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Basic Engine Construction

• Components and Function– Engine block– Cylinder head– Combustion chamber

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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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Engine Block

• Pistons:– Moves up and down in cylinders

• Creates low pressure to draw in mixture• Compresses mixture for ignition• Transmits forces of combustion to rotate

crankshaft• Pushes exhaust gases out of cylinder

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Engine Block

• Rings– Mounted in grooves on piston – Takes up clearance in cylinder required for piston

expansion• Compression

– 2 top rings

– Seal combustion chamber

• Oil control– Bottom ring on piston

– Consists of 3 parts: 2 rails and expander

– Scrapes oil from cylinder as piston moves down on power stroke

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Oil Control Rings

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Engine Block

• Connecting rods:– Connect pistons and crankshaft– Upper end is connected to piston pin

• Uses bushing to allow movement on pin

– Lower end is split to allow installation on crankshaft journal

• Uses precision insert (bearing) to allow rotation on crankshaft journal

• Bearing requires oil film at all times to prevent metal to metal contact with journal

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Engine Block

• Crankshaft:– Changes reciprocating motion to rotary motion– Provides turning force to wheels– Crankshaft “throws” connect to rods – Crank “journal” is machined surface for rod bearings

• Rod bearings allow rod to rotate on crank journal

– Flywheel or flexplate is mounted on rear of crank and transfers power to transmission

– Pulleys mounted on front of crank drive accessories such as alternator or A/C compressor

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Engine Block

• Bearings:– Rod and main bearings

• Bearing inserts are held in place with locking tab• Must have small hole for oil lubrication• Pressurized oil keeps bearing from contacting

journal

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Engine Block

• Timing gears:– Allows crankshaft to turn camshaft– Can be chain or belt

• Timing belts normally use plastic covers• Pushrod engines normally use chains

– Usually found on the front of the engine’

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Engine Block

• Oil pan and filter:– Pan serves as reservoir for oil– Covers bottom of crankcase– Made from:

• Stamped steel• Aluminum• Plastic

– Contains pickup assembly for oil pump– Oil filter is usually mounted on engine block

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Engine Block

• Camshaft and lifters (pushrod engines):– Camshaft lobes open valves– Lifters sit on top of lobes and transmit motion

to pushrods– Pushrods transmit motion to cylinder head

rocker arms to open valves– Contains distributor drive gear if equipped– Camshaft must be timed to crankshaft

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Engine Block

• Flywheel or flexplate:– Flywheel is heavy steel plate mounted to crankshaft

• Smoothes out power pulses to keep engine spinning smoothly

• Serves as mounting surface for clutch on manual transmission

– Flexplate is thin plate that bolts crankshaft to torque converter for automatic transmission

– Both have external ring gear for starter operation

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Cylinder Head

• Covers cylinders• Forms top of combustion chamber• Contains intake and exhaust valves and springs• Contains spark plugs• Bolted to engine block with head bolts• Head gasket is placed between block and

cylinder head• Overhead cam engines contain camshafts

– Single cam engine= SOHC– Dual cam engine= DOHC

• Can be made from cast iron or aluminum

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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 high temperatures