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Punjab PSEB Sr. Sec. NSQF Automotive (Four Wheel Service Technician) study materials
Punjab PSEB Sr. Sec. NSQF Automotive (Four Wheel Service Technician) study resources

Punjab PSEB Sr. Sec. NSQF Automotive (Four Wheel Service Technician) practice questions

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Question 1Automotive Workshop Safety and Environment

In a four-wheeler workshop, which fire extinguisher class is suitable for a petrol spill fire near the fuel tank area?

  1. Class A water extinguisher
  2. Class B foam or dry powder extinguisher Correct answer.
  3. Class D sodium chloride extinguisher
  4. Class K wet chemical extinguisher

Explanation

Petrol is a flammable liquid, so it falls in Class B, where foam, dry powder or CO2 are the accepted agents because they smother the vapour and do not spread the burning liquid. Water must be avoided because it spreads a burning liquid pool.

Question 2Automotive Workshop Safety and Environment

A technician must raise a car on a two-post hoist. What is the correct first step before the lift arms touch the vehicle?

  1. Check the vehicle's lifting points and the hoist's rated capacity Correct answer.
  2. Remove the drain plug to warm the oil for faster draining
  3. Loosen the wheel nuts while the wheels are still on the ground
  4. Start the engine to check for exhaust leaks under the ramp

Explanation

The lift points and rated capacity must be confirmed before any lifting so the arms sit on the reinforced jacking points and the load stays within the hoist's limit. Lifting at an incorrect point can crush sills, damage fuel lines, or cause the vehicle to slip.

Question 3Automotive Workshop Safety and Environment

Which personal protective equipment is most important when using an air blow gun to clean a brake assembly?

  1. Rubber insulating gloves rated for 1000 V
  2. Leather welding gauntlets
  3. Steel-toe boots only
  4. Impact-rated safety goggles and a dust mask Correct answer.

Explanation

Compressed air throws brake dust and metal particles at high speed, so eye protection against impact and a dust mask to limit inhalation of fine dust are the key items. Brake dust may also contain harmful fibres, so blowing it dry without respiratory protection is poor practice.

Question 4Automotive Workshop Safety and Environment

Why is it unsafe to leave a vehicle engine running inside a closed workshop bay while a colleague works underneath?

  1. The tyres will overheat from the exhaust heat
  2. The battery will overcharge and burst
  3. The engine oil will thicken too quickly in a closed bay
  4. Carbon monoxide in the exhaust can build up to a lethal concentration Correct answer.

Explanation

Engine exhaust contains carbon monoxide, an odourless gas that accumulates in an enclosed space and can cause unconsciousness or death. Bays therefore need extraction or the vehicle must be moved so exhaust is ducted outdoors.

Question 5Automotive Workshop Safety and Environment

What does the colour coding on a workshop's waste-oil drum typically indicate when it is marked with a red label and a flame symbol?

  1. It holds flammable liquid and needs a closed lid and bunding Correct answer.
  2. It contains scrap metal for recycling
  3. It is safe for general refuse collection
  4. It contains used coolant and must be diluted before disposal

Explanation

A flame symbol with a red flammable-liquid label means the contents ignite readily, so the drum must be kept closed and within a spill bund away from ignition sources. Used oil is a hazardous waste in most jurisdictions and cannot go into general refuse.

Question 6Automotive Workshop Safety and Environment

A workshop stores new tyres, lubricants and solvents. Which housekeeping practice best reduces the risk of a fire spreading?

  1. Keeping flammable liquids in a closed cabinet away from tyres and ignition sources Correct answer.
  2. Storing all items together so one extinguisher covers the whole area
  3. Leaving solvent lids open so vapours disperse slowly
  4. Stacking solvent cans next to the tyre rack for easy access

Explanation

Flammable liquids should be kept in a closed, labelled cabinet separated from combustible stock such as tyres, so a small ignition cannot grow into a large fire. Tyres burn fiercely and produce dense smoke, so separation is a key control.

Question 7Automotive Workshop Safety and Environment

During a road test, a technician notices the brake pedal sinks slowly to the floor when held under pressure. What is the most appropriate immediate action?

