Engine Fundamentals and Four-Stroke Cycle Lesson Test

Answer: B

Correct answer: Power. Each stroke prepares for the next: intake fills the cylinder, compression squeezes the charge so it burns quickly and forcefully, and the power stroke harvests that burn as the gas pushes the piston down. Only after the energy is used can exhaust clear the cylinder. A common slip is picking exhaust because burning sounds like an ending, but the charge must first do its work. A handy memory hook is suck, squeeze, bang, blow.

• A: Exhaust follows the power stroke; the charge must be burned before it can be pushed out.
• B (correct): After the charge is squeezed, it is ignited and the expanding gas drives the piston down on the power stroke.
• C: The same stroke does not repeat; compression is followed by a different stroke.
• D: Intake begins the cycle and comes after exhaust, not after compression.

Answer: D

Correct answer: Two. Each stroke moves the crank 180 degrees. Four strokes take

which is two revolutions.

• A: One crank turn covers only two strokes; that is the cycle length of a two-stroke engine.
• B: This counts one full turn per stroke, but each stroke is only half a turn.
• C: Half a turn is the length of a single stroke, not of the whole cycle.
• D (correct): Each of the four strokes takes half a turn, so the cycle takes two full turns of the crank.

Answer: D

Correct answer: Connecting rod. The piston only moves straight up and down, but the crankshaft must spin. The connecting rod bridges the two: its small end pivots on the piston's wrist pin, and its big end wraps around a crankpin set off-center from the crankshaft axis, so each push on the rod swings the crankpin in a circle, much like a foot on a bicycle pedal. The camshaft is tempting because it also rotates, but it only opens and closes the valves.

• A: The radiator transfers heat from coolant rather than transmitting piston force.
• B: The camshaft operates engine valves rather than transmitting the main piston force to the crankshaft.
• C: The exhaust manifold collects spent gases, not piston motion.
• D (correct): The connecting rod couples the piston to an offset crankshaft journal.

Answer: A

Correct answer: Only the intake valve is open. On the intake stroke the piston moves down from TDC to BDC. The intake valve is open to let in fresh charge, and the exhaust valve is closed.

• A (correct): The descending piston lowers cylinder pressure, and the fresh charge flows in through the open intake valve while the exhaust valve stays shut.
• B: Both valves are closed during compression and power, but intake needs an open path for the fresh charge.
• C: If both stayed wide open, the charge could flow straight out the exhaust; the basic diagram opens only one.
• D: That pattern belongs to the exhaust stroke, when burned gas is pushed out.

Answer: B

Correct answer: The inside diameter of a cylinder. Bore is the inside diameter of the cylinder. It sets the area of the piston top that the expanding gas pushes on.

• A: That offset is the crank throw, which sets the stroke, not the bore.
• B (correct): Bore is measured straight across the round cylinder that the piston fits into.
• C: That distance is the stroke length, from TDC to BDC.
• D: That space is the clearance volume used in the compression ratio.

Answer: D

Correct answer: Inside the combustion chamber above the piston. Combustion has to happen where the expanding gas can push on something that moves. The combustion chamber is the sealed space formed by the cylinder head, the cylinder walls and the piston crown while the valves are closed; when the mixture burns there, the pressure rise drives the piston down. That is why these are called internal combustion engines. Parts that only hold or move fluids, such as the oil pan or radiator, never contain a burning charge.

• A: A radiator cools fluid and is not the cylinder combustion space.
• B: The oil pan stores and collects engine oil under the crankshaft; no fuel burns there in normal operation.
• C: The differential splits driveline torque between the wheels; it holds gear oil, not a burning charge.
• D (correct): The chamber lies inside the cylinder/head enclosure above the piston.

Answer: C

Correct answer: The piston’s highest position nearest the cylinder head. TDC is one of the two points where the piston reverses direction; the other, at the bottom of its travel, is bottom dead center (BDC). At TDC the space above the piston is smallest, so the charge is most tightly squeezed there and the spark is timed near it. A common mistake is tying TDC to a valve state, but the piston reaches TDC twice per four-stroke cycle, once ending compression and once ending exhaust, with different valves open each time.

• A: One revolution is a crankshaft rotation, not a piston position.
• B: The lowest extreme is bottom dead center.
• C (correct): TDC is a geometric extreme nearest the head.
• D: The valve state at TDC depends on cycle phase and timing.

Answer: D

Correct answer: Knock, also called detonation. In a healthy engine, a flame front spreads smoothly across the chamber and builds pressure steadily. When pockets of mixture blow up suddenly, the result is knock (detonation or pinging), a fault that can damage pistons.

• A: Compression ignition is the normal way a diesel lights its fuel, not an abnormal sudden burn of mixture pockets.
• B: Valve overlap is the brief, intended period when both valves are partly open near TDC; it is not a combustion fault.
• C: A smoothly spreading flame front is the normal, healthy way the charge burns.
• D (correct): Sudden burning of mixture pockets is knock or pinging, which causes a metallic sound and harmful pressure spikes.

