I85PREP
⌘ K
Odisha CHSE +2 Vocational Automobile Technology study materials
Odisha CHSE +2 Vocational Automobile Technology study resources

Odisha CHSE +2 Vocational Automobile Technology practice questions

One question at a time. Build your Odisha CHSE +2 Vocational Automobile Technology understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Automobile Fundamentals and Workshop Practice

In a four-stroke petrol engine, the camshaft rotates at what speed relative to the crankshaft?

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

Explanation

Each cylinder needs one intake and one exhaust valve event in a two-revolution cycle of the crankshaft, so the camshaft that drives those valves turns once per two crank turns. This 2:1 crankshaft-to-camshaft ratio is set by the timing gears or chain and must be maintained for correct valve timing.

Question 2Automobile Fundamentals and Workshop Practice

A telescopic shock absorber on a light commercial vehicle controls wheel movement mainly by:

  1. Storing spring energy in a compressed gas chamber only
  2. Increasing the spring rate of the coil spring
  3. Forcing oil through small orifices so kinetic energy becomes heat Correct answer.
  4. Locking the suspension arm rigidly to the frame

Explanation

A hydraulic shock absorber damps oscillation by pushing oil through calibrated valves and orifices; the resistance converts the motion into heat that the body dissipates. It does not carry vehicle weight, which is the spring's job.

Question 3Automobile Fundamentals and Workshop Practice

Which property of engine oil is described by its SAE 20W-50 marking?

  1. Its flash point and fire point
  2. Its pour point only
  3. Its viscosity grade at low and high temperatures Correct answer.
  4. Its total base number and detergency

Explanation

The SAE viscosity grading system uses the W (winter) figure for low-temperature flow behaviour and the second figure for viscosity at about 100 degrees Celsius. A 20W-50 oil is therefore thinner when cold than a straight 50 grade yet retains high-temperature thickness.

Question 4Automobile Fundamentals and Workshop Practice

In a manual transmission, the synchroniser ring performs which function during a gear change?

  1. It locks the differential during cornering
  2. It absorbs torsional vibration from the propeller shaft
  3. It multiplies engine torque before the final drive
  4. It equalises the speeds of the gear and the output shaft before the dog teeth engage Correct answer.

Explanation

The baulk or synchroniser ring rubs against a cone on the gear so friction brings both parts to the same speed, allowing the sliding sleeve's dog teeth to mesh without clashing. This is why a worn ring causes gear crunching.

Question 5Automobile Fundamentals and Workshop Practice

The main purpose of a thermostat in a liquid-cooled engine cooling system is to:

  1. Reduce the pressure of the cooling system
  2. Circulate coolant through the radiator by mechanical drive
  3. Filter rust and scale from the coolant
  4. Regulate coolant flow so the engine reaches and holds its normal operating temperature Correct answer.

Explanation

The thermostat is a wax-pellet valve that stays closed while the coolant is cold, allowing quick warm-up, then opens to admit flow to the radiator and holds the engine near its design temperature. This improves combustion quality and reduces wear and emissions.

Question 6Automobile Fundamentals and Workshop Practice

The firing order 1-3-4-2 in a four-cylinder engine is used mainly to:

  1. Distribute power impulses evenly and reduce torsional vibration of the crankshaft Correct answer.
  2. Simplify the valve clearance adjustment procedure
  3. Allow the use of a single valve for intake and exhaust
  4. Increase the compression ratio of the engine

Explanation

A firing order spreads the power strokes at equal crank-angle intervals and balances the loads on the crankshaft bearings, reducing vibration and bearing stress. The choice of order also affects the layout of the crankshaft throws.

Question 7Automobile Fundamentals and Workshop Practice

A feeler gauge is the correct tool for which workshop task?

  1. Measuring the depth of a drilled hole
  2. Torquing cylinder head bolts to specification
  3. Checking valve clearance or spark plug gap Correct answer.
  4. Measuring the diameter of a cylinder bore

Explanation

A feeler gauge is a set of thin blades of known thickness used to check a small gap by trial fit, such as tappet clearance or an electrode gap. The blade that just drags in the gap indicates its size.