  1. Adjust the rear brake shoes and continue the road test
  2. Return to the workshop at low speed and report the fault before further driving Correct answer.
  3. Pump the pedal repeatedly and complete the planned route
  4. Continue the test at higher speed to confirm the fault

Explanation

A pedal that sinks under steady pressure suggests a hydraulic leak or internal master-cylinder bypass, so the vehicle should be brought back safely and the fault reported rather than driven further. Continuing a road test with a suspect brake system risks a total loss of braking.

Question 8Automotive Workshop Safety and Environment

Which practice correctly controls the risk of a used catalytic converter being removed and stored in the workshop?

  1. Placing it in the general metal skip outside the gate
  2. Handing it to any visitor who asks for scrap
  3. Leaving it on the floor beside the work bay for the next shift
  4. Storing it in a locked cage with other high-value parts and recording it Correct answer.

Explanation

Catalytic converters contain precious metals and are a common theft target, so they should be logged and held in a secure, locked store. Loose storage or open skips create both loss and environmental contamination risks.

Question 9Automotive Workshop Safety and Environment

A technician is about to arc-weld a chassis member on a vehicle with an electronic control unit. Which precaution protects the vehicle electronics?

  1. Wrap the ECU in plastic sheet and weld normally
  2. Disconnect the battery earth and clamp the welder earth close to the weld Correct answer.
  3. Connect the welder earth to the far end of the chassis
  4. Leave the battery connected so the ECU stays powered

Explanation

Welding current seeks the shortest path to earth, so disconnecting the battery earth and clamping the welder return close to the work keeps current out of wiring and the ECU. A remote earth clamp forces current through sensitive components.

Question 10Automotive Workshop Safety and Environment

What is the correct way to handle a spill of fresh engine oil on the workshop floor?

  1. Leave it to evaporate and place a chair over it
  2. Wash it into the floor drain with a hose
  3. Spread it thinly so it dries faster
  4. Cover it with sawdust or absorbent granules, collect it and dispose of it as hazardous waste Correct answer.

Explanation

Absorbent material soaks up the oil so it can be swept up and consigned as hazardous waste, keeping it out of drains and soil. Washing it away simply transfers the pollution to the drainage system.

Question 11Automotive Workshop Safety and Environment

When must a technician use axle stands rather than relying on a hydraulic trolley jack alone?

  1. Only when working on the exhaust system
  2. Never, because a trolley jack is designed to hold a load
  3. Only when the jack is more than ten years old
  4. Whenever any part of the body is placed under a raised vehicle Correct answer.

Explanation

A trolley jack is a lifting device, not a support, and can lose pressure or tip, so axle stands must carry the vehicle whenever anyone works beneath it. This applies to all under-vehicle work, not to particular systems or jack ages.

Question 12Automotive Workshop Safety and Environment

Which control best reduces exposure to respirable crystalline silica when sanding body filler?

  1. Opening a window slightly and working quickly
  2. Wearing a cotton handkerchief over the nose
  3. Using a compressed-air jet to blow dust away
  4. Wet sanding or on-tool dust extraction with a suitable respirator Correct answer.

Explanation

Silica dust is best controlled at source by wet methods or extraction, backed by a properly fitted respirator. A handkerchief does not seal or filter fine particles, and blowing dust with air simply makes it airborne again.

Question 13Automotive Workshop Safety and Environment

How should used engine coolant be handled after draining a radiator?

  1. Mixed with used oil in the same drum
  2. Collected in a labelled container for recycling or authorised disposal Correct answer.
  3. Poured onto the yard gravel so it soaks away
  4. Poured down the sink because it is mostly water

Explanation

Coolant contains ethylene glycol and corrosion inhibitors that are toxic to people and wildlife, so it must be collected separately and sent for recycling or licensed disposal. Mixing it with oil contaminates both waste streams.

Question 14Automotive Workshop Safety and Environment

A technician is replacing a fuel filter on a petrol vehicle. Which sequence best controls fire risk?

  1. Smoke only while standing at the rear of the vehicle
  2. Drain the fuel line into an open tray beside a space heater
  3. Work on a hot engine so the fuel evaporates quickly
  4. Relieve fuel pressure, work in a ventilated area, and keep ignition sources away Correct answer.