Answer: A

Correct answer: To meter and deliver fuel. An injector is an electrically controlled valve: the engine computer opens it for a precise number of milliseconds while pressurized fuel waits behind it, so the pulse width sets how much fuel enters. That lets the system hold the air-fuel ratio close to target as load and speed change. Students sometimes confuse it with the spark plug because both sit near the combustion chamber, but the injector only supplies fuel; ignition comes from a separate spark.

• A (correct): An injector supplies a measured amount of fuel into the intake passage or the cylinder.
• B: Valves are opened by the camshaft through the valve train.
• C: Producing the ignition spark is the job of the spark plug, not the injector.
• D: Burned gas is pushed out by the rising piston on the exhaust stroke.

Answer: C

Correct answer: Spark plug. Gasoline resists self-ignition, so a spark-ignition engine compresses the air-fuel charge only moderately and then lights it on cue. The ignition coil sends a high-voltage pulse to the plug, and the arc that jumps its electrode gap starts a flame front through the compressed mixture, timed near the end of the compression stroke. Diesels skip the plug and rely on hot compressed air instead. Exhaust valves and piston rings sit in the same chamber but only vent or seal it.

• A: The fuel filter removes contaminants from fuel.
• B: The exhaust valve allows burned gas to leave.
• C (correct): An electrical spark initiates combustion in the spark-ignition design.
• D: Rings help seal the piston and control oil.

Answer: D

Correct answer: 2100 rpm. Each valve opens once per cycle, and a cycle takes two crank turns, so the cam runs at half crank speed:

• A: This divides by 4, perhaps counting the four strokes, but the ratio is 2:1.
• B: This doubles the crank speed; the cam turns slower than the crank, not faster.
• C: This sets cam speed equal to crank speed, ignoring the 2:1 ratio between the shafts.
• D (correct): The camshaft turns once for every two crankshaft turns, so its speed is half of 4200 rpm.

Answer: B

Correct answer: Exhaust. Each stroke can be identified from two clues: which way the piston moves and which valves are open. The piston rises on both compression and exhaust, so direction alone is not enough. During compression both valves are closed to trap the charge, while on the exhaust stroke the exhaust valve opens and the rising piston sweeps burned gas out. The two downward strokes are intake, with the intake valve open, and power, with both valves closed.

• A: Expansion delivers work and piston moves down.
• B (correct): An upward piston pushes spent gas through the exhaust valve.
• C: During compression, the rising piston normally has both valves closed so the charge is trapped.
• D: Intake primarily admits a fresh charge with piston moving down.

Answer: D

Correct answer: 11:1. Compression ratio is the BDC volume divided by the TDC volume.

The ratio is 11:1.

• A: This subtracts the clearance volume from the swept volume before dividing, which is not how the ratio is built.
• B: This adds the clearance volume twice, using 600 cc on top instead of the true 550 cc BDC volume.
• C: This divides the swept volume alone by the clearance volume and leaves the clearance out of the top.
• D (correct): The volume at BDC is 500 + 50 = 550 cc, and 550 divided by the 50 cc clearance volume is 11.

Answer: C

Correct answer: 3.0 liters. Total displacement is the volume per cylinder times the number of cylinders:

cc. Since 1000 cc equal 1 liter, that is 3.0 liters.

• A: This would require ten cylinders of 500 cc, not six.
• B: That is the volume of just one cylinder converted to liters.
• C (correct): Six cylinders times 500 cc is 3000 cc, and 3000 cc divided by 1000 is 3.0 liters.
• D: This divides 3000 cc by 100 instead of by 1000 when converting to liters.

Answer: A

Correct answer: 5000. Each cylinder fires once every two revolutions, so one cylinder makes

power strokes per minute. Four cylinders give

• A (correct): Each cylinder fires 2500 / 2 = 1250 times per minute, and four cylinders give 5000.
• B: This counts one power stroke per cylinder every revolution, forgetting that each cylinder fires only every two turns.
• C: That is the number for a single cylinder; it still has to be multiplied by four.
• D: This divides by four cylinders instead of multiplying by them.

Answer: D

Correct answer: Gasoline uses a spark; diesel injects fuel into hot compressed air. Diesel engines use a much higher compression ratio, so squeezing the air heats it above the fuel's self-ignition temperature, and fuel injected near the end of compression lights on its own. Gasoline engines keep compression lower to avoid uncontrolled self-ignition, which causes knock, and instead rely on a timed spark. Remember the pair as spark ignition versus compression ignition. Glow plugs in some diesels only assist cold starts and are not a timed ignition spark.

• A: A typical diesel does not require a gasoline-type ignition spark; heat from compression lights its fuel.
• B: Exhaust timing is not the standard diesel ignition cause.
• C: Gasoline engines necessarily supply fuel, whether by port injection, direct injection or a carburetor.
• D (correct): The usual distinction is spark ignition versus compression ignition.

