ch 1 cylinder block cylinder head, gaskets

8/9/2019 CH 1 Cylinder Block Cylinder Head, Gaskets

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Basic Engine Construction

• Components and Function – Engine block

– Cylinder head

– Combustion chamber


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Engine Cylinder Block

The cylinder block is the basic frame of a liquid-cooled enginewhether it be in-line, horizontally opposed, or V-type. 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 of an iron

alloy that contains nickel and molybdenum. This is the best

overall material for cylinder blocks. It provides excellent wearing

qualities, low material and production cost, and it only changes

dimensions minimally when heated. Another material that is usedfor cylinder blocks, although not extensively, is aluminum.

Aluminum is used whenever weight is a consideration.


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Engine Block

• Contains:

– Cylinder bores – Pistons and rings

– Connecting rods

– Crankshaft – Bearings

– Timing gears

– Oil pan and filter

– Camshaft and lifters (pushrod engines)

– Flywheel or flexplate


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Engine Block

• Cylinder bores:

– Round hole cast in block• Bored to a precise diameter

• Honed to smooth finish

– Guide for piston

– Contains forces generated during 4-stroke

cycle – Some engines use steel sleeves


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It forms the base of the engine. Two types of cylinder

blocks are used in vehicles.

Single piece casting:

In this type cylinder block and crankcase are cast as

one piece.

It gives better rigidity and it is easy to cast, which

reduce the cost of manufacturing.

Two piece casting:

In this type the cylinder block and crankcase are cast

separately.

The crankcase is bolted to cylinder block.It reduces the problem of lifting the cylinder block from

the crankcase, during repairing or overhauling.

This type of casting is used in heavy generating sets.


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ARRANGEMENT IN CYLINDER BLOCK

• The cylinder block is made of cast iron or aluminiumalloy.

• Inside the cylinder block, passages for the coolent andlubracating oil are provided.

• The cylinder head along with the valve assembly is fittedon the top of the cylinder block by nut and bolts.

• The oil sump is bolted to the cylinder block/ crankcasefrom the bottom.

• The crankshaft is supported on the split bearings.


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• One half bearing is fixed on the web which is cast withthe cylinder block, the other half bearing is fixed in the

bearing cap.• The bearing cap is fastened with the web by nuts and

studs.

• This portion where the crankshaft is fixed is known asthe crankcase.

• In the cylinder block space is provided for the camshaftand camshaft bearings, push-rod, tappets etc.


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The cylinder block also provides the foundation for the coolingand lubricating systems. The cylinders of a liquid-cooled

engine are surrounded by interconnecting passages cast in

the block. Collectively, these passages form the water jacketthat allows the circulation of coolant through the cylinder block

and the cylinder head to carry off excessive heat created by

combustion.The water jacket is accessible through holes machined in the

head and block to allow removal of the material used for

casting of the cylinder block. These holes are called core

holes and are sealed by core hole plugs (freeze plugs). These

plugs are of two types: cup and disk.


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Cylinder Block:The cylinder block, also called engine block, is the main bottom end structure. Iron or

aluminum is normally used for its construction. Nickel may be added to the iron to

increase strength and wear.

Aluminum blocks weigh less and are better at dissipating heat. Core plugs (1), alsocalled freeze plugs, seal holes left in the block after casting. The plugs prevent the

leakage of coolant from the water jackets.


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Block Design:

The design of the cylinder block varies among manufacturers.

The block's geometry is determined by the number of cylinders(2), cylinder orientation (opposed, in-line, slant, V-shaped), and

camshaft location (overhead cam or in-block cam). Regardless

of design, the block must withstand the forces exerted by the

pistons and crankshaft, serve as a mounting structure for other

engine components, and be light in weight.


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Main Caps:

The main caps (3) secure the crankshaft to the engine block. When bolted in place,

they form the main bearing bore in which the crankshaft's main journals rotate. Two

or four bolts are used to secure the caps. Some blocks use a main cap girdle which

is a structure in which the caps rest. The caps and girdle are secured to the block.


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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 diameter of thecylinder must be uniform throughout its entire length. During

normal engine operation, cylinder walls wear out-of-round, or

they may become cracked and scored if not lubricated orcooled properly. The cylinders on an air-cooled engine are

separate from the crankcase. They are made of forged steel.

This material is most suitable for cylinders because of its

excellent wearing qualities and its ability to withstand hightemperatures that air-cooled cylinders obtain. The cylinders

have rows of deep fins cast into them to dissipate engine

heat. The cylinders are commonly mounted by securing thecylinder head to the crankcase with long studs and

sandwiching the cylinders between the two. Another way of

mounting the cylinders is to bolt them to the crankcase, andthen secure the heads to the cylinders.


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CYLINDER LINERS

In automobile engine two types of liners are used.

• Dry type liner • Wet type liner


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Cylinder Sleeves:

Cylinder sleeves (1) or liners are

removable, cylindrical inserts. Two types

are used. The dry sleeve is separated from

the water jacket (2) by the cylinder wall (3).

The wet sleeve is in direct contact with the

coolant and has thicker walls since nooutside structure provides support. Sleeves

are typically cast iron.


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Dry Sleeves:

Dry sleeves are thinner in construction since structural support

is provided by the engine block cylinder wall. The loads

generated by combustion pressure are absorbed by the engine

block and not the sleeve. Dry sleeves can be pressed into olderengines to repair damaged cylinders.

Wet Sleeves

Wet sleeves are designed to withstand the loads generated by

combustion pressure. The sleeves are in direct contact withengine coolant. A rubber or copper O-ring (yellow circle) is used

at the bottom flange to prevent coolant from leaking into the

crankcase. The cylinder head gasket prevents any coolant

leaking through the top.