Explanation

Petrol vapour ignites easily, so pressure must be relieved before opening the line and the work area kept ventilated and free of ignition sources. A hot engine, open flame or heater near released fuel can cause an immediate fire.

Question 15Automotive Workshop Safety and Environment

Which statement correctly describes the purpose of a spill bund under a used-oil storage drum?

  1. It filters the oil so it can be reused
  2. It contains leakage so it cannot reach drains or soil Correct answer.
  3. It raises the drum to make pumping easier
  4. It keeps the drum lid tightly closed

Explanation

A bund is a secondary containment structure sized to hold the drum's contents if it leaks or ruptures, preventing oil from reaching drains, soil or groundwater. It does not seal the drum or treat the oil.

Question 16Automotive Workshop Safety and Environment

A workshop's compressed-air line is used for cleaning components. Which practice is acceptable under good workshop safety rules?

  1. Pointing the air gun at skin to dry hands after washing
  2. Using full line pressure to blow brake dust off the wheels
  3. Using an air jet to clean dust off clothing worn by a colleague
  4. Regulating pressure and using a nozzle with a safety tip for bench work only Correct answer.

Explanation

Air should be regulated to a safe pressure and used with a safety nozzle for cleaning parts on a bench, never directed at people or clothing. Compressed air can force air into the skin or eyes and can drive dust deep into the lungs.

Question 17Automotive Workshop Safety and Environment

A vehicle on a two-post hoist begins to tilt slightly after being raised. What is the correct response?

  1. Raise it higher so the arms lock into place
  2. Climb under and push the vehicle back to level
  3. Send a colleague under to check while the vehicle stays raised
  4. Lower the vehicle fully, reposition the arms on the correct lifting points and re-lift Correct answer.

Explanation

A tilting load signals an unstable lift, so the only safe action is to lower it completely, re-check the lifting points and arm position, and lift again. Nobody should go under a vehicle that is not stable and properly supported.

Question 18Automotive Workshop Safety and Environment

A workshop uses a solvent parts washer. Which combination best reflects a safe and compliant operating routine?

  1. Leave the lid open for convenience and top up with any available thinner
  2. Keep the lid closed when not in use, label the unit, and change solvent through a licensed waste contractor Correct answer.
  3. Use petrol as a cheaper alternative cleaning solvent
  4. Dispose of spent solvent by mixing it with used coolant

Explanation

Solvent washers release flammable vapour, so the lid should stay closed when idle, the unit labelled, and spent solvent handled through a licensed contractor. Substituting petrol or mixing waste streams creates serious fire and compliance problems.

Question 19Automotive Workshop Safety and Environment

Two technicians disagree about jacking a vehicle with a space-saver spare fitted. Which reasoning is correct for workshop safety?

  1. The space-saver can be ignored because it only affects road handling
  2. A space-saver makes the vehicle lighter, so any jack point is acceptable
  3. The space-saver should be inflated to maximum before jacking to add stability
  4. The reduced-size wheel changes the vehicle's stability and ground clearance, so the jacking plan must account for it Correct answer.

Explanation

A space-saver changes ride height and weight distribution, so the jack and stand positions must be chosen to keep the vehicle level and stable, and the wheel must not be used as a support. Ignoring the difference can cause the vehicle to tilt off the jack.

Question 20Automotive Workshop Safety and Environment

A workshop wants to reduce both fire risk and environmental harm from its daily operations. Which measure gives the greatest combined benefit?

  1. Moving all flammable storage outdoors without any cover or bund
  2. Segregating wastes, using closed labelled containers, and keeping ignition sources away from flammables Correct answer.
  3. Buying more extinguishers and storing all waste in one open bin
  4. Increasing ventilation and allowing solvent lids to stay open

Explanation

Segregation with closed, labelled containers cuts both the fire load and the chance of soil or water pollution, while separation from ignition sources reduces fire risk. This single routine addresses the two goals together rather than trading one against the other.

Question 21Tools, Measuring Instruments and Workshop Equipment

A four-wheel service technician needs to remove a cylinder head bolt that is tightened to a high torque. Which tool is designed for this task and gives the correct leverage?