Answer: C

Correct answer: Valve overlap. Because gas takes time to start and stop flowing, real engines open the intake valve early and close the exhaust valve late. The short span when both are partly open near TDC is valve overlap; it does not change the four-stroke order.

• A: Compression ignition is how a diesel lights its fuel with hot compressed air, not a valve timing event.
• B: During the power stroke both valves are treated as closed while expanding gas pushes the piston down.
• C (correct): For a few crank degrees both valves are partly open at once, and outgoing exhaust helps draw in fresh charge.
• D: BDC is the lowest piston position; the event described happens near TDC.

Answer: A

Correct answer: Flywheel. Each cylinder pushes only during its power stroke, so the crankshaft receives force in pulses rather than continuously. The flywheel is a heavy disc bolted to the crankshaft; its rotational inertia absorbs energy during each power pulse and gives it back during the intake, compression and exhaust strokes, keeping speed even. This matters most in engines with few cylinders. A spark plug is tempting because it starts the power pulse, but it stores no energy to carry rotation between pulses.

• A (correct): The flywheel stores rotational kinetic energy and resists abrupt speed changes.
• B: The exhaust manifold receives burned gases after they leave a cylinder and does not store rotational energy.
• C: A spark plug initiates combustion but does not act as the main inertia store.
• D: The intake valve controls air or charge admission but cannot smooth rotational speed between power events.

Answer: D

Correct answer: 105 N·m. Torque equals force times the lever arm:

• A: This misplaces the decimal; 300 times 0.35 is 105, not 10.5.
• B: This divides the force by the lever arm instead of multiplying them.
• C: This adds the force and the distance, which have different units and cannot be added.
• D (correct): Torque is force times lever arm: 300 N × 0.35 m = 105 N·m.

Answer: A

Correct answer: 90 mm. As the crank turns half a revolution, the rod journal moves from one side of the shaft center to the other. The piston therefore travels twice the throw:

• A (correct): Stroke equals twice the crank throw, and 2 times 45 mm is 90 mm.
• B: This multiplies the throw by four, as if each of the four strokes added to the distance.
• C: This uses the throw itself, but the piston travels the throw distance on each side of the shaft center.
• D: This halves the throw; the stroke is twice the throw, not half of it.

Answer: A

Correct answer: 3000. A two-stroke engine finishes its whole cycle in one crankshaft revolution and fires once per turn. At 3000 rpm, one cylinder gives 3000 power strokes per minute.

• A (correct): A two-stroke completes its cycle in one crank revolution, so it fires once every turn.
• B: This counts two power strokes per revolution, but the two strokes are one upstroke and one downstroke, only one of which delivers power.
• C: This applies the four-stroke rule of one firing every two turns, which does not fit a two-stroke engine.
• D: This divides by four, mixing up the number of strokes with the firing rate.

Answer: B

Correct answer: Exhaust gas flowing through a turbine. A turbocharger uses energy in the exhaust gas to spin a turbine. The turbine turns a compressor that packs more air into the intake, while the engine still runs through the same four strokes.

• A: Normal combustion happens in the cylinders, not inside the turbocharger.
• B (correct): The exhaust stream spins a turbine, which is coupled to the compressor on the intake side.
• C: The battery runs the starter and electrical circuits; it is not what spins a conventional turbocharger.
• D: A belt or gear drive from the engine describes a supercharger, not a turbocharger.

Answer: B

Correct answer: Valve events fall out of step with piston position. The crankshaft sets piston position and the camshaft sets valve position, and the timing belt keeps them synchronized at a 2:1 ratio. If the belt slips a tooth, the valves open and close at the wrong piston positions, so the engine may run poorly or not at all.

• A: The core purpose of the timing drive is synchronization, not moving coolant.
• B (correct): The belt locks the camshaft to the crankshaft, so a slipped tooth shifts when the valves open relative to the pistons.
• C: A slipped tooth changes the phase between the shafts, not the 2:1 gear ratio set by the tooth counts.
• D: The timing drive does not carry fuel; fuel delivery is a separate system.

Answer: C

Correct answer: Cylinder head. The block holds the cylinders and crankshaft. The cylinder head sits on top, closes each cylinder and holds the parts that let gas in and out: the ports and valves, and often the camshafts.

• A: The manifold collects gas after it leaves the cylinder head ports; it is downstream of the valves.
• B: The oil pan is at the bottom of the engine and holds the oil supply.
• C (correct): The head closes off the cylinders, forms the chamber roof and carries the ports, valves and, in a gasoline engine, the spark plugs.
• D: The crankshaft turns in main bearings in the block and gives rotating output; it does not hold the valves.

Answer: B

Correct answer: Air only. A diesel takes in only air, compresses it until it is very hot, and then injects fuel, which ignites in the hot air.

• A: A premixed charge is typical of some gasoline engines, not of a diesel.
• B (correct): A diesel draws in air alone and injects fuel later, near the end of compression.
• C: Burned gas is pushed out on the exhaust stroke before intake begins.
• D: The piston draws in air on intake; the fuel comes from the injector later in the cycle.

