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Maharashtra HSC Automobile Technology - Vocational (MSBSHSE) study materials
Maharashtra HSC Automobile Technology - Vocational (MSBSHSE) study resources

Maharashtra HSC Automobile Technology - Vocational (MSBSHSE) practice questions

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Question 1Automobile Chassis and Body Systems

In a rear-wheel-drive vehicle, which component transmits torque from the gearbox output shaft to the final drive while allowing for suspension movement?

  1. The propeller shaft with universal joints Correct answer.
  2. The clutch release bearing
  3. The half shafts with constant-velocity joints
  4. The steering column shaft

Explanation

The propeller shaft carries drive from the gearbox to the differential on a rear-wheel-drive layout, and its universal joints let the shaft work through changing angles as the axle moves with the suspension. Half shafts are found after the final drive, and the other listed parts do not carry engine torque to the axle.

Question 2Automobile Chassis and Body Systems

A vehicle uses a rigid axle with leaf springs at the rear. Which function do the leaf springs perform besides supporting the vehicle weight?

  1. They convert rotary motion into linear wheel travel
  2. They disengage the drive during gear changes
  3. They locate the axle and resist driving and braking torque Correct answer.
  4. They provide the final gear reduction

Explanation

Leaf springs act as both spring and locating member, clamping the axle so it stays in position while resisting wind-up from driving and braking forces. This dual role is why many rigid-axle commercial vehicles need no separate trailing arms or Panhard rod.

Question 3Automobile Chassis and Body Systems

Which type of steering gear converts rotary steering-wheel motion into the swinging motion of a drop arm?

  1. Worm and nut steering
  2. Recirculating ball steering
  3. Worm and roller steering box Correct answer.
  4. Rack and pinion steering

Explanation

A worm and roller box uses a roller on a rocker shaft that follows the worm, so the output is a swinging drop arm rather than a linear rack movement. This layout is common on heavier vehicles where a drop arm operates the steering linkage.

Question 4Automobile Chassis and Body Systems

A car's front wheels are set with positive camber. What does this mean?

  1. The top of each wheel leans outward away from the vehicle centreline Correct answer.
  2. The steering axis is tilted rearward at the top
  3. The top of each wheel leans inward toward the vehicle centreline
  4. The front of each wheel points inward toward the centreline

Explanation

Camber is the inward or outward tilt of the wheel in the front view, measured from vertical. Positive camber tilts the top of the wheel outward, away from the car, while negative camber tilts it inward.

Question 5Automobile Chassis and Body Systems

Why is a small amount of toe-in often specified for the front wheels of a rear-wheel-drive car?

  1. To increase the tyre contact patch during cornering
  2. To compensate for the tendency of the wheels to splay outward as the vehicle rolls forward Correct answer.
  3. To increase the self-centring action of the steering at high speed
  4. To reduce the turning circle at low speed

Explanation

Rolling resistance and slight compliance in the linkage tend to push the front wheels outward when the car moves, so a static toe-in setting brings them parallel or slightly toed-in while running. This reduces scrub and evens out tyre wear.

Question 6Automobile Chassis and Body Systems

What is the main purpose of the caster angle in front-wheel steering geometry?

  1. To provide a self-centring force that helps the steering return after a turn Correct answer.
  2. To prevent the wheels from rubbing against the suspension springs
  3. To reduce the effort needed to turn the steering wheel at standstill
  4. To keep the tyre tread flat on the road during cornering

Explanation

Caster tilts the steering axis so the tyre contact point trails behind the axis, producing a self-aligning torque that straightens the wheels as the car moves. This is the same effect that makes a shopping-trolley caster wheel follow its direction of travel.

Question 7Automobile Chassis and Body Systems

A vehicle pulls to one side while braking and the steering wheel kicks. Which fault is the most likely cause?

  1. A worn steering rack gaiter
  2. Low tyre pressure in both rear tyres
  3. A seized caliper piston on one front brake Correct answer.
  4. A weak front suspension spring on both sides

Explanation

A sticking caliper on one side applies uneven braking force, so the vehicle steers toward the side with the stronger brake and the driver feels a pull or kick through the wheel. Uneven tyre pressures or a single weak spring can also cause a pull, but the symptom appears under braking rather than continuously.

