Question 1

Steering and suspension service — purpose of turning radius gauges In wheel-alignment work, turning radius gauges (turn plates) are used primarily to measure which parameter during steering checks?

Accepted Answer

Introduction / Context: Turning radius gauges (also called turntables or turn plates) are low-friction plates placed under the front wheels during alignment. They allow precise measurement of steering angles while the suspension is loaded at ride height. This is essential for checking Ackermann geometry and maximum lock. Given Data / Assumptions: Vehicle on alignment rack with turn plates under front wheels. Steering is centered and then turned to specified angles for measurements. Other alignment heads measure camber, caster, and toe. Concept / Approach: Turn plates have degree scales and allow smooth rotation of wheels. Technicians use them to measure inside and outside wheel steer angles, verify toe-out-on-turns, and confirm maximum steering lock against specifications. These plates are not for measuring steering wheel free play or direct toe values, which are read by alignment sensors and scales. Step-by-Step Solution: Place the vehicle's front wheels on the turn plates.Center the steering, zero the scales, then rotate to specified angles.Read inside/outside steer angles to assess turning radius/steering geometry. Verification / Alternative check: Comparing measured angles to manufacturer toe-out-on-turns data diagnoses bent steering arms or incorrect rack position. Why Other Options Are Wrong: Contact area: assessed by footprint methods, not turn plates. Steering free play: measured at the wheel rim or via scan-tool/angle sensor, not turn plates. Toe difference: measured by toe gauges or alignment heads; turn plates enable rotation but don’t directly display toe. Caster trail: derived from geometry; caster is measured by sweeping angles, not by turn plates alone. Common Pitfalls: Not zeroing plates before measurements; friction in seized plates causing erroneous readings. Final Answer: turning radius of the left and right wheels (steering angles/lock)

Question 2

Piston ring functions — specific role of the oil-control ring Which statement best describes the function of an oil-control ring in a piston assembly?

Accepted Answer

Introduction / Context: Piston rings are typically arranged as two compression rings and one oil-control ring (sometimes multi-piece). While compression rings focus on gas sealing and heat transfer, the oil-control ring manages lubrication on the liner to minimize oil consumption and smoke. Given Data / Assumptions: Four-stroke passenger car engine. Conventional ring pack with drain-back holes in the piston ring groove. Normal oil viscosity and operating clearances. Concept / Approach: The oil-control ring scrapes and meters oil on the cylinder wall during piston motion. Excess oil is collected through ring slots and returned to the crankcase via drain holes. By preventing oil from migrating into the combustion chamber, it reduces oil burning, deposits, and HC emissions while ensuring a thin film remains for lubrication. Step-by-Step Solution: During the downstroke, the ring scrapes surplus oil and channels it to the groove ports.Oil flows through piston drain holes back to the sump.A controlled residual film remains, preventing metal-to-metal contact. Verification / Alternative check: Engines with worn oil rings show blue smoke, high oil consumption, and fouled plugs/catalysts. Restoring oil-control ring function cures these symptoms. Why Other Options Are Wrong: Releasing oil: rings do not dispense oil; they meter and return excess. Only holding oil in a channel: incomplete; the key is scraping and returning. Gas sealing: primarily the role of compression rings. Heat transfer to the pin: rings transfer heat to cylinder walls, not specifically to the pin. Common Pitfalls: Installing expander-type oil rings upside down; blocked drain holes causing oil pumping; using incorrect oil viscosity. Final Answer: prevents engine oil from reaching the combustion chamber and returns excess oil from the cylinder wall to the oil pan via piston drain holes

Question 3

Automotive engines — primary function of the first (top) compression ring In an internal combustion engine piston assembly, what is the main role of the first compression ring located closest to the combustion chamber?