Answer: C

Correct answer: Intake. Check the piston direction, then the valves. Down means intake or power; an open intake valve rules out power, so the stroke is intake.

• A: During compression the piston moves up with both valves closed.
• B: The power stroke also moves the piston down, but both valves are closed during it.
• C (correct): A falling piston with only the intake valve open is drawing fresh charge into the cylinder.
• D: During exhaust the piston moves up and only the exhaust valve is open.

Answer: A

Correct answer: To spin the crankshaft until combustion keeps the engine running. An engine cannot fire until its pistons have taken in and compressed a charge. The battery-powered starter cranks the engine through those first cycles, then combustion keeps it running on its own.

• A (correct): The starter gives the crank its first turns so the cylinders can draw in and compress charge until firing takes over.
• B: Once the engine starts, combustion turns the crankshaft; the starter is not meant to supply continuous drive.
• C: The spark comes from the spark plug, not from the starter motor.
• D: The fuel is the energy source for the running engine; the starter and battery are only used to get it going.

Answer: B

Correct answer: Cylinder bore. The bore is the precisely machined round hole in the block in which the piston slides; its diameter, together with the stroke, sets the engine's displacement. Piston rings press against the bore wall to seal compression and scrape oil, so the bore both guides piston travel and forms one wall of the combustion chamber. Wear in the bore lets gas leak past the rings, called blow-by, and reduces compression. The other parts listed work outside the cylinder.

• A: An exhaust tailpipe conducts spent gases outside the engine and cannot guide a piston inside the cylinder.
• B (correct): The cylinder wall or bore guides the reciprocating piston.
• C: A stator belongs to an electrical machine rather than the piston guide.
• D: A clutch transmits or disconnects drive torque.

Answer: A

Correct answer: Exhaust manifold. The exhaust path runs from the exhaust valve to the exhaust manifold, then through the catalytic converter and muffler, and out the tailpipe.

• A (correct): The manifold attaches to the cylinder head and collects gas from all the cylinders before it moves down the system.
• B: The converter comes after the manifold has gathered the gas from the cylinders.
• C: The tailpipe is the last part of the system, where gas finally leaves the vehicle.
• D: The muffler is farther downstream, after the catalytic converter.

Answer: A

Correct answer: It keeps coolant in the engine until it warms up, then opens. The water pump moves coolant and the radiator sheds its heat. The thermostat acts as a valve that holds coolant in the engine until it is warm, then opens so it can circulate.

• A (correct): The thermostat stays closed on a cold engine and opens to let coolant flow to the radiator once operating temperature is reached.
• B: Oil is moved by the oil pump; the thermostat controls coolant flow.
• C: Moving coolant is the job of the water pump.
• D: That is what the radiator does, with air flowing through its fins.

Answer: C

Correct answer: 636 cc. Use the bore as the diameter in the quarter-pi formula.

• A: This uses pi instead of pi over 4 with the bore, which treats the diameter as if it were the radius.
• B: This multiplies by the bore without squaring it.
• C (correct): With the full bore squared, 0.7854 times 81 times 10 is about 636 cc.
• D: This uses 4.5 cm, the radius, in the quarter-pi formula that already expects the full bore, so the result is four times too small.

Answer: B

Correct answer: 440 cc. The ratio compares the BDC volume to the clearance volume, so the BDC volume is

cc. That volume equals swept plus clearance, so the swept volume is

cc.

• A: This is the total volume at BDC, 9 times 55; it still includes the 55 cc clearance volume.
• B (correct): The BDC volume is 9 times 55, or 495 cc; removing the 55 cc clearance leaves 440 cc swept.
• C: This subtracts the clearance volume twice from the BDC volume.
• D: This adds the clearance to 495 cc instead of subtracting it.

Answer: C

Correct answer: 200. Per cylinder:

power strokes per minute. For eight cylinders:

per minute. Per second:

• A: This forgets that each cylinder fires only once every two revolutions, doubling the answer.
• B: That is the firing rate of a single cylinder per second; it was not multiplied by eight.
• C (correct): Each cylinder fires 1500 times a minute; eight cylinders give 12,000 per minute, which is 200 per second.
• D: This is the count per minute; it was not divided by 60 to get a per-second rate.

Answer: B

Correct answer: It doubles. Swept volume is proportional to $B^2\times S$. Doubling the bore gives a factor of

and halving the stroke gives a factor of 1/2, so the volume changes by

• A: This counts the effect of the doubled bore but ignores the halved stroke.
• B (correct): Doubling the bore multiplies the volume by 4, and halving the stroke divides it by 2, for a net factor of 2.
• C: This assumes doubling one size and halving the other cancel out, but the bore is squared while the stroke is not.
• D: This multiplies the factors instead of letting the shorter stroke reduce the volume.

