© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only

Publisher

The Goodheart-Willcox Co., Inc.Tinley Park, Illinois

by

Russell Krick



Engine operation Engine bottom end Engine top end Engine front end


The engine is the source of power for the vehicle

It converts the energy stored in fuel into motion


Fuel is burned inside the engine’s combustion chamber to produce heat

Heat causes expansion of gases in the engine

Expansion in the combustion chamber produces pressure

Engine components convert pressure into rotating motion

Engine Operation


Engine Operation


Piston Travel(TDC, BDC)

Top dead center (TDC)piston is at its highest point in the cylinder

Bottom dead center (BDC)piston is at its lowest point in the cylinder

Piston strokedistance the piston slides up or down

from TDC to BDC


Piston Travel

(TDC, BDC)


Four-Stroke Cycle Requires four piston strokes to

complete one cycle Every four strokes, the engine

produces one power stroke Two complete crankshaft rotations are

required to complete the four-stroke cycle

Almost all automobiles use four-stroke-cycle engines


Intake Stroke Draws fuel and air into the engine Intake valve is open Exhaust valve is closed Piston slides down and forms a low

pressure area in the cylinder Atmospheric pressure pushes the air-

fuel mixture into the cylinder


Compression Stroke

Compresses (squeezes) the air-fuel mixture, making it more combustible

Piston slides upward Both valves are closed


Power Stroke Burns the air-fuel mixture and pushes

the piston down with tremendous force Both valves are closed Spark plug fires, igniting the air-fuel

mixture Pressure forms on the top of the piston Piston is forced down, rotating the

crankshaft


Exhaust Stroke Removes the burned gases from the

cylinder Piston moves upward Intake valve is closed Exhaust valve is open Burned gases are pushed out the

exhaust port


Four-Stroke Cycle


Refers to the block, crankshaft, connecting rods, pistons, and related components

Another name for the bottom end is the short block


Engine Block

Forms the main body of the engine


Engine Block Parts Cylinders

large, round holes machined through the block

Water jackets coolant passages through the blockallow a solution of water and antifreeze to

cool the cylinders


Engine Block Parts Core (freeze) plugs

round metal plugs that seal holes left in the block after casting

Main bearing boresholes machined in the bottom of the block

to hold the crankshaft Main caps

hold the crankshaft and main bearing inserts in place


Crankshaft

Harnesses the tremendous force produced by the downward thrust of the pistons

Changes the reciprocating (up-and-down) motion of the pistons into rotating motion


Fits into the bottom of the block

Crankshaft


Journals are precision-ground surfaces for the bearings

Crankshaft Parts


Crankshaft Parts

Counterweight offsets the weight of the piston, rod, rings, and journal offset to prevent vibration


Crankshaft snout sticks through the front of the blockprovides a mounting place for the

camshaft drive mechanism, front damper, and pulleys

Crankshaft flangeholds the flywheel

Crankshaft Parts


Removable inserts that fit between the block main bore and the crankshaft main journals

One-half of each insert fits into the block, while the other half fits into the block main cap

A main thrust bearing has flanges to control crankshaft end play

Engine Main Bearings


Engine Main Bearings

Oil holes and grooves allow oil to lubricate the bearings


Main Bearing Clearance

Space between the crankshaft main journal and the main bearing insert

Allows lubricating oil to enter and separate the journal and bearing this allows the journal to rotate without

rubbing on the bearing and causing excess wear


Engine Bottom End


Crankshaft Oil Seals Keep oil from leaking out the front and

rear of the engine Seals are placed around the front and

rear of the crankshaft to contain this oil Rear main oil seal

one- or two-piece seal that fits around the rear of the crankshaft to prevent oil leakage

Front main oil sealone-piece seal pressed into the front

cover


Flywheel Large metal disk mounted on the rear

of the crankshaft Flywheel functions:

connects the crankshaft to the transmission or transaxle through a clutch or torque converter

helps smooth engine power pulses contains a large ring gear, which meshes

with the starting motor gear to start the engine


Connecting Rod

Fastens the piston to the crankshaft Transfers piston movement and

combustion pressure to the crankshaft rod journals

Causes piston movement during the non-power producing strokes intake, compression, and exhaust


Connecting Rod


Connecting Rod Bearings

Ride on the crankshaft rod journals Fit between the connecting rods and

the crankshaft Rod bearing clearance

small space between the rod bearing and crankshaft journal

allows oil to enter the bearing, preventing metal-to-metal contact


Piston

Transfers the pressure of combustion to the connecting rod and crankshaft


Piston (Wrist) Pin

Allows the piston to swing on the connecting rod


Piston Clearance The amount of space between the

sides of the piston and the cylinder wall Allows a lubricating film of oil to form

between the piston and the cylinder Allows for expansion when the piston

heats up


Piston Rings Seal the clearance between the outside

of the piston and the cylinder wall Keep combustion pressure from

entering the crankcase Keep oil from entering the combustion

chambers


Piston Rings


Compression Rings

Prevent blowby (compression pressure leaking into the engine crankcase)