  1. A torque wrench
  2. A combination spanner used as a lever extension
  3. A screwdriver with an adapter bit
  4. A breaker bar with the correct socket Correct answer.

Explanation

A breaker bar is a long, non-ratcheting handle that provides high leverage for loosening tight fasteners without damaging the ratchet mechanism of a torque wrench. A torque wrench is a measuring instrument for tightening to a specified value, not for breaking loose seized bolts. Using a spanner as a lever extension or a screwdriver adapter risks rounding the bolt head and personal injury.

Question 22Tools, Measuring Instruments and Workshop Equipment

When using a hydraulic floor jack to lift a car for wheel service, where should the jack pad be placed?

  1. Under the plastic side skirt
  2. Under the sump of the engine
  3. At the manufacturer's designated lifting point on the chassis Correct answer.
  4. Under the fuel tank

Explanation

The vehicle manufacturer marks specific reinforced lifting points on the chassis that can carry the vehicle's weight without deformation. Placing the jack under plastic trim, the fuel tank, or the engine sump can crush components and cause the vehicle to fall. After lifting, axle stands must be placed at the recommended support points before any work is done under the car.

Question 23Tools, Measuring Instruments and Workshop Equipment

A vernier caliper is used to measure the outside diameter of a brake disc. Which reading is taken from the main scale and vernier scale?

  1. The vernier reading only
  2. The average of the two jaws
  3. The main scale reading minus the vernier reading
  4. The main scale reading plus the vernier coincidence value Correct answer.

Explanation

The total measurement on a vernier caliper equals the main scale reading at the zero of the vernier plus the vernier division that coincides with a main scale line multiplied by the least count. This gives a resolution typically of 0.02 mm or 0.05 mm. Subtracting or using only one scale gives an incorrect diameter and would lead to machining errors.

Question 24Tools, Measuring Instruments and Workshop Equipment

A micrometer screw gauge has a least count of 0.01 mm. The sleeve shows 4.5 mm and the thimble reads 23 divisions. What is the measured thickness?

  1. 4.23 mm
  2. 4.68 mm
  3. 4.50 mm
  4. 4.73 mm Correct answer.

Explanation

The reading is the sleeve value plus the thimble divisions multiplied by the least count: 4.5 mm + (23 × 0.01 mm) = 4.73 mm. The sleeve already includes the half-millimetre mark, so no additional adjustment is needed. Recording only the sleeve value or only the thimble value loses precision.

Question 25Tools, Measuring Instruments and Workshop Equipment

A technician is using a dial indicator to check brake disc runout. What does the total indicator reading represent?

  1. The disc thickness variation
  2. The torque of the wheel bolts
  3. The static weight of the disc
  4. The maximum minus minimum deflection during one revolution Correct answer.

Explanation

Runout is measured as the difference between the highest and lowest dial indicator readings as the disc rotates one full turn. This total indicator reading (TIR) shows how far the disc surface deviates from a true plane. Thickness variation is a separate measurement taken with a micrometer at several points.

Question 26Tools, Measuring Instruments and Workshop Equipment

Which instrument is used to check the specific gravity of the electrolyte in a lead-acid battery?

  1. A feeler gauge
  2. A compression tester
  3. A multimeter set to ohms
  4. A hydrometer Correct answer.

Explanation

A hydrometer draws electrolyte into a float chamber and indicates its specific gravity, which corresponds to the battery's state of charge. A fully charged lead-acid cell typically reads around 1.265. A multimeter measures voltage, not electrolyte density, and a compression tester is for engine cylinders.

Question 27Tools, Measuring Instruments and Workshop Equipment

A torque wrench is stored after use. Which practice preserves its calibration?

  1. Store it with the handle locked at maximum torque
  2. Store it with the spring fully compressed at the set torque
  3. Store it in a bucket of oil
  4. Store it with the scale set to its lowest value and the spring relaxed Correct answer.

Explanation

Returning a click-type torque wrench to its lowest setting relaxes the internal spring and prevents fatigue that would shift calibration over time. Storing it at a high setting keeps the spring compressed and causes drift. The tool should also be kept clean and dry, not soaked in oil.