Question 8Automobile Fundamentals and Workshop Practice

In a simple carburettor, the venturi performs which job?

  1. It maintains a constant fuel level in the float chamber
  2. It creates a low-pressure region that draws fuel from the main jet Correct answer.
  3. It closes the air supply at idle
  4. It stores fuel to supply the accelerator pump

Explanation

As air accelerates through the narrowed venturi, its pressure falls according to Bernoulli's principle, and atmospheric pressure in the float chamber pushes fuel out through the main jet into the air stream. The pressure drop therefore meters fuel in proportion to airflow.

Question 9Automobile Fundamentals and Workshop Practice

A vehicle battery reads 12.4 V at rest with the engine and all loads off. What does this indicate for a 12 V lead-acid battery?

  1. It is being overcharged by the alternator
  2. It is about half charged and needs charging Correct answer.
  3. It is fully charged and healthy
  4. It has a shorted cell

Explanation

Open-circuit voltage of a lead-acid battery tracks state of charge, with roughly 12.6 to 12.7 V at full charge and about 12.4 V at around half charge. The reading must be taken after the surface charge is removed and with no load, otherwise it is misleading.

Question 10Automobile Fundamentals and Workshop Practice

When using a micrometer screw gauge to measure a valve stem diameter, the reading is taken as:

  1. The largest division visible on the sleeve
  2. Thimble reading divided by the barrel length
  3. Main scale reading plus thimble reading times least count Correct answer.
  4. Main scale reading minus the zero error only

Explanation

The micrometer combines the sleeve (main scale) value with the thimble division multiplied by the least count, commonly 0.01 mm. Any zero error found when the jaws are closed must be added or subtracted from the result.

Question 11Automobile Fundamentals and Workshop Practice

A clutch slips when the vehicle climbs a gradient under load. Which condition is the most likely cause?

  1. Low coolant level
  2. Insufficient pressure plate clamping force or a worn friction disc Correct answer.
  3. Excessive clutch pedal free play
  4. A leaking wheel cylinder

Explanation

The clutch transmits torque through friction created by the pressure plate clamping the disc against the flywheel. If the disc is worn thin, glazed or oil-contaminated, or the diaphragm spring has weakened, the clamp load falls and the clutch slips under high torque demand.

Question 12Automobile Fundamentals and Workshop Practice

In a rack-and-pinion steering system, the purpose of the pinion is to:

  1. Hold the front wheel alignment angle fixed
  2. Convert rotary motion of the steering column into linear movement of the rack Correct answer.
  3. Act as a damper for road shocks
  4. Increase the engine speed signal for the tachometer

Explanation

The pinion gear at the end of the steering column meshes with the toothed rack, so turning the wheel slides the rack sideways and moves the track rods. The gear ratio between pinion teeth and rack teeth sets the steering reduction.

Question 13Automobile Fundamentals and Workshop Practice

A tyre is marked 165/80 R14. What does the 80 represent?

  1. The aspect ratio, meaning section height is 80 per cent of section width Correct answer.
  2. The maximum speed rating
  3. The load index of the tyre
  4. The rim diameter in inches

Explanation

In this size code, 165 is the nominal section width in millimetres, 80 is the aspect ratio giving sidewall height as a percentage of width, R denotes radial construction and 14 is the rim diameter in inches. The section height here is therefore about 132 mm.

Question 14Automobile Fundamentals and Workshop Practice

Which brake component automatically maintains a small running clearance between the shoe and drum as lining wears?

  1. The proportioning valve
  2. The brake pedal return spring
  3. The master cylinder residual valve
  4. The automatic adjuster mechanism Correct answer.

Explanation

As lining wears, the shoe travel increases, and the adjuster strut or ratchet takes up the slack so pedal travel stays within limits and clearance stays small. Without it, the pedal would sink progressively lower.

