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Chapter Automotive Engine Designs and Diagnosis Engine Classifications • Operational cycles • Number of cylinders • Cylinder arrangement • • • • Ignition type Cooling system Fuel type Valve train type – OHV, OHC, DOHC Four-Stroke Cycles • Intake Stroke – The piston moves down and the intake valve opens to draw air and fuel into the cylinder • Compression Stroke – The piston moves up with both valves closed to compress the mixture 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 cylinder is firing • For a four-cylinder firing order of 1342 – #1 is at TDC compression – #3 is at BDC intake – #4 is at TDC exhaust – #2 is at BDC power Engine Measurement and Performance • • • • • Bore and stroke Displacement Compression ratio Engine Efficiency Torque vs Horsepower Bore and Stroke Displacement Compression Ratio 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 • Fluid Leaks – Be sure to identify the correct fluid that is leaking • Exhaust Smoke – Exhaust smoke diagnosis chart 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 • Tappet Noise – A light, regular, clicking sound • Ping or Detonation – Rattling noise during acceleration OHC Valvetrain DOHC Valvetrain ... power Engine Measurement and Performance • • • • • Bore and stroke Displacement Compression ratio Engine Efficiency Torque vs Horsepower Bore and Stroke Displacement Compression Ratio Engine. .. 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. .. 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 –