Question 8Automobile Chassis and Body Systems

In a hydraulic braking system, what is the function of the proportioning valve fitted to the rear circuit?

  1. It limits rear hydraulic pressure so the rear wheels do not lock before the front wheels Correct answer.
  2. It increases rear pressure to shorten stopping distance
  3. It bleeds air from the rear circuit automatically
  4. It stores fluid to compensate for pad wear

Explanation

Weight transfer during braking reduces load on the rear axle, so the rear wheels need less braking force to lock. The proportioning valve reduces rear line pressure relative to the front, keeping the rear just below its locking point and preserving directional stability.

Question 9Automobile Chassis and Body Systems

Which component in a hydraulic brake system converts pedal force into hydraulic pressure?

  1. The residual pressure valve
  2. The brake servo
  3. The wheel cylinder
  4. The tandem master cylinder Correct answer.

Explanation

The master cylinder piston is pushed by the pedal or servo, forcing fluid into the lines and building pressure. Wheel cylinders convert that pressure back into mechanical movement of the shoes or caliper pistons.

Question 10Automobile Chassis and Body Systems

A drum brake has a leading and a trailing shoe. Why does the leading shoe produce more braking force than the trailing shoe for the same hydraulic pressure?

  1. The leading shoe lining has a higher coefficient of friction by design
  2. Friction between the shoe and the rotating drum tends to rotate the shoe into the drum, adding self-energising force Correct answer.
  3. The trailing shoe is held off the drum by a return spring
  4. The leading shoe has a larger wheel-cylinder piston

Explanation

On the leading shoe the drum drags the lining in the direction that wedges it more firmly against the drum, so the friction force adds to the applied force. The trailing shoe is pushed away by drum rotation, so it relies only on hydraulic force and contributes less.

Question 11Automobile Chassis and Body Systems

What is the primary advantage of disc brakes over drum brakes in passenger cars?

  1. Greater self-energising effect at low speed
  2. Lower cost of manufacture and simpler servicing
  3. Better heat dissipation and more consistent braking during repeated hard stops Correct answer.
  4. Complete sealing against water and dust ingress

Explanation

The exposed disc sheds heat quickly and the pads sweep the surface clean, so fade is reduced during repeated hard braking. Drum brakes enclose the friction surfaces and lose performance sooner when hot.

Question 12Automobile Chassis and Body Systems

A customer reports a spongy brake pedal that sinks slowly when held under pressure. Which fault best explains this?

  1. Worn brake discs below minimum thickness
  2. Glazed brake pads on the front axle
  3. Air in the hydraulic circuit or a leaking master cylinder seal Correct answer.
  4. A loose wheel bearing on the rear axle

Explanation

Air is compressible, so it gives a soft, spongy feel, while a fluid leak past the master cylinder seal lets the pedal creep down when held. Either fault must be corrected by bleeding the circuit and inspecting the master cylinder.

Question 13Automobile Chassis and Body Systems

What is the role of the kingpin inclination, also called steering-axis inclination, in a front suspension?

  1. It changes the camber angle as the wheel moves vertically
  2. It sets the rearward tilt of the steering axis
  3. It places the tyre contact point closer to the steering axis to reduce steering effort and improve straight-line stability Correct answer.
  4. It determines the amount of toe-out on turns

Explanation

Inclining the steering axis in the front view brings the contact patch nearer the axis, reducing the moment the driver must overcome when steering and helping the wheels return to straight ahead. The effect is similar to caster but acts in the front view.

Question 14Automobile Chassis and Body Systems

A double-wishbone front suspension is designed with unequal-length upper and lower arms. What is the main reason for the unequal lengths?

  1. To eliminate the need for a stabiliser bar
  2. To control camber change so the outer wheel stays flatter on the road during body roll Correct answer.
  3. To allow the use of leaf springs instead of coil springs
  4. To reduce the unsprung weight of the suspension

Explanation

Making the upper arm shorter than the lower arm lets the designer tune how camber changes as the wheel moves in bump and roll, typically keeping the outer tyre flatter in a corner for better grip. This is a geometry choice, not a weight-saving one.