Question 15Automobile Fundamentals and Workshop Practice

During a compression test on a petrol engine, one cylinder reads much lower than the others, but the reading rises to normal when a little oil is added to the cylinder. This indicates:

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

Explanation

Oil temporarily seals the gap between rings and bore, so a wet reading that is much higher than the dry reading points to ring or bore wear. A valve or gasket leak would not be sealed by oil and would stay low.

Question 16Automobile Fundamentals and Workshop Practice

The function of the differential in a rear-wheel-drive vehicle is to:

  1. Reduce engine speed before the gearbox
  2. Allow the rear wheels to turn at different speeds while transmitting drive to both Correct answer.
  3. Support the weight of the rear axle
  4. Provide engine braking on long descents

Explanation

When the vehicle turns, the outer wheel travels a longer path than the inner wheel; the differential's planet and sun gears let the two half-shafts rotate at different speeds while still delivering torque. The crown wheel and pinion also provide the final drive reduction.

Question 17Automobile Fundamentals and Workshop Practice

In a 12 V starting system, a starter motor that clicks but does not crank most directly suggests:

  1. A faulty radiator thermostat
  2. A blocked fuel filter
  3. Insufficient current reaching the starter, such as a poor earth or discharged battery Correct answer.
  4. An open circuit in the alternator field winding

Explanation

A single loud click often means the solenoid pulls in but the battery cannot supply the high cranking current, or the earth/terminal resistance is too high. Voltage drop tests across the cables and terminals locate the excessive resistance.

Question 18Automobile Fundamentals and Workshop Practice

Which type of bearing is best suited to carry a heavy radial load combined with a small axial load at the front wheel hub of a car?

  1. Plain bronze bush
  2. Thrust ball bearing
  3. Taper roller bearing Correct answer.
  4. Needle roller bearing without inner race

Explanation

Taper roller bearings have conical rollers that can accept both radial and axial loads, and they are commonly used in opposed pairs at wheel hubs to set preload. This makes them suitable for carrying vehicle weight plus cornering thrust.

Question 19Automobile Fundamentals and Workshop Practice

A vehicle's headlights dim at idle but brighten when engine speed rises. Which explanation fits best?

  1. Alternator output is low at idle, so the battery supplements the load Correct answer.
  2. The tyre pressure is below specification
  3. The headlight relay is opening at high speed
  4. The brake proportioning valve is faulty

Explanation

Alternator output rises with rotor speed, so at idle the charging system may not cover a heavy electrical load and system voltage falls, dimming the lamps. Checking the drive belt, battery condition and charging voltage confirms whether the system is normal or defective.

Question 20Automobile Fundamentals and Workshop Practice

A mechanic must loosen a stubborn wheel nut. Which practice applies correct workshop procedure?

  1. Use an adjustable spanner with an extension pipe and strike it with a hammer
  2. Heat the nut with an oxy-acetylene flame until it glows
  3. Use a breaker bar of the correct socket size and apply steady force while the vehicle is safely supported Correct answer.
  4. Loosen the nut with the wheel jacked up and the wheel free to spin

Explanation

A properly fitting six-point socket on a breaker bar spreads the load over the full nut flats and reduces the risk of rounding, and steady force is safer than impact. The vehicle should be on level ground with the wheel on the ground or the axle on stands, never on a jack alone.

Question 21Automobile Fundamentals and Workshop Practice

During valve timing checks, the inlet valve is found to open too early and close too late. Which condition does this represent?

  1. Excessive valve overlap, which can cause poor idling and backfiring into the inlet Correct answer.
  2. Insufficient valve lift, which reduces volumetric efficiency
  3. Advanced ignition timing
  4. Incorrect tappet clearance on the exhaust valve only

Explanation

If the inlet opens before top dead centre and closes after bottom dead centre by more than the specified angles, it overlaps more with the exhaust event. The result is exhaust gas reversion into the inlet at idle, giving rough running and spit-back.

Question 22Automobile Fundamentals and Workshop Practice

A technician calculates the swept volume of one cylinder with bore 80 mm and stroke 90 mm. Using pi as 3.1416, which value is closest?

