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Karnataka SSLC Automobile - NSQF (KSEAB) study materials
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Karnataka SSLC Automobile - NSQF (KSEAB) practice questions

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Question 1Automobile Workshop Safety, Tools and Equipment

A trainee in the automobile workshop must lift a heavy gearbox from the floor. Which practice best protects the spine while lifting?

  1. Twist the trunk while lifting to turn the load quickly
  2. Keep the back straight, bend the knees and hold the load close to the body Correct answer.
  3. Bend at the waist and keep the legs straight
  4. Hold the load at arm's length to keep it away from the body

Explanation

Safe manual lifting keeps the spine neutral, uses the strong leg muscles by bending the knees, and keeps the load close to the body's centre of gravity. Twisting or bending at the waist concentrates stress on the lower back and is a common cause of workshop injury.

Question 2Automobile Workshop Safety, Tools and Equipment

In a four-stroke engine workshop, the tool used to measure the diameter of a cylinder bore accurately is the:

  1. Torque wrench
  2. Vernier caliper
  3. Inside micrometer or bore gauge Correct answer.
  4. Feeler gauge

Explanation

Cylinder bore diameter is an internal dimension, so it is measured with an inside micrometer or a dial bore gauge set to a known size. A vernier caliper is used for external and some internal sizes but is less precise for deep bores.

Question 3Automobile Workshop Safety, Tools and Equipment

While grinding a chisel on a bench grinder, which combination of PPE is most appropriate?

  1. A dust mask only
  2. Ordinary prescription spectacles only
  3. Leather gloves while holding the work against the wheel
  4. Safety goggles and a face shield over them Correct answer.

Explanation

Grinding throws high-speed sparks and metal particles, so eye protection must be supplemented with a face shield for full coverage. Gloves near a rotating wheel are dangerous because they can be caught and drag the hand in.

Question 4Automobile Workshop Safety, Tools and Equipment

The main purpose of chocking the wheels of a vehicle before working underneath it is to:

  1. Protect the tyres from flat spots
  2. Align the wheels for steering measurement
  3. Reduce noise from the suspension
  4. Prevent the vehicle from rolling or shifting Correct answer.

Explanation

Wheel chocks stop a vehicle from rolling when it is raised or when the parking brake alone may not hold it. This is a basic control measure before any under-vehicle work.

Question 5Automobile Workshop Safety, Tools and Equipment

In the workshop, a fire involving petrol or diesel should be extinguished with:

  1. A foam or dry powder extinguisher Correct answer.
  2. Water from a bucket
  3. Compressed air
  4. A wet cloth

Explanation

Fuel fires are Class B fires, and foam or dry powder extinguishers smother them by cutting off oxygen. Water spreads burning fuel because it is denser than the fuel and does not mix with it.

Question 6Automobile Workshop Safety, Tools and Equipment

The correct way to carry a file or a hacksaw across the workshop is to:

  1. Toss it to the person who needs it
  2. Carry it over the shoulder
  3. Hold it with the point or blade down and away from the body Correct answer.
  4. Hold it with the point or blade forward

Explanation

Sharp-edged and pointed tools are carried with the dangerous end pointing down and away from the body to prevent accidental stabbing if the carrier stumbles. Passing a tool by tossing it risks injury and damage.

Question 7Automobile Workshop Safety, Tools and Equipment

A technician uses a micrometer to measure the diameter of a valve stem. The barrel reads 6.5 mm and the thimble reads 24 divisions. If the thimble has 50 divisions and one barrel division equals 0.5 mm, the reading is:

  1. 6.740 cm
  2. 6.524 mm
  3. 6.500 mm
  4. 6.740 mm Correct answer.

Explanation

Each thimble division represents 0.5 mm divided by 50, which is 0.01 mm, so 24 divisions equal 0.24 mm. Adding this to the barrel reading of 6.5 mm gives 6.74 mm.

Question 8Automobile Workshop Safety, Tools and Equipment

When using a torque wrench to tighten a cylinder head bolt, the most accurate and safe practice is to:

  1. Oil the threads heavily so the bolt turns easily
  2. Apply torque smoothly and continuously until the wrench clicks or signals Correct answer.
  3. Use the torque wrench as a breaker bar to loosen tight bolts
  4. Add a pipe extension to the handle for extra leverage

Explanation

A torque wrench is a precision instrument that should be loaded smoothly to its set value and then released. Using it to loosen bolts or extending its handle overloads the mechanism and destroys calibration.