Accepted Answer

Introduction / Context: The first compression ring (often called the top ring) is critical to engine sealing and efficiency. It operates in the most severe thermal and pressure environment, immediately below the combustion space, and its performance directly affects power, blow-by, oil control, and emissions. Given Data / Assumptions: Piston has a typical ring pack: top compression ring, second ring, and an oil control ring. Question asks the principal function of the top compression ring. Four alternatives include actions like swirl generation and fuel leakage control. Concept / Approach: The top compression ring must seal high-pressure gases during compression and power strokes. By limiting blow-by (gas leakage into the crankcase), it preserves peak cylinder pressure, which translates into torque. Secondary effects include transferring heat from the piston crown to the cooler cylinder wall and stabilising the ring pack dynamics, but the dominant purpose is gas sealing at the combustion edge. Step-by-Step Solution: Identify the ring closest to the combustion chamber: the top compression ring.Recall the primary function: provide a gas-tight seal to retain pressure.Match with the option stating prevention of burned gas escape and pressure loss. Verification / Alternative check: Engine texts list primary duties of the top ring as gas sealing and heat transfer. Oil control is managed mainly by the oil ring; mixture swirl is a function of intake porting/combustion chamber design, not the ring. Why Other Options Are Wrong: Increases combustion temperature: rings do not intentionally raise temperature. Creates swirl: swirl is generated by intake design, piston crown shapes, and valves. Prevents fuel leakage: fuel is largely vaporised and past injection timing; the concern is gas sealing, not liquid fuel sealing. Common Pitfalls: Confusing the compression ring with the oil control ring; assuming rings manage mixture motion inside the chamber. Final Answer: maintains a seal and prevents escape of burned gases and loss of pressure in the combustion chamber

Question 4

Engine layout — number of exhaust manifolds on a V-6 engine For a conventional V-6 automotive engine with two cylinder banks, how many exhaust manifolds are used?

Accepted Answer

Introduction / Context: Exhaust manifolds collect combustion products from cylinders and route them to downstream exhaust components. In multi-bank layouts like V-engines, manifold count relates to the number of cylinder banks. Given Data / Assumptions: Engine type: V-6 with two banks of three cylinders each. Typical automotive configuration with separate manifolds per bank. No special siamesed or cross-over integral manifold design assumed. Concept / Approach: A V-6 has two banks arranged in a V. Each bank requires an exhaust manifold to gather gases from its cylinders. These two manifolds may feed a single or dual exhaust system, but the manifold count at the engine remains two. Step-by-Step Solution: Recognise two cylinder banks in a V-6.Standard practice: one manifold per bank.Hence total manifolds = 2. Verification / Alternative check: Workshop manuals for common V-6 engines show left-bank and right-bank exhaust manifolds, sometimes feeding separate catalytic converters. Why Other Options Are Wrong: One: would require a complex cross-over at the cylinder head level, not standard. Four or eight: exceed the number of banks and cylinder head exits. Common Pitfalls: Confusing number of manifolds with number of tailpipes; dual exhaust downstream does not change the count of cylinder-head manifolds. Final Answer: two

Question 5

Brake systems — component contacted by the brake shoe lining during braking When a drum brake is applied, the shoe pivots outward so that its friction lining presses against which component?

Accepted Answer

Introduction / Context: In drum brakes, hydraulic pressure moves wheel cylinders to force shoes outward. Understanding which component the lining contacts clarifies inspection, wear patterns, and noise diagnosis. Given Data / Assumptions: System type: leading-trailing shoe or duo-servo drum brake. Brake actuation: wheel cylinder expands shoes. Question focuses on the contact surface during braking. Concept / Approach: The friction lining on each shoe is bonded or riveted onto the shoe web. When actuated, the lining arcs outward to contact the inner cylindrical surface of the rotating brake drum fixed to the wheel hub, converting kinetic energy to heat via friction. Step-by-Step Solution: Identify brake type: drum brake.Apply actuation: wheel cylinder pushes shoes outward.Determine contact: lining presses on the inner surface of the brake drum. Verification / Alternative check: Exploded diagrams show wheel cylinder at the top, anchor pin at the bottom; neither is the friction surface. The drum is the rotating element that the lining rubs against. Why Other Options Are Wrong: Wheel piston or cylinder: actuating component, not the friction surface. Anchor pin: pivot/support, not a friction element. Wheel rim or axle: not involved in brake lining contact. Common Pitfalls: Confusing disc vs drum brakes; in disc brakes, pads contact a rotor, not a drum. Final Answer: brake drum

Question 6

Engine cylinder sizing — conventional dimensions used to specify size In engine specifications, the size of a cylinder is generally stated in terms of which two dimensions?

