Engine Parts and Their Functions

PARTS OF THE ENGINE
 ENGINE BLOCK
 CYLINDER HEAD
 CRANK CASE
 PISTON
 PISTON RINGS
 PISTON PINS
 CONNECTING RODS
 CRANKSHAFT
 VALVES AND
VALVE ACTUATING
MECHANISMS
 ROCKER ARM
 CAM SHAFT
 ACCESSORIES
3

CYLINDER BLOCK
 Basic frame work of the engine is formed by Engine Block.
 The cylinder block is a solid casting made of cast iron or
aluminum that contains the crankcase, the cylinders, the
coolant passages, the lubricating passages, and, in the case of
flathead engines, the valves seats. the ports, and the guides.
 The cylinder block is a one-piece casting usually made up of
an iron alloy that contains nickel and molybdenum.
 It provides excellent wearing qualities, low material and
production cost, and it only changes dimensions minimally
when heated .
4

 Aluminum is used whenever weight is a consideration.
 It is not practical to use for the following reasons:
Aluminum is more expensive than cast iron.
Aluminum is not as strong as cast iron.
Because of its softness, it cannot be used on any surface
of the block that is subject to wear.
Aluminum has a much higher expansion rate than
iron when heated. `
 The CYLINDERS are bored right into the block.
 A good cylinder must be round, not varying in diameter by
more than approximately 0.0005 inch (0.012 mm).
 The cylinders on an AIR-COOLED engine are separate
from the crankcase. They are made of forged steel.
5

 At the top of the cylinder block is attached the cylinder head.
 Other parts like timing gear, water pump, ignition distributor,
flywheel, fuel pump etc are also attached to it.
 The centre lines of all cylinders must be at exact right angles
to the crank shaft centre line to avoid side stresses on the
piston, connecting rods and cylinders.
CYLINDER BLOCK contd…
 The cylinders in the block are machined and honed to a very
accurate finish for good lubrication and proper ring seating.
 They are finished to 1 micron finish with a fine rotating
hone.
 The cylinder block basically is a casting product. Both
monoblock and individual cylinder casting techniques have
been tried but the former is employed universally.
7

Advantages of monoblock
 Better water circulation.
 Simplified manufacturing operations.
 Closer cylinder spacing, thus reducing engine size.
 Rigid structure, reduced tendency to vibrate.
8

Advantages of individual cylinder.
 Replacement of single cylinder casting is less costly than
replacing a multi cylinder casting.
 Lesser weight of individual cylinder, easy handling.
 Adopting fins around air cooled cylinders increases heat
transfer area.
 Cylinder blocks of Diesel engines are similar to Petrol
engines but are heavier in construction.
9

CYLINDER HEAD
 It is attached to the top surface of the cylinder block.
 Gaskets are used to provide tight leak proof joint at the
interface of the head and the block.
 It forms the combustion chamber above each cylinder.
 It also contains valve guides, valve seats, ports, cooling water
jackets and threaded holes for spark plugs or injections.
 On over head cam shaft engine, the provisions for mounting
the camshaft and related parts also exists.
 Materials generally employed is CI and Aluminium.
 Apart from weight reduction, more uniform temperature is
maintained in case of Al cylinder head because of greater
thermal conductivity.
10

 Quite often Al alloy head is used with CI cylinder block and
crank case.
 Grey CI for cylinder head is same as that of cylinder block
but Al alloys are different.
 A typical composition of Al alloy contains 3% copper, 5%
silicon and 0.5% manganese.
 Copper increases the hardness and strength of Al with time
on account of age –hardening, decreases the corrosion
resistance.
CYLINDER HEAD contd….
 For certain heavy duty engines, where the cool running of
the engine is major consideration, copper cylinder heads are
used.
 Copper cylinder heads are not used in ordinary engines
because the engine tends to over cooled, there by decreases
the thermal efficiency and increases the fuel consumption. 11

Types of cylinder head
 Depending on Valve and Port Layout, cylinder head may be
classify as
 Loop flow type
 Offset cross-flow type
 In-line –cross flow type.
13

Loop Flow type
I I I I
E E E E
Facilitate preheating of intake air
14

Offset Cross-flow Type
I I I I
E E E E
Provides lower exhaust temperatures
15

Inline Cross-flow type
I
E
I
E
I
E
I
E
Gives Better performance, but costlier.
16

 Simplified production.
 Operations like decarbonizing and valve grinding are
simplified.
 The compression ratios can be changed slightly by changing
the thickness of the gasket used between the block and the
head.
Advantages of Detachable head types
 Cylinder heads cast integral with blocks have also been
produced in racing engines which obviates the necessity of
gas tight joint.
 This advantage is not so important because use of gaskets
gives a reasonably good gas tight joint.
17

OIL PAN or OIL SUMP
 It forms the bottom half of the crank case.
 It is attached to the crank case through the set of screws and
with a gasket to make the joint leak proof.
 The plane of the joint between the crank case and the oil pan
may be either on the level of the crank shaft axis or it may be
lower.
 If it is in the level of crank shaft axis, the bottom portion
increases and if it is lower, it increases the upper portion of
the crank case thus increase the rigidity.
18

Assembly of Oil sump to Crankcase.
19

Functions
 To store the oil for engine lubricating system.
 To collect the return oil draining from the main bearings or
from the crank case walls.
 To serve as a container in which any impurities or foreign
matter can settle down.
 To enable the hot churned up lubricating oil to settle for a
while before being circulated.
20

 The sump is made up of pressed steel sheet since it is not
expected to have much rigidity.
 In some cases, sump of aluminium alloy casting is used,
which has adequate stiffness and rigidity.
 This also provides better oil cooling on account its higher
thermal conductivity, reduces the vibrations and noise.
 However, cast sump cannot withstand shocks, which may
cause shocks but pressed steel sheet sump may be dented but
will not crack.
Materials
21

