
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• Separating successive cylinders which are

exhausting are even more important than fuel
supply.

• If exhaust period overlaps with the cylinders

exhaust gas back pressure may prevent
escaping product of combustion from the
cylinders.

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Engine Balance

• Due to presence of number of reciprocating parts,

like piston, connecting rods, etc. which move once
in one direction and then in another direction.
Vibration develops during operation of the engine.
• Excessive vibration occurs if the engine is
unbalance. Design , Poor maintenance.
• Primary balance, component balance, firing interval,
secondary balance.

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Single cylinder engines.

• A single cylinder engine has a power stroke every

720° of crankshaft rotation for a four - stroke engine.
• Generally for scooters and motor cycles.
• Maximum size of the single cylinder engine is
restricted to about 500-600cc
• Bcs of higher unbalance forces, - difficult to be
balanced.
• Further the weight of the flywheel required becomes
excessive for higher engine sizes.

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Two cylinder engines

• Apart from providing more power, gives more uniform

torque and balancing is also better as compared to
single cylinder engines.
• In practice two cylinder engines are rarely employed
for automotive
(a) In-line type cylinders placed side by side. This
type has two single cylinders placed side by side
vertically so that their pistons are in phase. Such an
engine will have a power impulse every 360 degrees of
crankshaft rotation.

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(b) In-line type cylinders 180° out of phase. In this

the two single cylinders are in effect, placed side by
side vertically, so that their cranks are 180°out of
phase. This type provides good balancing, but the
disadvantage is in unequal firing intervals: the spark
takes place at 0°, 180°, 720°, 900° and so on.

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Three-cylinder engines
• In three-cylinder in-line engine the power impulse
occurs every 240deg of crankshaft rotation.
• These are dynamically balanced, but there remain
some unbalanced rocking forces.
• The three cylinders smooth out the cyclic torque
adequately so that this has become a good
competitor of the more popular four cylinder in-line
engine for small cars.
• Its other advantages are reduced weight, length and
drag besides improved fuel consumption. Maruti 800
Vehicles in India employ this engine.
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Four-cylinder engines.
• In this type, the torque obtained, as compared to a
single cylinder engine, is much more uniform because
two working strokes per revolution are obtained.
Further, the balancing is also better.
• Apart from this, the maintenance is also easier as
compared to the engines with larger number of
cylinders.
• (a) In-line vertical type. This is perhaps the most
popular engine for ordinary cars of medium size (from
0.75to 2.0 liters). It has a power impulse every 180
deg of crankshaft rotation. The four cylinders are all in
a line.
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• The second and third cylinders are in I 2 3 4

phase, while cylinders I and 4 are also in phase,
but in the direction opposite to 2 and 3. Thus the
reciprocating forces are also nearly balanced.

• Firing order is 1-3-4-2 or 1-2-4-3. Regarding

crankshaft torsional wind-up and uneven
breathing spacing between adjacent cylinders.
both these firing orders have equal merits and
demerits.

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