Accepted Answer

Introduction / Context: Bore and stroke are fundamental to engine geometry. They determine displacement, influence torque and power characteristics, and guide component design choices. Given Data / Assumptions: Bore = cylinder diameter. Stroke = distance the piston travels between top dead centre and bottom dead centre. Question asks the standard pair used to describe cylinder size. Concept / Approach: Engine displacement per cylinder equals (pi/4) * bore^2 * stroke. Thus, bore and stroke are the canonical size descriptors. Terms like efficiency are performance metrics, not geometric size descriptors. Similarly, “diameter and bore” is redundant. Step-by-Step Solution: Identify geometric variables: bore and stroke.Relate to displacement formula and engine tuning implications.Select the option matching both: bore and stroke. Verification / Alternative check: Manufacturers list engines as, for example, 86 mm bore × 86 mm stroke (square), undersquare, or oversquare. Why Other Options Are Wrong: Diameter and bore: duplicate descriptors. Displacement and efficiency: not raw cylinder size terms. Bore and length: cylinder block length is not a standard size descriptor. Common Pitfalls: Confusing engine displacement (derived) with the base dimensions used to compute it. Final Answer: bore and stroke

Question 7

Spark plug reading — interpreting black sooty deposits When a spark plug shows a dry, black, sooty coating on its insulator and electrodes, what does this typically indicate about mixture strength or combustion?

Accepted Answer

Introduction / Context: Spark plug inspection is a quick diagnostic for air–fuel mixture and ignition health. Colour and texture of deposits reflect combustion quality and mixture richness. Given Data / Assumptions: Observation: black, sooty, powder-like deposits. Operating on gasoline spark ignition engine. No oil fouling symptoms (wet, oily, shiny deposits) reported. Concept / Approach: A rich mixture supplies excess fuel relative to available oxygen, causing incomplete combustion and carbon soot formation. The soot appears as a dry black film. Lean mixtures tend to cause white or light grey deposits and can raise combustion temperature, risking knock or pre-ignition. Step-by-Step Solution: Identify deposit type: dry black soot.Relate to mixture condition: over-fuelling leads to sooting.Choose the option indicating a too rich mixture. Verification / Alternative check: Tuning guides show coffee-brown/light tan as ideal, black soot as rich, and white blistered insulators as lean/overheated. Why Other Options Are Wrong: Too lean or stoichiometric: would not leave heavy soot; may show pale deposits. Most economical mixture: typically slightly lean of stoichiometric, again not sooty. Common Pitfalls: Confusing wet, oily black (oil burning) with dry soot (rich mixture). Oil fouling indicates mechanical issues such as worn guides or rings. Final Answer: too rich mixture

Question 8

Fuel properties — typical boiling range of Diesel fuel What is the approximate boiling point range for common Diesel fuel fractions used in compression ignition engines?

Accepted Answer

Introduction / Context: Diesel fuel distillation characteristics influence volatility, ignition delay, cold start behaviour, and emissions. The boiling range reflects the mix of hydrocarbons chosen during refinery fractionation. Given Data / Assumptions: Conventional road Diesel (not kerosene or heavy fuel oil). Atmospheric distillation followed by blending to meet standards. Boiling range asked in degrees Celsius. Concept / Approach: Diesel is heavier than gasoline with higher final boiling point. Typical initial boiling point is around 180°C and final boiling point near 360°C. This supports compression ignition by achieving suitable cetane and volatility characteristics without excessive light ends. Step-by-Step Solution: Recall that gasoline boils roughly 30°C to 220°C.Diesel is heavier; use 180°C to 360°C as canonical range.Select the matching option. Verification / Alternative check: Fuel standards specify distillation curves (e.g., at 10%, 50%, 90% recovered) within this overall envelope for automotive Diesel grades. Why Other Options Are Wrong: 70–100°C, 100–120°C, 120–180°C: far too light; these relate to gasoline/naptha cuts. Common Pitfalls: Equating flash point with boiling range; Diesel has a much higher flash point than gasoline and a heavier distillation profile. Final Answer: 180°C to 360 °C

Question 9

Alternative fuels — typical octane number of CNG for spark-ignition use Compressed natural gas used in SI engines typically has an octane number nearest to which of the following values?

