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BTEB Motorcycle Servicing study materials
BTEB Motorcycle Servicing study resources

BTEB Motorcycle Servicing practice questions

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Question 1Occupational Health, Safety and Environment

Which type of fire extinguisher is suitable for a petrol fire in a motorcycle workshop?

  1. Water extinguisher
  2. Wet chemical extinguisher
  3. Carbon dioxide extinguisher Correct answer.
  4. Foam extinguisher

Explanation

Petrol is a flammable liquid fire (Class B), and carbon dioxide smothers it without leaving residue or conducting electricity. Water and foam can spread burning fuel, and wet chemical extinguishers are designed for cooking oils.

Question 2Occupational Health, Safety and Environment

What is the main purpose of wearing safety goggles while grinding or wire-brushing metal parts?

  1. To improve close-up vision of the workpiece
  2. To reduce noise from the grinder
  3. To keep dust off the face
  4. To protect the eyes from flying particles Correct answer.

Explanation

Grinding and wire brushing throw off high-speed metal chips and abrasive fragments that can injure or blind an eye. Goggles form a sealed barrier around the eyes so these particles cannot strike them.

Question 3Occupational Health, Safety and Environment

Why should a motorcycle engine be allowed to cool before the coolant drain plug is removed?

  1. To make the coolant drain faster
  2. To prevent scalding from pressurised hot coolant Correct answer.
  3. To avoid damaging the drain plug thread
  4. To stop the coolant from freezing

Explanation

A hot cooling system is under pressure, so releasing the plug can spray boiling coolant onto the skin. Letting the engine cool lowers both temperature and pressure, removing the scalding risk.

Question 4Occupational Health, Safety and Environment

Which practice best prevents carbon monoxide exposure when running an engine during servicing?

  1. Closing all doors to keep noise inside
  2. Running the engine only in a sealed bay
  3. Routing the exhaust to an extraction system or outdoors Correct answer.
  4. Opening a small window nearby

Explanation

Carbon monoxide is colourless, odourless and deadly, so exhaust gas must be captured at source or discharged outside. A dedicated extraction hose or running the engine outdoors keeps the gas out of the breathing zone.

Question 5Occupational Health, Safety and Environment

What does the term 'manual handling' refer to in a motorcycle workshop?

  1. Lifting, carrying and moving loads by hand or bodily force Correct answer.
  2. Adjusting controls on a test bench
  3. Operating hand tools such as spanners
  4. Handing over a job to another technician

Explanation

Manual handling covers any transporting or supporting of a load using the body, such as lifting an engine or pushing a bike. Correct technique and mechanical aids reduce strain injuries to the back and limbs.

Question 6Occupational Health, Safety and Environment

Why is it important to disconnect the battery negative terminal first when working on a motorcycle electrical system?

  1. It prevents accidental short circuits to the frame Correct answer.
  2. It resets the engine control unit
  3. It increases the charging current
  4. It protects the battery from overcharging

Explanation

The frame is connected to the negative terminal, so a spanner touching it and a live positive point can create a spark or burn. Removing the negative lead first breaks that return path and reduces short-circuit risk.

Question 7Occupational Health, Safety and Environment

A technician must lift a motorcycle engine weighing about 60 kg from a bench to a stand. What is the most appropriate control?

  1. Twist the torso while lifting to place it accurately
  2. Lift it quickly to reduce the time under load
  3. Use a hoist or two-person team lift Correct answer.
  4. Hold it at arm's length for better balance

Explanation

A 60 kg load exceeds safe single-person lifting limits, so mechanical assistance or a team lift is required. Keeping the load close and avoiding twisting further reduces spinal strain.

Question 8Occupational Health, Safety and Environment

During spray painting of a fuel tank, which combination of controls gives the best protection?

  1. A face shield only
  2. A supplied-air or cartridge respirator plus local exhaust ventilation Correct answer.
  3. A cotton cloth over the nose and mouth
  4. A dust mask and open workshop door

Explanation

Paint mists and solvent vapours require both respiratory protection matched to the substance and ventilation to remove contaminants at source. Local exhaust plus a suitable respirator gives layered protection.

Question 9Occupational Health, Safety and Environment

A grinder's abrasive disc is rated for 11,000 rpm but the tool runs at 13,000 rpm. What is the correct action?