Answer: A

Correct answer: Power, piston moving down. Each stroke takes 180 degrees: intake 0 to 180, compression 180 to 360, power 360 to 540, exhaust 540 to 720. An angle of 500 degrees lies in the power stroke, when the piston is pushed down.

• A (correct): Power runs from 360 to 540 degrees, and on the power stroke the piston travels down from TDC toward BDC.
• B: Exhaust runs from 540 to 720 degrees, so 500 degrees has not reached it yet.
• C: Intake covers 0 to 180 degrees; 500 degrees is in the second crank revolution of the cycle.
• D: Compression runs from 180 to 360 degrees; by 500 degrees that stroke is over.

Answer: C

Correct answer: 2.0 liters. One cylinder:

Four cylinders: about

cc. Dividing by 1000 gives about 2.0 liters.

• A: This multiplies by the bore without squaring it.
• B: This is the swept volume of only one cylinder, about 503 cc.
• C (correct): One cylinder sweeps about 503 cc; four cylinders give about 2011 cc, or about 2.0 liters.
• D: This uses pi instead of pi over 4 with the bore, which treats the diameter as a radius.

Answer: C

Correct answer: Worn piston rings that leak gas. Compression ratio is fixed by cylinder volumes at BDC and TDC. Compression pressure also depends on sealing, so leaking rings lower the gauge reading without altering any volume, while the other changes alter the geometry and therefore the ratio.

• A: A smaller clearance volume raises the compression ratio, a geometric change.
• B: Changing the clearance volume changes the geometry, so the compression ratio itself would change.
• C (correct): Leaking rings let trapped gas escape, lowering gauge pressure, but they do not change the cylinder's geometry.
• D: A longer throw lengthens the stroke and increases swept volume, which changes the compression ratio.

Answer: D

Correct answer: 42 teeth; 1600 rpm. The camshaft must turn once for every two crankshaft turns, so its gear has twice the teeth:

Its speed is half of crank speed:

• A: The tooth count is right, but a larger driven gear turns slower, not faster.
• B: Equal gears would turn the cam at crank speed, opening each valve twice per cycle.
• C: A 4:1 gear set would turn the cam at quarter speed, too slow to open each valve once per cycle.
• D (correct): The cam gear needs twice as many teeth so the cam turns at half crank speed, and half of 3200 rpm is 1600 rpm.

Answer: D

Correct answer: 3.1 L. Convert to centimeters: bore 9 cm, stroke 8 cm. One cylinder:

Multiply by 6 cylinders: about 3,054 cc, which is about 3.1 L.

• A: This uses the 4.5 cm radius in place of the bore, which makes the result one quarter of the true value.
• B: This leaves out the divide-by-4 in the quarter-pi formula, giving four times the true value.
• C: This is the swept volume of only one cylinder, before multiplying by six.
• D (correct): Each cylinder is about 509 cc; six cylinders give about 3,054 cc, or about 3.1 L.

Answer: B

Correct answer: About 84 kW.

The engine produces about 84 kW.

• A: This halves the rpm as if using camshaft speed; the formula uses crankshaft rpm directly.
• B (correct): Multiplying 200 by 4000 gives 800,000, and dividing by 9549 gives about 83.8 kW.
• C: This is a decimal-place slip; 800,000 divided by 9549 is about 84, not 8.4.
• D: This is a decimal-place slip in the other direction; the quotient is about 84.

Answer: A

Correct answer: Chemical energy, heat, gas pressure, piston motion, rotation. Fuel holds chemical energy. Burning it releases heat, the heated gas expands and builds pressure on the piston, the piston moves in a straight line, and the connecting rod and crankshaft change that into rotary motion.

• A (correct): Burning releases the fuel's stored chemical energy as heat, the hot gas builds pressure, the pressure drives the piston straight down, and the crank turns that into rotation.
• B: This scrambles the chain; the chemical energy in the fuel comes first, and rotation is the final product, not a middle step.
• C: Rotation cannot come before the piston is pushed; the gas must be heated and pressurized first.
• D: The spark only starts the burn; the energy that drives the shaft comes from the fuel, and pressure must act before rotation occurs.

Answer: C

Correct answer: Camshaft. The camshaft carries one lobe per valve. As the lobe rotates, its raised side pushes the valve open, directly or through lifters, pushrods and rocker arms.

• A: The crankshaft drives the camshaft through the timing drive, but its throws work the connecting rods, not the valves.
• B: The flywheel stores rotational energy to smooth crank speed; it has no lobes and does not touch the valves.
• C (correct): Each lobe on the camshaft pushes a follower to open one valve, and the valve spring closes it after the high point passes.
• D: The connecting rod links the piston to the crankshaft and plays no part in opening valves.

Answer: A

Correct answer: Compression, piston moving up. Each stroke takes 180 degrees: intake 0 to 180, compression 180 to 360, power 360 to 540, exhaust 540 to 720. Since 270 degrees lies between 180 and 360, the cylinder is on compression, and the piston is rising from BDC toward TDC.