Accepted Answer

Introduction / Context: CNG (mostly methane) is an excellent spark-ignition fuel due to its high resistance to knock. Knowing its octane number helps set compression ratio and ignition timing strategies. Given Data / Assumptions: CNG composition dominated by methane with minor ethane, propane, and inert gases. Octane number asked as a representative single value. Automotive-grade CNG considered. Concept / Approach: Methane has very high knock resistance; research octane numbers for CNG are commonly around 120 or higher. This allows higher compression ratios than typical gasoline without detonation, improving thermal efficiency in dedicated CNG engines. Step-by-Step Solution: Identify fuel: CNG for SI engines.Recall typical RON values: near or above 120.Choose the closest option: 120. Verification / Alternative check: Engine calibration sources cite effective methane number and RON for CNG in the 120–130 band depending on composition. Why Other Options Are Wrong: 90, 100, 110: appropriate for some gasoline grades or alcohol blends, but below CNG's common rating. Common Pitfalls: Confusing octane (knock resistance in SI engines) with cetane (ignition quality in CI engines); CNG is not suitable for compression ignition without pilot injection. Final Answer: 120

Question 10

Automatic transmissions — purpose of smooth shift mechanisms In an automatic transmission, why is a smooth shift mechanism desirable during gear changes?

Accepted Answer

Introduction / Context: Automatic transmissions use hydraulic control, clutches, and bands to change ratios. Shift quality influences vehicle comfort, driveline durability, and traction management. Given Data / Assumptions: Question asserts that smooth shift mechanisms reduce shock at gear changes. Applies to torque-converter automatics and modern automated units with clutch-to-clutch shifting. Passenger vehicle context. Concept / Approach: Shift shock is a rapid change in torque transmitted through the driveline, felt as a jolt. Smooth shift strategies modulate clutch pressure rise, synchronise turbine and gearset speeds, and momentarily adjust engine torque to reduce impact loads and improve comfort. Step-by-Step Solution: Recognise shift shock arises from sudden torque handover.Use controlled hydraulic pressure and timing to coordinate element engagement.Result: reduced shock, smoother shift feel, less component stress. Verification / Alternative check: Transmission control modules incorporate adaptive learning for clutch fill times and pressure ramps precisely to minimise shift shock. Why Other Options Are Wrong: Answering “No” ignores well-established design goals and control methods aimed at improving shift quality. Common Pitfalls: Confusing shift shock with engine surge or mount judder; proper diagnostics distinguish between control calibration and mechanical faults. Final Answer: Yes

Question 11

Lead–acid batteries — active material on negative plates In a fully charged lead–acid starting battery, which material forms the active mass on the negative plates?

Accepted Answer

Introduction / Context: Understanding electrochemistry of lead–acid batteries helps in maintenance and diagnostics. The active materials on positive and negative plates change during charge and discharge. Given Data / Assumptions: Battery is fully charged and in normal service. Negative and positive plate compositions are standard for automotive batteries. Electrolyte is aqueous sulphuric acid. Concept / Approach: In the charged state, the positive plate active material is lead dioxide (PbO2), while the negative plate is porous or spongy lead (Pb). During discharge, both convert to lead sulphate (PbSO4) as sulphate ions combine with lead from each plate, and water content in electrolyte increases. Step-by-Step Solution: Identify charged-state materials.Positive: PbO2; Negative: Pb.Select “spongy lead (Pb)” for the negative plate. Verification / Alternative check: Charge reactions confirm conversion pathways between Pb, PbO2, and PbSO4 depending on current direction. Why Other Options Are Wrong: Lead peroxide (PbO2): positive plate material when charged. Lead sulphate (PbSO4): discharge product on both plates. Sulphuric acid: electrolyte, not plate active mass. Common Pitfalls: Assuming both plates use the same material at all times; ignoring that plate chemistry depends on state of charge. Final Answer: spongy lead (Pb)

Question 12

Engine configurations — the three basic cylinder arrangements in automobiles Among common automotive engine layouts, which trio best represents the fundamental cylinder arrangements used by manufacturers?

Accepted Answer

Introduction / Context: Automotive engines are categorised by cylinder arrangement, which influences packaging, vibration, and manufacturing cost. Three basic architectures dominate modern vehicles. Given Data / Assumptions: Passenger and light commercial vehicles. Focus on architecture, not specific cylinder counts. Opposed layout is also called flat or boxer. Concept / Approach: The mainstream arrangements are: in line (all cylinders in one bank), V (two banks sharing a common crankshaft), and opposed/flat (two horizontal banks opposed by 180 degrees). Radial and double-row radial are aircraft-centric and uncommon in automobiles. Step-by-Step Solution: Identify the three automotive staples: in line, V, opposed.Map synonyms: opposed equals flat/boxer.Select the option listing these three together. Verification / Alternative check: Manufacturer lineups show inline-3/4/6, V-6/V-8, and boxer-4/6 as standard offerings across decades. Why Other Options Are Wrong: Flat, radial, and V: radial is not a standard automotive engine layout. In a row, in line, and opposed: “in a row” duplicates “in line.” V, double row, and opposed: “double row” is not a standard automotive term; suggests radial. Common Pitfalls: Equating opposed with radial; radial has cylinders arranged like spokes around a crank, not two banks. Final Answer: in line, V, and opposed