  1. Fit the disc and run the tool at reduced speed
  2. Do not fit the disc; select one rated at or above the tool speed Correct answer.
  3. Fit the disc and check it for cracks first
  4. Use the disc but stand to one side

Explanation

A disc must be rated at least as high as the tool's free speed, otherwise centrifugal force can burst it. Reducing trigger pressure does not reliably limit governed tool speed, so the disc must simply not be used.

Question 10Occupational Health, Safety and Environment

A workshop floor is often contaminated with engine oil. Which measure most directly reduces slip risk?

  1. Increasing lighting in the area
  2. Cleaning spills promptly and using absorbent or anti-slip flooring Correct answer.
  3. Placing warning cones near the spill
  4. Asking staff to walk more slowly

Explanation

Slips are best prevented by removing the contaminant and improving floor grip, not by warning alone. Prompt cleaning with absorbents plus suitable flooring addresses the hazard at its source.

Question 11Occupational Health, Safety and Environment

Which statement correctly describes the purpose of a risk assessment?

  1. It identifies hazards and evaluates controls to reduce harm Correct answer.
  2. It lists the tools required for a service job
  3. It proves that a workshop is completely safe
  4. It records accidents that have already happened

Explanation

A risk assessment systematically identifies hazards, judges who might be harmed and how, and sets out controls proportional to the risk. It is a living process, not a guarantee of zero harm.

Question 12Occupational Health, Safety and Environment

Why must used engine oil never be poured down a workshop drain?

  1. It contains toxic contaminants and pollutes watercourses Correct answer.
  2. It corrodes plastic pipework immediately
  3. It makes the drain smell unpleasant
  4. It evaporates too quickly to drain away

Explanation

Used oil carries heavy metals and other contaminants that harm aquatic life and contaminate water supplies. It must be stored in labelled containers and collected by a licensed waste contractor.

Question 13Occupational Health, Safety and Environment

A technician notices a frayed live wire on a bench lamp. What should be done first?

  1. Wear insulating gloves and keep using it
  2. Take the lamp out of use and isolate it Correct answer.
  3. Tape the frayed section and continue working
  4. Move the lamp to another bench

Explanation

Damaged insulation exposes live conductors and creates a shock and fire risk, so the equipment must be taken out of service and isolated before any repair. Only a competent person should then repair or replace it.

Question 14Occupational Health, Safety and Environment

Which action best controls noise exposure when using an air impact wrench for long periods?

  1. Combine quieter tools or methods with hearing protection and exposure limits Correct answer.
  2. Turn up the compressor pressure
  3. Rely on hearing protection alone
  4. Work faster to shorten the exposure

Explanation

Noise should be controlled at source first, then by reducing exposure time and providing hearing protection. Relying on ear defenders alone ignores the hierarchy of control and may exceed exposure limits.

Question 15Occupational Health, Safety and Environment

A fuel tank is being drained in a pit with poor ventilation. Which hazard is most significant?

  1. Excessive lighting levels
  2. Increased tyre wear
  3. Flammable vapour accumulating at low level Correct answer.
  4. High humidity causing rust

Explanation

Petrol vapour is heavier than air and collects in low areas such as pits, where a spark can ignite it. Ventilation and removal of ignition sources are essential before draining fuel in such spaces.

Question 16Occupational Health, Safety and Environment

Which document should be consulted before handling a chemical degreaser for the first time?

  1. The vehicle service schedule
  2. The safety data sheet and product label Correct answer.
  3. The workshop parts catalogue
  4. The tool calibration record

Explanation

A safety data sheet gives the hazards, exposure controls and first-aid measures for a substance, while the label gives immediate handling and storage information. Together they inform safe use and required PPE.

Question 17Occupational Health, Safety and Environment

A workshop stores petrol in an unmarked plastic bottle on a shelf. Why is this a serious breach of safe practice?

  1. Petrol should only be stored in glass bottles
  2. Shelves are not strong enough for any liquids
  3. Unlabelled containers can be mistaken for other fluids and the fuel is not properly contained Correct answer.
  4. Plastic bottles are always too weak for liquids

Explanation

Chemicals must be kept in suitable, clearly labelled containers so they cannot be confused with drinks or other fluids. Approved fuel containers also resist permeation and reduce fire risk.