Question 15Automobile Chassis and Body Systems

Which suspension component is fitted to reduce body roll during cornering without changing the spring rate in a straight line?

  1. The lower ball joint
  2. The bump stop
  3. The shock absorber
  4. The anti-roll bar Correct answer.

Explanation

An anti-roll bar links the two sides of an axle through a torsion section; when both wheels move together it has little effect, but in roll it twists and adds resistance. This controls body roll while leaving straight-line ride largely unaffected.

Question 16Automobile Chassis and Body Systems

What does the term unsprung mass refer to in a vehicle suspension?

  1. The mass of components not carried by the springs, such as wheels, tyres, hubs and part of the axle Correct answer.
  2. The total mass of the vehicle including payload
  3. The mass of the engine and gearbox assembly
  4. The mass of the body supported by the springs

Explanation

Unsprung mass is everything between the road and the springs: wheels, tyres, brake assemblies, hubs and, depending on layout, part of the axle or suspension arms. Lower unsprung mass lets the wheel follow road irregularities more easily and improves ride and grip.

Question 17Automobile Chassis and Body Systems

A vehicle's shock absorbers are worn. Which symptom is most directly associated with this fault?

  1. The steering wheel vibrates at a steady high speed
  2. The body continues to bounce for several cycles after a bump Correct answer.
  3. The engine idles unevenly
  4. The brake pedal pulses when the brakes are applied

Explanation

A shock absorber damps spring oscillation; when it is worn, the spring keeps rebounding and the body floats or bounces repeatedly after a bump. Poor damping also lengthens stopping distances because the tyre loses contact with the road.

Question 18Automobile Chassis and Body Systems

In a recirculating ball steering box, what is the purpose of the recirculating ball bearings between the nut and the worm?

  1. They lock the steering when the engine is switched off
  2. They replace sliding friction with rolling friction to reduce steering effort and wear Correct answer.
  3. They provide the self-centring force after a turn
  4. They act as a hydraulic seal for the power steering fluid

Explanation

In a plain worm and nut, the nut slides along the worm with high friction. Fitting balls in the thread converts that to rolling contact, so the driver's effort drops and the worm wears less.

Question 19Automobile Chassis and Body Systems

What is the function of the Ackermann steering geometry in a vehicle?

  1. To keep both front wheels parallel at all steering angles
  2. To make the inner front wheel turn through a larger angle than the outer wheel in a turn Correct answer.
  3. To increase the steering effort at high speed
  4. To adjust rear-wheel alignment during cornering

Explanation

In a turn the inner wheel follows a smaller radius than the outer wheel, so it must steer more. Ackermann geometry, achieved through the layout of the steering arms, approximates this so both wheels roll without excessive sideways scrub.

Question 20Automobile Chassis and Body Systems

A vehicle has excessive free play in the steering wheel. Which inspection is the most appropriate first step?

  1. Check the engine coolant level and thermostat
  2. Replace the front tyres and rebalance the wheels
  3. Measure the rear axle toe setting
  4. Check the steering linkage joints, the steering box adjustment and the column couplings for wear Correct answer.

Explanation

Free play is a mechanical looseness somewhere between the steering wheel and the road wheels, so the linkage, steering box and column joints should be checked for wear or maladjustment. Tyre and balance faults cause vibration, not lost motion.

Question 21Automobile Chassis and Body Systems

Why are constant-velocity joints preferred over simple universal joints on the driveshafts of a front-wheel-drive car?

  1. They eliminate the need for wheel bearings
  2. They allow the driveshaft to be disconnected for towing
  3. They maintain a constant angular velocity of the driven shaft even when the shaft angle is large and changing Correct answer.
  4. They reduce the need for a differential

Explanation

A simple Hooke's joint causes speed fluctuation when the shaft is at an angle, which is acceptable for a propeller shaft with a matched second joint but not for a steered drive wheel. Constant-velocity joints transmit uniform rotational speed at large angles, so front wheels can steer and move without vibration.

Question 22Automobile Chassis and Body Systems

In a live rear axle, what is the function of the differential?