Question 9Automobile Workshop Safety, Tools and Equipment

A hydraulic trolley jack is used to raise a car for a tyre change. Which practice is essential before any part of the body goes beneath the vehicle?

  1. Place axle stands under the chassis at the specified points Correct answer.
  2. Lower the jack slightly to settle the car
  3. Leave the engine running to keep the brakes powered
  4. Put the gear in neutral

Explanation

A jack is only a lifting device and can fail or sink, so the raised vehicle must be supported on axle stands at manufacturer-specified jacking points. Only then is it safe to work beneath it.

Question 10Automobile Workshop Safety, Tools and Equipment

The dial gauge reading on a cylinder bore shows a variation of 0.12 mm between the top and bottom of the stroke. In workshop terms this indicates:

  1. Excessive valve clearance
  2. Incorrect ignition timing
  3. Correct piston ring end gap
  4. Cylinder taper requiring reboring or replacement Correct answer.

Explanation

A significant difference in bore diameter from top to bottom is taper, which results from uneven wear. Taper beyond the service limit causes poor ring sealing and requires reboring or cylinder replacement.

Question 11Automobile Workshop Safety, Tools and Equipment

When jump-starting a vehicle with a flat battery, the final connection should be made to:

  1. The fuel line bracket
  2. The positive terminal of the flat battery
  3. A clean bare metal point on the engine block of the disabled vehicle Correct answer.
  4. The negative terminal of the flat battery

Explanation

The last connection is made to a bare metal earth point away from the battery so that any spark occurs away from hydrogen gas vented by the battery. This reduces the risk of a battery explosion.

Question 12Automobile Workshop Safety, Tools and Equipment

The safe procedure for using a hydraulic press to remove a wheel bearing is to:

  1. Press against the bearing outer race while supporting the inner race
  2. Hold the workpiece by hand to feel the alignment
  3. Stand directly in line with the ram to watch the movement
  4. Support the workpiece squarely and keep hands clear of the ram path Correct answer.

Explanation

A press exerts very high force, so the workpiece must be squarely supported and hands kept away from the ram and the point of contact. If a component shatters, standing out of line reduces injury.

Question 13Automobile Workshop Safety, Tools and Equipment

A feeler gauge is the correct tool for checking which of the following?

  1. Brake disc thickness
  2. Tyre tread depth
  3. Battery electrolyte level
  4. Valve clearance or spark plug gap Correct answer.

Explanation

A feeler gauge is a set of thin blades of known thickness used to measure small gaps such as valve clearance and spark plug gap. Each blade is tried in turn until one just fits the gap.

Question 14Automobile Workshop Safety, Tools and Equipment

Which statement best explains why compressed air must never be directed at a person's skin in the workshop?

  1. It damages clothing
  2. It cools the skin too quickly
  3. It removes protective oil from the skin
  4. It can force air into the bloodstream through a small cut, causing serious injury Correct answer.

Explanation

Compressed air at workshop pressure can penetrate skin through a tiny break and enter the bloodstream, causing air embolism, which is a medical emergency. Air should only be used for cleaning with reduced pressure and proper nozzles.

Question 15Automobile Workshop Safety, Tools and Equipment

An apprentice notices that the insulation on the live lead of an electric hand drill is cracked and the inner conductor is visible. The correct action is to:

  1. Stop using the drill and report it for repair or replacement Correct answer.
  2. Wear rubber gloves and continue using the drill
  3. Wrap the lead in insulation tape and continue
  4. Use the drill only for short jobs

Explanation

Damaged insulation on a power tool is a serious electric shock hazard, so the tool must be taken out of service and tagged for repair. Tape repairs are not acceptable for portable electrical equipment.

Question 16Automobile Workshop Safety, Tools and Equipment

In a workshop, the colour code of a fire extinguisher containing carbon dioxide is:

  1. Red with a cream label
  2. Red with a green label
  3. Red with a blue label
  4. Red with a black label Correct answer.