Question 18Occupational Health, Safety and Environment

An apprentice is asked to weld a motorcycle frame but has no welding training. What is the correct response?

  1. Ask a colleague to watch while the weld is done
  2. Practise on a scrap piece first, then weld the frame
  3. Refuse the task and report it to the supervisor Correct answer.
  4. Carry out the weld under verbal guidance

Explanation

Welding involves fire, fume, radiation and structural safety risks that require training and competence. An untrained person must not undertake the task and should raise it through the supervisor so a competent person is assigned.

Question 19Occupational Health, Safety and Environment

A risk assessment for a task identifies a hazard with high severity but very low likelihood. Which approach is most appropriate?

  1. Remove it from the register to avoid confusion
  2. Ignore it because the likelihood is low
  3. Record it and apply controls proportionate to severity and likelihood together Correct answer.
  4. Treat it as the highest priority in every case

Explanation

Risk combines the severity of harm with the likelihood of occurrence, so both must be judged together when setting controls. A high-severity hazard still needs recorded controls even when likelihood is low.

Question 20Occupational Health, Safety and Environment

Two technicians disagree about whether a lifting sling is safe to use. What is the most defensible action?

  1. Use the sling for lighter loads only
  2. Cut the sling up so it cannot be used
  3. Use the sling because it looks undamaged
  4. Quarantine the sling and have it inspected by a competent person Correct answer.

Explanation

When equipment condition is in doubt, it should be withdrawn from service and formally inspected by a competent person against its inspection criteria. This preserves the equipment for assessment and prevents use of a potentially failed sling.

Question 21Hand Tools, Measuring Instruments and Workshop Practice

Which tool is designed to remove the axle nut on a motorcycle wheel while allowing the torque wrench to be used accurately on reassembly?

  1. A six-point socket with a breaker bar Correct answer.
  2. A ring spanner of the correct size
  3. An adjustable wrench
  4. A box-end wrench

Explanation

A six-point socket grips all flats of the nut and, combined with a breaker bar, gives the leverage needed to loosen a tight axle nut without rounding the corners. Sockets also fit a torque wrench directly, so the same fastener can be tightened to specification afterwards.

Question 22Hand Tools, Measuring Instruments and Workshop Practice

What is the main purpose of using a torque wrench when tightening engine covers and case bolts?

  1. To tighten fasteners to a specified force without stripping threads Correct answer.
  2. To measure the diameter of the bolt head
  3. To speed up the tightening of many bolts
  4. To check that bolts are made of the correct steel

Explanation

A torque wrench releases or signals at a set force so each fastener is clamped to the manufacturer's specification. This prevents over-tightening that strips aluminium threads and under-tightening that lets covers leak or loosen.

Question 23Hand Tools, Measuring Instruments and Workshop Practice

A Vernier caliper is being used to measure the thickness of a brake disc. Which reading practice gives the most reliable result?

  1. Close the jaws firmly and read the main scale only
  2. Read the scale once with the jaws only lightly touching
  3. Measure across the disc with the depth rod
  4. Measure at several points around the disc with the jaws square to the surface Correct answer.

Explanation

Disc thickness varies with wear, so several readings around the disc show the thinnest point, which is the value compared with the service limit. Holding the jaws square to the surface avoids a tilted reading that would be too large.

Question 24Hand Tools, Measuring Instruments and Workshop Practice

Which instrument is most suitable for checking the diameter of a piston skirt to an accuracy of 0.01 mm?

  1. A dial test indicator
  2. An outside micrometer Correct answer.
  3. A feeler gauge
  4. A steel rule

Explanation

An outside micrometer has a fine screw thread that resolves 0.01 mm and its anvils contact the piston skirt squarely. This makes it the standard tool for checking piston-to-bore clearance.

Question 25Hand Tools, Measuring Instruments and Workshop Practice

Before using a micrometer, the spindle is closed on the anvils with the ratchet and the zero line is checked. What should be done if the zero does not align?

  1. Replace the micrometer immediately
  2. Adjust the barrel or thimble to zero using the supplied spanner Correct answer.
  3. Add the error to every reading mentally
  4. Use the micrometer only for comparative measurements

Explanation

A micrometer that does not read zero introduces a constant error into every measurement. Most micrometers allow the thimble or barrel to be reset to zero with a small spanner or pin so readings stay accurate.

