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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
Unit 8Title: Cylinder Block and Cylinder Head
General objective:
To understand the application and structure of the cylinder block
and head.
Specific objectives:
At the end of this unit you should be able to:
1. explain the application of the cylinder block.
2. explain the material selected to provide cylinder block.
3. explain two types of sleeve
3.1 Wet sleeve
3.2 Dry sleeve
4. explain the advantages and disadvantages of sleeve.
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
5. discuss the design of a cylinder head.
6. discuss a cylinder head type CVCC and TGP.
Input This section introduces the subject matter that you are going to learn.
8.0 Introduction
A cylinder block and cylinder head are the main supporting structures to which
all other engine parts are attached to. This unit is about the cylinder block and
cylinder head of an engine.
8.1 Cylinder Block
The cylinder block is the main component of an engine. It houses, supports,
and positions other parts for precise operation. Engineers have developed many
types of cylinder blocks, such as the L- head (side valve), V twin, and twin-
opposed types, to fit equipment requirements. Small, single-cylinder, air-cooled
engine blocks are generally cast in two pieces, the removable end-wall section
(the oil sump on vertical models) and the main block. The block is made up of the
crankcase and the cylinder. The end wall (sump) and block are pin-aligned and
bolted together. Precise machining is accomplished for camshaft and crankshaft
bearings.
The blocks of the engines are generally made of aluminium but may have a
steel cylinder liner (sleeve). Cast-iron engines fill the need for heavy-duty
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
commercial works. Figure 8.1 shown a cylinder block four cylinder engine.
Cylinder blocks can be categorized into two categories: replaceable cylinder
liners and fixed cylinder liners. Engines with replaceable cylinder liners are
usually called sleeved engines
Figure 8.1 : Cylinder Block Construction
8.2 Cylinder Block Material Selection
A cylinder block is made by casting process due to its complex feature.
Once the cylinder block is cast , and after it has been cooled and cured,
surfaces are machined so other parts can be attached to the block. These
surfaces include the cylinders, top of block (deck),camshaft bore, crankshaft
bore, and oil pan surfaces. The front and rear of the block mounts are also
machined so that the parts can be attached and sealed correctly. Materials that
are used to make a cylinder block are:
i) Cast Iron/steel
i) Aluminum ( for smaller engine)
8.3 Differences between Aluminum and Cast Iron
In theory, cylinder block which contains iron heads do not conduct as
much heat away from the cylinder as aluminum does, so the iron heads
should be made more powerful. With the increased concern for improving
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
gasoline mileage, however, car manufactures are trying to make the vehicle
lighter. Besides that, aluminum weighs less and is generally much easier to
repair. One way to reduce the weight in the block, aluminum is used for this
purpose. Iron is less expensive but weighs more. Silicon is also added to the
aluminum. Through a special process, the silicon is concentrated on the
cylinder walls. This design is called silicon-impregnated cylinder wall.
8.4 Cylinder Sleeves
Some manufacturers use cylinder sleeves. Rather than casting the
cylinder bores directly into the block, they insert a machined sleeve (Figure
8.2). Sleeves are inserted after the block has been machined. The purpose of
using a sleeve is that, if the cylinder is damaged, the sleeve can be removed
and replaced rather easily. Blocks which already have sleeves have to be
bored out to remove any damage. After boring, larger piston will be needed.
There are two types of sleeves; a wet sleeves and a dry sleeve.
The dry sleeve is pressed into a hole in the block. It can be machined quite
thinly because the sleeve is supported from the top to the bottom by the cast
iron block. The wet sleeve is also pressed into the block. The cooling water
touches the center part of the sleeve. This is why it is called wet sleeve. Seal
must be used on the top and at the bottom of the wet sleeve. Seals are used to
keep the cooling water from leaking out of the cooling system. Wet sleeves are
used on some larger diesel engines.
Advantages of a sleeved engine:
i) easily reconditioned “ in frame”
ii) engine manufacturers are able to produce cylinder liners from special
wear-resistant and heat-treated alloys
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
Figure 8. 2: Types Of Cylinder Sleeves
Activity 8AThis section tests your understanding of the subject matter. You are to answer the following questions.
8.1 List down two types of cylinder blocks in single-cylinder air-cooled engine
blocks that are cast.
i. _____________________________________________________________
ii. ____________________________________________________________
8.2 What are the materials used to make cylinder block?
_______________________________________________________________
_______________________________________________________________
8.3 Name two categories of a cylinder block
i. ____________________________________________________________
ii. ____________________________________________________________
8.4 List two types of Cylinder Sleeve:
i. _______________________
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
ii. _______________________
8.4 Cylinder Head
The cylinder head closes one end of the cylinder and encloses the
combustion chamber, which is cast into cylinder head. The cylinder head
includes the valve guides, valve seats, ports, combustion chamber, water
jackets, threaded holes for spark plug, other threaded hole for attaching parts,
and several machined surfaces. The size of the chamber and stroke of the
piston determine the compression ratio of the engine. The spark plug is
threaded into the cylinder head with the spark plug electrodes protruding into
the combustion chamber for each cylinder or piston. This establishes the point
where ignition takes place. The cylinder head also has fins to release the heat
of combustion into passing air flow. Figure 8. 3 shows the structure of the
cylinder heads.
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Toyota 1985-1995 22R Cylinder Heads...
Special purchase of brand new cylinder heads, for Toyota 22R engines... Cylinder heads are complete with; valves, valve springs, retainers and keepers.
Larger Image
Larger Image
The 2.4 liter 4-cylinder 22R engine came in certain year Toyota Celicas, 4Runners and Pickup trucks.
CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
Figure 8.3: Structure Of Cylinder Head
8.5 Cylinder Head Materials
Cylinder head can be made from cast iron or aluminum. Aluminum is
used to make the engine lighter, but it transfers heat more rapidly and expands
more than cast iron with the addition of heat. The cylinder head must have an
intake and exhaust port. After the cylinder head has been cast, it must be
machined. Areas must be machined so that intake and exhaust manifolds can
be attached, valves can be seated, sparks plugs and injectors can be installed,
and a good seal can be provided to the block.
Intake and exhaust ports must be cast into the cylinder head. These
ports are made so the air and fuel can pass through the cylinder head into the
combustion chamber. Figure 8.4 shows the parts of the cylinder head.
Figure 8.4: Cylinder Head Construction
8.6 Combustion Chamber
The shape of the Combustion Chamber affects the operating efficiency
of the engine. Two types of combustion chamber designs are commonly used
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
and they are the Wedge- Shaped Combustion Chamber and The
Hemispherical Combustion Chamber.
The Wedge–Shape Combustion Chamber was used on cast until about
1968. Refer to Figure 8.5. As the piston comes up on the compression stroke,
the air and fuel mixture are squashed in the quench area. The quench area
causes the air and fuel to be mixed thoroughly before combustion chamber.
This helps to improve the combustion efficiency of the engine. Spark plugs are
positioned to get the greatest advantage for combustion. When the spark
occurs, smooth and rapid burning moves from the spark plug outward. The
Wedge Shaped Combustion Chamber is also called a Turbulence-Type
Combustion Chamber.
Figure 8. 5: Wedge Shaped Combustion Chamber
The Hemispherical Combustion Chamber is also called the Hemi-Head.
The valves are located as shown in Figure 8.6. The Hemispherical
Combustion Chamber is considered a No turbulence-Type Combustion
Chamber. The air and fuel mixture is compressed evenly on the compression
stroke. The spark plug is located directly in the center of valve. The advantages
of the Hemispherical Combustion Chamber are that air and fuel can enter the
chamber very easily.
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
Figure 8.6 : Hemispherical Combustion Chamber
The Swirl Chamber is designed to provide better mixing of the air and fuel
particles to improve combustion. This results in better fuel economy and lower
exhaust emissions since fewer unburned hydrocarbons enter the exhaust
system. The swirl effect is achieved by intake port design, port location in the
combustion chamber, and the shapes of the chamber itself. This design factor
results in a corkscrew type of flow of the air-fuel mixture in the cylinder as the
piston move up and down on the intake stroke. As the piston come up on the
compression stroke this agitation of the air-fuel mixture continues and is
compounded by compression ( Figure 8. 7).
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
Figure 8. 7: Swirl Chamber
The MCA (Mitsubishi Clean Air) Combustion Chamber uses three
valves : intake, exhaust and A jet valve. The jet valve is also an intake valve.
Air from the carburetor throttle plate is directed to the jet valve at lower engine
speed. This results in a swirling action in the chamber and increase turbulence
(Figure 8.8 ).
Figure : 8.8: MCA Combustion Chamber
The Honda CVCC (Controlled Vortex Combustion Chamber) is a
stratified charge chamber ( Air-fuel mixture is layers or strata). It has two
chambers – the main combustion chamber and auxiliary chamber- and three
valves – the regular intake and exhaust valve and a smaller auxiliary intake
valve that opens into the auxiliary chamber ( Figure 8.9). The small valve
admits a rich air fuel mixture into the auxiliary chamber, while a leaner mixture
is admitted past the intake valve into the main chamber. This results in an
overlap of the rich and lean mixture near these openings.
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
In operation, the spark plug ignites the rich mixture in the auxiliary
chamber, causing rapid flame propagation through the rich mixture first, then
through the overlap mixture, and finally through the lean mixture in the main
chamber. This results in good combustion and reduces exhaust emission.
The multivalve design is used in across-flow arrangement with intake
valve on one side and exhaust valve on the other side (Figure 8.9). There are
two camshafts, one for intake valves and one for exhaust valves. This result in
more complex camshaft mounting and camshaft drive requirements.
The advantages of the multivalve chamber include greater volumetric
efficiency resulting from the increased flow rate, central spark plug location for
better combustion, reduced emissions, better performance, and increase fuel
economy.
Figure 8.9: CVCC (Controlled Vortex Combustion Chamber)
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
Activity 8BThis section tests your understanding of the subject matter. You are to answer the following questions.
8.5 What is the main function of a cylinder head at the engine?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
8.6 Based on the figure below, label the parts of CVCC Combustion Chamber
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
8.7 List down three types of Combustion Chamber found in Internal combustion
engine.
i.________________________________________
ii. _______________________________________
iii._______________________________________
8.8 List the steps in the process of manufacturing cylinder head.
i. Casting
ii. Line boring
iii. Machining
iv. Honing
a. i and iii
b. i and ii
c. ii and iv
d. i,ii, iii and iv
8.9 Explain the purpose of Combustion Chamber in the internal engine.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
8.10 What are the materials needed to make a cylinder head?
_______________________________________________________________
_______________________________________________________________
Self –AssessmentSelf-assessment evaluates your understanding of each unit.
Question 9.0
List the different types of engine blocks produced
Question 9.1
Explain the differences between aluminium and iron particularly in making cylinder
block
Question 9.2
Name two types of sleeves and the advantages of sleeves
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CYLINDER BLOCK AND CYLINDER HEAD J3182 / UNIT 8/
Question 9.3
Why most engines use the sleeve cylinder at the engine block
Question 9.4
Describe the operation of a Controlled Vortex Combustion chamber (CVCC )
Question 9.5
Explain the advantages when an engine uses a multivalve design at the combustion
chamber.
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