Explanation

Under the common Indian and British convention, CO2 extinguishers are red with a black label. CO2 is preferred for live electrical equipment because it leaves no residue and does not conduct electricity.

Question 17Automobile Workshop Safety, Tools and Equipment

A mechanic must remove a seized exhaust manifold nut that has corroded onto a stud. Which approach best balances safety and the risk of damaging the stud?

  1. Apply maximum force with a long breaker bar immediately
  2. Cut the stud off straight away
  3. Use an undersized socket hammered onto the nut
  4. Apply penetrating oil, use a correctly sized six-point socket and steady force, and heat only if permitted Correct answer.

Explanation

Penetrating oil and a correctly fitting six-point socket spread the load on the nut flats and reduce rounding. Controlled heat can help break corrosion, but it must be used with fire precautions near fuel and oil lines.

Question 18Automobile Workshop Safety, Tools and Equipment

During a road test after brake overhaul, the pedal feels spongy and travels further than specified. Which combination of causes and checks is most appropriate?

  1. Worn tyre tread; rotate the tyres
  2. Air in the hydraulic circuit; bleed the brakes and recheck pedal feel Correct answer.
  3. Incorrect wheel alignment; adjust the toe setting
  4. Low engine oil; top up the sump

Explanation

A spongy pedal usually means air is trapped in the hydraulic system, because gas compresses while brake fluid does not. Bleeding the circuit at the correct sequence removes the air and restores a firm pedal.

Question 19Automobile Workshop Safety, Tools and Equipment

A workshop stores petrol for cleaning parts. Which storage arrangement meets basic safety requirements?

  1. A plastic bottle kept under the workbench
  2. A glass jar on a high shelf in sunlight
  3. An open tray near the welding bay
  4. A labelled, approved closed metal container in a ventilated area away from ignition sources Correct answer.

Explanation

Flammable liquids must be kept in approved, labelled, closed containers in a ventilated area away from heat and ignition sources. This limits vapour release and the chance of ignition.

Question 20Automobile Workshop Safety, Tools and Equipment

A dial indicator is set up to check the runout of a brake disc mounted on the hub. The needle swings from -0.03 mm to +0.07 mm as the disc rotates. What is the total indicated runout and what does it mean?

  1. 0.03 mm, which is the base setting error
  2. 0.04 mm, which is within any limit
  3. 0.07 mm, which is the only reading that matters
  4. 0.10 mm, which may exceed the manufacturer's limit and needs machining or replacement Correct answer.

Explanation

Total indicated runout is the difference between the maximum and minimum readings, so 0.07 minus (-0.03) equals 0.10 mm. If this exceeds the maker's limit it causes pedal pulsation and requires disc machining or replacement.

Question 21Automotive Engine Systems and Components

In a four-stroke petrol engine, which component seals the combustion chamber at the top of the cylinder and transmits the force of combustion to the connecting rod?

  1. The camshaft
  2. The flywheel
  3. The oil pump
  4. The piston Correct answer.

Explanation

The piston is the moving part that closes the top of the cylinder, receives the pressure of burning gas and passes that force through the gudgeon pin to the connecting rod. The camshaft only operates the valves, the flywheel stores energy and the oil pump circulates lubricant, so none of them forms the combustion boundary.

Question 22Automotive Engine Systems and Components

A technician measures the bore of a single-cylinder engine as 70 mm and the stroke as 80 mm. Using the swept-volume formula, what is the approximate engine displacement?

  1. About 392 cm³
  2. About 154 cm³
  3. About 308 cm³ Correct answer.
  4. About 616 cm³

Explanation

Swept volume of one cylinder equals π/4 × bore² × stroke. With bore 7 cm and stroke 8 cm this gives 0.7854 × 49 × 8, which is roughly 308 cm³. Displacement is reported per cylinder here because the engine has only one cylinder.

Question 23Automotive Engine Systems and Components

Which statement correctly describes the sequence of events in the four strokes of a diesel engine?