  1. 905 cubic centimetres
  2. 226 cubic centimetres
  3. 452 cubic centimetres Correct answer.
  4. 1810 cubic centimetres

Explanation

Swept volume equals pi times the square of the bore radius times the stroke, so 3.1416 times 40 squared times 90 gives about 452,390 cubic millimetres, or roughly 452 cubic centimetres. The bore must be halved to get the radius before squaring.

Question 23Automobile Fundamentals and Workshop Practice

In a hydraulic brake system, a pedal that feels spongy and travels further than normal most likely indicates:

  1. A weak return spring on the pedal
  2. A seized brake caliper piston
  3. Worn brake pads with correct adjustment
  4. Air trapped in the hydraulic circuit Correct answer.

Explanation

Liquid is essentially incompressible, but air is not, so bubbles in the lines or caliper absorb pedal movement and give a soft, long-travel feel. The remedy is correct bleeding of the circuit in the specified sequence.

Question 24Automobile Fundamentals and Workshop Practice

A diesel engine produces excessive black smoke under acceleration while power is acceptable. Which cause is most consistent with this symptom?

  1. Air entering the fuel injection line
  2. Coolant entering the combustion chamber
  3. Engine oil burning in the cylinder
  4. Over-fuelling or restricted intake air causing an over-rich mixture Correct answer.

Explanation

Black smoke is unburnt carbon from an over-rich air-fuel ratio, so too much fuel delivered or too little air reaching the cylinders produces it. Common causes include a restricted air filter, faulty boost control or incorrect injection quantity.

Question 25Engine Systems and Overhauling

In a four-stroke SI engine, during which stroke does the intake valve normally close to give the best volumetric efficiency at low speed?

  1. At mid-point of the compression stroke
  2. Exactly at top dead centre of the exhaust stroke
  3. Immediately at top dead centre of the intake stroke
  4. Shortly after bottom dead centre of the intake stroke Correct answer.

Explanation

Intake valve closing is delayed past bottom dead centre so the incoming charge continues to fill the cylinder because of its inertia. This late closing improves volumetric efficiency at low and moderate speeds. Closing exactly at TDC or at BDC would reduce the trapped charge.

Question 26Engine Systems and Overhauling

The clearance volume of a cylinder is 50 cm³ and the swept volume is 450 cm³. What is the compression ratio?

  1. 11:1
  2. 8:1
  3. 10:1 Correct answer.
  4. 9:1

Explanation

Compression ratio equals total cylinder volume divided by clearance volume, that is (swept + clearance)/clearance. Here (450 + 50)/50 = 500/50 = 10. So the ratio is 10:1.

Question 27Engine Systems and Overhauling

Which component in a pressurised liquid cooling system maintains system pressure and absorbs expansion of the coolant as it heats?

  1. Coolant temperature sensor
  2. Water pump
  3. Thermostat
  4. Radiator pressure cap Correct answer.

Explanation

The radiator pressure cap contains a spring-loaded valve that holds a set pressure in the system and opens to release coolant to the overflow when it expands. This raises the boiling point of the coolant and prevents loss. The thermostat only controls flow, and the pump only circulates.

Question 28Engine Systems and Overhauling

During a cylinder bore measurement with a bore gauge, readings taken at three heights and two perpendicular directions are used mainly to detect which condition?

  1. Camshaft lobe lift
  2. Valve seat concentricity
  3. Taper and out-of-roundness of the bore Correct answer.
  4. Crankshaft end float

Explanation

Measuring at several heights along the bore reveals taper, and measuring in two perpendicular planes reveals out-of-roundness. These are the standard checks before deciding on reboring. Valve, crankshaft and camshaft checks need different instruments.

Question 29Engine Systems and Overhauling

A piston ring end gap measured in the cylinder is smaller than the specification. What is the correct workshop action?

