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WBCHSE HS Vocational Automobile study materials
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WBCHSE HS Vocational Automobile practice questions

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Question 1Automobile Fundamentals and Workshop Safety

In an automobile workshop, which personal protective equipment is most important when grinding metal with a pedestal grinder?

  1. A leather apron only
  2. Safety goggles or a face shield Correct answer.
  3. Ear plugs only
  4. Cotton hand gloves

Explanation

Grinding throws hot metal particles and abrasive dust at high speed, so eye and face protection is the first requirement. Goggles or a face shield must be worn even for a short job. Other protection may be added but cannot replace eye protection.

Question 2Automobile Fundamentals and Workshop Safety

A four-stroke petrol engine completes one full working cycle in how many revolutions of the crankshaft?

  1. Half a revolution
  2. Four revolutions
  3. One revolution
  4. Two revolutions Correct answer.

Explanation

In a four-stroke engine the piston makes four strokes, namely suction, compression, power and exhaust, during one cycle. These four strokes need two complete turns of the crankshaft. Hence the camshaft turns once for every two crankshaft turns.

Question 3Automobile Fundamentals and Workshop Safety

Which component transmits the rotary motion of the engine to the gearbox while allowing it to be engaged and disengaged smoothly?

  1. Propeller shaft
  2. Differential
  3. Radiator
  4. Clutch Correct answer.

Explanation

The clutch sits between the engine flywheel and the gearbox and can connect or disconnect the drive. This lets the driver change gears and start from rest without shock. The differential and propeller shaft are further down the transmission line.

Question 4Automobile Fundamentals and Workshop Safety

Why is a fuse fitted in an electrical circuit of a motor vehicle?

  1. To melt and break the circuit when current is excessive Correct answer.
  2. To convert direct current into alternating current
  3. To increase the current in the circuit
  4. To store electrical energy for later use

Explanation

A fuse contains a thin wire that melts when the current exceeds its rating, opening the circuit. This protects wiring and components from overheating and fire. It is a deliberate weak point in the circuit.

Question 5Automobile Fundamentals and Workshop Safety

In a hydraulic braking system, which property of the brake fluid makes it suitable for transmitting pedal force?

  1. It is incompressible Correct answer.
  2. It is a good conductor of electricity
  3. It is flammable
  4. It is compressible

Explanation

Liquids are almost incompressible, so pressure applied at the master cylinder is transmitted almost undiminished to the wheel cylinders. This gives a firm pedal and reliable braking force. A compressible medium would make the pedal spongy.

Question 6Automobile Fundamentals and Workshop Safety

Which instrument is used to measure the diameter of a cylinder bore to check for wear?

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

Explanation

A bore gauge or inside micrometer is designed to measure internal diameters accurately. Cylinder wear is judged by comparing readings at several heights and directions. A vernier caliper is less precise for deep bores.

Question 7Automobile Fundamentals and Workshop Safety

Which of the following is the correct first action when a person receives an electric shock from workshop equipment?

  1. Pour water on the person
  2. Switch off the power supply immediately Correct answer.
  3. Pull the person away with bare hands
  4. Give the person a hot drink

Explanation

The supply must be isolated first so that the rescuer does not also become part of the circuit. Only then should the casualty be moved and first aid given. Touching the casualty while the current flows is extremely dangerous.

Question 8Automobile Fundamentals and Workshop Safety

A mechanic must lift a heavy gearbox from the floor. Which method best follows correct manual handling practice?

  1. Twist the body while lifting
  2. Hold the load at arm's length
  3. Bend the back and lift quickly
  4. Keep the back straight, bend the knees and lift with leg muscles Correct answer.

Explanation

Bending the knees and keeping the back straight lets the strong leg muscles do the work. Twisting or jerking while loaded is a common cause of back injury. Heavy items should be lifted close to the body or with a hoist.

Question 9Automobile Fundamentals and Workshop Safety

In a four-stroke diesel engine, fuel is introduced into the cylinder at which stage?

  1. During the power stroke
  2. During the suction stroke
  3. At the start of the exhaust stroke
  4. Near the end of the compression stroke Correct answer.

Explanation

A diesel engine draws in only air, compresses it to a high pressure and temperature, and then injects fuel. The heat of compression ignites the fuel without a spark plug. Injection near the end of compression gives the best power and efficiency.

Question 10Automobile Fundamentals and Workshop Safety

The purpose of providing a clearance between the piston and the cylinder wall is to allow for which of the following?