  1. Induction of air, spark ignition, compression, exhaust of gases
  2. Compression of air, induction of air, injection, exhaust of gases
  3. Induction of air, compression of air, injection and combustion, exhaust of gases Correct answer.
  4. Induction of fuel-air mixture, compression, spark ignition, exhaust of gases

Explanation

In a diesel engine only air is drawn in during the induction stroke; it is compressed to a high pressure and temperature, fuel is then injected and ignites by itself, and burnt gases leave on the exhaust stroke. The order suction, compression, power, exhaust must always be preserved for the cycle to work.

Question 24Automotive Engine Systems and Components

During which stroke of a four-stroke engine does the piston move from bottom dead centre to top dead centre with both valves closed?

  1. The induction stroke
  2. The compression stroke Correct answer.
  3. The power stroke
  4. The exhaust stroke

Explanation

With both valves shut, the rising piston squeezes the trapped charge, so this is the compression stroke. The induction stroke also has the piston rising in some layouts, but then the inlet valve is open, and the power and exhaust strokes start from top dead centre and move downwards.

Question 25Automotive Engine Systems and Components

What is the main function of the crankshaft in an internal combustion engine?

  1. It converts the reciprocating motion of the piston into rotary motion Correct answer.
  2. It opens and closes the inlet and exhaust valves
  3. It filters dust from the incoming air
  4. It stores fuel for delivery to the injector

Explanation

The crankshaft, together with the connecting rod, turns the up-and-down movement of the piston into rotation that can drive the vehicle. Its crank throws and counterweights also balance the rotating assembly. Valve operation, air filtration and fuel storage belong to other systems.

Question 26Automotive Engine Systems and Components

A mechanic finds that the engine misfires and backfires through the inlet manifold. Which valve timing fault is the most likely cause?

  1. The oil pressure relief valve is stuck open
  2. The inlet valve is opening too early or closing too late Correct answer.
  3. The spark plug gap is too small
  4. The exhaust valve is opening too late

Explanation

Backfiring into the intake means combustion is escaping past an inlet valve that is not properly seated at the wrong moment, typically because the inlet valve opens too early or closes too late. Valve timing errors change when the valve is on its seat, so the charge can be ignited while the inlet is still open. Spark gap and oil pressure do not control when the inlet valve seals.

Question 27Automotive Engine Systems and Components

Which component in a petrol engine is responsible for mixing fuel with air in the correct proportion before it enters the cylinder on older engines?

  1. The fuel tank
  2. The fuel injector
  3. The carburettor Correct answer.
  4. The fuel filter

Explanation

A carburettor uses the venturi effect and jets to atomise fuel into the airstream, producing a combustible mixture for the engine. Modern engines use electronic fuel injection instead, but the question refers to older petrol engines. Filters and tanks only store or clean fuel and do not meter it.

Question 28Automotive Engine Systems and Components

In a multi-point fuel injection system, what does the oxygen sensor fitted in the exhaust pipe allow the engine control unit to do?

  1. Measure the engine coolant temperature
  2. Detect the engine speed from the flywheel teeth
  3. Control the ignition coil dwell time
  4. Correct the air-fuel ratio by feeding back information on oxygen content in the exhaust Correct answer.

Explanation

The oxygen or lambda sensor reports how much oxygen remains in the exhaust gas, which tells the control unit whether the mixture is rich or lean. The control unit then adjusts injection duration to keep the mixture close to stoichiometric for efficient catalytic conversion. Speed, temperature and dwell are handled by other sensors and outputs.

Question 29Automotive Engine Systems and Components

What is the purpose of the thermostat valve in an engine cooling system?

  1. It increases the pressure inside the radiator to raise the boiling point
  2. It regulates coolant flow to keep the engine at its designed operating temperature Correct answer.
  3. It drives the coolant pump through a belt
  4. It removes scale from the coolant passages

Explanation

The thermostat stays closed while the engine is cold so that it warms up quickly, then opens progressively to let coolant circulate through the radiator and hold the temperature near the design value. This reduces wear and keeps combustion efficient. Pressure regulation and pump drive are separate functions.

Question 30Automotive Engine Systems and Components

An engine overheats only when the vehicle is stationary in traffic, but the temperature is normal at highway speed. Which fault best explains this pattern?

