Page 1 of 65
NYC AUTO MECHANIC (DIESEL) EXAM PREP -
DCAS EXAM NO. 2105 | FREQUENTLY TESTED
QUESTIONS AND VERIFIED ANSWERS |100%
ACCURATE ANSWERS | ALREADY GRADED A+
NYC Auto Mechanic (Diesel) Exam Prep 2026
DCAS Exam No. 2105
Subject: Diesel Engine Mechanics and Repair
Section 1: Questions 1–50
1. A diesel engine relies on which principle for ignition?
A) Spark ignition
B) Compression ignition
C) Electrical ignition
D) Vacuum ignition
❖ 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
,Page 2 of 65
25:1, raising its temperature above the autoignition point
of diesel fuel.
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
❖ 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.
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
❖ Rationale: Diesel engines compress air alone to high
pressures, creating extreme temperatures; diesel fuel is
,Page 3 of 65
then injected and ignites spontaneously due to the heat,
with no spark plug.
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
❖ Rationale: The crankshaft transforms the up-and-down
motion of the pistons into rotational motion to drive the
transmission and accessories.
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
❖ Rationale: The camshaft controls the opening and closing
of the intake and exhaust valves, ensuring proper timing of
the engine's breathing cycle.
6. The component that seals the combustion chamber and
transfers force to the connecting rod is the:
A) Cylinder head
B) Piston ring
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C) Piston
D) Valve
❖ Rationale: The piston seals the combustion chamber via
piston rings and transfers the force of combustion to the
connecting rod.
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
❖ 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.
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
NYC AUTO MECHANIC (DIESEL) EXAM PREP -
DCAS EXAM NO. 2105 | FREQUENTLY TESTED
QUESTIONS AND VERIFIED ANSWERS |100%
ACCURATE ANSWERS | ALREADY GRADED A+
NYC Auto Mechanic (Diesel) Exam Prep 2026
DCAS Exam No. 2105
Subject: Diesel Engine Mechanics and Repair
Section 1: Questions 1–50
1. A diesel engine relies on which principle for ignition?
A) Spark ignition
B) Compression ignition
C) Electrical ignition
D) Vacuum ignition
❖ 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
,Page 2 of 65
25:1, raising its temperature above the autoignition point
of diesel fuel.
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
❖ 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.
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
❖ Rationale: Diesel engines compress air alone to high
pressures, creating extreme temperatures; diesel fuel is
,Page 3 of 65
then injected and ignites spontaneously due to the heat,
with no spark plug.
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
❖ Rationale: The crankshaft transforms the up-and-down
motion of the pistons into rotational motion to drive the
transmission and accessories.
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
❖ Rationale: The camshaft controls the opening and closing
of the intake and exhaust valves, ensuring proper timing of
the engine's breathing cycle.
6. The component that seals the combustion chamber and
transfers force to the connecting rod is the:
A) Cylinder head
B) Piston ring
, Page 4 of 65
C) Piston
D) Valve
❖ Rationale: The piston seals the combustion chamber via
piston rings and transfers the force of combustion to the
connecting rod.
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
❖ 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.
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