• A (correct): 270 degrees falls between 180 and 360 degrees, the compression stroke, when the piston travels from BDC up to TDC.
• B: Intake covers only 0 to 180 degrees; by 270 degrees the piston has already passed BDC and turned upward.
• C: Power runs from 360 to 540 degrees; 270 degrees is a full stroke earlier.
• D: The piston is rising, but exhaust spans 540 to 720 degrees, not 180 to 360 degrees.

Answer: A

Correct answer: 9:1. Compression ratio compares total volume at BDC with clearance volume at TDC. Here the BDC volume of 540 cc already includes the clearance, so the ratio is simply the quotient below, written 9:1.

• A (correct): The ratio is the volume at BDC divided by the volume at TDC: 540 divided by 60 is 9.
• B: This divides the swept volume alone (540 minus 60, or 480 cc) by 60; the top of the ratio must be the full BDC volume.
• C: This adds the 60 cc clearance to 540 cc a second time; 540 cc already includes the clearance space.
• D: The ratio is written with the larger BDC volume first; 1:9 turns the comparison upside down.

Answer: B

Correct answer: 2700 rpm. The camshaft turns at half crankshaft speed, so working backward you multiply the cam speed by 2.

• A: This halves the cam speed; dividing by 2 goes from crank to cam, not from cam to crank.
• B (correct): The crank turns twice for each cam turn, so the crank speed is 1350 times 2.
• C: This assumes the shafts turn at the same speed, ignoring the 2:1 timing ratio.
• D: This doubles the speed twice; one doubling is enough to go from cam speed to crank speed.

Answer: C

Correct answer: Compression. BDC alone could mean the end of intake or the end of power, so check the other clues. The charge is fresh and unburned, both valves are closed and the piston is starting upward, so intake has just finished and compression is beginning.

• A: Exhaust also starts at BDC with the piston rising, but the cylinder would hold burned gas and the exhaust valve would be opening.
• B: The power (expansion) stroke begins near TDC after ignition and drives the piston down, not up from BDC.
• C (correct): A full cylinder of fresh charge, both valves shut and the piston heading up from BDC is the start of compression.
• D: The intake (induction) stroke starts at TDC with the piston moving down; this one has just ended, since the cylinder is already full.

Answer: C

Correct answer: Squeezing the air harder makes it hot enough to ignite the injected fuel. A diesel uses compression ignition. It compresses air alone, commonly 15:1 to over 20:1, which makes the air very hot, so fuel sprayed in near TDC lights on its own without a spark.

• A: A diesel takes in air only on the intake stroke; its fuel is injected near the end of compression.
• B: Diesels do not use spark plugs to ignite the fuel, so there is no spark to strengthen.
• C (correct): A diesel has no spark plug, so strong compression must raise the air temperature high enough to light the fuel when it is sprayed in.
• D: Compressing air heats it rather than cooling it, and that heat is exactly what a diesel relies on.

Answer: A

Correct answer: Rotational energy stored in the flywheel and crankshaft by the last power stroke. Only the power stroke pushes on the crankshaft. That push stores rotational kinetic energy in the flywheel and crankshaft, and they release part of it during exhaust, intake and compression, which keeps the piston moving between power pulses.

• A (correct): The power stroke speeds up the heavy rotating parts, and they give back some of that stored energy to carry the piston through the non-power strokes.
• B: The starter only spins the engine until it fires on its own; after that it disengages.
• C: The camshaft only opens the valves; it does not drive the piston.
• D: Exhaust gas leaves through the exhaust valve above the piston and never pushes the piston upward.

Answer: D

Correct answer: The distance the piston travels from TDC to BDC. Stroke length is a distance along the cylinder: how far the piston moves between TDC and BDC. It equals twice the crank throw.

• A: That is the bore, the other main cylinder measurement.
• B: That space is the clearance volume, which is used in the compression ratio, not a length of travel.
• C: A four-stroke cycle has four piston movements, but stroke length is a distance, not a count.
• D (correct): Stroke length is the straight-line travel of the piston from one dead center to the other.

Answer: C

Correct answer: About 4.0 L. Convert to centimeters (9.6 cm bore, 9.2 cm stroke), find one cylinder's volume, then multiply by 6.

• A: This is the volume of one cylinder only; it still has to be multiplied by six cylinders.
• B: This uses pi times the bore squared, treating the diameter as if it were the radius, which makes the answer four times too large.
• C (correct): Each cylinder sweeps about 666 cc, and six cylinders give about 3996 cc, or 4.0 L.
• D: This forgets to square the bore, multiplying 9.6 cm by 9.2 cm once instead of using 9.6 squared.

Answer: D

Correct answer: The oil pan. An oil pump draws oil from the oil pan, pushes it through a filter and drilled passages to the bearings and other moving parts, and the oil then drains back to the pan to be used again.

