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NAVTTC Auto Mechanic Practice Questions - NAVTTC Trade Test - Auto Mechanic Motor Vehicle Mechanic (Pakistan) Exam
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Question
1
of 25
QUESTION 1 / 25
What is the primary function of the piston rings in an internal combustion engine?
Choose one answer below.
A
To connect the piston to the connecting rod
✓
B
To seal the combustion chamber and regulate oil consumption
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C
To open and close the intake and exhaust valves
✓
D
To balance the rotation of the crankshaft
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QUESTION 2 / 25
In a standard four-stroke internal combustion engine, which stroke immediately follows the compression stroke?
Choose one answer below.
A
Intake stroke
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B
Exhaust stroke
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C
Power stroke
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D
Scavenging stroke
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QUESTION 3 / 25
What is the main purpose of a spark plug in a petrol engine?
Choose one answer below.
A
To spray pressurized fuel into the cylinder
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B
To ignite the compressed air-fuel mixture
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C
To monitor the oxygen content in the exhaust
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D
To heat the engine block before starting
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QUESTION 4 / 25
What is the primary difference in ignition methods between petrol and diesel engines?
Choose one answer below.
A
Petrol engines use compression ignition, while diesel engines use spark ignition
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B
Petrol engines require glow plugs, while diesel engines require spark plugs
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C
Petrol engines use spark ignition, while diesel engines use compression ignition
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D
Petrol engines use battery ignition, while diesel engines use magneto ignition
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QUESTION 5 / 25
Which engine component is responsible for controlling the opening and closing of the intake and exhaust valves?
Choose one answer below.
A
The crankshaft
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B
The connecting rod
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C
The piston pin
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D
The camshaft
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QUESTION 6 / 25
What is the main purpose of the cylinder block in an engine?
Choose one answer below.
A
To house the transmission gears
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B
To support the engine valves and fuel injectors
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C
To provide the cylinders for pistons and structural support for the engine
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D
To contain the radiator coolant for cooling
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QUESTION 7 / 25
What is defined as the ratio of the maximum cylinder volume (piston at BDC) to the minimum cylinder volume (piston at TDC)?
Choose one answer below.
A
Displacement ratio
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B
Compression ratio
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C
Volumetric efficiency
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D
Thermal efficiency
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QUESTION 8 / 25
In a standard four-stroke engine, what is the speed ratio of the crankshaft to the camshaft?
Choose one answer below.
A
1:1 (they rotate at the same speed)
✓
B
1:2 (camshaft rotates at twice the speed of the crankshaft)
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C
2:1 (crankshaft rotates at twice the speed of the camshaft)
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D
4:1 (crankshaft rotates at four times the speed of the camshaft)
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QUESTION 9 / 25
What is the primary function of the engine flywheel?
Choose one answer below.
A
To cool down the clutch plate
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B
To store rotational energy and smooth out power fluctuations
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C
To drive the alternator and water pump belts
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D
To lubricate the rear main seal of the crankshaft
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QUESTION 10 / 25
What is the primary function of the thermostat in a liquid-cooled internal combustion engine?
Choose one answer below.
A
To increase the engine's maximum power output
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B
To regulate coolant flow between the engine and radiator to maintain optimal operating temperature
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C
To measure the coolant temperature for the dashboard gauge
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D
To pressurize the cooling system and prevent boiling
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QUESTION 11 / 25
Which piston crown shape is most commonly used in direct-injection diesel engines to aid in air-fuel mixing?
Choose one answer below.
A
Flat top
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B
Dome top
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C
Piston cavity or bowl-in-piston
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D
Trunk type
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QUESTION 12 / 25
What is the purpose of the pressure cap on the radiator of a liquid-cooled engine?
Choose one answer below.
A
To increase the boiling point of the coolant by pressurizing the closed cooling system
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B
To pump coolant through the engine block
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C
To filter debris out of the coolant before it enters the engine
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D
To measure the engine oil level
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QUESTION 13 / 25
What does 'engine blow-by' refer to in automotive terminology?
Choose one answer below.
A
Exhaust gases escaping through a leaking manifold gasket
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B
Combustion gases leaking past the piston rings into the crankcase
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C
Coolant leaking into the oil passages through a blown head gasket
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D
Fuel vapors venting from the carbon canister to the atmosphere
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QUESTION 14 / 25
What is the most common firing order for a standard inline four-cylinder automotive engine?
Choose one answer below.
A
1-2-3-4
✓
B
1-4-3-2
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C
1-3-4-2
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D
1-3-2-4
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QUESTION 15 / 25
What is the standard recommended mixture ratio of ethylene glycol antifreeze to distilled water for most automotive engine cooling systems?
Choose one answer below.
A
100% antifreeze for maximum cooling
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B
90% antifreeze and 10% water
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C
50% antifreeze and 50% distilled water
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D
100% plain water for best cooling
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QUESTION 16 / 25
What is the primary function of the Positive Crankcase Ventilation (PCV) valve?
Choose one answer below.
A
To inject fresh air into the exhaust manifold to burn residual hydrocarbons
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B
To route harmful blow-by gases from the crankcase back into the intake manifold
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C
To prevent engine oil from entering the combustion chamber
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D
To regulate the pressure inside the fuel tank
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QUESTION 17 / 25
What is the primary function of a fuel injector in an Electronic Fuel Injection (EFI) system?
Choose one answer below.
A
To filter impurities out of the petrol before it enters the cylinder
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B
To spray a precisely metered amount of pressurized fuel into the intake manifold or directly into the cylinder
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C
To ignite the air-fuel mixture with an electric spark
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D
To store reserve fuel for the engine
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QUESTION 18 / 25
What is the function of the fuel pressure regulator in an EFI petrol engine?
Choose one answer below.
A
To maintain a constant pressure difference between the fuel rail and the intake manifold so fuel delivery stays accurate
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B
To increase the engine's compression ratio
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C
To cool the engine oil
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D
To mix air and fuel in the carburetor
✓
QUESTION 19 / 25
What is the primary advantage of Electronic Fuel Injection (EFI) over a carburetor for mixing air and fuel?
Choose one answer below.
A
EFI is mechanically simpler and has fewer electronic components
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B
EFI uses sensors and an ECU to continuously adjust the air-fuel ratio for better efficiency, emissions control, and cold starting
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C
EFI does not require any fuel pump to deliver fuel to the engine
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D
EFI eliminates the need for spark plugs in petrol engines
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QUESTION 20 / 25
What is the primary purpose of the air filter in an internal combustion engine?
Choose one answer below.
A
To increase the temperature of the intake air for better combustion
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B
To remove dust, dirt, pollen, and debris from the air before it enters the engine cylinders
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C
To measure the amount of air entering the engine
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D
To add fuel to the incoming air
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QUESTION 21 / 25
What is the primary purpose of using a torque wrench during engine assembly?
Choose one answer below.
A
To tighten bolts as quickly as possible to save time
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B
To measure the length of a bolt before installation
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C
To apply a precise, specified twisting force to critical fasteners
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D
To lock nuts permanently in place without washers
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QUESTION 22 / 25
Which measuring tool is best suited to check the clearance between a rocker arm and a valve stem?
Choose one answer below.
A
A vernier caliper
✓
B
A feeler gauge
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C
A micrometer
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D
A dial indicator
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QUESTION 23 / 25
What is the primary function of a diesel fuel injection pump?
Choose one answer below.
A
To lubricate the diesel engine cylinders
✓
B
To deliver precisely metered, highly pressurized fuel to each injector at the correct time for each cylinder's combustion stroke
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C
To cool the diesel fuel in the tank
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D
To filter water out of the diesel fuel
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QUESTION 24 / 25
Which of the following measurements is a standard metric outside micrometer primarily designed to take?
Choose one answer below.
A
The internal diameter of a cylinder bore
✓
B
The depth of a blind bolt hole
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C
The outer diameter of a crankshaft journal or piston pin
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D
The clearance between a piston ring and its groove
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QUESTION 25 / 25
What is the primary role of the water pump in an engine's liquid cooling system?
Choose one answer below.
A
To spray water onto the hot exhaust pipes to cool them
✓
B
To circulate coolant through the engine block, cylinder head, and radiator
✓
C
To separate water from the oil inside the engine block
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D
To pressurize the radiator cap to prevent boiling
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