  1. Escape of combustion gases
  2. Movement of the crankshaft
  3. Lubricating oil storage only
  4. Thermal expansion of the piston Correct answer.

Explanation

The piston becomes hotter than the cylinder during operation and expands more. A small running clearance prevents seizure while keeping blow-by low. The clearance is set by the manufacturer and checked during overhaul.

Question 11Automobile Fundamentals and Workshop Safety

Which type of gearbox provides an uninterrupted flow of power to the wheels while gear ratios are changed?

  1. Synchromesh gearbox
  2. Constant mesh gearbox with dog clutch
  3. Epicyclic gearbox used with a torque converter Correct answer.
  4. Sliding mesh gearbox

Explanation

An epicyclic gear train combined with a torque converter changes ratio by locking or releasing brake bands, so drive is never cut. A conventional synchromesh still needs the clutch and a brief break in drive. This is why automatic transmissions feel smooth.

Question 12Automobile Fundamentals and Workshop Safety

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

  1. Reduce engine noise
  2. Allow the rear wheels to rotate at different speeds while turning Correct answer.
  3. Increase engine torque before the gearbox
  4. Change the direction of the engine crankshaft only

Explanation

When a vehicle turns, the outer rear wheel travels a longer path than the inner one. The differential lets the two half-shafts rotate at different speeds while still delivering torque. Without it, tyres would scrub and the axle would be stressed.

Question 13Automobile Fundamentals and Workshop Safety

A vehicle pulls to one side when the brakes are applied. Which is the most likely cause?

  1. A worn clutch plate
  2. A weak return spring on the accelerator
  3. Low engine oil level
  4. Unequal braking force at the wheels, such as a seized wheel cylinder on one side Correct answer.

Explanation

If one wheel brakes harder than the other, the vehicle yaws towards the stronger side. Common causes are a seized or leaking wheel cylinder, a blocked brake line or contaminated linings on one side. The fault must be corrected before the vehicle is used.

Question 14Automobile Fundamentals and Workshop Safety

Which of the following best explains why the radiator cap of a modern cooling system is pressurised?

  1. To reduce the pressure inside the engine block
  2. To reduce the coolant flow rate
  3. To raise the boiling point of the coolant Correct answer.
  4. To increase the freezing point of the coolant

Explanation

Raising the pressure inside the cooling system raises the boiling point of the coolant. The engine can then run hotter without the coolant boiling, which improves heat transfer and efficiency. The cap also releases pressure to the overflow tank when it exceeds the rated value.

Question 15Automobile Fundamentals and Workshop Safety

What is the main function of the alternator in a vehicle charging system?

  1. To store fuel for the engine
  2. To start the engine
  3. To convert mechanical energy into electrical energy and charge the battery Correct answer.
  4. To ignite the air-fuel mixture

Explanation

The alternator is belt-driven by the engine and converts mechanical energy into electrical energy. Its rectifier converts AC into DC to charge the battery and run the electrical loads. The starter motor, not the alternator, cranks the engine.

Question 16Automobile Fundamentals and Workshop Safety

A tyre shows heavy wear on both outer edges with the centre tread still deep. Which condition most likely explains this?

  1. Over-inflation
  2. Under-inflation Correct answer.
  3. Excessive wheel camber only
  4. Worn shock absorbers only

Explanation

Under-inflation makes the tyre sag so the outer shoulders carry most of the load, wearing both edges. The centre stays relatively unworn. Correct inflation pressure and regular checking prevent this pattern.

Question 17Automobile Fundamentals and Workshop Safety

Which of the following is the correct way to store a charged lead-acid battery in a workshop?

  1. On a metal shelf in direct sunlight
  2. On a dry, ventilated rack away from sparks and direct sunlight Correct answer.
  3. Near an open flame to keep it warm
  4. Lying on its side on the floor

Explanation

A lead-acid battery gives off hydrogen, which can form an explosive mixture with air. It should be kept upright on a dry, ventilated rack away from sparks, flames and direct sun. Terminals should be protected against accidental short circuits.

Question 18Automobile Fundamentals and Workshop Safety

During a compression test on a petrol engine, one cylinder reads much lower than the others. Adding a little oil to that cylinder raises the reading. What does this indicate?

  1. Worn piston rings or cylinder bore Correct answer.
  2. A burnt exhaust valve
  3. A leaking cylinder head gasket
  4. A blocked air filter

Explanation

Oil added to the cylinder temporarily seals the gap between the piston rings and the bore. If compression rises, the loss was past the rings. A valve or gasket leak would not be sealed by the oil.