Question 26Hand Tools, Measuring Instruments and Workshop Practice

A feeler gauge is the correct tool for which of these checks?

  1. Brake disc thickness
  2. Tyre tread depth
  3. Valve clearance between the cam and follower Correct answer.
  4. Wheel bearing preload torque

Explanation

A feeler gauge is a set of thin blades of known thickness used to check a small gap between two surfaces. Valve clearance is set by finding the blade that slides with slight drag between cam and follower.

Question 27Hand Tools, Measuring Instruments and Workshop Practice

When a dial test indicator is used to check wheel runout, where should the magnetic base normally be attached?

  1. To the plastic mudguard
  2. To the tyre sidewall
  3. To the brake hose
  4. To the fork leg or a rigid part of the stand Correct answer.

Explanation

The base must be fixed to a rigid, non-moving part so the indicator measures only the wheel's runout. A fork leg or sturdy stand provides a stable reference while the wheel is rotated.

Question 28Hand Tools, Measuring Instruments and Workshop Practice

What is the correct way to store a precision steel rule and calipers after use?

  1. Loose in a toolbox with other tools
  2. Oiled and laid flat in a protective case Correct answer.
  3. Hanging from a hook by the measuring jaw
  4. Wrapped in emery cloth

Explanation

A light film of oil protects measuring faces from rust, and laying the tool flat in a case prevents bending or knocks that destroy accuracy. Measuring faces must never be used as a hook or lever.

Question 29Hand Tools, Measuring Instruments and Workshop Practice

A bolt head is badly corroded and a twelve-point socket keeps slipping. Which approach best avoids rounding the head further?

  1. Increase the impact gun power to maximum
  2. Use a six-point socket of the exact size, with penetrating oil and steady pressure Correct answer.
  3. Use a larger imperial socket hammered on
  4. Use locking pliers on the head

Explanation

A six-point socket contacts the flats rather than the corners, giving the best grip on a damaged head. Penetrating oil and steady, square pressure reduce the chance of slipping and further rounding.

Question 30Hand Tools, Measuring Instruments and Workshop Practice

Which workshop practice best prevents a motorcycle from falling while the front wheel is removed?

  1. Resting the bike on its side stand only
  2. Tying the handlebar to a shelf
  3. Leaning the bike against a wall
  4. Supporting the frame or engine under a sturdy stand with the rear wheel secured Correct answer.

Explanation

Removing the front wheel shifts the centre of gravity and removes one support point, so the machine must be held by a proper stand under a strong frame or engine point. Securing the rear wheel stops the bike rolling or pivoting during the work.

Question 31Hand Tools, Measuring Instruments and Workshop Practice

Why should a motorcycle be lifted so that its wheels are just clear of the floor rather than raised to maximum height?

  1. It reduces the height the machine could fall from and keeps it stable Correct answer.
  2. It is required to charge the battery
  3. It makes the lift look tidier
  4. It stops the oil from draining

Explanation

Lifting only as high as needed keeps the centre of gravity low and shortens any fall if the stand is knocked. A lower working height also makes it easier to reach fasteners safely.

Question 32Hand Tools, Measuring Instruments and Workshop Practice

A thread pitch gauge is used to identify a fastener. What does the gauge actually measure?

  1. The length of the bolt shank
  2. The distance between adjacent thread crests Correct answer.
  3. The hardness of the bolt
  4. The outside diameter of the thread

Explanation

A thread pitch gauge has blades with known tooth spacings that mesh with the thread to show the distance between crests. Matching the blade identifies the pitch, which together with diameter defines the thread.

Question 33Hand Tools, Measuring Instruments and Workshop Practice

Which file cut is most appropriate for removing a large amount of aluminium from a rough bracket before finishing?

  1. A needle file
  2. A double-cut coarse file Correct answer.
  3. A single-cut smooth file
  4. A diamond lapping file

Explanation

A double-cut coarse file has deep, crossing teeth that clear material quickly, making it suitable for roughing out soft metal. Finishing is then done with a finer single-cut file.

Question 34Hand Tools, Measuring Instruments and Workshop Practice

When using a hacksaw to cut a steel tube, what is the correct blade selection and technique?

  1. A blade with no tension in the frame
  2. A coarse wood blade with heavy pressure
  3. A blade fitted with teeth facing backwards
  4. A fine-tooth blade with light pressure and full strokes Correct answer.