  1. It changes the direction of drive by 90 degrees only
  2. It disconnects the drive when the vehicle is stationary
  3. It locks the two wheels together at all times
  4. It allows the two driven wheels to rotate at different speeds while distributing torque to both Correct answer.

Explanation

When a vehicle turns, the outer driven wheel travels further than the inner one, so the differential lets the two half shafts rotate at different speeds. The crown wheel and pinion also provide the 90-degree turn and final reduction, but the defining function is speed differentiation.

Question 23Automobile Chassis and Body Systems

A clutch is slipping when the vehicle accelerates in a high gear. Which measurement best confirms a worn friction plate?

  1. Road test showing engine speed rises without a matching increase in road speed Correct answer.
  2. A brake fluid level below the minimum mark
  3. A noise from the release bearing that disappears when the pedal is pressed
  4. Free play at the clutch pedal exceeding the specified value

Explanation

Slipping shows up as engine rpm climbing while the vehicle does not accelerate in proportion, because the plate cannot transmit full torque. Excessive pedal free play usually causes incomplete disengagement rather than slip.

Question 24Automobile Chassis and Body Systems

What is the main purpose of the body shell's crumple zones in a passenger car?

  1. To provide mounting points for the suspension springs
  2. To deform in a controlled way in a collision and absorb kinetic energy before it reaches the occupant cell Correct answer.
  3. To increase the torsional stiffness of the chassis for better handling
  4. To reduce the weight of the body panels for fuel economy

Explanation

Crumple zones are designed to collapse progressively, converting kinetic energy into deformation and reducing the deceleration forces on the occupants. The passenger cell is kept rigid so survival space is preserved.

Question 25Automobile Chassis and Body Systems

A vehicle's front wheels show uneven tyre wear with the inner edge worn much faster than the outer edge. Which alignment condition is the most likely cause?

  1. Incorrect caster angle on the front wheels
  2. Excessive negative camber on the front wheels Correct answer.
  3. Excessive positive camber on the front wheels
  4. Excessive toe-in on the front wheels

Explanation

Negative camber tilts the top of the wheel inward, so the inner edge of the tyre carries more load and wears faster. Toe errors usually produce feathered wear across the tread, and caster mainly affects steering feel and stability.

Question 26Automobile Chassis and Body Systems

In a vehicle chassis, which structural member normally carries the engine, transmission and suspension loads while also forming the base to which the body is bolted?

  1. The bumper bar
  2. The chassis frame Correct answer.
  3. The windscreen frame
  4. The radiator grille

Explanation

The chassis frame is the load-bearing skeleton of a conventional body-on-frame vehicle; it supports the engine, gearbox, suspension mountings and towing loads, and the body is fastened to it through rubber or solid mountings. Body panels and trims do not carry these major loads.

Question 27Automobile Chassis and Body Systems

A car uses a MacPherson strut front suspension. Which component of this layout performs the combined job of locating the wheel and acting as the upper damper mounting?

  1. The hub carrier steering arm
  2. The telescopic strut with its integral spring seat Correct answer.
  3. The anti-roll bar drop link
  4. The lower transverse wishbone

Explanation

In a MacPherson strut layout the telescopic damper unit is rigidly attached to the body at its top mounting and carries the coil spring on a seat welded to the strut tube. This single strut therefore provides the upper wheel location and the spring/damping function, which is why no upper wishbone is needed.

Question 28Automobile Chassis and Body Systems

A front-wheel-drive car is found with a torn rubber bellows on its outer constant-velocity joint, and the joint now clicks loudly on full lock. Which repair is the correct course of action?

  1. Top up the gearbox oil to the filler level
  2. Tighten the hub nut to the upper torque limit
  3. Replace the wheel bearing on that side
  4. Renew the joint and fit a new bellows and grease Correct answer.

Explanation

A split bellows lets water and grit into the joint and throws out the grease, so the joint races and balls wear and click on lock. Once the joint is noisy the damage is already done, so the joint must be renewed together with a fresh bellows and the specified grease.

Question 29Automobile Chassis and Body Systems

A customer complains that the steering wheel shudders at about 80 km/h but the vibration disappears at low speed. Static wheel balance has already been checked and found correct. Which cause best explains this pattern?