MANIFOLDS
 They are separate sets of pipes attached to the cylinder head
which carry the air fuel mixture and the exhaust gases.
 The inlet manifold carries the air fuel mixture from the
carburettor to the cylinders.
 The shape and size of the inlet manifold must be such that it
prohibit the formation of fuel droplets with out restricting the
air flow.
 The manifold must be large enough to allow sufficient flow
for max. power yet it has to be small enough to maintain
adequate velocities for keeping the fuel droplets in
suspension in air.
23

 Sharp bends in the inlet manifold tend to increase the fuel
separation.
 Smooth walls and a minimum of bends that collect fuel to
reduce the condensing of the mixture. Smooth flowing intake
manifold passages also increase volumetric efficiency
INTAKE MANIFOLD
25

EXHAUST MANIFOLD
 It connects all of the engine cylinders to the rest of
the exhaust system.
 It is usually made of cast iron, either singly or in
sections.
 If the exhaust manifold is made properly, it can
create a scavenging action that causes all of the
cylinders to help each other get rid of the gases.
Back pressure (the force that the pistons must exert
to push out the exhaust gases) can be reduced by
making the manifold with smooth walls and without
sharp bends
26

GASKETS
 They are used to provide a tight fitting joint between two
surfaces.
 They are mainly used between cylinder head and block,
crank case and oil pan, cylinder block and manifolds.
 They are usually made of a deformable material in the
shape of a sheet or ring, which conforms to the irregularities
in mating surfaces when compressed.
28

 The proper material used in gasket construction depends on
the temperature, type of fluid to be contained, smoothness of
mating surfaces, fastener tension, pressure of the substance to
be confines, material used in construction of mating parts and
part clearance relationship.
GASKETS
29

Requirements
 Conformity
 Resistance
 Impermeability
 Resistance to chemical attack
 Resistance to operating conditions
Provision for apertures
30

 CYLINDER HEAD GASKET which is placed
between the cylinder head and the cylinder block to
maintain a gastight and coolant-tight seal. It is made in
the form of two thin plates of soft metal with asbestos
tilling between them.
 INTAKE AND EXHAUST GASKETS are made from
asbestos and formed to a desired shape. Some of them
are metal-covered and similar in construction to a
cylinder head gasket.
 OIL PAN GASKET is generally made from pressed
cork. It may be made in one piece but is often made as
two pieces.
Types of GASKETS
31

Materials
 Cork: Oldest gasket material, Limited to
lightly loaded joints with uneven surfaces,
highly impermeable and conforms easily.
Asbestos: Fibers alone or with cellulose
bonded together, binder determines the gasket
properties, used in high pressures, not
conformable as cork, necessitates better
parting surface smoothness.
32

Materials
 Rubber: Oil resistant synthetic rubber is
generally used in pan corner joints and on the
end joints of the intake manifold.
33

Manufacturers and Gasket types
1. Fel-Pro. Inc, U.S.A
 Cylinder Head Gaskets:
o Embossed steel: I-head engine
o Metal Sandwich Type: Made up of either Copper
and asbestos or Steel and asbestos; mainly used on
passenger cars, trucks.
o Shimbestos: Combination of thin steel heat shield on
one side and highly resilient specially treated metal
reinforced asbestos on the top of side.
o Felbestoes: Made up of perforated steel sandwiched
between two treated asbestos sheets.
34

 Oil Pan Gaskets:
o Cork: Highly compressible
o Felcoid: improvement over cork, Highly
compressible, can withstand considerable bending
and twisting, less subject to shrinkage and
expansion.
o Felcoprene: Synthetic rubber compound that is
highly resilient and compressible and is not affected
by oils and greases, not subjected to expansion or
shrinkage and can withstand rough handling
35

 Manifold Gaskets:
o Metal encased asbestos: Are more resistant to burn out,
more expensive.
o Felbestos is perforated steel base with asbestos
mechanically bonded to one or both sides.
o Metal embossed shim gaskets
 Pump Gaskets:
o Asbestos
o Karropak: high quality vegetable fibre.
o Felcoid : combination of fibre and cork granules that is
more compressible and resilient.
All treated to withstand oil, water, petrol and anti-freezing
liquids. This treatment also provides softness, flexibility
and tensile strength
36

2. Dana Corporation of U.S.A (under the name of VICTOR)
 Cylinder head Gaskets:
 Victocor: Has a steel core which gives excellent strength, core is
mechanically clinched to a facing material which is resistant to
temperature, oil and coolant, prevents seperation and shape changes
under extreme engine operating conditions.
37

CYLINDER LINERS or SLEEVES
 The problem of cylinder wear can be over come by
the use of Cylinder Liners.
 These can be replaced when they are worn out.
 They are made in the form of barrels from special
alloy iron containing silicon, manganese, nickel and
chromium.
 They are cast centrifugally.
 They are further hardened by Nitriding or
Chromium plating.
 In Nitriding, the liners are exposed to ammonia
vapour at about 500°C and Quenched.
 Chromium plating improves the resistance to wear
and corrosion.
38

 Aluminium liners with chromium plating on
the inside have also been used especially in
combination with aluminium cylinder block.
 It increases the thermal efficiency due to
better heat conduction.
 Because the pistons are made up of Al alloy,
the relative thermal expansion between the
liner does not exists.
39

Types
1. Dry Cylinder Liners
2. Wet Cylinder Liners :
A dry-type sleeve does not contact the coolant.
The dry-type sleeve is pressed into a full cylinder
that completely covers the water jacket. Because
the sleeve has the block to support it, it can be
very thin
 It has to be machined very accurately both
from inside and the outside. It is put in position
by shrinking the liner.
This introduces some stresses due to shrinkage
and hence the liner bore has to be machined
accurately again after the liner has been put into
the cylinder casting.
41

Dry Liners
 Too loose, a liner will result in poor heat dissipation
because of absence of good contact with the cylinder
block, result in higher operating temperatures.
 If lubrication is also deficient, may cause scuffing.
 Too tight liner produces the distortion of cylinder block,
liner cracking, hot spots and scuffing.
 Even if a correct liner is inserted in to the cylinder block
which is it self distorted, will result in poor sealing action
of rings if the liner is thin because the liner tends to adopt
the shape of the distorted block in which it is fitted.
 Even the liner is thick enough, there will be some hot
spots which will lead to scuffing of the liner inner surface.
42