Question 19Automobile Fundamentals and Workshop Safety

A torque wrench is used to tighten a cylinder head bolt. Which statement describes the correct use?

  1. Apply torque to the bolt head with a pipe extension
  2. Use the wrench as a hammer to seat the bolt
  3. Set the wrench to the maximum scale to save time
  4. Set the wrench to the specified torque and tighten the bolt in the recommended sequence Correct answer.

Explanation

Cylinder head bolts must be tightened to the manufacturer's torque and in the correct sequence to avoid distorting the head. A torque wrench clicks or signals when the set value is reached. It should never be overloaded or used as a lever.

Question 20Automobile Fundamentals and Workshop Safety

Which statement correctly describes the function of a catalytic converter fitted in the exhaust system of a petrol car?

  1. It converts harmful gases such as carbon monoxide and unburnt hydrocarbons into less harmful substances Correct answer.
  2. It increases engine power by supercharging the intake
  3. It reduces the noise of the exhaust pulse
  4. It cools the exhaust gases before they leave the tailpipe

Explanation

A catalytic converter uses a platinum or palladium catalyst to oxidise carbon monoxide and hydrocarbons and reduce nitrogen oxides. It turns them into carbon dioxide, water vapour and nitrogen. It does not add power or silence the exhaust.

Question 21Automobile Fundamentals and Workshop Safety

A vehicle with a manual gearbox jumps out of gear when accelerating. Which is the most likely cause?

  1. A dirty air filter
  2. A weak battery
  3. Worn gear teeth and detent springs in the gearbox Correct answer.
  4. Low coolant level

Explanation

Jumping out of gear usually points to worn gear teeth, a worn selector detent or a loose selector fork. The gear cannot stay engaged under load. The gearbox must be inspected and the worn parts replaced.

Question 22Automobile Fundamentals and Workshop Safety

Which of the following best explains why a turbocharger fitted to a diesel engine improves power output?

  1. It reduces the compression ratio of the engine
  2. It forces more air into the cylinder, allowing more fuel to be burnt Correct answer.
  3. It changes the valve timing automatically
  4. It cools the fuel before injection

Explanation

A turbocharger uses exhaust gas energy to drive a compressor that forces extra air into the cylinder. With more air, more fuel can be burnt, giving greater power from the same engine size. An intercooler may further increase the effect by cooling the compressed air.

Question 23Automobile Fundamentals and Workshop Safety

An engine has a bore of 80 mm and a stroke of 90 mm. Using the formula for cylinder volume, what is the swept volume of one cylinder approximately?

  1. 180 cc
  2. 904 cc
  3. 226 cc
  4. 452 cc Correct answer.

Explanation

Swept volume is π/4 × bore² × stroke. Here π/4 × 8² × 9 = 0.7854 × 64 × 9 ≈ 452 cc. The bore and stroke must be converted to centimetres before the calculation.

Question 24Automobile Fundamentals and Workshop Safety

During a road test, a car's steering wheel vibrates at high speed but the vibration is absent at low speed. Which is the most probable cause?

  1. Incorrect wheel balance or a distorted tyre Correct answer.
  2. A worn clutch release bearing
  3. A faulty horn switch
  4. Low brake fluid level

Explanation

Vibration that appears only at higher road speed is typical of wheel imbalance or a distorted tyre casing. The centrifugal force increases with speed, so the shake becomes noticeable. Wheel alignment can also contribute but imbalance is the first check.

Question 25Engine Systems and Overhauling

In a four-stroke petrol engine, during which stroke does the intake valve normally remain open?

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

Explanation

The intake (suction) valve opens as the piston moves down from TDC so the air-fuel mixture is drawn into the cylinder. It closes near bottom dead centre to trap the charge for compression. The other strokes involve closed valves or the exhaust valve opening.

Question 26Engine Systems and Overhauling

The firing order of a four-cylinder in-line engine is commonly arranged as 1-3-4-2. What is the main reason for spacing the firing of cylinders in this sequence?

  1. To balance the load on the crankshaft and reduce vibration Correct answer.
  2. To make the camshaft rotate at crankshaft speed
  3. To keep the intake valve of every cylinder open together
  4. To allow all four spark plugs to fire at the same instant

Explanation

A staggered firing order distributes power impulses evenly along the crankshaft, reducing torsional vibration and bearing load. Firing all cylinders together would concentrate stress and give uneven running. Valve timing and camshaft speed ratio are fixed by design, not by firing order.