  1. Fit the ring as it is and let it wear in
  2. Grind the ring ends squarely to obtain the specified gap Correct answer.
  3. Increase the bore size to suit the ring
  4. Reduce the ring thickness on a lathe

Explanation

A too-small end gap will close up when the ring heats and can seize or break the ring and score the bore. The correct remedy is to file or grind the ring ends squarely, checking the gap in the bore until it matches specification. Fitting as-is or machining the bore or ring thickness is wrong.

Question 30Engine Systems and Overhauling

Which type of bearing is used for the big end of a connecting rod in most modern automotive petrol engines?

  1. Needle roller bearing
  2. Thin-wall shell bearing Correct answer.
  3. Taper roller bearing
  4. Ball bearing

Explanation

Connecting rod big ends normally use thin-wall steel-backed shell bearings with a bearing material lining, supplied in standard and undersize grades. They are easy to replace and give a large load-bearing area for the crankpin. Ball, taper and needle bearings are used elsewhere.

Question 31Engine Systems and Overhauling

A compression test on a petrol engine shows one cylinder reading about 40 percent below the others, and a wet test raises that reading considerably. What does this indicate?

  1. Worn piston rings or cylinder bore Correct answer.
  2. Blown cylinder head gasket between two cylinders
  3. Incorrect ignition timing
  4. Leaking intake valve

Explanation

When oil added to the cylinder raises compression, the oil is sealing the gap between rings and bore, so the fault lies in the rings or cylinder wall. A leaking valve would not be sealed by oil, and a head gasket fault would affect two adjacent cylinders. Ignition timing does not change compression readings.

Question 32Engine Systems and Overhauling

In a diesel engine, fuel is injected near the end of the compression stroke mainly because compression ignition requires which condition?

  1. Air at high pressure and therefore high temperature Correct answer.
  2. A throttle plate to regulate manifold vacuum
  3. A spark timed by the distributor
  4. A rich air-fuel mixture from the carburettor

Explanation

A diesel draws only air, and compressing it to a high ratio raises its temperature above the self-ignition point of the fuel. Injecting fuel into this hot air causes spontaneous ignition without a spark. Carburettors, distributors and throttle plates belong to petrol engines.

Question 33Engine Systems and Overhauling

When assembling an engine, a Plastigauge strip is placed across a bearing journal and the cap is torqued. What is being measured?

  1. Journal taper
  2. Crankshaft end play
  3. Oil clearance between journal and bearing Correct answer.
  4. Bearing crush

Explanation

Plastigauge is a calibrated plastic thread that flattens by an amount proportional to the gap it is squeezed into. Comparing its flattened width with the scale gives the running oil clearance between the journal and the bearing shell. End play and taper need a dial gauge or micrometer.

Question 34Engine Systems and Overhauling

Which valve train layout uses a single camshaft in the cylinder block operating both valves through pushrods and rocker arms?

  1. Overhead valve with pushrods Correct answer.
  2. DOHC
  3. SOHC with direct bucket tappets
  4. Desmodromic overhead cam

Explanation

An overhead valve pushrod engine keeps the camshaft in the block and transfers motion upward through lifters, pushrods and rocker arms. DOHC and SOHC layouts place the camshaft in the cylinder head. Desmodromic systems use closing cams rather than springs.

Question 35Engine Systems and Overhauling

During a cylinder leakage test, air escapes continuously through the radiator filler neck with bubbles. Which fault is most likely?

  1. Worn valve guides
  2. Cracked cylinder head or failed head gasket Correct answer.
  3. Leaking exhaust valve
  4. Worn piston rings only

Explanation

Bubbles at the radiator filler during a leakage test show that compressed air is entering the cooling system. This points to a crack in the head or block or a failed head gasket between the combustion chamber and a water passage. Ring wear would show air from the oil filler, and a valve leak from the intake or exhaust.

Question 36Engine Systems and Overhauling

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

  1. To speed up coolant circulation at all times
  2. To regulate coolant flow so the engine reaches and maintains operating temperature Correct answer.
  3. To keep the coolant at a constant high temperature
  4. To prevent coolant boiling at high altitude

Explanation

The thermostat stays closed when the engine is cold so the coolant warms quickly, then opens progressively to allow flow through the radiator. This keeps the engine near its designed operating temperature. It does not maintain a fixed temperature regardless of load, nor does it control boiling point.