Question 28Tools, Measuring Instruments and Workshop Equipment

A technician must measure the valve clearance on an engine with a feeler gauge. Why is the blade drawn through the gap with a slight drag?

  1. To wear the blade to the correct size
  2. To measure the camshaft lift
  3. To check the oil pressure
  4. To confirm the blade fits with the specified slight resistance Correct answer.

Explanation

The correct feeler blade should pass through the clearance with a light, even drag, indicating the gap matches the blade thickness. If it will not enter, the gap is too small; if it passes freely, the gap is too large. This method verifies the clearance against the manufacturer's specification.

Question 29Tools, Measuring Instruments and Workshop Equipment

Which piece of workshop equipment is used to raise a vehicle so a technician can work underneath it safely?

  1. A bench vice
  2. A parts washer
  3. A tyre inflator
  4. A two-post hydraulic hoist Correct answer.

Explanation

A two-post hoist lifts the vehicle by its lifting points and holds it at working height with mechanical locks, giving access to the underside. It must be rated for the vehicle weight and inspected regularly. A bench vice, parts washer, and tyre inflator serve other workshop functions.

Question 30Tools, Measuring Instruments and Workshop Equipment

An impact wrench is being selected for removing wheel nuts. Which specification is most relevant to ensure adequate loosening force?

  1. Its air hose diameter only
  2. Its colour
  3. Its maximum breakaway torque rating Correct answer.
  4. Its handle length

Explanation

Breakaway torque is the peak torque an impact wrench can deliver to loosen a seized or tightened fastener, and it must exceed the wheel nut torque. The tool's working torque rating is lower than its breakaway figure. Handle length and colour do not determine loosening capability.

Question 31Tools, Measuring Instruments and Workshop Equipment

A compression tester shows low and uneven readings across the cylinders of a petrol engine. What is the most appropriate next step?

  1. Change the engine oil
  2. Replace the battery
  3. Perform a wet compression test by adding a little oil to each cylinder Correct answer.
  4. Increase the tyre pressure

Explanation

A wet test adds a small amount of oil to the cylinder to seal the rings temporarily. If compression rises, the rings are worn; if it stays low, the problem is likely valves or a head gasket. This distinguishes ring wear from valve leakage before any repair is authorised.

Question 32Tools, Measuring Instruments and Workshop Equipment

Which measuring instrument is best suited to check the diameter of a valve stem to an accuracy of 0.01 mm?

  1. An outside micrometer Correct answer.
  2. A tape measure
  3. A vernier caliper with 0.05 mm least count
  4. A steel rule

Explanation

An outside micrometer with a 0.01 mm least count provides the resolution and repeatability needed for a valve stem diameter check. A vernier caliper with 0.05 mm least count is not fine enough for this tolerance. Steel rules and tape measures are far too coarse.

Question 33Tools, Measuring Instruments and Workshop Equipment

A technician is checking a wheel for lateral runout using a dial indicator mounted on a magnetic base. Where should the base be attached?

  1. To a rigid, stationary part of the suspension or hub carrier Correct answer.
  2. To the tyre sidewall
  3. To the brake hose
  4. To the wheel rim itself

Explanation

The magnetic base must be fixed to a rigid, non-moving part of the vehicle so the indicator measures only wheel movement, not base movement. Attaching it to the rotating wheel or flexible parts introduces false readings. A stable reference is essential for accurate runout measurement.

Question 34Tools, Measuring Instruments and Workshop Equipment

Why should a torque wrench be calibrated periodically in a workshop?

  1. To convert it into an impact wrench
  2. To change its colour coding
  3. To ensure the applied torque remains within the manufacturer's tolerance Correct answer.
  4. To increase its maximum range

Explanation

Over time, use and storage cause a torque wrench's spring and mechanism to drift, so periodic calibration confirms it still applies the set torque within tolerance. Incorrect torque can cause fastener failure or component damage. Calibration does not change the tool's range or function.

Question 35Tools, Measuring Instruments and Workshop Equipment

A technician uses a tyre pressure gauge and gets 30 psi, but a second gauge reads 34 psi on the same tyre. What is the most reasonable conclusion?