  1. A worn steering idler bush
  2. Excessive toe-in on the front wheels
  3. Low tyre pressure on the rear axle
  4. Dynamic imbalance or a distorted tyre casing at speed Correct answer.

Explanation

Vibration that appears only in a narrow high-speed band is typical of a rotating mass problem, such as dynamic imbalance, a shifted belt or an out-of-round tyre casing that only becomes noticeable at speed. Static balancing alone does not correct the dynamic couple, and a tyre defect can remain after balancing.

Question 30Automobile Chassis and Body Systems

A body-on-frame light commercial vehicle is being assessed after a collision. The frame shows a diamond deformation, in which one side rail is displaced longitudinally relative to the other so that the frame plan view resembles a diamond. Which statement correctly describes the effect and the correct repair approach?

  1. Only the wheel alignment angles are affected, so a simple toe setting will restore the frame
  2. The frame should be straightened by heating the rails to bright red and cooling them in water
  3. The deformation is cosmetic and the body can be refitted without measurement
  4. Cross-member diagonals will be unequal, and the frame must be realigned on a jig to the manufacturer's diagonal dimensions Correct answer.

Explanation

Diamond damage swings one side rail forward relative to the other, so the diagonal measurements taken between opposite cross-member points no longer match the manufacturer's figures. Correct repair requires pulling and measuring on a chassis straightening jig until the diagonals and datum heights are restored, because the frame controls suspension pick-up positions.

Question 31Automotive Engines: Construction and Working

In a four-stroke petrol engine, during which stroke does the intake valve remain open while the piston moves from TDC to BDC?

  1. Power stroke
  2. Exhaust stroke
  3. Suction stroke Correct answer.
  4. Compression stroke

Explanation

The suction (intake) stroke draws the air-fuel charge into the cylinder as the piston descends from top dead centre to bottom dead centre with the inlet valve open. The other three strokes involve closed valves or an open exhaust valve, so they cannot admit fresh charge.

Question 32Automotive Engines: Construction and Working

The function of the flywheel fitted to a single-cylinder engine is best described as:

  1. Increasing the compression ratio by reducing the clearance volume
  2. Storing energy during the power stroke and releasing it during the other strokes Correct answer.
  3. Cooling the cylinder head by circulating water through internal passages
  4. Filtering impurities from the lubricating oil before it reaches the bearings

Explanation

A single-cylinder engine produces torque only during the power stroke, so the flywheel absorbs surplus energy then and returns it to keep the crankshaft rotating smoothly through the idle strokes. Its large mass gives inertia, not filtration, compression change or cooling.

Question 33Automotive Engines: Construction and Working

Which component converts the reciprocating motion of the piston into rotary motion of the crankshaft?

  1. Connecting rod Correct answer.
  2. Rocker arm
  3. Pushrod
  4. Camshaft

Explanation

The connecting rod joins the piston pin to the crankpin, so as the piston reciprocates the rod swings and forces the crank to rotate. The camshaft, pushrod and rocker arm belong to the valve train and do not transmit piston force to the crank.

Question 34Automotive Engines: Construction and Working

In a diesel engine, the air-fuel mixture is ignited by:

  1. The high temperature of air compressed to a high pressure ratio Correct answer.
  2. The residual heat of the exhaust valve head
  3. A glow plug that remains energised throughout the power stroke
  4. A spark plug firing at the end of the compression stroke

Explanation

A diesel draws only air, compresses it to a high pressure ratio so its temperature rises above the fuel's ignition point, then injects fuel that self-ignites. There is no spark during normal running, and a glow plug is only a cold-start aid.

Question 35Automotive Engines: Construction and Working

The clearance volume of a cylinder is the volume of the space above the piston when the piston is at:

  1. The point of maximum inlet valve lift
  2. Mid-stroke while descending
  3. Top dead centre Correct answer.
  4. Bottom dead centre

Explanation

Clearance volume is measured with the piston at top dead centre, since that is the smallest volume left above it. Together with swept volume it fixes the compression ratio of the engine.