Question 37Engine Systems and Overhauling

A crankshaft journal measures 54.72 mm and the specified standard diameter is 55.00 mm with a permissible undersize of 0.25 mm. Which bearing grade should be selected?

  1. The journal must be scrapped
  2. 0.25 mm undersize bearing Correct answer.
  3. 0.50 mm undersize bearing
  4. Standard bearing

Explanation

The journal is 0.28 mm smaller than standard, which is within the 0.25 mm regrind limit only if it is ground to the 0.25 mm undersize size. A 0.25 mm undersize bearing matches a journal ground to 54.75 mm. A standard bearing would give excessive clearance and a 0.50 mm bearing would be too tight.

Question 38Engine Systems and Overhauling

Which device in a carburettor supplies extra fuel when the throttle is opened suddenly to prevent a weak mixture and hesitation?

  1. Accelerating pump Correct answer.
  2. Choke valve
  3. Idle jet
  4. Float chamber

Explanation

When the throttle snaps open, manifold vacuum falls and fuel tends to condense on the manifold walls, making the mixture momentarily weak. The accelerating pump delivers a measured squirt of fuel to compensate. The float chamber stores fuel, the idle jet feeds the idle circuit, and the choke enriches only during cold starting.

Question 39Engine Systems and Overhauling

Why is a valve seat ground to a specified width rather than being made as narrow as possible?

  1. A wide seat always gives better gas flow
  2. Seat width sets the tappet gap
  3. Seat width controls valve stem clearance
  4. A very narrow seat overheats and wears quickly under high load Correct answer.

Explanation

A narrow seat concentrates combustion heat and load on a small area, so it burns and wears rapidly. Grinding to the specified width balances heat transfer against gas flow. Seat width does not control stem clearance or tappet gap.

Question 40Engine Systems and Overhauling

The function of a turbocharger wastegate is to:

  1. Lubricate the turbine shaft
  2. Reduce turbo lag at low engine speed
  3. Limit boost pressure by bypassing exhaust gas around the turbine Correct answer.
  4. Cool the compressed air before it enters the engine

Explanation

The wastegate is a valve that opens when boost reaches a set level and diverts part of the exhaust flow around the turbine wheel. This limits turbine speed and boost pressure, protecting the engine. Charge cooling is done by an intercooler and lubrication by the oil supply.

Question 41Engine Systems and Overhauling

After reassembling an engine, the valve clearances are found to be too tight on several valves. What is the most likely result if the engine is run?

  1. Excessive oil consumption from the guides
  2. Valves may not seat fully, causing compression loss and possible burning Correct answer.
  3. Noisy valve operation with reduced lift
  4. Higher compression and better power

Explanation

Too little clearance means the valve cannot fully seat once the engine warms and parts expand. Compression leaks past the seat, and hot combustion gas can burn the valve face. Excessively tight clearance also risks the valve being held off its seat by the cam.

Question 42Engine Systems and Overhauling

Which material is commonly used for the cylinder block of modern light automotive engines because it gives good thermal conductivity with low weight?

  1. Cast iron
  2. Aluminium alloy Correct answer.
  3. Bronze
  4. Mild steel

Explanation

Aluminium alloy blocks are widely used because they are light and conduct heat well, often with cast iron or sprayed liners to resist wear. Cast iron is stronger and cheaper but heavier. Mild steel and bronze are not used for blocks.

Question 43Engine Systems and Overhauling

In an engine overhaul, the cylinder head is checked for warpage using a straight edge and feeler gauge. Where must the measurement be taken?

  1. Only along the centre line of the head
  2. Only across the exhaust port face
  3. Along the length, across the width and diagonally on the gasket face Correct answer.
  4. Only at the combustion chamber edges

Explanation

Warpage can occur in any direction, so the straight edge must be placed along the length, across the width and along both diagonals of the head gasket face. The greatest feeler gauge reading indicates the maximum warpage. Checking only one direction can miss distortion.