Question 27Engine Systems and Overhauling

A technician measures the cylinder bore of an engine and finds it tapered, being wider at the top than at the bottom. Which component is most directly responsible for this wear pattern?

  1. The oil control ring scraping the lower bore
  2. The top compression ring pressing against the upper bore Correct answer.
  3. The valve stem seal leaking oil
  4. The crankshaft counterweight rubbing the liner

Explanation

The uppermost compression ring is forced hardest against the cylinder wall near top dead centre, where combustion pressure and temperature peak, so the top of the bore wears more. This produces the characteristic taper. Oil control rings act lower down and do not cause top-end widening.

Question 28Engine Systems and Overhauling

Which instrument is most suitable for checking the internal diameter of a cylinder bore at several depths?

  1. A vernier caliper used only on the outside jaws
  2. A torque wrench
  3. A bore gauge (dial bore gauge) Correct answer.
  4. A feeler gauge

Explanation

A dial bore gauge is designed to measure internal diameters and can be positioned at different depths to reveal taper and ovality. A feeler gauge measures gaps, and outside jaws of a caliper measure external dimensions. A torque wrench measures tightening force, not size.

Question 29Engine Systems and Overhauling

In a diesel engine, fuel is injected near the end of the compression stroke rather than mixed with air during suction. What does this allow the engine to do?

  1. Operate without any compression of the intake air
  2. Run on a fixed air-fuel ratio controlled by a carburettor
  3. Use a spark plug to ignite a premixed charge
  4. Achieve a very high compression ratio and ignite fuel by heat of compression Correct answer.

Explanation

Because only air is compressed, diesel engines can use high compression ratios that raise air temperature enough to ignite injected fuel spontaneously. There is no spark plug and no premixed carburetted charge. This is the basis of compression ignition.

Question 30Engine Systems and Overhauling

During valve clearance adjustment on an overhead valve engine, the feeler gauge should be inserted between which two parts?

  1. The camshaft lobe and the tappet base circle
  2. The piston crown and the cylinder head
  3. The valve face and the valve seat
  4. The rocker arm and the valve stem tip Correct answer.

Explanation

Valve clearance is the gap between the rocker arm (or tappet) and the valve stem tip when the valve is fully closed. The feeler gauge of the specified thickness should slide with slight drag. Measuring at the valve face or piston gives unrelated dimensions.

Question 31Engine Systems and Overhauling

A cylinder head gasket has failed between two adjacent cylinders. Which symptom combination would most likely be observed?

  1. Only the radiator cap releases pressure
  2. The engine oil level rises with no other change
  3. Two adjacent cylinders show low compression and the engine misfires Correct answer.
  4. The spark plugs in all cylinders foul equally

Explanation

A breach between two cylinders lets compression leak from one into the other, so both lose pressure and misfire. A compression test would show two neighbouring cylinders reading low. Other gasket failures such as coolant passage leaks give different symptoms.

Question 32Engine Systems and Overhauling

What is the primary function of the piston rings fitted in the grooves of a piston?

  1. To transfer torque from the piston to the camshaft
  2. To lock the piston pin to the connecting rod
  3. To cool the cylinder head
  4. To seal combustion gases and control oil on the cylinder wall Correct answer.

Explanation

Compression rings seal the combustion chamber against blow-by, while the oil control ring scrapes excess oil from the bore. Rings do not transmit torque to the camshaft or lock the piston pin. Cooling is handled by the cooling system.

Question 33Engine Systems and Overhauling

An engine is being reassembled and the connecting rod bolts must be tightened to a specified torque. Which practice is correct?

  1. Tighten by feel until the bolt stops turning
  2. Tighten all bolts fully before fitting the bearing caps
  3. Apply maximum force with a long pipe extension
  4. Use a calibrated torque wrench and follow the specified sequence Correct answer.

Explanation

Connecting rod bolts must be tightened with a calibrated torque wrench to the manufacturer's figure and in the specified sequence to ensure even clamping. Over-tightening by feel or with cheater bars can stretch or break the bolts. Bearings must be correctly seated before final tightening.

Question 34Engine Systems and Overhauling

Which of the following best describes the purpose of the radiator thermostat in an engine cooling system?