Explanation

A fine-tooth blade suits thin steel walls and reduces snagging, while full, light strokes cut evenly and keep the line straight. The blade must be tensioned and the teeth must point forward for the cutting stroke.

Question 35Hand Tools, Measuring Instruments and Workshop Practice

A chisel is being used to shear off a damaged bolt head. Which safety precaution is most important?

  1. Wear safety goggles and direct the chisel away from the body Correct answer.
  2. Strike with a light hammer to save effort
  3. Work with the part held only by hand
  4. Hold the chisel with the fingers over the cutting edge

Explanation

Chiselling produces flying chips and the chisel can slip, so eye protection and directing force away from the body are essential. The workpiece must also be firmly supported so the blow goes into the metal, not the hand.

Question 36Hand Tools, Measuring Instruments and Workshop Practice

A tap is used to cut a thread in a hole. What is the purpose of the taper or first tap in a set?

  1. To measure the hole diameter
  2. To start the thread straight and gradually engage the metal Correct answer.
  3. To finish the thread to full depth
  4. To remove broken taps

Explanation

The taper tap has a long chamfer that guides the tool into the hole and starts cutting gradually, keeping the thread aligned. The plug or bottoming tap then finishes the thread to full form and depth.

Question 37Hand Tools, Measuring Instruments and Workshop Practice

A motorcycle workshop uses a bench vice to hold a fork tube while loosening a stubborn cap. What is the best practice?

  1. Clamp the tube by its thin upper end
  2. Clamp the tube directly in the serrated jaws and tighten hard
  3. Hold the tube by hand and strike the cap with a hammer
  4. Use soft jaws or a cloth pad and clamp only enough to prevent rotation Correct answer.

Explanation

Soft jaws or a pad spread the clamping load and prevent the serrated jaws from scoring or crushing the tube. Clamping only enough to stop rotation avoids ovalising the thin-walled tube.

Question 38Hand Tools, Measuring Instruments and Workshop Practice

A hole must be drilled in a steel bracket with a hand drill. Which step best ensures the hole starts in the marked position?

  1. Drill without marking and judge by eye
  2. Apply heavy side pressure to steer the drill
  3. Start with a large drill at high speed
  4. Centre-punch the mark and start with a small pilot drill Correct answer.

Explanation

A centre punch creates a seat that stops the drill wandering, and a small pilot drill establishes the position before enlarging. Side pressure bends the drill and enlarges the hole off-centre.

Question 39Hand Tools, Measuring Instruments and Workshop Practice

What does a Plastigauge strip measure when checking a plain bearing clearance?

  1. The hardness of the bearing shell
  2. The oil pressure in the bearing
  3. The torque of the bearing cap bolts
  4. The squashed width of the plastic strip, which indicates clearance Correct answer.

Explanation

Plastigauge is a calibrated plastic thread placed across the journal and crushed by the tightened cap. Its squashed width is compared with a scale that gives the bearing clearance directly.

Question 40Hand Tools, Measuring Instruments and Workshop Practice

A torque wrench has been dropped on the workshop floor. What is the correct action before it is used again?

  1. Oil the mechanism and increase the setting by ten percent
  2. Have it recalibrated or checked against a known standard Correct answer.
  3. Use it only for low-torque fasteners
  4. Use it as normal because the setting scale is unchanged

Explanation

A drop can bend the beam or disturb the internal mechanism, so the wrench may read inaccurately even if the scale looks normal. Checking against a calibration standard confirms whether it is still within tolerance.

Question 41Motorcycle Engine Construction and Working Principles

In a four-stroke engine, which stroke immediately follows the intake stroke?

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

Explanation

The four-stroke cycle runs intake, compression, power, then exhaust in that fixed order. After the piston has drawn in the air-fuel charge on the intake stroke, both valves close and the piston rises to compress the charge. Compression must precede ignition, so it is the stroke that follows intake.

Question 42Motorcycle Engine Construction and Working Principles

What is the main function of the piston rings fitted to a motorcycle piston?

  1. To seal combustion gases and control oil on the cylinder wall Correct answer.
  2. To balance the crankshaft at high speed
  3. To open and close the intake valve
  4. To lock the piston to the connecting rod

Explanation

Piston rings seat against the cylinder bore to contain combustion pressure and to scrape excess oil back down the wall. The top compression rings handle gas sealing while the lower oil ring regulates lubrication. This sealing and oil control is their primary duty.