  1. The tyre has no valve core
  2. The tyre pressure changed instantly
  3. At least one gauge is inaccurate and both should be checked against a known reference Correct answer.
  4. The wheel is out of balance

Explanation

A discrepancy between two gauges indicates that at least one is out of calibration, so both should be compared against a master gauge. Pressure does not change instantly without a leak or inflation. Valve core or balance issues would not cause a gauge reading difference.

Question 36Tools, Measuring Instruments and Workshop Equipment

Which tool is used to check the alignment of a vehicle's front wheels against the manufacturer's specification?

  1. A hacksaw
  2. A wheel alignment machine with laser or camera targets Correct answer.
  3. A bearing puller
  4. A grease gun

Explanation

A wheel alignment machine measures camber, caster, and toe using laser or camera targets mounted on the wheels and compares them with the specification. It is the standard workshop instrument for alignment. Bearing pullers, grease guns, and hacksaws serve unrelated tasks.

Question 37Tools, Measuring Instruments and Workshop Equipment

A technician uses a vacuum gauge on a petrol engine and observes a steady low reading at idle. Which condition is most consistent with this result?

  1. Correct tyre inflation
  2. A fully charged battery
  3. A new air filter
  4. A vacuum leak or late ignition timing Correct answer.

Explanation

A steady low vacuum reading at idle commonly indicates a vacuum leak, late ignition timing, or low compression. The gauge measures intake manifold vacuum, so any leak or timing fault lowers it. Battery charge, tyre pressure, and air filter condition are not indicated by manifold vacuum.

Question 38Tools, Measuring Instruments and Workshop Equipment

What is the purpose of a bearing puller in four-wheel vehicle service?

  1. To remove bearings or gears from shafts without damaging them Correct answer.
  2. To check battery voltage
  3. To tighten wheel nuts
  4. To measure bearing clearance

Explanation

A bearing puller uses a central screw and jaws or a split plate to draw a bearing or gear off a shaft evenly, avoiding damage to the component and shaft. It is a removal tool, not a measuring instrument. Measurement of clearance requires a micrometer or Plastigauge.

Question 39Tools, Measuring Instruments and Workshop Equipment

A technician must measure the thickness of a brake pad lining. Which tool gives the most direct and reliable reading?

  1. A vernier caliper or brake pad thickness gauge Correct answer.
  2. A tyre depth gauge
  3. A torque wrench
  4. A feeler gauge

Explanation

A vernier caliper or a dedicated brake pad thickness gauge directly measures the friction material thickness against the wear limit. A tyre depth gauge is designed for tread depth and not for pad lining. Feeler gauges and torque wrenches measure gaps and torque respectively.

Question 40Tools, Measuring Instruments and Workshop Equipment

A workshop uses a hydraulic press to install a wheel bearing. Which precaution protects both the press and the component?

  1. Apply force only to the outer race when pressing into the hub Correct answer.
  2. Use a hammer to help the press
  3. Exceed the press's rated capacity briefly
  4. Press on the inner race regardless of fit

Explanation

When pressing a bearing into a hub, force should be applied to the race that is being fitted, which is usually the outer race, so the load path does not pass through the rolling elements. Pressing on the wrong race can brinell the balls and ruin the bearing. The press must never exceed its rated capacity.

Question 41Engine Systems: Construction, Operation and Service

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

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

Explanation

The intake stroke is the first stroke of the Otto cycle, where the descending piston creates a partial vacuum and the open intake valve admits the air-fuel charge. The valve closes near BDC so the following compression stroke can raise the charge pressure.

Question 42Engine Systems: Construction, Operation and Service

A technician measures cylinder bore wear and finds the bore is 0.12 mm larger than the standard dimension. Which service action is normally required?

  1. Increase valve clearance to compensate for the wear
  2. Replace only the piston rings with standard rings
  3. Rebore to the next oversize and fit matching oversize pistons Correct answer.
  4. Reduce the compression ratio by fitting a thicker head gasket

Explanation

When bore taper and wear exceed the manufacturer's limit, the cylinder must be rebored or honed to the next oversize and oversize pistons and rings fitted to restore correct piston-to-bore clearance. Standard rings cannot seal an oversized, out-of-round bore.