Wet Liners
 The wet-type liner comes in direct contact with the
coolant. It is also press-fitted into the cylinder. The
difference is that the water jacket is open in the block and
is completed by the sleeve. Because it gets no central
support from the block, it is made thicker than a dry
sleeve.
 Because the liner completes the water jacket, it must fit
so it seals in the coolant. This is accomplished by using a
metallic sealing ring at the top and a rubber sealing ring at
the bottom.
43

 There are three basic ways of securing the sleeves in the
cylinder block as follows:
Press in a sleeve that is tight enough to be held by
friction.
Provide a flange at the top of the block that locks the
sleeve into place when the cylinder head is bolted into
place. This is more desirable than a friction fit, because
it locks the sleeve tightly.
Cast the sleeve into the cylinder wall. This is a
popular means of securing a sleeve in an
aluminum block.
 At the bottom, either the block or the liner is provided
with grooves, generally 3 in number. The middle groove is
left empty and in the top and bottom ones are inserted
packing rings made up of synthetic rubber.
 They are some times coated with coated Al on the
outside, which makes them corrosion resistant.
44

Troubles with Wet Liners
1. Breaking of flange :
This may be caused by wrong tightening
sequence of cylinder head bolts or their
excessive tightening, uneven counter bore in the
block to receive the liner, or the worn out
counter bore seat at the inner edge causing the
seat to tilt downward.
:
:
45

2. Scuffing near sealing ring area
3. Possibility of ineffective sealing
The rubber sealing rings at the lower deck may
get locally twisted or rolled while installing.
Because of which, the rubber becomes hard and
this is accelerated under high temperature of the
cylinder, thus exerts very high pressures against
the cylinder liners resulting distortion of liners.
When the sealing rubber rings are damaged or
lower deck is either eroded or pitted or unclean
at the sealing ring surface of the bore, cooling
water may leak in to the crank case.
46

Comparison between Dry and Wet
S.no Characteristics Dry Liners Wet Liners
1 Consideration in original cylinder design
May or May not
be considered
Have to be
considered.
2
Leak proof joint between cylinder and
liner.
Not Required Required
3 Robustness of Cylinder More Less
4 Complexity of cylinder block More Less
5 Cooling Efficiency Less More
6 Relieving Stresses Not possible Possible
7 Finishing Accuracy High Medium
47

Moving Parts of the Engine
 The moving parts of an engine serve an important
function—turning heat energy into mechanical energy. They
further convert reciprocal motion into rotary motion.
 The principal moving parts are the piston
assembly, the connecting rods, the crankshaft assembly
(including flywheel and vibration dampener), the camshaft,
the valves, and the gear train.
 Burning of the air-fuel mixture within the cylinder exerts a
pressure on the piston, thus pushing the cylinder down. The
action of the connecting rod and crankshaft converts this
downward motion to a rotary motion.
48

PISTON
 Pistons are usually made of an aluminum alloy.
 This serves several purposes as follows:
 Transmits the force of combustion to the
crankshaft through the connecting rod.
 Acts as a guide for the upper end of the
connecting rod.
Serves as a carrier for the piston rings that are used
to seal the compression in the cylinder.
 They are a sliding fit in the cylinders.
49

Characteristics
 Be silent in operation
 Smooth reciprocating movement
 Sufficient corrosion resistant towards
combustion products
 Shortest possible length to reduce overall engine
size
 Light weight
 High Thermal Conductivity
 Long life
50

Constructional Features
 The structural components of the pistons are the
HEAD, SKIRT, RING GROOVES, and LANDS.
51

 Towards top of the piston, some grooves are
cut to house the piston rings.
 The band left between the grooves is called
lands, which support the rings against the gas
pressure and guide them so that they can flux
freely in the radial direction.
 The supporting web transmits the force of
explosion directly from the crown to the
piston pin bosses thus preventing the ring
grooves from deformation .
 The part of the piston below the rings is called
skirt. It forms a guide suitable for absorbing
side thrust due to gas pressure and the
reaction of connecting rod. 52

 Generally, Low cost, low performance engines
have flat head.
 When the piston is very close to the valves,
the crown has some relief for valves.
 Pistons in High power engines may have
raised dome, which is used to increase the
compression ratio as well as to control the
combustion.
 Pistons may be specially dished to form
desired shape of the combustion chamber.
 In the above case, the compression ratio can
be accurately controlled, but the disadvantage
is much larger heat has to be dissipated through
the piston and the rings. 53

MATERIAL
o The earlier pistons were made up of CI because of
good wear qualities.
o As the technology developed, present day pistons
are made up of Al alloy which possesses the
following advantages:
 Al alloy is 3 times lighter than CI which is desirable
in inertia point of view.
 Al alloy has higher thermal conductivity than CI,
which cause it to run cool.
55

o Al alloy has its own disadvantages too.
 Al alloy is not as strong as CI hence thicker sections
has to be used.
 Al alloy is relatively soft due to this fine particles in the
lubricating become embedded in it, causing abrasions of
cylinder walls and thus reduces the life of the cylinder.
 The co-efficient of expansion of Al alloy is relatively high
compared to CI, which creates the problem of fixing up the
value of cold clearance.
56

1. Keeping the heat away from the lower part of the piston
 Cutting horizontal slot in the piston on thrust and
non-thrust sides of piston skirt.
 Making a heat dam.
EXPANSION CONTROLL IN PISTONS
57

59
2. Use of Vertical T-Slots
• They are provided on the non thrust side of the piston
• Decreases the mechanical strength.
• Increases the slap.
• Never used for heavy duty pistons.

3. Taper Pistons
• Pistons are some times turned taper, the crown side
being smaller in diameter than the skirt end.
60

61
4. Cam Ground Pistons
• Pistons are cam ground such that they have elliptical
section instead of circular one.
• The minor dia of the ellipse lies in the direction of piston
pin axis, when operating becomes circular due to
expansion.
• Taper and ovality are combined in the same piston, and
is varied along the skirt height.
• Ovality is maximum at the piston bossed and gradually
reduced towards bottom of the skirt.