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AIR COOLED ENGINE


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• Cylinder Barrel

• ___________________ or nickel-molybdenum

steel• Used to guide and seal piston and to mount

cylinder assembly to head

• Barrel _______ into head to form cylinderassembly


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Cylinder interior wall

Cylinder Walls


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• Cylinder Walls• Inside surface of cylinder barrel is _________

to a controlled amount of roughness

• Rough enough to __________ but smoothenough to minimize friction and wear

• Plain steel cylinder walls are not _______ to

prevent wear or corrosion• Nitrided cylinder walls are _________ to reduce

wear but still rust as easily as plain steel walls.

Nitriding is exposing the cylinder wall toammonia at high temperatures and it hardensthe wall to a thickness of approximately .005”


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• Chrome cylinder wallsuse ______________ toresist wear and provide

a corrosion resistantsurface.

• Cylinders may be

chromed back to __________ insidedimensions if they

become worn• Chrome is too smooth to

hold oil without etching

or channeling during the ____________________


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• Cylinder wall “CHOKE”

• The cylinder wall is

tapered inward

towards the top so that

as the engine warms

up, the hotter top of

the wall expands more

than the bottom,creating a round barrel

at operating

temperature.


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Combustion Chamber

• Area formed by bottom of cylinder head and top of piston

• Air and fuel mixture is compressed and ignited in

chamber and applies force from combustion to piston

• Spark plug protrudes into chamber

• Chamber is sealed by:

– Valves – Piston rings

– Head gasket

• Chamber is exposed to very high pressures and hightemperatures


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Types of Combustion Chambers

Hemispherical or Pentroof - The "Hemi" Combustion Chamber


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A chamber of this design is considered to offer the least

amount of compromise for the efficiency gained.

Effectively, a hemispherical combustion chamber is one half of

a sphere cast into the bottom of the cylinder head. The valves

are placed at the outside of the bore area and at a specificangle from the crankshaft centerline. Optimizing this position

allows for huge airflow gains, since it moves the valve away

from the wall to keep it from creating turbulence.


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This creates a more efficient cross-flow movement of thecharge during valve overlap and limits thermal transfer from

the exhaust valve to the fresh charge. As mentioned

previously, this design offers the best surface-to-volume

ratio and also creates a very short direct exhaust port,essential in limiting heat rejection into the coolant.

Hemispherical chambers generally have a central sparkplug, which offers excellent octane tolerance. An additional

benefit is the distance between the intake and exhaust

valves, which further limits heat transfer.


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Wedge-Shaped Chambers


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Used over the years by almost every manufacturer, this type

of chamber resembles an inclined basin recessed into thedeck of the head. Inline valves are normally tilted to

accommodate the sloping roof of this design. The spark plug

is located on the thick side of the wedge and is usually

positioned midway between the valves.

The relatively steep walls in such chamber design force the

air/fuel flow path and deflect and force it to move in adownward spiral around the cylinder axis. During the

compression stroke, the compressed air/fuel area reduces to

such an extent that the trapped mixture is violently thrust fromthe thin to the thick end of the chamber. This builds up

significant kinetic energy, which when ignited contributes to

overall power.


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Bathtub or Heart-shaped Combustion Chamber


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The bathtub designation is generally reserved for any

chamber that's not a wedge or hemispherical. Most domestic

engines of pushrod design have used it in varying forms.In some instances the shape of the combustion chamber

was almost oval, with later trends being the more efficient

heart shape.

The valves are inline and partially masked by the chamber

wall, being more exposed on the plug side. The area across

from the major squish region is generally tapered and doesnot have the steep wall of a wedge style. Spark plug location

is maximized by biasing toward the exhaust valve and as

central as possible, making the overall design very efficientfor producing power. However, heat transfer from the close

proximity of the valves limits volumetric efficiency and

octane tolerance


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Bowl in Piston

Bowl & Piston with flathead on right.


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• Cylinder heads• Constructed of cast

aluminium

• Provides combustion

chamber, and mounting

areas for spark plug andvalve parts


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• The cylinder head is designed to transfer heatby conduction to the fins and then from the

fins to the air by convection

• The exhaust side of the head has the mostfins as it runs the hottest

• The head also may incorporate a drain linefitting to allow excess oil to return to the

crankcase (inter cylinder drain lines on

radials)


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• The crankcase is that part of the cylinder block below thecylinders. It supports and encloses the crankshaft andprovides a reservoir for lubricating oil. The lower part ofthe crankcase is the oil pan, which is bolted at thebottom. The oil pan is made of cast aluminum or pressedsteel and holds the lubricating oil for the engine. Sincethe oil pan is the lowest part of the engine, it must bestrong enough to withstand blows from flying stones andobstructions sticking up from the road surface.

• The crankcase also has mounting brackets to support theentire engine on the vehicle frame. These brackets areeither an integral part of the crankcase or are bolted to itin such a way that they support the engine at three orfour points. These points are cushioned by rubbermounts that insulate the frame and body of the vehiclefrom engine vibration. This prevents damage to enginesupports and the transmission.

Crankcase


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• The crankcase is the basic foundation of all air-cooledengines. It is made as a one- or two-piece casting that

supports the crankshaft, provides the mounting surfacefor the cylinders and the oil pump, and has thelubrication passages cast into it. It is made of aluminumsince it needs the ability to dissipate large amounts' ofheat. On air-cooled engines, the oil pan usually is madeof cast aluminum, and it is covered with cooling fins. Theoil pan on an air-cooled engine plays a key role in the

removal of waste heat from the engine through itslubricating oil.

ch 1 cylinder block cylinder head, gaskets

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