Question 36Automotive Engines: Construction and Working

The main purpose of the cooling fins cast on an air-cooled engine cylinder is to:

  1. Increase the surface area available for heat transfer to the surrounding air Correct answer.
  2. Guide the piston rings during their travel
  3. Retain lubricating oil on the bore surface
  4. Strengthen the cylinder against combustion pressure

Explanation

Fins add surface area so more heat passes from the metal to the air stream, which is the essence of air cooling. They are not structural reinforcements, ring guides or oil-retaining features.

Question 37Automotive Engines: Construction and Working

Which of the following is a component of the valve train in an overhead-valve engine?

  1. Oil pump
  2. Rocker arm Correct answer.
  3. Crankpin
  4. Piston pin

Explanation

The valve train includes the camshaft, tappets, pushrods, rocker arms and valves, all of which open and close the valves in time with the crankshaft. The piston pin and crankpin are reciprocating and rotating parts of the crank mechanism, and the oil pump belongs to the lubrication system.

Question 38Automotive Engines: Construction and Working

The stroke of an engine is defined as the distance travelled by the piston between:

  1. Top dead centre and bottom dead centre Correct answer.
  2. The inlet valve opening and closing points
  3. The cylinder head and the crankcase floor
  4. Two successive firing strokes

Explanation

Stroke is the linear travel of the piston from one dead centre to the other, and it equals twice the crank radius. It is a fixed geometric dimension, not a timing interval or a clearance distance.

Question 39Automotive Engines: Construction and Working

A four-cylinder four-stroke engine has a bore of 80 mm and a stroke of 90 mm. Using π/4 × d² × L for one cylinder, the swept volume of one cylinder is closest to:

  1. 724 cm³
  2. 181 cm³
  3. 90 cm³
  4. 452 cm³ Correct answer.

Explanation

Swept volume equals (π/4) × 8² × 9 cm³ = 0.7854 × 64 × 9 ≈ 452 cm³. The bore and stroke must be converted to centimetres before applying the formula so the answer comes out in cubic centimetres.

Question 40Automotive Engines: Construction and Working

If the swept volume of one cylinder is 400 cm³ and the clearance volume is 50 cm³, the compression ratio is:

  1. 8 : 1
  2. 9 : 1 Correct answer.
  3. 10 : 1
  4. 7 : 1

Explanation

Compression ratio equals (swept + clearance) ÷ clearance, i.e. (400 + 50) ÷ 50 = 9. The clearance volume must be added to the swept volume first because the charge is compressed into the total space above the piston at TDC.

Question 41Automotive Engines: Construction and Working

In a four-stroke engine, the camshaft rotates at:

  1. One quarter of the crankshaft speed
  2. Twice the crankshaft speed
  3. The same speed as the crankshaft
  4. Half the crankshaft speed Correct answer.

Explanation

Each valve must open once in every two crankshaft revolutions, so the camshaft turns once per two crank turns, that is half speed. This is achieved by a camshaft drive gear or sprocket twice the size of the crank gear.

Question 42Automotive Engines: Construction and Working

Valve overlap in an engine refers to the period when:

  1. The exhaust valve reopens during the power stroke
  2. The inlet valve is open for the whole compression stroke
  3. Both valves are closed at the end of the compression stroke
  4. Both inlet and exhaust valves are open near the end of the exhaust stroke and start of the suction stroke Correct answer.

Explanation

Overlap is deliberately provided around top dead centre between exhaust and suction so the outgoing gases help scavenge the clearance space and incoming charge starts early. It never extends into compression or the power stroke.

Question 43Automotive Engines: Construction and Working

In a two-stroke petrol engine, the transfer port serves to:

  1. Supply lubricating oil directly to the big-end bearing
  2. Carry the fresh charge from the crankcase into the cylinder Correct answer.
  3. Admit exhaust gases back into the crankcase for recirculation
  4. Release burnt gases from the cylinder to the exhaust pipe

Explanation

In a crankcase-scavenged two-stroke, the descending piston pressurises the mixture in the crankcase and the transfer port carries it into the cylinder. The exhaust port, not the transfer port, releases burnt gases.

