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Vehicle Design II
ENGINE BLOCK
Dr. Nouby M. Ghazaly
Automotive and Tractor Engineering Dept.
College of Engineering,Minia University-61111
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Engine block
The engine block is the main body
of the engine; all parts of the
engine are either inside the engine
block or attached to the outside of
it.
The engine block is casting of cast
iron, it is considered in two parts,
the crankcase and the cylinder
block.
The crankcase, which supports the
crankshaft, is hollow inside with one
or more rib-like castings that form
the main frame
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Cylinder block
The upper portion of the engine block is the cylinder block. This
portion contains the cylinders, the water passages (commonly
known as the "water jacket") (fig. 1), and oil passages (fig. 2).
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Cylinder block
Core plugs
Core (frost or expansion) plugs are used to seal core
holes in all cast cylinder blocks.
The purpose of the core holes is to allow the sand fromthe sand core moulds to exit the block after the blocks
are cast.
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Cylinder Block Material
The cylinder blocks are casting from:
Gray cast iron
Cast iron alloy containing nickel and chromium for high
strength and wear resistance. Some cylinder blocks are cast from a silicon aluminium
alloy.
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Cylinder-block material
The cylinder-block material should
(a) be relatively cheap,
(b) readily produce castings with good impressions,
(c) be easily machined,
d) be rigid and strong enough in both bending and torsion,
(e) have good abrasion resistance,(f) have good corrosion resistance,
g) have high thermal expansion,
(h) have a high thermal conductivity,
(i) hold its strength at high operating temperatures, and
(J) have a relatively low density.
Note: Although cast iron meets most of these requirements, it has a low thermal
conductivity and is comparatively heavier. Due to these limitations, light
aluminium alloys have been used as alternative cylinder-block materials for
petrol engines.
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Advantages of aluminium
cylinder blocks Advantages of aluminium cylinder blocks are ;
(i) Lighter in weight.
(ii) Attractive appearance.
(Hi) Easier machining during production.
(iv) Better heat dissipation.
A common aluminium alloy composition is 11.5% silicon, 0.5% manganese,
and 0.4% magnesium, with the balance (87.6%) aluminium. The high silicon
content in this alloy reduces expansion but improves cast-ability, strength,and abrasion resistance, while the other two elements strengthen the
aluminium structure. While this alloy provides a good corrosion resistance, it
can absorb only moderate shock loads.
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Cylinder Liners
(Sleeves)
The cylinder liners are :
the most loaded parts of an engine.,
They resist to the stresses due to the
action of gas pressures, side pressureof the piston, and heat stresses.
There are two types:
Dry liner
Wet liner
L
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y n er L ners
(Sleeves)
(i) dry liners are in direct contact
with the cylinder bore walls of
the cylinder block.
(ii) Wet Liners are supported only at
each end in the cylinder block and are
elsewhere in direct contact with the
engine coolant.
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Dry Liners.
Normally dry cylinder liners are provided under the following considerations:
(a) When the cylinder block is made from aluminium alloy, the cylinder bore
wall should be stronger and of much harder wear resistant material.
(b) For heavy duty operating conditions, the normal wear resistance of a cast-iron cylinder block can be improved through sleeves with superior properties.
(c) When the cylinder block is designed with siamesed adjacent cylinder bores in
order to reduce the over all length, then only dry liners are suitable.
(d) When a cylinder block has been rebored two or three times, then dry liners
are used to restore to the original size of the cylinder bore.
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Wet Liners.
Wet cylinder liners provide the following advantages if used in petrol engines
with aluminium alloy cylinder block having a high coefficient of expansion.
(a) Due to isolation of the bulk of the sleeve from the block, difficult expansion
problems can be resolved at one or two locations only.
(b) The use of wet liners simplifies the casting of the cylinder block. Also,
castings of suitable material can be used with an appropriate heat treatment for
structural requirements, rather than the cylinder-bore wear-resistance
treatments.
(c) With better outside surface finish and constant wall thickness the liner
improves the thermal conductance and uniformity of cylinder cooling.
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Wet liners fit
Wet liners fit into the cylinder block at the top and near the bottom, and the
remaining portion of the sleeve is unsupported.
O-rings are used to prevent leakage of the coolant. Some wet liner sleeves
have a flange at the top, which sits into a recess machined in the upper deck
of the block.
The liner is sealed at the bottom by one or more rubber O-rings, usually fitted
in grooves.
A flat gasket is used between these two joint faces . Since the top of the liner
sleeve has no side support, it depends totally on vertical compression of the
liner caused by the cylinder head and gasket during tightening down.
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Liner Materials
Some commonly used liner materials are
Steel alloy,
Nickel cast iron
alloy cast irons,
and heat treated chromium and other alloy cast irons.
The wear resistance of these metals is at least 50% more than the
cylinder block material. The typical specification of liner material is :
Iron 93.92 to 92.22%
Carbon 3 to 3.5%Silicon 1.8 to 2.4%
Manganese 0.5 to 0.8%
Phosphorous 0.4 to 0.7%
Sulphur 0.08%)
Chromium 0.3%
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Gaskets
Gaskets or static seals are used between attaching engine parts to seal thejoints for preventing either internal or external leakage. A gasket must
withstand the high pressure and temperature of the engine. Therefore, the
gasket
(i) must be prevent to the fluids in contact,
(ii) must fit to any existing surface imperfections,(iii) must be resilient to maintain sealing pressure, even when the joints are
slightly loosened as a result of temperature changes or vibration,
(iv) must be resistant to all expected changes in its environment due to
temperature, pressure variations, and age
(v) must be stable under compression conditions, avoiding excessive setting.
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Gasket
The following gaskets are commonly used in automobile engines.
(a) Copper-asbestos gasket.
(b) Steel-asbestos gasket.
(c) Steel-asbestos-copper gasket.
(d) Single steel ridged or corrugated gasket.
(e) Stainless steel gasket.
(f) Asbestos-coated steel sheet with separate steel beading around bore.
(g) Laminated steel and graphitized asbestos sheet with formed steel bore
bead.
(h) Asbestos impregnated rubber bonded with reinforced ferrule bead.(i) Asbestos/steel wire-reinforced tissue.
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Gaskets
Copper-Asbestos Gaskets.
This consists of an asbestos sheet cut to the required form, which is protected
with thin sheet copper. There is a copper sheet on each side of the asbestos
sheet, and the two copper sheets lap along the outer edges of the asbestos
sheet, so that the latter is completely covered.
Steel-Encased Gaskets.
Cylinder-head gaskets are made also of asbestos sheet covered in steel instead
of copper. Steel being harder does not have as good sealing properties as
copper, and a sealing coat of some heat-resistant, non-hardening material isgenerally applied to the gasket, either in the manufacturing process or during
installation. The edges of the steel sheet, of course, are not rust-proofed, and
some steel-encased gaskets are fitted with copper grommets at the waterways.
The principal advantage of steel- over copper-encased gaskets is that the
production cost of the former is about 20 per cent less.
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Cylinder Wear
The characteristic which is most important in judging cylinder irons is their
resistance to wear under engine- operating conditions.
Abrasion, which is due to foreign particles in the oil film;
Erosion, which is due to metal-to-metal contact between the cylinder wallon the one hand and the piston and rings on the other; and
Corrosion, which results from chemical action on the cylinder walls by the
products of combustion.
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LINER DIMENSIONS
Wet liner dim.
Dry liner dim.
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Questions?