Question 43Motorcycle Engine Construction and Working Principles

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

  1. Crankshaft Correct answer.
  2. Camshaft
  3. Rocker arm
  4. Clutch basket

Explanation

The connecting rod links the piston to the crankshaft offset, so as the piston moves up and down the crank is forced to rotate. This is the mechanism that turns linear piston travel into usable rotary output. The crankshaft therefore delivers the engine's torque to the transmission.

Question 44Motorcycle Engine Construction and Working Principles

What does the term 'stroke' mean in engine terminology?

  1. The distance the piston travels from top dead centre to bottom dead centre Correct answer.
  2. The total swept volume of all cylinders
  3. The angle between the two valves
  4. The time taken for one full cycle

Explanation

Stroke is a linear measurement of piston travel between its two extreme positions, top dead centre and bottom dead centre. It is combined with bore area to calculate swept volume. It is a distance, not a volume or a time.

Question 45Motorcycle Engine Construction and Working Principles

In a four-stroke engine, which component drives the camshaft so that valves open at the correct time?

  1. The starter motor
  2. The timing chain or belt from the crankshaft Correct answer.
  3. The alternator rotor
  4. The oil pump drive gear

Explanation

The camshaft must stay synchronised with the crankshaft so valves open in step with piston position. A chain, belt, or gear train running at half crankshaft speed provides that timed drive. Correct valve timing depends entirely on this relationship.

Question 46Motorcycle Engine Construction and Working Principles

What is the purpose of the flywheel on a motorcycle engine?

  1. To cool the cylinder head
  2. To increase the compression ratio
  3. To filter the engine oil
  4. To store rotational energy and smooth out power pulses Correct answer.

Explanation

The flywheel's inertia carries the crankshaft through the intervals between power strokes, smoothing torque delivery and helping idle stability. It absorbs energy on the power stroke and releases it on the other strokes. This makes running smoother and more consistent.

Question 47Motorcycle Engine Construction and Working Principles

Which valve is normally larger in a motorcycle engine cylinder head?

  1. Both are always identical in size
  2. The valve size depends only on camshaft lift
  3. The intake valve Correct answer.
  4. The exhaust valve

Explanation

The intake charge enters at low pressure and needs a large flow area to fill the cylinder, so the intake valve is generally made larger. Exhaust gas leaves under pressure and needs less area. This size difference improves volumetric efficiency.

Question 48Motorcycle Engine Construction and Working Principles

What is meant by the compression ratio of an engine?

  1. The ratio of engine speed to road speed
  2. The ratio of cylinder bore to piston stroke
  3. The ratio of intake valve area to exhaust valve area
  4. The ratio of total cylinder volume to combustion chamber volume at top dead centre Correct answer.

Explanation

Compression ratio compares the cylinder volume with the piston at bottom dead centre to the remaining volume with the piston at top dead centre. A higher ratio means the charge is squeezed into a smaller space. It is a volume ratio, not a dimensional or speed ratio.

Question 49Motorcycle Engine Construction and Working Principles

A single-cylinder four-stroke engine has a bore of 60 mm and a stroke of 50 mm. Using π ≈ 3.14, what is its swept volume approximately?

  1. 226 cc
  2. 113 cc
  3. 170 cc
  4. 141 cc Correct answer.

Explanation

Swept volume equals the cylinder cross-sectional area multiplied by stroke. Area is π times radius squared, giving 3.14 × 30² = 2826 mm², and multiplying by 50 mm stroke gives about 141,300 mm³, or roughly 141 cc.

Question 50Motorcycle Engine Construction and Working Principles

Why does a two-stroke engine typically produce a power stroke on every revolution of the crankshaft?

  1. Because the exhaust and transfer ports are opened by the piston rather than by valves Correct answer.
  2. Because its flywheel is heavier than a four-stroke's
  3. Because its compression ratio is always higher
  4. Because it uses two spark plugs per cylinder

Explanation

In a two-stroke engine the piston itself uncovers intake, transfer, and exhaust ports as it moves, so gas exchange happens within a single up-and-down cycle. That allows a power stroke every crankshaft revolution. Valve gear is not used to time this exchange.