5. Use of special alloys
• Alloys with low co-efficient of thermal expansion or
whose is nearly equal to CI are chosen.
• One of such material is Lo-Ex alloy. Its composition is
Silicon: 12-15%
Nickel: 1.5-3%
Mg & Cu: 1%
6. Wire wound pistons
• A band of steel wire is under initial tension
is wound between piston pin and
oil control ring thus restricting
the expansion of skirt.
62

63
7. Autothermic Pistons
• Contains low expansion steel inserts at the piston bosses
• The ends of the steel inserts are anchored in the piston
skirt with mechanical bonding.

8. Bimetal Piston
• Made up of both Steel and Al alloy.
• Skirt is formed by steel and the Al alloy cast inside it
forms piston head and piston pin bosses.
64

1. Offset piston
• It eliminates the slapping tendency of piston by offsetting
from the cylinder centerline towards the major thrust side.
• As the piston approaches TDC during compression stroke,
the offset causes it to tilt slightly so that the top skirt
surface on the minor thrust face and the bottom surface
of the piston skirt on the major thrust side is also placed
against the cylinder wall.
• When moving towards bottom dead centre, the inclination
of the connecting rod forces the piston against the major
thrust side.
PISTON SLAP ELIMINATION METHODS
65

2. Pistons with inserted ring carrier
• Special ring inserts are made from austinitic form of CI
has been used for resisting the corrosive action.
3. Cast Steel Pistons
• Pistons cast from alloy steel containing silicon and copper,
with cadmium plating have been found to be highly wear
and heat resistant.
4. Anodized Pistons
• It increases the bearing properties of pistons.
• It is done by sulphuric acid process and resulted a coating
is in dark grey colour.
5. Tinned Pistons
• Tin deposits of about 0.007 mm thickness ensure good
lubrication during starting operations of the piston and
This avoids wearing out of the piston 68

PISTON FAILURES
1. Piston Scuffing
 Occurs when due to excessive heat the piston
expands and becomes tight in the cylinder.
Reasons
A. Insufficient lubrication of cylinder walls.
B. Detonation resulting high engine temperatures.
C. Insufficient cooling system.
D. Leakage of cooling water in the cylinder causing
lubricant film breakdown.
E. Piston pin may be too tight either in piston pin or
connecting rod bush thus putting restraint on free
expansion or contraction of the piston due to
increase or decrease of its temperature.
70

2. Burnt Piston
 Occurs mainly because of detonation or preignition.
3. Damage to Ring land
a) Excessive ring groove clearance
b) Detonation or preignition
c) Ring not compressed properly while installing.
d) Leakage of water into cylinder.
3. Damaged piston boss
a) Bent connecting rod, which produces a lateral
rocking movement on the piston as well as the pin.
b) Tapered crank pins or out of parallel with the
crank shaft journals will produce the similar effect
as that of above.
c) Too much end play in the crank shaft will produce
lateral rocking motion of the piston pin.
71

PISTON RINGS
FUNCTIONS
1. To form a seal for the high pressure gases from the
combustion chamber against leak into the crank case.
2. To provide easy passage for heat flow from the piston
crown to the cylinder wall.
3. To maintain sufficient lubricating oil on cylinder walls
throughout the entire length of the piston travel,
minimizing the ring and cylinder wear; Control the
thickness of oil film so that satisfactory oil control is
maintained.
72

CONSTRUCTION
 The ring is cast individually and machined carefully, when
in position, it exerts uniform pressure on the cylinder walls.
 A gap has to be cut into the ring so that while inserting, it
can be expanded, slipped over the piston head and released
into the ring groove .
 The gap is almost closed when the piston is in the cylinder.
 The circumferential expansion of the ring under high
temperatures is also accommodated by the gap.
 The sealing action of the top ring is due to the high pressure
in the combustion chamber, which press the top of the ring
tightly on the base of the piston ring groove
 However some leakage does take place through the end gap
of the top compression ring which is useful in providing the
pressure for sealing action of the second piston ring.
73

 Excessive end gap would result in blow-by and scuffing of
the rings and lesser clearance would cause the ring ends to
butt at higher temperatures, resulting in excessive and non
uniform pressure on the cylinders causing excessive wear.
 In practice, piston ring gap is kept about 0.30 to 0.35 mm
when installed.
Butt Type – Common, cheap
Tapered Type – Effective leakage
proof, costly
Seal cut Type – Effective leakage
proof, costly
TYPES
75

MATERIALS
 Material generally used for piston rings is fine grained alloy
cast Iron containing Silicon and Manganese.
 It has good wear and heat resistance with the Rockwell B
scale about 100.
 Chromium plated rings are usually used as top ring, which is
subjected to high temperatures and the corrosive action of
the combustion products.
 In heavy duty engines, the other rings are also chromium
plated.
 The fine finish of chromium will increase the cylinder bore
life.
 It prevents the ring scuffing as it is very difficult to be
welded to the CI cylinder bore.
 Chromium plated rings should not be used for the cylinders
which are chromium plated or any such hard material.
76

 A porous phosphate coating is generally provided to reduce
the scoring of the surface during running in, which is formed
by immersing the ring in a bath of phosphoric acid and
manganese forming Manganese phosphate.
 The porous surface has cavities for worn particles and also
acts as reservoir, which remains even after the coating has
worn away.
 Rings with Molybdenum filled face have also been
introduced which has larger oil carrying capacity, longer life
and resist scuffing due to larger melting point (2620°C).
 Alloy steels are also used as ring materials.
 Stainless steel rings resist pitting and corrosion to remain
clean and do not clog with carbon as quickly as others.
77

No. of Rings
 Two compression rings and one oil control rings are used in
modern engines.
 A minimum of two compression rings are required as the
pressure difference in the combustion chamber and the
crank case is very high about 70 atm., single piston ring
cannot take such high pressure.
 Increasing the no. of rings also reduces the design pressure
between the rings and the cylinder walls which results in
decreased wear and consequently increased life.
78