Question 43Engine Systems: Construction, Operation and Service

The main function of the flywheel on a four-cylinder four-stroke engine is to:

  1. Drive the oil pump through a direct gear train
  2. Store kinetic energy and smooth out the power pulses between strokes Correct answer.
  3. Filter the engine oil before it reaches the bearings
  4. Increase the compression ratio during the intake stroke

Explanation

Only one power stroke occurs per two crankshaft revolutions per cylinder, so the flywheel absorbs energy during the power stroke and releases it during the other strokes. This keeps crankshaft rotation smooth and helps the engine idle steadily.

Question 44Engine Systems: Construction, Operation and Service

A compression test on a four-cylinder petrol engine gives readings of 11.5, 11.4, 6.2 and 11.6 bar. A wet test on the low cylinder raises it to 11.3 bar. What is the most likely cause?

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

Explanation

A dry compression reading that rises substantially after adding oil indicates the oil is sealing the piston rings, so the loss is past the rings or bore. A valve or gasket fault would not improve with the wet test.

Question 45Engine Systems: Construction, Operation and Service

In a valve train, the function of the rocker arm is to:

  1. Seal combustion gases at the valve guide
  2. Increase valve spring tension at high engine speed
  3. Change the direction of cam or pushrod motion to open the valve Correct answer.
  4. Drive the distributor through a gear on the camshaft

Explanation

The rocker arm pivots on a shaft or stud and transfers motion from the cam lobe or pushrod to the valve stem, reversing the direction of movement. Its rocker ratio also multiplies lift relative to cam lift.

Question 46Engine Systems: Construction, Operation and Service

A hydraulic lash adjuster in an overhead cam engine is noisy on cold start. Which condition is the most likely cause?

  1. Incorrect spark plug heat range
  2. Oil draining from the adjuster causing slow refill at start-up Correct answer.
  3. Too large a valve seat width
  4. Excessive valve spring free length

Explanation

Hydraulic lash adjusters rely on oil pressure to maintain zero clearance; if oil drains out overnight, the adjuster collapses and the valve train rattles until oil pressure refills it. Worn check valves or low oil pressure worsen the condition.

Question 47Engine Systems: Construction, Operation and Service

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

  1. Connecting rod Correct answer.
  2. Camshaft
  3. Pushrod
  4. Timing belt

Explanation

The connecting rod links the piston pin to the crankshaft journal and, as it swings through its arc, converts the piston's straight-line motion into crankshaft rotation. Its length and bearing condition affect both stroke geometry and engine balance.

Question 48Engine Systems: Construction, Operation and Service

The purpose of the thermostat in an engine cooling system is to:

  1. Control the speed of the radiator cooling fan
  2. Maintain a fixed coolant pressure in the radiator
  3. Prevent coolant from boiling at high altitude
  4. Regulate coolant flow so the engine reaches and maintains operating temperature Correct answer.

Explanation

The thermostat stays closed during warm-up so the engine reaches operating temperature quickly, then opens to allow coolant flow to the radiator and modulates opening to hold temperature steady. This improves combustion efficiency and heater performance.

Question 49Engine Systems: Construction, Operation and Service

A diesel engine runs but produces excessive blue-white smoke at idle. Which condition best explains this?

  1. Injector nozzle wear causing poor atomisation Correct answer.
  2. Over-advanced injection timing
  3. Too high a compression ratio
  4. Excessive coolant temperature

Explanation

Blue-white smoke indicates unburnt fuel in the exhaust, often caused by poor atomisation from worn or dirty injector nozzles, low compression, or cold engine operation. Poor atomisation prevents complete combustion and creates visible smoke.

Question 50Engine Systems: Construction, Operation and Service

In a multi-point fuel injection system, the engine coolant temperature sensor signal is used by the ECM mainly to:

  1. Enrich the fuel mixture during cold start and warm-up Correct answer.
  2. Control the fuel pump relay during cranking
  3. Adjust ignition timing based on knock
  4. Set the idle speed based on vehicle speed

Explanation

The coolant temperature sensor tells the ECM how warm the engine is, so the ECM can add extra fuel during cold starting and warm-up when fuel vaporises poorly. Once the engine is warm, the ECM trims fuel back to normal.