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TERMINOLOGYAtkinson cycle, Bore, Bottom dead center (BDC), Cam, Combustion chamber, Crank throw, Detonation, Diesel engine, Direct injection (DI), Double overhead camshaft (DOHC), Efficiency, Firing order, Glow plug, Homogeneous charge compression ignition (HCCI) Lobe Overhead camshaft (OHC) Overhead valve (OHV) Oversquare Ping Preignition Rotary Selective catalytic reduction (SCR) Stroke Top dead center (TDC) Undersquare Wankel SUMMARY¦ Automotive engines are classified by several different design features such as operational cycles, number of cylinders, cylinder arrangement, valve train type, valve arrangement, ignition type, cooling system, and fuel system. ¦ The basis of automotive gasoline engine operation is the four-stroke cycle. This includes the intake stroke, compression stroke, power stroke, and exhaust stroke. The four strokes require two full crankshaft revolutions. ¦ The most popular engine designs are the inline (in which all the cylinders are placed in a single row) and V-type (which features two rows of cylinders). The slant design is much like the inline, but the entire block is placed at a slant. Opposed cylinder engines use two rows of cylinders located opposite the crankshaft. ¦ The two basic valve and camshaft placement configurations currently in use on four-stroke engines are the overhead valve and overhead cam. ¦ Bore is the diameter of a cylinder, and stroke is the length of piston travel between top dead center (TDC) and bottom dead center (BDC). Together these two measurements determine the displacement of the cylinder. ¦ Compression ratio is a measure of how much the air and fuel are compressed during the compression stroke. ¦ In an Atkinson cycle engine the intake valve is held open longer than normal during the compression stroke. As a result, the amount of mixture in the cylinder and the engine's effective displacement and compression ratio are reduced. ¦ Diesel engines have compression ignition systems. Rather than relying on a spark for ignition, a diesel engine uses the heat produced by com pressing the intake air to ignite the fuel. ¦ A hybrid electric vehicle has two different types of power or propulsion systems: an internal combustion engine and an electric motor. ¦ A compression test is conducted to check a cylinder's ability to seal and therefore its ability to compress the air-fuel mixture inside the cylinder. ¦ A cylinder leakage test is performed to measure the percentage of compression lost and to help locate the source of leakage. ¦ A cylinder power balance test reveals whether all of an engine's cylinders are producing the same amount of power. ¦ Vacuum gauge readings can be interpreted to identify many engine conditions, including the ability of the engine's cylinders to seal, the timing of the opening and closing of the engine's valves, and ignition timing. ¦ An oil pressure test measures the pressure of the engine's oil as it circulates throughout the engine. This test is very important because abnormal oil pressures can cause a host of problems, including poor performance and premature wear. ¦ Carefully observing the exhaust can aid engine diagnosis. ¦ An engine malfunction often reveals itself as an unusual noise. When correctly interpreted, engine noise can be a very helpful diagnostic aid. EXAM1. What occurs in the combustion chamber of a four-stroke engine? 2. Name the four strokes of a four-stroke cycle engine. 3. As an engine's compression ratio increases, what should happen to the octane rating of the gasoline? 4. What test can be performed to check the efficiency of individual cylinders? 5. Describe tappet noise. 6. Which of the following statements about engines is not true? a. The engine provides the rotating power to drive the wheels through the transmission and driving axle. b. Only gasoline engines are classified as internal combustion. c. The combustion chamber is the space between the top of the piston and the cylinder head. d. For the combustion in the cylinder to take place completely and efficiently, air and fuel must be combined in the right proportions. 7. Which stroke in the four-stroke cycle begins as the compressed fuel mixture is ignited in the combustion chamber? a. power stroke b. exhaust stroke c. intake stroke d. compression stroke 8. True or False? In an HCCI engine, combustion immediately and simultaneously produces a steady flame across the mixture. 9. Which of the following is not a true statement about diesel engines? a. The operation and main components of a diesel engine are comparable to those of a gasoline engine. b. Diesel and gasoline engines are available as four-stroke combustion cycle engines. c. Diesel engines rely on glow plugs instead of spark plugs to initiate ignition. d. The compression ratio of diesel engines is typically three times that of a gasoline engine. 10. True or False? When looking at the front of a running engine, it will be rotating in a counter clockwise direction. 11. Which engine system removes burned gases and limits noise produced by the engine? a. exhaust system b. emission control system c. ignition system d. air-fuel system 12. In a six-cylinder engine with a firing order of 1-4 5-2-3-6, what stroke is piston #5 on when #1 is on its compression stroke? 13. The stroke of an engine is the crank throw. a. half c. four times b. twice d. equal to 14. True or False? The camshaft for a two-stroke cycle engine is always located in the engine block. 15. Which of the following is an expression of how much of the heat formed during the combustion process is available as power from the engine? a. mechanical efficiency b. engine efficiency c. volumetric efficiency d. thermal efficiency ASE-STYLE REVIEW QUESTIONS1. While diagnosing the cause for black smoke from the tailpipe of a gasoline engine: Technician A says that a faulty fuel injection system is a likely cause. Technician B says that it’s most likely caused by oil leaking into the combustion chamber. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 2. While discussing piston slap: Technician A says that it’s a high-pitched clicking that becomes louder during deceleration caused by detonation. Technician B says that it’s the noise made by the piston when it contacts the cylinder wall due to excessive clearances. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 3. While determining the cause for air leaking out of the oil dipstick tube during a cylinder leakage test: Technician A says that a burnt exhaust or intake valve is indicated. Technician B says that a warped cylinder head or bad head gasket is indicated. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 4. While diagnosing the cause for an engine having good results from a compression test and cylinder leakage test but poor results from a cylinder power balance test: Technician A says that incorrect valve timing is the most likely cause. Technician B says that a collapsed lifter is a likely cause. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 5. While looking at the results of an oil pressure test: Technician A says that higher than normal readings can be caused by a defective pressure regulator. Technician B says that higher than normal readings can be expected on a cold engine. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 6. A vehicle is producing a sharp, metallic rapping sound originating in the upper portion of the engine. It’s most noticeable during idle. Technician A diagnoses the problem as piston pin knock. Technician B says that the problem is most likely a loose crankshaft thrust bearing. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 7. While conducting an engine vacuum test: Technician A says that a steady low vacuum reading can be caused by a burned intake valve. Technician B says that an overall low vacuum reading is caused by something that affects all of the engine's cylinders. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 8. While determining the most likely problem of an engine with poor compression test results but acceptable cylinder leakage readings: Technician A says that the problem may be incorrect valve timing. Technician B says that the problem is a leaking valve guide. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 9. When a customer refers to the engine component that opens and closes the intake and exhaust valves: Technician A believes that the customer is referring to the camshaft. Technician B thinks that the component in question is the intake manifold. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 10. Technician A says that if an engine had good results from a compression test, it will have good results from a cylinder leakage test. Technician B says that if an engine had good results from a cylinder leakage test, it will have good results from a compression test. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B Next: Engine Disassembly and Cleaning Prev.: Case Study Home Article Index top of page |