Types
1. Compression Rings
2. Oil control Rings
The top compression ring has to do the hard work of
sealing and transfer of heat from the piston crown to the
cylinder walls.
The compression rings perform two function
I. Seal the gas and transfer the heat.
II. Assist the oil rings in controlling the oil in cylinder.
79

PISTON MOTION Compressed
Charge
Cylinder Wall
Force due to
Compressed
charge
Or combustion
pressure
Ring
Expanding Gas
Piston Motion
80

Oli Control Ring
 Oil control ring prevent the excessive amount of oil from
passing :
i. Between the ring face and the cylinder wall
ii. Through the ring end gap
iii. Around behind the ring.
 When the piston moves up, the lower face of piston ring is
pressed against the lower ring face which makes the outer ring
face to slide over the oil on the cylinder wall and scrapes some
oil and sends out through oil drain holes.
 As the piston moves down, the sharp edge of oil control ring
scraps the oil on the cylinder wall.
 The oil holes in the ring groove should be adequate to ensure
free flow of oil to the sump or back pressure may build up in
the groove causing the oil to move up into the combustion
chamber and get burnt there.
81

Design Considerations and Trends
I. Compression Rings
1. Ring Width: About 1.5mm from 3mm.
a) Advantages
i. Better resistance to ring scuffing.
ii. Lower piston height.
iii. Better resistance to ring flutter.
iv. Problems of ring inertia are reduced.
b) Disadvantages
i. Machining narrow grooves in the piston accurately.
ii. Instability in ring grooves.
83

2.Shape
(b) Taper face reduces the
contact of the cylinder to
a line contact.
(c) Machining inner side
Upper corner makes Torsional
Twist ring; in the cylinder, it
Rotate about its own axis.
(d) The narrow face of the
scraper type torsional ring has
the advantage of high unit face
Loading.
(e) Taper face torsional twist
Ring is combination of torsional
And taper face ring.
(f) Keystone rings have inclined
side faces and operate in the
Grooves of similar geometries.
The disadvantage is carbon
deposites in the grrooves.
84

 A recent development for torsional twist ring is the reverse
twist ring whose lower edge is beveled instead of upper.
 The outer face is tapered to compensate the twist in the opposite
direction.
 It offers better oil control than normal twist ring but later offer
better Blow-by control.
85

3. Rings for Worn out cylinders
 The ordinary piston rings will not work effectively when the
cylinder is worn out.
 In such cases, spring expander piston rings are used.
They are made up of spring steel with crimps spaced uniformly
along the circumference.
 The cast Iron ring exerts only a part of the total pressure and
the rest being contributed by spring expander.
Spring Expander
86

II. OIL CONTROL RINGS
(a) Most simple oil control ring
(b) The pressure between the ring and the
Wall is increased due to reduced outer face
area and there fore better scrapping.
(c) It has recess on the outer face which
results in the formation of narrow ring lands
Providing higher radial pressure against the
Cylinder wall and two way scrapping action.
(d)There is a central raised land, which wear
Out during run-in period until both the outer
lands control the scraping.
(e) Contains two scraper rings in the same
groove with an expander at the back to
Increase the radial pressure against the
Cylinder.
(f) Used for worn out cylinders having ovality
Or taper in the bores.
87

FACTORS AFFECTING RING SELECTION
1. Dimensions of Engine
Block
2. Piston Design
3. Piston Displacement
4. Piston speed
5. Cylinder bore material
6. Carburation
7. Bore to stroke ratio
8. Compression Ratio
9. Cooling Capacity
10.Engine performance
expected
11.Horse Power Requirement
12.Type of cylinder bore
lubrication
13.Peak manifold vacuum
88

CAUSES OF RING FAILURES
1. RAPID WEAR
► Excessive ring or ring groove-wear is caused by the
scraping action of abrasive in the engine.
► Most commonly experienced.
2. SCUFFING
► Caused by break down of protective lubrication oil film
on the cylinder wall.
3. RING BREAKAGE
► Caused due to overstressing due to shock loading, fatigue.
89

PISTON PIN
 It is also called Gudgeon pin or wrist pin.
 It connects piston with the small end of the connecting rod.
 For lightness, it is made in tubular form.
90

 It is made up of low carbon case hardened steel having
0.15% carbon, 0.3% silicon, 0.5% manganese and remainder
iron.
 It is carburized at 900°C, hardened by quenching from 780°C
and finally, tempered at 150°C.
 Piston pins are usually lapped to a very fine surface finish of
about 0.1μm., without which the pin fails due to surface
irregularities.
 The piston pin operating clearances are generally kept about
7.5μm, the larger clearance, the more noise thus decreased
life.
91

 The piston pin- connecting rod connections are three types:
1. Piston pin is fastened to the piston by set screws through
the piston bosses. It has a bearing connected to
connecting rod.
2. The pin is fastened to the connecting rod by means of a
bolt while it forms a bearing in the piston pin boss.
92

3. The pin floats both in pin boss and the small end of the
connecting rod.
• This arrangement is generally used.
• To prevent the end movement, circlips are used,
93

CRANK SHAFT
 It is the engine component from which the power is taken.
 It receives the power from the connection rods in the
designated sequence for onward transmission to the clutch
and subsequently to the wheels.
 The crankshaft assembly includes the crankshaft and
bearings, the flywheel, vibration damper, sproket or gear to
drive camshaft and oil seals at the front and rear.
 Crank shaft consists of
Main Journals
Crank pins
Crank webs
Counterweights
Oil holes
94

 The main journals are supported in the crank case.
 Their no. is always one more or less than the no. of cylinders.
 Crank pins are the journals for the big end of the connecting
rod and are supported by crank webs.
 The crank web should adequately withstand the twisting and
the bending loads.
 The distance between the axis of the main journal and the
crank pin should be half of the engine stroke and is called
crank throw.
 Oil holes are drilled from main journals to the crank pin
through crank webs to provide lubrication of big end
bearings.
 The main bearings are lubricated using oil galleries of engine
block.
96

 When the engine is running, the centrifugal force acting at
each crank pin due to rotation of both the crank shaft and
crank pin tend to distort the crank shaft.
 To counter this tendency, counter weights are either formed
as integral part of the crank or attached separately.
97