  1. To regulate coolant flow so the engine reaches and maintains operating temperature Correct answer.
  2. To pump coolant through the engine block
  3. To cool the lubricating oil separately
  4. To increase the octane rating of the fuel

Explanation

The thermostat stays closed when the engine is cold, allowing it to warm up quickly, then opens at a set temperature to allow coolant flow to the radiator. This maintains an efficient operating temperature. The water pump circulates coolant, and oil cooling is separate.

Question 35Engine Systems and Overhauling

During a compression test on a petrol engine, one cylinder reads significantly lower than the others. Adding a small amount of oil to that cylinder raises the reading noticeably. What does this indicate?

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

Explanation

Oil temporarily seals the gap between worn rings and the bore, so compression rises. If the reading does not improve, the leak is more likely at the valves or gasket. Ignition timing does not affect a compression reading.

Question 36Engine Systems and Overhauling

What is the main reason for fitting a flywheel to an engine?

  1. To increase the compression ratio
  2. To drive the camshaft at half speed
  3. To filter the engine oil
  4. To store rotational energy and smooth out power impulses Correct answer.

Explanation

The flywheel's inertia carries the crankshaft through the non-power strokes, giving smoother running and helping starting. It does not change compression ratio or drive the camshaft, which is done by the timing chain or belt. Oil filtration is a separate system.

Question 37Engine Systems and Overhauling

A valve seat in a cylinder head is found to be badly pitted. Which overhauling action is most appropriate?

  1. Advance the ignition timing
  2. Recut or replace the valve seat and lap the valve to it Correct answer.
  3. Fit a thicker head gasket
  4. Increase the valve clearance to compensate

Explanation

A pitted seat prevents proper sealing, so it must be recut with a seat cutter or replaced, then the valve is lapped to match. Adjusting clearance or gasket thickness does not restore the sealing surface. Ignition timing has no effect on valve sealing.

Question 38Engine Systems and Overhauling

Which statement correctly describes the relationship between crankshaft speed and camshaft speed in a four-stroke engine?

  1. The camshaft rotates only during the power stroke
  2. The camshaft rotates at twice the crankshaft speed
  3. The camshaft rotates at half the crankshaft speed Correct answer.
  4. The camshaft rotates at the same speed as the crankshaft

Explanation

A four-stroke cycle takes two crankshaft revolutions, during which the camshaft completes one revolution to open each valve once. Hence the camshaft runs at half crankshaft speed. This ratio is set by the size of the timing gears or sprockets.

Question 39Engine Systems and Overhauling

Excessive valve tappet clearance on an engine will most likely cause which of the following?

  1. Noisy operation and reduced valve lift Correct answer.
  2. Excessive oil consumption through the guides
  3. Burning of the valve due to tight seating
  4. Overheating of the spark plug

Explanation

Too much clearance means the rocker strikes the valve stem late and lifts it less, producing a rattling noise and reduced breathing. Tight clearance, not excessive clearance, keeps valves from seating and can burn them. Oil consumption and plug heat range are unrelated.

Question 40Engine Systems and Overhauling

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

  1. The camshaft
  2. The connecting rod Correct answer.
  3. The pushrod
  4. The timing belt

Explanation

The connecting rod links the piston to the crankshaft crankpin, converting straight-line piston motion into rotation. The camshaft operates the valves, the pushrod transfers cam action to the rocker, and the timing belt drives the camshaft.

Question 41Engine Systems and Overhauling

During an engine overhaul the cylinder liners are found to be worn beyond the specified limit. Which course of action is correct?

  1. Increase the ring end gap to compensate
  2. Reduce the compression ratio by skimming the head
  3. Fit oversize piston rings to the worn bore only
  4. Rebore and fit oversize pistons, or replace the liners Correct answer.

Explanation

When bore wear exceeds the limit, the cylinder must be rebored and honed to accept oversize pistons, or a replaceable liner renewed. Fitting oversize rings to a worn, tapered bore will not restore correct clearances. Altering the head does not correct bore wear.

Question 42Engine Systems and Overhauling

What is the purpose of the oil pump relief valve in a lubrication system?

  1. To indicate low oil level on the dashboard
  2. To filter metal particles from the oil
  3. To limit maximum oil pressure by bypassing excess oil Correct answer.
  4. To cool the oil before it reaches the bearings

Explanation

The relief valve opens when oil pressure exceeds a set value, diverting excess oil back to the sump so pressure stays within safe limits. Filtration is done by the oil filter, and cooling by an oil cooler. The dipstick or sensor indicates level.