Question 44Automotive Engines: Construction and Working

A technician finds that a petrol engine runs but has low power and a hissing sound at the cylinder head joint. The most likely cause is:

  1. An over-tightened fan belt
  2. A leaking cylinder head gasket reducing compression Correct answer.
  3. A weak ignition coil producing a colder spark
  4. A clogged air filter restricting the intake

Explanation

A hiss at the head joint plus power loss points to combustion gas escaping past a failed head gasket, which lowers compression pressure. An air filter or coil fault would not produce a hiss at the head joint, and belt tension does not affect compression.

Question 45Automotive Engines: Construction and Working

Which material is most commonly used for the cylinder block of a modern light automotive engine because of its good castability and heat conduction?

  1. Cast iron or aluminium alloy Correct answer.
  2. Copper sheet
  3. Reinforced rubber
  4. High-carbon tool steel

Explanation

Cylinder blocks are generally cast iron for strength and wear resistance or aluminium alloy for light weight, with cast iron liners where needed. Tool steel, copper sheet and rubber lack the required combination of strength, casting quality and stiffness.

Question 46Automotive Engines: Construction and Working

The purpose of a turbocharger in an engine is to:

  1. Mix lubricating oil with the incoming air for better sealing
  2. Use exhaust gas energy to drive a compressor that raises intake air density Correct answer.
  3. Cool the exhaust gases before they enter the silencer
  4. Reduce the compression ratio at high engine speed

Explanation

Exhaust gas spins a turbine on a common shaft with a compressor, which packs more air into the cylinder so more fuel can be burnt for the same swept volume. It does not meter oil, alter compression ratio mechanically or act as an exhaust cooler.

Question 47Automotive Engines: Construction and Working

An engine's firing order is specified mainly to:

  1. Keep the coolant flowing in one direction
  2. Distribute the power impulses evenly and reduce torsional vibration of the crankshaft Correct answer.
  3. Allow a single cam lobe to operate all the valves
  4. Ensure all pistons reach top dead centre at the same moment

Explanation

By choosing a firing order the power strokes are spaced evenly along the crankshaft, which smooths torque delivery and limits vibration and bearing loads. Pistons in a multi-cylinder engine are phased, not simultaneous, and firing order has no relation to cooling flow.

Question 48Automotive Engines: Construction and Working

In a petrol engine, detonation (knocking) is most likely to occur when:

  1. The exhaust valve opens late and hot gases remain in the cylinder
  2. The spark plug fires too early and the flame travels slowly and smoothly
  3. The air-fuel mixture is extremely lean and burns very slowly
  4. The charge ignites spontaneously ahead of the flame front under high pressure and temperature Correct answer.

Explanation

Detonation happens when end gas in the cylinder reaches its auto-ignition temperature before the advancing flame front consumes it, producing a sharp pressure spike heard as knock. High compression, hot spots and low-octane fuel all promote it.

Question 49Automotive Engines: Construction and Working

The main advantage of an overhead camshaft layout compared with a side-valve layout is that it:

  1. Removes the requirement for a cylinder head gasket
  2. Eliminates the need for a camshaft entirely
  3. Allows the use of a single valve per cylinder
  4. Reduces the number of moving valve-train parts and permits higher engine speeds Correct answer.

Explanation

An overhead camshaft acts more directly on the valves, so heavy pushrods and their flex are avoided, which reduces inertia and permits higher speeds. It does not do away with the camshaft, the head gasket or multiple valves.

Question 50Automotive Engines: Construction and Working

Which statement correctly describes the sequence of events in a four-stroke compression-ignition engine?

  1. A rich mixture is drawn in, compressed, spark-ignited, then scavenged by fresh charge
  2. Air alone is drawn in, compressed to a high temperature, fuel is injected and ignites, then gases are exhausted Correct answer.
  3. Fuel is injected during suction, compressed with air, then ignited by a glow plug
  4. Air and fuel are mixed in the crankcase and transferred through ports after compression

Explanation

In a diesel, only air enters during suction and is compressed to a temperature above the fuel's ignition point; injection near the end of compression causes self-ignition, followed by the power and exhaust strokes. The other sequences describe petrol or two-stroke crankcase-scavenged operation.