CH09 automotive engine designs and diagnosis STUDENT VERSION

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Chapter 9

Automotive Engine Designs and Diagnosis

• Valve train type –

OHV, OHC, DOHC

Four-Stroke Cycles (cont’d)

• Power Stroke

– With both valves still closed, the mixture is ignited, and the expansion pushes the piston back down

• Exhaust Stroke

– The piston moves up and pushes the spent gasses out the open exhaust valve

The Four-Stroke Cycle

Firing Order

• The sequence in which the cylinders are ignited.

• Also indicates position of the pistons when a

Bore and Stroke

Displacement

Compression Ratio

Engine Volumetric Efficiency

Engine Thermal Efficiency

Engine Mechanical Efficiency

Torque vs Horsepower

Diesel Engines

• Main power source for heavy-duty

applications.

• Operates similar to a gasoline engine.

• Use high compression pressure to ignite fuel.

• Larger than comparable gas engine.

• Produce large amount of torque

• Run at low speeds.

Engine Identification

Engine Identification (cont’d)

Engine Diagnostics

• Compression Test

– Checks the compression of each cylinder.

• Cylinder Leakage Test

– Helps determine where compression is leaking.

• Power balance Test

– Checks to see if all cylinders are producing the same

power.

• Vacuum Test

– Helps to determine the engine’s efficiency by measuring manifold vacuum.

Engine Diagnostics (cont’d)

• Engine Oil Pressure Testing

– Determines the wear on internal engine parts

Common Engine Noises

• Abnormal Combustion Noises

– Detonation or ping is most noticeable during acceleration

• Usually caused by advanced timing, overheating, or lean mixtures.

– Preignition or spark knock occurs when

ignition occurs before the spark plug fires

• Caused by carbon deposits, incorrect spark plug, and cross firing.

Common Engine Noises (cont’d)

• Ring Noise

– A high-pitched rattling during acceleration

• Piston Slap

– Normally heard when the engine is cold

• Piston Pin Knock

– A sharp, metallic rap

• Ridge Noise

– High-pitched rapping, louder on deceleration

Common Engine Noises (cont’d)

• Rod-Bearing Noise

– Usually heard at idle

• Main Bearing Noise

– A dull, steady knock

OHC Valvetrain DOHC Valvetrain