Question 43Engine Systems and Overhauling

A petrol engine shows pre-ignition and knocking under load. Which of the following is a likely cause that an overhaul technician should check?

  1. Carbon deposits raising the compression ratio and creating hot spots Correct answer.
  2. Low coolant level in the radiator
  3. A clogged air filter reducing air supply
  4. A loose alternator belt

Explanation

Carbon deposits in the combustion chamber reduce chamber volume and can glow red-hot, causing knocking and pre-ignition. Removing deposits during overhaul restores the intended compression ratio. Air filter restriction, coolant level and belt tension do not create hot spots.

Question 44Engine Systems and Overhauling

Which of the following best explains why cylinder bores are honed to a fine cross-hatch pattern after reboring?

  1. To increase the bore diameter beyond the piston size
  2. To harden the cylinder surface by heat treatment
  3. To remove the piston from the connecting rod
  4. To help retain an oil film and assist ring bedding-in Correct answer.

Explanation

The cross-hatch honing marks hold oil on the bore walls and allow new rings to bed in properly during running-in. Honing is a controlled finishing process that does not oversize the bore or harden it. It has nothing to do with piston removal.

Question 45Engine Systems and Overhauling

An engine is difficult to start and a compression test shows uniformly low readings across all cylinders. Which cause is most consistent with this result?

  1. A faulty spark plug in one cylinder
  2. A leaking gasket between two cylinders
  3. A single burnt exhaust valve
  4. Worn piston rings across the whole engine Correct answer.

Explanation

Uniformly low compression on every cylinder points to a common cause such as general ring and bore wear or incorrect valve timing. A single burnt valve or a local gasket leak would affect only one or two cylinders. A faulty plug affects ignition, not compression.

Question 46Engine Systems and Overhauling

What is the function of the valve spring in a poppet valve assembly?

  1. To rotate the valve during operation
  2. To seal the valve guide against oil
  3. To close the valve and keep it seated when the cam is not lifting it Correct answer.
  4. To open the valve against cam pressure

Explanation

The valve spring returns the valve to its seat and holds it closed against cylinder pressure between cam lifts. Opening is done by the cam acting through the tappet or rocker. The spring does not seal the guide or rotate the valve.

Question 47Engine Systems and Overhauling

A mechanic is measuring the ring end gap of a new compression ring before fitting. Where should the ring be placed for this measurement?

  1. Squarely inside the cylinder bore using a piston to push it down Correct answer.
  2. Between the connecting rod and the crankshaft
  3. Around the piston skirt outside the bore
  4. On a flat bench beside the cylinder

Explanation

Ring end gap must be checked with the ring squared in the actual bore at the correct depth, because the gap depends on bore size. Measuring outside the bore or on the bench gives a false reading. The connecting rod area is unrelated to ring gap.

Question 48Engine Systems and Overhauling

Which of the following describes the correct order of operations when removing a cylinder head from an engine?

  1. Pry the head up at one corner with a chisel
  2. Remove the head while it is still hot to save time
  3. Slacken the head bolts gradually in the specified reverse sequence and remove the head without distortion Correct answer.
  4. Loosen all bolts fully one by one from the centre outwards

Explanation

Head bolts should be slackened progressively in the reverse of the tightening sequence, working from the ends towards the centre, to avoid warping the head. Removing bolts fully in one pass or prying can distort or damage the head and gasket faces.

Question 49Engine Systems and Overhauling

What does the term 'valve overlap' refer to in a four-stroke engine?

  1. The period when both intake and exhaust valves are open near top dead centre Correct answer.
  2. The gap between the valve stem and the rocker arm
  3. The clearance between the piston and the cylinder head
  4. The distance the valve moves from its seat

Explanation

Valve overlap occurs near the end of the exhaust stroke and start of the intake stroke, when both valves are briefly open together to improve scavenging and cylinder filling. It is a timing characteristic, not a clearance or lift dimension.

Question 50Engine Systems and Overhauling

When measuring the crankshaft journal for out-of-round using a micrometer, at which points should the readings be taken?

  1. At the centre of the journal only, in one direction
  2. At two positions 90 degrees apart around the journal circumference Correct answer.
  3. At the oil hole and at the parting line only
  4. At the fillet radius on each side of the journal

Explanation

Out-of-round is the difference between the maximum and minimum diameter of a journal, so measurements must be taken at several points around the circumference, typically at 90-degree intervals, and compared. A single reading cannot reveal taper or ovality, and measuring only at the oil hole or fillet does not give the diametric variation.