 On the fly wheel end of the main bearing journals, thrust
bearing is located so as to support the loads in the direction of
shaft axis.
 Those loads are produced due to the clutch release forces, forces
in the helical gear train, oil pumps, water pump, supercharger, .
 On the front of the crank shaft,
 Timing gear or sprocket which drives the crankshaft,
Vibration damper
 Pulley for driving the water pump, fan and the generator.
 On rear end is mounted the fly wheel.
 Flywheel has a ring mounted on its periphery having teeth
which mesh with the pinion of the starting drive to start the
engine.
 Flywheel also provide frictional surface for clutch.
 It also contain timing marks indicating the positions of TDC and
BDC of cyl.1 and are used to determine the ignition timings.
98

 Crankshafts are generally two types viz. one piece and built
up.
 In built up, the crank pins and the journals are bolted to the
crank arms, which also serves as fly wheel.
 One piece construction is almost universally used for
automotive engines.
99

 For cars, which are petrol engines, the crank pin length is at
least 30% of its diameter, which itself is not less than 60% of
the bore diameter.
 The thickness of the crank web is about 20% of the cylinder
bore size, the main journal diameter bigger than the crank pin
diameter and is usually 75% of the bore diameter where as
the length is half of the diameter.
 The angles between the crank throws are selected from the
consideration of smooth power output.
 In 4-cylinder inline engines, it is 180°, 6-cylinder is 120° and
V-8 engine is 90°.
100
DESIGN FEATURES

Materials and Manufacture
 Crank shaft must be adequately strong, tough, hard and
should possess high fatigue strength.
 S.A.E Steels 1045 and 3140 are used as materials for forged
crank shafts.
 S.A.E 1045 contains Manganese (0.60- 0.90 %),
 Where as S.A.E 3140 contains Nickel (1.10 – 1.40 %) and
chromium (0.55 – 0.75) besides manganese (0.70 – 0.90 %).
 Chrome-Vanadium and Chrome molybdenum steels are also
used.
 Chromium forms hard carbides and molybdenum improves
the impact strength and machinability.
101

 For forged crankshafts, the steel with the following
composition is used.
0.3% carbon
2.5% Nickel
0.65% chromium
0.55% Molybdenum.
 In case of Cast crankshaft, the following composition is used.
Carbon 1.35-1.6 %
Chromium 0.05-0.5 %
Silicon 0.85-1.1 %
Manganese 0.6-0.8 %
Copper 1.5-2.0 %
Phosphorus 0.10 %
Sulphur 0.9 %
102

 In forged crankshafts, the drop forging process with closed
dies is used.
 The forging maybe done either in-place or alternatively i.e.,
the crankshaft is forged in one plane and wound to place the
crank throws at desired angles.
 The blank so produced is then heat treated and machined to
final dimensions .
 The machining includes rough turning, final grinding and
final lapping of main journals and crankpins.
 Crankshaft is manufactured by shell moulding process in
case of casted crankshafts, in which the shell mould is made
from sand and synthetic resin
 This method has high accuracy and close tolerances.
103

Comparison
S.No
Forged Crank shaft Cast crank shaft
1
Grains parallel to principal Direction Randomly distributed
2
Dense and tough Less dense compared to forged CS
3
Comparatively Costlier Cheaper due to reduced machining
104

Engine Valves
 To admit the air fuel mixture into the cylinder, and to force
the exhaust gases out at correct timing, Valves are employed.
 The engine valves are broadly classified into 3 main
categories.
1. Poppet Valve
2. Sleeve Valve
3. Rotary Valve
Out of these, poppet valve is the one which is being universally
used for automobile engines.
105

Poppet Valves
 Derives its name from popping up and down; and is also
called Mushroom valve because of its shape.
 Consists of a head and a stem.
106

 The advantages over other types are
1. Simplicity of construction
2. Self centering
3. Free to rotate about the stem to new position.
4. Maintenance of sealing efficiency is easier in this case.
 Generally, the inlet valves are larger than the exhaust valves
because the speed of in coming air fuel mixture is less than
the speed of exhaust gases.
 More over, the density of the exhaust gases are also high
and the smaller valve provides shorter path of heat flow and
reduced thermal loading.
 The dimensions of inlet and Exhaust valves are 45% and
38% of the cylinder bore diameter.
 To improve the heat transfer to the cylinder head, the stem
diameter of the exhaust valve is generally 10% to 15%
greater than that of the inlet valve. 107

 The lift in both inlet and outlet should be equal to 25% of the
valve head diameter.
 If the lift is less, the volumetric efficiency will be less; if the
lift is more, the inertia of the valve actuating mechanism will
increase and results in excessive noise and wear.
 The Valve face angle is generally kept 45° or 30°.
 Smaller face angle provides greater valve opening for a given
lift but poor sealing because of the reduced seating pressure
for a given valve spring load.
 The inlet valve face angle may be kept at 30° or 45° but for
exhaust vale, the face angle is only 45°.
108

 A further differential angle of about ½ deg. to 1 deg. is
provided between the valve and the seating which results in
better sealing conditions.
109

Operating Conditions
110
Exhaust valves operate under relatively
More severe conditions than Inlet valve.
The exhaust valves are subjected to:
1. Longitudinal cyclic stresses due to
return spring load.
2. Thermal stresses in the
circumferential and longitudinal
due to the large temperature
gradient.
3. Creep conditions due to very high
temperatures.
4. Corrosion conditions.

Exhaust Valve Material Requirement
1. High strength and hardness to resist tensile load and stem
wear.
2. High hot strength and hardness to combat head cupping and
wear of seat.
3. High fatigue and creep resistance.
4. Adequate corrosion resistance.
5. Least coefficient of thermal expansion to avoid excessive
thermal stresses in the head.
6. High thermal conductivity for better heat dissipation.
111

MATERIALS
 Materials for inlet and exhaust valves are different.
 Silicon-chrome steel containing about 0.4% carbon, 0.5%
nickel, 0.5% manganese, 3.5% silicon and 8% chromium is
the material generally used for inlet valves.
 Austinitic steels and precipitation hardened steels are used
for exhaust valves.
 A typical Austinitic steel is the ‘21-12’, which contains
0.25% carbon, 1.5% manganese, 1% silicon, 21% chromium
and 12% nickel.
 Another improved austinitic steel ‘21-4N’ contains 0.5%
carbon, 9% manganese, 0.25% silicon, 4%nickel, 21%
chromium and 0.4% nitrogen.
112

 A typical precipitation hardening steel has the following
composition:
Carbon 0.4-0.5
Chromium 23.0-24.0
Nickel 4.5-5.0
Molybdenum 2.5-3.0
Phosphorus 0.035
Sulphur 0.035
 For modern day heavy duty engines, ‘nimonic alloys’ are
used. These have higher hardness, fatigue and creep
strengths and corrosion resistance but these are very costly.
 The exhaust valves of heavy duty engines are some times
made in two parts and then welded together. This is done
only when a single material cannot satisfy all the stringent
requirements.
113

 The valve heads are made up of special high strength
corrosion resistance and creep resistance alloy and welded on
the stem made up of wear resistance alloy.
114
MISCELLANEOUS CONSIDERATIONS
1. Adequately designed valve may fail due to local stress
concentration.
2. Excessive surface finish of the valve will result in loss of
lubrication oil film where as the excessive roughness will
increase the wear. A thin coating of chromium of thickness
0.5μm will provide the optimum conditions.
3. Lower valve temperatures will result in higher compression
ratio which in turn increases thermal efficiency.

VALVE COOLING
 The maximum temperature in the exhaust valve is around
750°C.
 Hence the exhaust valve cooling has to be done.
 The cooling jackets are arranged near the valves.
 In heavy duty engines, sodium cooled valves are used.
 Sodium is high conductivity metal which melts at 150°C.
 Sodium remains in liquid state in operating temperature.
 The amount of sodium filled is 40% of the hollow stem.
115

 When the valve is operating , the sodium goes down and
collect the heat and gives the same to the stem, then to the
valve guide ,to the cylinder head and then to the cooling
water.
 This method achieves valve cooling about 100°C.
117

VALVE SEATS
 The valve seats must be faced very accurately, so that there is
complete contact between the valve seat when the former
closes.
 The valve face seat must have the same angle as that of the
valve face.
 It is generally maintained between 30° to 45°.
 For the cylinder blocks made up of CI, the valve seats are
directly machined on the cylinder heads or blocks for inlet
valve, which is called integral seats.
 For the cylinder heads made up of Al alloy, separate valve
seats has to be used even for inlet valve.
 For exhaust valve, irrespective of the material of cylinder
block, separate valve seat has to be used.
118

 Valve seat inserts are simply rings made up of alloy steel
consisting of chromium, silicon, tungsten or cobalt with the
conical seat on one of the inner edges.
 These are force fitted in to the recesses machines in the
cylinder head.
 When worn out, they can be replaced easily.
119

Valve Guide
 The stem of the poppet valve needs a guide for the alignment
of its up and down motion so that the face of the valve is
maintained in a central position w.r.t. the valve seat while
opening and closing.
 The simplest valve guide is the reamed hole in the cylinder
head or block.
 It reduces the cost and weight of the engine.
 In the modern engines, separate guides are provided when
the valve stem and the cylinder head are not compatible.
 These are of cylindrical shape made up of pearlitic cast iron
having minimum hardness of the order of 220 BHN.
 Sometimes alloy irons containing nickel and chromium are
used.
 Silicon, aluminium or bronze guides offer maximum
resistance to fatigue, corrosion and heat.
121

Valve Springs
122
►Helical Springs are used to keep the valve in constant
contact with the tappet and the tappet with cam.
►It is ground flat at each end to ensure
even pressure distribution.
► The coil ends are also placed
diametrically opposed to avoid the bending
tendency under compression.
►The arrangement for retention is quite
simple.
►A ring split into two halves with internal
projection to fit into the valve spring
retainer groove and the outer surface is
tapered.

 The valve springs are subjected to heavy service, there fore
made from high grade steel wire, the materials being
generally hard-drawn carbon steel or chrome –Vanadium
steel.
 They are often shot peened to make them fatigue resistance.
123

Valve Actuating Mechanisms
 All the valves are cam driven at the half the crank shaft
speed.
 There are different methods of operating the valves from the
cam.
 They can be classified as:
1. Mechanisms with side cam shaft
2. Mechanisms with over head cam shafts.
124

Mechanisms with Side Camshafts.
 The camshaft is on the side of the engine and the valves are
operated either directly by cams or by push rods..
 These are further classified as:
1. Double row side valve mechanism(T-Head):
 This is the oldest type.
 Inlet & outlet valves are operated by separate cam
shafts.
 More design complication.
 Poor performance of the combustion chamber.
125

2. Single row Side valve Mechanism(L-head):
 The inlet and the exhaust valves are arranged in a single row
and operated from the same camshaft.
 Advantages:
 Low engine height.
 Low production Cost.
 Quite operation.
 Ease of lubrication.
 Disadvantages:
 More prone to detonation.
 Restriction on size of inlet valve.
 Difficulty in cooling of exhaust valve.
127

3. Overhead inlet and side exhaust valve mechanisms(F-head):
 Overhead mechanism is used for inlet valve and side valve
mechanism is used for exhaust valve.
 It is used in F-head engines.
 It is simpler than the overhead cam shaft operated types.
 Allows the use of larger inlet valves.
 The F-head engines are found less efficient and more
expensive; so obsolete now.
129

4. Single row overhead valve mechanism (I-Head):
 Used quite extensively.
 Cam operates the valve lifter which in turn actuates the
push rod.
 The push rod further operates the rocker arm and rocker
arm operates the valve.
 Advantages:
I. Higher Volumetric efficiency.
II. Higher Compression ratios.
III. Leaner air-fuel mixture.
IV. Possibility of imparting desired lift multiplication to
the system, thus smaller cam lobes can also be used.
131

 Disadvantages:
I. Not very precise while accelerating and operating at
high speeds.
II. Larger valve lifter clearances are required.
III. Noisy operations.
IV. Greater maintenance.
133

Mechanisms with overhead camshafts
 Highly efficient, require more lubrication oil between cam
and follower, Higher initial cost.
1. Overhead camshaft operated mechanism with inverted
bucket follower:
134

 The camshaft is arranged directly over the valve stem.
 It is direct and very rigid so that valve movement follows
precisely the designed cam profile lift..
 The valve stems are not subjected to side thrust there by less
wear occurs.
 The drive in cam shaft is quite complicated, sufficient
lubrication is required, adjustment of the valve lifter
clearance is relatively more difficult.
135

136
• Provides a leverage ratio, which enables the designer to provide
smaller cam profiles.
• Lesser inertia but reduced precision, side thrust in the valve stem
and more wear.