  1. The radiator cap is releasing pressure too early
  2. The radiator cooling fan is not operating Correct answer.
  3. The thermostat is stuck open
  4. The water pump belt is slipping at all speeds

Explanation

At highway speed the ram air through the radiator provides enough cooling, but when the vehicle is stationary only the fan moves air through the core. If the fan fails, temperature climbs only in traffic, which matches the symptom exactly. A stuck-open thermostat would make the engine run cold, not hot.

Question 31Automotive Engine Systems and Components

Which property makes a good engine lubricating oil?

  1. It should mix readily with coolant to improve heat transfer
  2. It should maintain adequate viscosity across the operating temperature range Correct answer.
  3. It should become thinner as its temperature rises to reduce friction
  4. It should evaporate quickly at high temperature to cool the engine

Explanation

Lubricating oil must keep a film strong enough to separate moving surfaces when hot and still flow freely when cold, which is why multigrade oils are specified. Viscosity index describes how little the viscosity changes with temperature. Evaporation, coolant mixing and excessive thinning all reduce protection.

Question 32Automotive Engine Systems and Components

What does the 'W' in a multigrade oil designation such as 15W-40 indicate?

  1. The oil is a waste-recycled product
  2. The oil is suitable for winter conditions, and the first number refers to its low-temperature viscosity Correct answer.
  3. The oil contains water-resistant additives
  4. The oil is intended for warm climates only

Explanation

In SAE 15W-40, the W stands for winter and the number before it grades the oil's cold-flow behaviour. The number after the hyphen gives the viscosity at high operating temperature. Together they show the oil behaves like a 15-grade oil when cold and a 40-grade oil when hot.

Question 33Automotive Engine Systems and Components

Which type of bearing is normally used for the big-end connection between the connecting rod and the crankshaft in a small engine?

  1. A solid bronze bush pressed into the rod
  2. A taper roller bearing
  3. A sealed deep-groove ball bearing
  4. A split shell bearing with a renewable lining Correct answer.

Explanation

The big end must wrap around a crankpin and be assembled in two halves, so split shell bearings with thin renewable linings are used and lubricated by oil pressure. Ball and roller bearings cannot be split around the crankpin, and a solid bush cannot be fitted over the crank throw.

Question 34Automotive Engine Systems and Components

What is the function of the gudgeon pin in a piston assembly?

  1. It connects the piston to the small end of the connecting rod Correct answer.
  2. It holds the piston rings in their grooves
  3. It seals the combustion chamber against blow-by
  4. It locks the cylinder head to the block

Explanation

The gudgeon pin, also called the piston pin, passes through the piston bosses and the small end of the connecting rod so that the piston can pivot as the rod swings. It is usually hollow to save weight and is retained by circlips or interference fit. Sealing and ring retention are done by other parts.

Question 35Automotive Engine Systems and Components

Why are the compression rings on a piston usually fitted with a small end gap?

  1. To reduce the weight of the piston assembly
  2. To let lubricating oil drain back into the sump
  3. To allow the ring to be removed without tools
  4. To allow for thermal expansion and to maintain a gas-tight seal without binding Correct answer.

Explanation

A piston ring must expand as it heats up, so a controlled end gap prevents the ends from butting and scoring the bore. The gap is kept small enough that gas leakage remains negligible. Oil drainage and weight reduction are not its purpose.

Question 36Automotive Engine Systems and Components

A compression test on a petrol engine shows one cylinder much lower than the others, and adding a little oil to that cylinder raises the reading. What does this indicate?

  1. Worn piston rings or cylinder bore Correct answer.
  2. A burnt exhaust valve
  3. Incorrect ignition timing
  4. A leaking cylinder head gasket

Explanation

Oil temporarily seals the gap between rings and bore, so if the reading improves after adding oil the leakage is past the rings rather than the valves. A burnt valve would not be sealed by oil and the reading would stay low. Ignition timing does not affect a compression gauge reading.

Question 37Automotive Engine Systems and Components

Which component in a battery ignition system steps up the low battery voltage to the high voltage needed at the spark plug?

  1. The contact breaker
  2. The distributor cap
  3. The ignition coil Correct answer.
  4. The condenser

Explanation

The ignition coil contains primary and secondary windings, and the sudden collapse of current in the primary induces a very high voltage in the secondary. That high voltage is then distributed to the plugs. The condenser suppresses arcing at the points, the contact breaker interrupts primary current and the cap only routes the high voltage.