Question 44Engine Systems and Overhauling

A petrol engine has a knocking sound under acceleration that disappears when the ignition timing is retarded. Which cause is most consistent with this observation?

  1. Over-advanced ignition timing or low-octane fuel Correct answer.
  2. A blocked radiator
  3. A loose fan belt
  4. Worn main bearings

Explanation

Detonation occurs when the end gas ignites spontaneously before the flame front arrives, producing a metallic knock. Retarding the spark or using higher-octane fuel reduces it. Bearing wear gives a deep knock at all loads, and cooling or belt faults do not respond to timing changes.

Question 45Engine Systems and Overhauling

What is the main reason for using a multi-plate clutch pack instead of a single dry plate in an automatic transmission?

  1. It needs no hydraulic pressure
  2. It eliminates the need for transmission fluid
  3. It allows manual gear selection only
  4. It can transmit high torque in a compact space with smooth engagement Correct answer.

Explanation

Multiple plates increase the friction area and torque capacity within a small diameter and give progressive engagement. They are operated hydraulically and run in oil for cooling and wear control. They do not remove the need for fluid or restrict manual selection.

Question 46Engine Systems and Overhauling

Which statement correctly describes the firing order of a four-cylinder inline engine with a firing order of 1-3-4-2?

  1. Cylinders 1 and 4 fire consecutively
  2. All four cylinders fire at top dead centre together
  3. The power strokes are spaced evenly at 180 degrees of crankshaft rotation Correct answer.
  4. The order applies only to V-type engines

Explanation

In a four-cylinder four-stroke engine the crankshaft turns 720 degrees per cycle, so four power strokes occur at 180-degree intervals. A firing order such as 1-3-4-2 spreads the power strokes evenly and balances the loads on the crankshaft. Firing order is defined for inline engines as well.

Question 47Engine Systems and Overhauling

During a cylinder honing operation after reboring, what is the purpose of producing a cross-hatch pattern on the bore surface?

  1. To remove the piston ring end gap
  2. To help retain oil for lubrication and assist ring bedding-in Correct answer.
  3. To increase the compression ratio
  4. To reduce the bore diameter

Explanation

Honing with a rotating and reciprocating stone produces a cross-hatch of fine scratches. These hold oil on the bore surface for lubrication and help the new rings bed in during running-in. Honing does not change compression ratio or ring gap.

Question 48Engine Systems and Overhauling

A mechanic finds that the valve tappet clearance on an engine with hydraulic lifters is set too large. What effect is most likely?

  1. The camshaft will rotate in the wrong direction
  2. The oil pump will lose pressure
  3. The lifter plunger will over-extend and cause valve hold-open
  4. The valve will open late and close early, reducing lift and increasing noise Correct answer.

Explanation

Hydraulic lifters rely on oil pressure to take up clearance automatically, so an excessive lash setting shortens effective valve opening and increases noise. Too small a setting can hold the valve off its seat. Oil pressure and camshaft rotation are not affected by lash setting.

Question 49Engine Systems and Overhauling

Which of the following best explains why the exhaust valve of a diesel engine is often made of two different materials joined together?

  1. To combine a heat-resistant head with a wear-resistant stem Correct answer.
  2. To allow the valve to be adjusted without a feeler gauge
  3. To reduce the valve stem diameter
  4. To eliminate the need for a valve guide

Explanation

The valve head must withstand high combustion temperatures, while the stem must resist wear in the guide. Joining a heat-resistant alloy head to a wear-resistant stem gives both properties economically. The joint does not affect adjustment, stem size or the need for a guide.

Question 50Engine Systems and Overhauling

In a four-stroke petrol engine, during which stroke does the piston travel upward while both valves remain closed, compressing the air-fuel mixture?

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

Explanation

The compression stroke begins with the piston at bottom dead centre and both valves closed; as the piston moves upward, it reduces the cylinder volume and compresses the trapped air-fuel mixture. This compression is essential for efficient combustion and power output.