Comparison between Side camshaft and Overhead
Camshaft Mechanisms.
Side Camshaft Mechanisms
1. Delayed valve
opening/closing.
2. Valve lift can be suitably
adjusted.
3. Smaller cams.
4. Less costlier.
Overhead Camshaft Mechanisms
1. Quicker valve opening or
closing.
2. Valve lift remains equal to
cam lift in certain methods.
3. Comparatively larger cam
sizes.
4. More costlier compared to
side cam shaft M/sums.
140

Valve train components
 The components of valve train are
1. Cam shaft
2. Cam shaft Drive
3. Valve tappet or Valve lifter
4. Rocker Arm
5. Valve Rotators
141

CAMSHAFT
 Provides means of operating and controlling the valves.
 It also provides the drive for ignition distributor and
mechanical fuel pump.
 It contain no. of cams at suitable angular positions.
 It contain two lobes for each cylinder.
 There is an integral toothed spiral gear on the camshaft to
drive the distributer and the oil pump.
 Camshaft is forged from alloy steel or cast from hardenable
cast iron and is case hardened.
142

Camshaft Drive
 The drive for cam shaft may be either chain drive or gear drive.
 For the side camshaft engines, gear drive is employed where as for overhead
camshafts, chain drive is employed.
 Latest type of drive by means of a toothed rubber belt which is made up of
rubber moulded on to a non-stretching cord.
143

Valve Tappet or Valve Lifter
 It follows the cam lobe on the cam shaft.
 It is placed between the cam and the push rods.
 Some clearance has to be maintained between the tappet and
the cam to allow for expansion due to heat, which is called
Valve Lash.
 Types:
1. Fixed type valve tappet
2. Adjustable type valve tappet.
3. Hydraulic Tappet
144

Valve Troubles
1. Burning of valve face:
– Poor valve seating that allows the high temperature and
high gas pressure to leak between valve and seat.
– Lean mixture.
– Detonation and Pre-ignition.
– Incorrect valve timing.
2. Necking of the valve stem:
– Leakage of gases at valve seat.
3. Valve face wear:
– Weak springs.
– Excessive guide wear.
– Narrow valve seat.
– Leakage at seat.
145

4. Valve stem and Guide wear:
– Excess clearance.
– Lack of sufficient lubrication.
5. Valve cracking or breakage:
– Excessive lash.
– Excessive stem to guide clearance.
– Loose seat inserts.
– Defective valve springs.
– Excessive vibrations and loading due to over speed.
6. Noisy valve operation:
– Wrongly adjusted tappet.
– Sticking of valves due to gumming deposits.
– Improper rocker arm adjustment.
– Worn out valve train components.
146

Sleeve Valves
 They are cylindrical in shape.
 They surround the piston and
actually form the working cylinder.
 Types:
– Single sleeve
– Double sleeve
 Advantages:
– Simplicity in construction
– Silent in operation.
– Longer running period before
carbonization.
– Reduced tendency to detonate.
– Higher thermal efficiency.
147

 Disadvantages:
– High oil consumption.
– Gumming due to deposits.
Rotary Valves
 Advantages:
– Uniform and noise free motion.
 Disadvantages:
– Difficulty in pressure sealing.
– Economical valve lubrication not possible.
148

Mufflers or Silencers
 When the exhaust gases are released in to the air, the high
pressure wave in the gases causes explosion.
 As the gases are released rapidly one after the other, the
explosions occurring very fast combine together to form a
steady noise.
 This noise contains different notes of various frequencies;
The predominant notes are categorized as low frequency
notes from 50 to 500 Hz and high frequency notes from
3,000 to 10,000 Hz.
 Thus the silencer must be employed to absorb all the
frequencies.
 These silencers are connected to engine exhaust via exhaust
pipe.
 A tail pipe carries the exhaust gases from the muffler to the
rear or side of the vehicle near the rear wheel 149

Types
 There are basically, 5 types of mufflers, namely:
1. Baffle type
2. Wave cancellation
3. Resonance type
4. Absorber type
5. Combined resonance and absorber type.
1. Baffle type:
– It is generally cylindrical in shape with a no. of baffles
spot welded inside.
– The principle is closing the direct passage for the gas.
– The major drawback is their low efficiency and back
pressure causing loss in engine horse power.
150

2. Wave cancellation Muffler:
– The exhaust gases are divided in to two parts.
– The lengths of the path are adjusted such a way that
when the gases leave the muffler, the crest of on wave
coincides with the trough of the other wave, thus
cancelling each other and the noise becomes theoretically
zero.
– In practice, the noise is not completely eliminated as this
type cancels out the noise frequency for which it is
designed.
153

3. Resonance Type Muffler:
– Also called Helmholtz type.
– Contain a series of Helmholtz resonators, through which
a pipe containing access ports passes.
– The exhaust gases flow through this pipe and thus
experience no resistance.
– The resonators eliminate the fundamental and higher
harmonics of the engine noise.
154

4. Absorber Muffler:
– The sound absorbing material like fiber glass is placed
around the perforated tube through which the exhaust
gases pass.
155

5. Combined resonance and Absorber Type:
– The absorber type cannot eliminate the noise completely.
– The combination of absorber and Resonance can
eliminate the noise completely.
157

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