Question 38Automotive Engine Systems and Components

What is the effect of fitting a spark plug with too large an electrode gap in a petrol engine?

  1. The fuel consumption always falls
  2. The engine idle speed rises steadily
  3. The voltage required to jump the gap rises and misfiring may occur at high load Correct answer.
  4. The compression ratio of the engine increases

Explanation

A larger gap needs a higher voltage to break down the air, and if that voltage exceeds what the coil can supply the plug misfires, especially under high cylinder pressure. The gap has no effect on compression ratio, and fuel consumption would worsen rather than improve.

Question 39Automotive Engine Systems and Components

In a distributor-type ignition system, what is the function of the vacuum advance unit?

  1. It advances the ignition timing as engine load decreases Correct answer.
  2. It limits the maximum spark voltage
  3. It retards timing whenever the engine speed increases
  4. It controls the dwell angle of the contact points

Explanation

The vacuum advance senses manifold depression, which is high at light load, and rotates the contact plate to advance the spark for better economy. At heavy load the depression falls and the advance reduces to avoid detonation. Speed-related advance is handled by the centrifugal mechanism.

Question 40Automotive Engine Systems and Components

Which statement best explains why a diesel engine does not need a spark plug?

  1. Diesel fuel has a very high octane rating that makes ignition easy
  2. A glow plug provides the spark for every combustion cycle
  3. The fuel is preheated electrically before injection
  4. The high compression raises air temperature enough for injected fuel to ignite spontaneously Correct answer.

Explanation

A diesel engine compresses only air to a high ratio, and the resulting temperature rise is sufficient to ignite the fuel as it is injected. Glow plugs are only starting aids in cold weather and do not fire continuously. Diesel fuel is rated by cetane number, not octane.

Question 41Automotive Engine Systems and Components

What is the primary function of the turbocharger in a small automotive diesel engine?

  1. It cools the exhaust gas before it leaves the tailpipe
  2. It meters the quantity of fuel delivered to each injector
  3. It reduces the compression ratio during starting
  4. It uses exhaust gas energy to drive a compressor that increases the mass of air entering the cylinder Correct answer.

Explanation

The exhaust turbine drives a compressor on the same shaft, so more air is packed into the cylinder and more fuel can be burnt to raise power without increasing engine size. The charge is often passed through an intercooler afterwards. Fuel metering and exhaust after-treatment are separate functions.

Question 42Automotive Engine Systems and Components

Which of the following is a correct description of valve overlap in a four-stroke engine?

  1. The inlet valve opens after the exhaust valve has closed completely
  2. Both valves remain closed throughout the compression stroke
  3. Both inlet and exhaust valves are open together for a short period around top dead centre Correct answer.
  4. The exhaust valve stays open during the whole induction stroke

Explanation

Valve overlap occurs near the end of the exhaust stroke and the start of induction, when the inlet valve has already begun to open while the exhaust valve is still closing. The incoming charge helps scavenge the remaining burnt gas. Overlap is measured in degrees of crankshaft rotation.

Question 43Automotive Engine Systems and Components

A vehicle with a manual gearbox jumps out of second gear when the accelerator is released. Which cause is most consistent with this symptom?

  1. A blocked fuel filter
  2. Worn gear teeth or a faulty detent and selector mechanism for that gear Correct answer.
  3. Low coolant level
  4. A weak ignition coil

Explanation

Jumping out of gear under overrun load points to the gear train or the selector and detent parts that hold the gear engaged. Worn teeth, worn bearings or a weak detent spring allow the sliding sleeve to move back to neutral. Fuel, ignition and cooling faults affect engine running, not gear retention.

Question 44Automotive Engine Systems and Components

What is the purpose of the clutch in a vehicle with a manual transmission?

  1. It locks the differential during cornering
  2. It changes the direction of rotation of the wheels
  3. It connects and disconnects engine power from the gearbox smoothly Correct answer.
  4. It increases engine torque at low road speed

Explanation

The clutch allows the driver to break the drive between the engine and gearbox so gears can be selected, and it slips during take-up to give a smooth start. Torque multiplication is done by the gearbox, and directional change is done by the reverse gear.