• A: The radiator holds coolant and sheds heat to the air; it is part of the cooling system, not the oil system.
• B: The fuel tank supplies fuel for combustion, not lubricating oil.
• C: The combustion chamber is where the charge burns; oil is kept out of it as much as possible.
• D (correct): The pump pulls oil from the pan at the bottom of the engine, sends it through the filter and passages, and the oil drains back to the pan.

Answer: B

Correct answer: 5400. First find power strokes per cylinder, then multiply by the number of cylinders.

• A: This counts one power stroke per revolution in each cylinder, forgetting that a four-stroke cylinder fires only every two turns.
• B (correct): Each cylinder fires 3600 divided by 2, or 1800, times a minute; three cylinders give 5400.
• C: This is the count for one cylinder; it still needs to be multiplied by three.
• D: This divides the rpm by the number of cylinders instead of multiplying the per-cylinder rate by it.

Answer: A

Correct answer: 90 degrees. Every cylinder fires once per 720 degree cycle, so evenly spaced firing puts the power strokes 720 divided by the number of cylinders apart. For eight cylinders that is 720 divided by 8, or 90 degrees.

• A (correct): Eight power strokes spread over a 720 degree cycle gives 720 divided by 8, or 90 degrees.
• B: This divides 360 degrees by 8, but a four-stroke cycle takes 720 degrees, not 360.
• C: That is the spacing for a four-cylinder engine, where four firings share 720 degrees.
• D: That is the spacing for a six-cylinder engine, 720 divided by 6.

Answer: D

Correct answer: It increases. Compression ratio is (swept volume plus clearance volume) divided by clearance volume. With swept volume fixed, shrinking the clearance volume makes the denominator fall faster than the numerator, so the ratio rises.

• A: Shrinking the bottom of the ratio, the clearance volume, raises the ratio rather than lowering it.
• B: Compression ratio depends on clearance volume, so changing that volume changes the ratio.
• C: The ratio rises, but by how much depends on how much clearance is removed; there is no automatic doubling.
• D (correct): The swept volume is unchanged, so a smaller clearance volume makes the ratio of total volume to clearance volume larger.

Answer: D

Correct answer: About 78.5 kW. Multiply torque by crankshaft speed, then divide by 9549.

• A: This halves the speed to 2500 rpm, as if the 2:1 cam rule applied; power uses the crankshaft speed directly.
• B: This is a decimal slip, ten times too small; recheck the division of 750,000 by 9549.
• C: This doubles the correct result, as if the torque were 300 N·m.
• D (correct): 150 times 5000 is 750,000, and 750,000 divided by 9549 is about 78.5 kW.

Answer: B

Correct answer: It packs more air mass into each cylinder to burn more fuel. A naturally aspirated engine fills its cylinders with atmospheric pressure alone. A boosted engine forces air in above atmospheric pressure, so each cylinder holds more air, can burn more fuel each cycle and produces more power from the same displacement.

• A: A turbo engine still uses intake, compression, power and exhaust, with one power stroke per cylinder per cycle.
• B (correct): Boost raises intake pressure above atmospheric, filling the same cylinder with denser air that supports burning more fuel.
• C: Swept volume comes from bore and stroke, which a turbo does not change.
• D: No combustion happens in the turbo; exhaust flow spins its turbine, which drives the compressor.

Answer: D

Correct answer: Passes coolant heat to the air flowing through its fins. The water pump circulates coolant through passages in the block and head, where it absorbs heat. The hot coolant then flows through the radiator, and air moving through the fins carries the heat away.

• A: Moving the coolant is the water pump's job.
• B: That is what the thermostat does before it opens; the radiator does not hold coolant back.
• C: The radiator handles coolant, not oil, and it sits outside the engine rather than inside the cylinders.
• D (correct): Coolant picks up heat in the block and head, and the radiator gives that heat off to the air passing through it.

Answer: A

Correct answer: 50 cc. Write the ratio and solve for the clearance volume.

That means

cc. Check: (475 + 50) divided by 50 is 10.5.

• A (correct): The total volume is 10.5 times the clearance, and the swept volume is the other 9.5 parts, so 475 divided by 9.5 gives 50 cc.
• B: This divides the swept volume by 10.5, treating 475 cc as if it were the total volume and leaving clearance out.
• C: This is the total volume at BDC, 475 plus 50 cc; the question asks for the clearance volume alone.
• D: This divides by 8.5, subtracting 2 from the ratio instead of 1.

Answer: B

Correct answer: Intake, compression, power, exhaust. A four-stroke engine completes one power cycle in two crankshaft revolutions. On intake, the piston moves down and draws in air and fuel. On compression, it moves up and squeezes the mixture. On power, the burning mixture forces the piston down. On exhaust, the piston moves up and pushes out burned gases. Each step needs the one before it, so the mixture must be compressed before ignition.

• A: The charge must be compressed before it is burned, so compression comes before power.
• B (correct): This matches the fixed sequence: draw in the charge, squeeze it, burn it, then push it out.
• C: Exhaust clears burned gas, so it can only follow the power stroke.
• D: Burned gas is pushed out after the power stroke, not before it.