Compression and combustion pressure push the compression rings down in their grooves and out against the cylinder wall, improving sealing


Compression Rings


Oil Rings Prevent engine oil from entering the

combustion chamber Scrape excess oil off the cylinder wall If too much oil gets into the combustion

chamber, it will burn, causing blue exhaust smoke and increased exhaust emissions


Oil Rings


Ring Gap Split, or space, between the ends of a

piston ring Allows the ring to be spread open and

installed on the piston Allows the ring to be made slightly

larger in diameter than the cylinderwhen installed in the cylinder, the ring

spreads outward and presses on the cylinder wall, aiding ring sealing


Refers to the cylinder heads, valves, camshaft, and other related components

These parts work together to control the flow of air and fuel into the engine cylinders

They also control the flow of exhaust out of the engine



Bolts to the deck of the cylinder block Covers and encloses the top of the

cylinders Combustion chambers are small

pockets formed in the cylinder head combustion occurs in these small pockets

Cylinder Head


Cylinder Head

Combustion chambers contain the spark plug tip and valve seats


Cylinder Head Parts Intake ports

route air (diesel engine) or air and fuel (gasoline engine) into the combustion chamber

Exhaust ports route burned gases out of the combustion

chamber


Cylinder Head Parts Valve guides

small holes machined through the cylinder head for the valves

valves slide in these guides Valve seats

machined surfaces in the combustion chamber port openings


Cylinder Head Parts

When the valve is closed, it sealsagainst the valve seat


Valve Train

Consists of the valves and the partsthat operate them


Valve Train Operation

The camshaft lobe turns into the lifter and the valve

is pushed open

The lobe rotates away from the lifter and the valve spring

pushes the valve closed


Camshaft

Located in the engine block or in the cylinder head


Camshaft Parts Cam lobes

egg-shaped protrusions machined on the camshaft

one lobe is provided for each engine valve

Eccentricmay be machined on the camshaft for a

mechanical fuel pump Camshaft journals

machined surfaces for the cam bearings


Valve Lifters Usually rides on the cam lobes and

transfers motion to the rest of the valve train

Located in the engine block or cylinder head

Fit into lifter bores, which are machined holes in the block or head


Push Rods Transfer motion between the lifters and

the rocker arms Needed when the camshaft is located

in the cylinder block Made from a hollow metal tube with a

ball or socket formed on each end One end fits into the lifter, while the

other end fits against the rocker arm


Rocker Arms Used to transfer motion to the valves Mount on top of the cylinder head Rocker arm movement allows the

camshaft lobe to force the valve open Valve spring force closes the valve and

keeps the rocker arm in contact with the push rod


Valves

Open and close the ports inthe cylinder head


Intake Valve Larger than the exhaust valve Controls the flow of the air-fuel mixture

(gasoline engine) or air (diesel) into the combustion chamber

Fits into the port leading from the intake manifold


Exhaust Valve

Controls the flow of exhaust gases out of the cylinder

Smaller than the intake valve Fits into the port leading to the exhaust

manifold


Valve Seals

Prevent oil from entering the combustion chambers through the valve guides


Valve Spring Assembly

Used to close the valve


Intake Manifold

Bolts to the side of the cylinder head Contains runners going to each

cylinder head port Air and fuel (gasoline engine) are

routed through these runners


Exhaust Manifold

Bolts to the cylinder head Fastens over the exhaust ports to carry

burned gases to the exhaust system Made of cast iron, lightweight

aluminum, or stainless steel tubing


Engine Manifolds


Valve (Rocker) Cover

Thin metal or plastic cover over the top of the cylinder head

Keeps valve train oil spray from leaking out of the engine


Operates the engine camshaft and sometimes the oil pump, distributor, engine sensors, and diesel injection pump

Consists of a drive mechanism, a front cover, an oil seal, and a crankshaft damper


Camshaft Drive

Needed to turn the camshaft at one-half engine speed

Often called the timing belt, timing chain, or timing gears because they time the camshaft with the crankshaft


Camshaft Drive

A belt-drive, chain-drive, or gear-drivemay be used to turn the camshaft


Front Cover Bolts over the crankshaft snout Holds an oil seal that seals the front of

the crankshaft When the engine uses a gear- or

chain-type camshaft drive, the front cover may be called the timing cover


Engine Front End


Timing Belt

The front cover houses the front oil seal. The timing cover fits over the belt.


Timing Chain

Timing chain and sprockets operate

the camshaft in this engine


Crank Damper Heavy wheel on the crankshaft snout Mounted in rubber Helps prevent crankshaft vibration and

damage Also called the harmonic balancer or

vibration damper

Documents

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois