NYC Auto Mechanic (Diesel) - DCAS Exam No. 2105
Complete Practice Examination: 150+ Questions with
Rationales EXAM GAURANTEED PASS WITH
QUESTIONS 2026 CARRICULUM BASSED VERRIFIED
TEST INSTANT PDF
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Question 1
A diesel engine relies on which principle for ignition?
A) Spark ignition
B) Compression ignition
C) Electrical ignition
D) Vacuum ignition
Correct Answer: B
Rationale: Diesel engines ignite fuel using the heat generated by high compression of air in the
cylinder, rather than spark plugs. The air is compressed to a ratio of 14:1 to 25:1, raising its
temperature above the autoignition point of diesel fuel.
Question 2
What are the four strokes of a four-stroke diesel engine in correct order?
A) Intake, compression, power, exhaust
B) Intake, power, compression, exhaust
C) Compression, intake, power, exhaust
D) Intake, exhaust, compression, power
,Correct Answer: A
Rationale: In a four-stroke diesel engine, the piston moves down for the intake of air, up for
compression, down during the power stroke after fuel injection ignites, and up for exhaust.
Question 3
During the compression stroke of a diesel engine, what occurs?
A) Air and fuel mixture is compressed and ignited by a spark plug
B) Only air is compressed, raising its temperature above the autoignition point of diesel fuel
C) Exhaust gases are forced out through the open exhaust valve
D) The intake valve opens to allow fresh air into the cylinder
Correct Answer: B
Rationale: Diesel engines compress air alone to high pressures, creating extreme temperatures; diesel
fuel is then injected and ignites spontaneously due to the heat, with no spark plug.
Question 4
The crankshaft converts the reciprocating motion of the pistons into what type of motion?
A) Oscillating motion
B) Rotary motion
C) Linear thrust
D) Hydraulic pressure
Correct Answer: B
Rationale: The crankshaft transforms the up-and-down motion of the pistons into rotational motion
to drive the transmission and accessories.
,Question 5
A camshaft in a diesel engine is responsible for:
A) Driving the oil pump
B) Opening and closing the intake and exhaust valves
C) Delivering fuel to the injectors
D) Converting linear motion to rotary motion
Correct Answer: B
Rationale: The camshaft controls the opening and closing of the intake and exhaust valves, ensuring
proper timing of the engine's breathing cycle.
Question 6
The component that seals the combustion chamber and transfers force to the connecting rod is the:
A) Cylinder head
B) Piston ring
C) Piston
D) Valve
Correct Answer: C
Rationale: The piston seals the combustion chamber via piston rings and transfers the force of
combustion to the connecting rod.
Question 7
Which of the following is a function of the piston rings?
, A) Transferring torque to the crankshaft
B) Sealing the combustion chamber, controlling oil, and transferring heat
C) Opening valves at correct timing
D) Injecting fuel into the cylinder
Correct Answer: B
Rationale: Compression rings seal combustion gases, oil control rings scrape excess oil from cylinder
walls, and rings transfer heat from the piston to the cylinder walls.
Question 8
A warped cylinder head is most likely to cause which problem?
A) Low oil pressure
B) Coolant leaking into the combustion chamber or combustion gas entering the coolant
C) Improper fuel injection timing
D) Starter motor failure
Correct Answer: B
Rationale: Warpage breaks the head gasket seal, allowing coolant and combustion gases to mix,
leading to overheating and white exhaust smoke.
Question 9
What does the term "valve lash" refer to?
A) The clearance between the valve stem and rocker arm when the valve is closed
B) The tension on the timing chain
Complete Practice Examination: 150+ Questions with
Rationales EXAM GAURANTEED PASS WITH
QUESTIONS 2026 CARRICULUM BASSED VERRIFIED
TEST INSTANT PDF
DOWNLOAD
Question 1
A diesel engine relies on which principle for ignition?
A) Spark ignition
B) Compression ignition
C) Electrical ignition
D) Vacuum ignition
Correct Answer: B
Rationale: Diesel engines ignite fuel using the heat generated by high compression of air in the
cylinder, rather than spark plugs. The air is compressed to a ratio of 14:1 to 25:1, raising its
temperature above the autoignition point of diesel fuel.
Question 2
What are the four strokes of a four-stroke diesel engine in correct order?
A) Intake, compression, power, exhaust
B) Intake, power, compression, exhaust
C) Compression, intake, power, exhaust
D) Intake, exhaust, compression, power
,Correct Answer: A
Rationale: In a four-stroke diesel engine, the piston moves down for the intake of air, up for
compression, down during the power stroke after fuel injection ignites, and up for exhaust.
Question 3
During the compression stroke of a diesel engine, what occurs?
A) Air and fuel mixture is compressed and ignited by a spark plug
B) Only air is compressed, raising its temperature above the autoignition point of diesel fuel
C) Exhaust gases are forced out through the open exhaust valve
D) The intake valve opens to allow fresh air into the cylinder
Correct Answer: B
Rationale: Diesel engines compress air alone to high pressures, creating extreme temperatures; diesel
fuel is then injected and ignites spontaneously due to the heat, with no spark plug.
Question 4
The crankshaft converts the reciprocating motion of the pistons into what type of motion?
A) Oscillating motion
B) Rotary motion
C) Linear thrust
D) Hydraulic pressure
Correct Answer: B
Rationale: The crankshaft transforms the up-and-down motion of the pistons into rotational motion
to drive the transmission and accessories.
,Question 5
A camshaft in a diesel engine is responsible for:
A) Driving the oil pump
B) Opening and closing the intake and exhaust valves
C) Delivering fuel to the injectors
D) Converting linear motion to rotary motion
Correct Answer: B
Rationale: The camshaft controls the opening and closing of the intake and exhaust valves, ensuring
proper timing of the engine's breathing cycle.
Question 6
The component that seals the combustion chamber and transfers force to the connecting rod is the:
A) Cylinder head
B) Piston ring
C) Piston
D) Valve
Correct Answer: C
Rationale: The piston seals the combustion chamber via piston rings and transfers the force of
combustion to the connecting rod.
Question 7
Which of the following is a function of the piston rings?
, A) Transferring torque to the crankshaft
B) Sealing the combustion chamber, controlling oil, and transferring heat
C) Opening valves at correct timing
D) Injecting fuel into the cylinder
Correct Answer: B
Rationale: Compression rings seal combustion gases, oil control rings scrape excess oil from cylinder
walls, and rings transfer heat from the piston to the cylinder walls.
Question 8
A warped cylinder head is most likely to cause which problem?
A) Low oil pressure
B) Coolant leaking into the combustion chamber or combustion gas entering the coolant
C) Improper fuel injection timing
D) Starter motor failure
Correct Answer: B
Rationale: Warpage breaks the head gasket seal, allowing coolant and combustion gases to mix,
leading to overheating and white exhaust smoke.
Question 9
What does the term "valve lash" refer to?
A) The clearance between the valve stem and rocker arm when the valve is closed
B) The tension on the timing chain