Answer: D

Correct answer: It increases by about 30 percent. Because volume is proportional to bore squared times stroke, multiply the scale factors.

The new volume is about 1.30 times the old, an increase of about 30 percent.

• A: This simply subtracts the stroke change from the bore change, ignoring that the bore is squared.
• B: This multiplies 1.2 by 0.9 without squaring the bore factor.
• C: This squares the bore change correctly but forgets that the shorter stroke cuts the volume.
• D (correct): Volume follows bore squared times stroke: 1.2 squared is 1.44, and 1.44 times 0.9 is about 1.30.

Answer: A

Correct answer: The piston briefly stops there before reversing direction. At top dead center and bottom dead center the piston comes to a momentary stop and reverses direction. That instant of zero piston motion is why both points are called dead centers.

• A (correct): At TDC and BDC the piston's motion drops to zero for a moment as it changes from moving one way to the other.
• B: The name refers to the piston's motion, and burning actually starts near TDC at the end of compression.
• C: Valve status at TDC and BDC depends on the stroke; the name comes from the piston stopping, not from the valves.
• D: The crankshaft keeps rotating smoothly; only the piston pauses as it reverses.

Answer: C

Correct answer: Power has ended; exhaust comes next. BDC occurs at the end of intake and at the end of power, so position alone is not enough. Hot burned gas filling the cylinder shows the power stroke has just finished, and the exhaust valve opening confirms that the exhaust stroke is next.

• A: Intake also ends at BDC, but the cylinder would hold fresh charge, and both valves would be closing for compression.
• B: Compression ends at TDC, not BDC, with the piston at the top of the cylinder.
• C (correct): Burned gas at BDC means the power stroke just drove the piston down, and the opening exhaust valve sets up the exhaust stroke.
• D: Exhaust ends at TDC after the burned gas has been pushed out, not at BDC with the cylinder still full.

Answer: C

Correct answer: 25. Each valve opens once per cycle, which takes two crank revolutions, so it opens at camshaft speed: 3000 divided by 2 is 1500 times a minute. Divide by 60 seconds.

• A: This counts one opening per crank revolution and forgets that each valve opens only once every two turns.
• B: This is the number of openings per minute; it still has to be divided by 60 to get openings per second.
• C (correct): The valve opens once per cycle, and there are 3000 divided by 2, or 1500, cycles per minute, which is 25 per second.
• D: This multiplies the per-second rate of one valve by the six cylinders, but the question asks about a single cylinder.

Answer: B

Correct answer: Engine block. The engine block holds the parts that move up, down and around: the cylinders guide the pistons, and main bearings in the block carry the crankshaft. The cylinder head on top holds the parts that let gas in and out.

• A: The head bolts on top and holds the valves and ports; it does not hold the crankshaft.
• B (correct): The block is the main body of the engine; it holds the cylinders and carries the crankshaft in its main bearings.
• C: The oil pan stores oil below the crankshaft but does not support it or form the cylinders.
• D: The manifold collects burned gas leaving the cylinders; it is outside the engine's main structure.

Answer: B

Correct answer: One. Each stroke is half a crank revolution. A two-stroke engine finishes its cycle in two strokes, so it needs one revolution and fires once every turn.

• A: Two revolutions per cycle is the rule for a four-stroke engine.
• B (correct): A two-stroke cycle uses one up stroke and one down stroke, which is one turn of the crankshaft.
• C: This confuses the number of strokes in a four-stroke cycle with crank revolutions.
• D: Half a revolution is a single stroke, not a complete two-stroke cycle.

Answer: C

Correct answer: About 80 mm. Find the volume of one cylinder, then divide by the piston area. 1.6 L is 1600 cc, and 1600 divided by 4 is 400 cc per cylinder.

That is about 80 mm.

• A: This divides the whole 1600 cc by one piston area, forgetting to split the displacement among four cylinders.
• B: This uses pi times the bore squared for area, treating the diameter as a radius, which makes the area four times too big.
• C (correct): Each cylinder is 400 cc; the piston area is 0.7854 times 8 squared, about 50.3 square centimeters, and 400 divided by 50.3 is about 8.0 cm.
• D: This divides 400 cc by 8 squared and leaves out the 0.7854 factor that turns bore squared into a circle's area.

Answer: B

Correct answer: 10 milliseconds. Convert to revolutions per second: 3000 divided by 60 is 50, so one revolution takes 1/50 of a second, or 20 ms. Each stroke is 180 degrees, half a revolution, so one stroke takes 10 ms.

• A: This is the time for a full crank revolution, which covers two strokes.
• B (correct): At 3000 rpm the crank makes 50 turns a second, so one turn takes 20 ms, and a stroke is half a turn, or 10 ms.
• C: This is the time for one complete four-stroke cycle of two revolutions.
• D: This treats a stroke as a quarter turn of the crank, but each stroke is half a turn, or 180 degrees.