Question 45Automotive Engine Systems and Components

In a four-stroke engine, the camshaft turns at half the speed of the crankshaft. What is the reason for this ratio?

  1. The valves need to open twice per crankshaft revolution
  2. The camshaft is fitted with fewer bearings than the crankshaft
  3. Each valve must open once for every two revolutions of the crankshaft Correct answer.
  4. The camshaft must drive the oil pump at a lower speed

Explanation

A four-stroke cycle needs two crankshaft revolutions to complete induction, compression, power and exhaust, while each valve operates once in that cycle. The camshaft therefore completes one turn for every two turns of the crank, which is achieved by the camshaft drive ratio.

Question 46Automotive Engine Systems and Components

In a four-stroke petrol engine, what is the purpose of the valve clearance (tappet gap) specified for the rocker arm?

  1. To keep the valve open slightly during the compression stroke
  2. To increase the lift of the valve for better breathing
  3. To reduce the noise produced by the valve train
  4. To allow for thermal expansion of the valve stem and maintain proper sealing Correct answer.

Explanation

Valve clearance is a small gap provided in the valve train to accommodate the expansion of the valve stem and other components as the engine heats up. Without this gap, the valve may not seat fully when hot, leading to compression loss and burnt valves. It also ensures the valve closes completely during the compression and power strokes.

Question 47Automotive Engine Systems and Components

A mechanic observes that the engine oil pressure warning light stays on at idle even after the oil level is checked and found correct. Which component is most likely to be the cause?

  1. A defective spark plug
  2. A worn crankshaft pulley
  3. A clogged air filter
  4. A faulty oil pressure switch Correct answer.

Explanation

The oil pressure warning light is triggered by the oil pressure switch, which senses low oil pressure. If the oil level is correct and the light remains on, the switch itself may be faulty and giving a false indication. Other common causes include a worn oil pump or a blocked oil filter, but the switch is a primary suspect for an electrical false warning.

Question 48Automotive Engine Systems and Components

In a four-cylinder engine with a firing order of 1-3-4-2, the piston in cylinder 1 is at top dead centre on compression stroke. Which piston is at top dead centre on exhaust stroke?

  1. Cylinder 3
  2. Cylinder 2
  3. Cylinder 1
  4. Cylinder 4 Correct answer.

Explanation

In a four-stroke engine, the crankshaft completes two revolutions for all cylinders to fire once. With firing order 1-3-4-2, when cylinder 1 is on compression (firing), the cylinder that is 360 degrees out of phase (one full crankshaft revolution later) will be on exhaust stroke. That cylinder is the one that fires last in the order, which is cylinder 4. Thus, cylinder 4 is on exhaust stroke when cylinder 1 is on compression.

Question 49Automotive Engine Systems and Components

Which type of fuel supply system uses a mechanically driven high-pressure pump to deliver fuel to the injectors in a diesel engine?

  1. Carburettor system
  2. Port fuel injection system
  3. Common rail system Correct answer.
  4. Distributorless ignition system

Explanation

In a common rail diesel system, a high-pressure pump pressurises fuel and stores it in a common rail, from which it is distributed to individual injectors. The pump is mechanically driven by the engine and can generate very high pressures. Carburettor and port fuel injection are petrol systems, and distributorless ignition is electrical, not fuel supply.

Question 50Automotive Engine Systems and Components

A technician is diagnosing a turbocharged diesel engine that lacks power and produces black smoke. On inspection, the turbocharger compressor wheel is found to have damaged blades. Which effect does this damage most directly have on engine performance?

  1. Advanced injection timing causing knocking
  2. Increased lubricating oil consumption due to seal leakage
  3. Reduced boost pressure leading to insufficient air for combustion Correct answer.
  4. Higher compression ratio resulting in detonation

Explanation

Damaged compressor blades reduce the turbocharger's ability to compress air, lowering boost pressure. This results in less air entering the cylinders, causing an over-rich mixture that burns inefficiently, producing black smoke and reduced power. Oil consumption and injection timing are separate issues not directly caused by blade damage.