Question 13

Automobile fuels — typical density At standard test conditions for road vehicles, the specific gravity (relative density at 15°C with respect to water) of diesel fuel is approximately:

Accepted Answer

Introduction / Context: Specific gravity (also called relative density) of automotive fuels is an essential property for engine calibration, fuel metering, and emissions control. For diesel engines, a typical value is expected in a narrow band because the fuel's density influences energy per unit volume, injection characteristics, and atomization. Given Data / Assumptions: Reference temperature for density comparison is 15°C (a common standard in fuel specification). Specific gravity is the ratio of diesel density to water density at the same temperature. We consider conventional automotive diesel (not biodiesel blends or special winterized extremes). Concept / Approach: Typical automotive diesel has density around 820 to 860 kg/m^3 at 15°C. Since water is approximately 1000 kg/m^3 at this temperature, the specific gravity is roughly 0.82 to 0.86. A representative rounded value used for quick engineering estimates is 0.85. Step-by-Step Solution: Let rho_diesel ≈ 850 kg/m^3 and rho_water ≈ 1000 kg/m^3.Compute SG = rho_diesel / rho_water.SG ≈ 850 / 1000 = 0.85.Select the closest option to the typical midrange value. Verification / Alternative check: Fuel datasheets for automotive diesel list density bands 0.82–0.86 at 15°C, confirming that 0.85 is a reasonable nominal figure for calculations. Why Other Options Are Wrong: 0.65 and 0.55 are closer to light hydrocarbons or LPG and are far too low for diesel. 0.75 is typical of some kerosenes or light fractions, still low for automotive diesel. 0.95 is near heavy oils and is significantly higher than standard road diesel. Common Pitfalls: Confusing specific gravity at different temperatures; density decreases as temperature rises, so use the specified reference temperature. Also, biodiesel blends (e.g., B20) can shift density slightly higher than mineral diesel. Final Answer: 0.85

Question 14

Engine components — connecting rod cross-section In reciprocating internal combustion engines, connecting rods are generally manufactured with an I-shaped cross-section because it provides a high stiffness-to-weight ratio. Which letter best describe…

Accepted Answer

Introduction / Context: The connecting rod is a highly stressed component transmitting gas and inertia forces between the piston and the crankshaft. Its cross-sectional geometry must resist bending and buckling while remaining as light as possible to reduce reciprocating mass. Given Data / Assumptions: Static and dynamic loads act alternately in tension and compression over each cycle. Design objective: high bending stiffness with minimum weight. Manufacturing methods include forging or powdered metal, often followed by machining. Concept / Approach: An I-shaped section concentrates material away from the neutral axis, maximizing second moment of area for a given mass. This enhances resistance to bending and column-type instability, particularly important along the rod shank where compressive loads can cause buckling. Step-by-Step Solution: Identify required property: high stiffness-to-weight ratio.Compare candidate sections: I-section has flanges and a web that place material efficiently.Industry practice confirms I-section for most steel connecting rods.Select the I-shaped cross-section. Verification / Alternative check: Finite element and classical beam theory both show I-sections yield higher second moment of area than compact shapes of the same mass. Why Other Options Are Wrong: C, L, H, or T shapes do not provide the same efficiency for the loading path and may introduce asymmetry or excess mass for equivalent stiffness. Common Pitfalls: Assuming solid rectangular sections are stronger; they are heavier for the same stiffness and increase reciprocating mass, harming engine balance. Final Answer: I

Question 15

Power flow in a manual transmission driveline Select the correct sequence of power flow from the engine to the wheels in a conventional front-engine, rear-wheel-drive vehicle with a manual gearbox and differential.

Accepted Answer

Introduction / Context: Understanding the power path through a vehicle's driveline is fundamental for diagnosing faults, optimizing performance, and appreciating how gears multiply torque. In a typical manual transmission with a rear differential, power flows through specific shafts and gear pairs before reaching the wheels. Given Data / Assumptions: Clutch is between engine flywheel and gearbox input. Gearbox uses an input shaft driving a countershaft (layshaft), which then drives the main/output shaft through selected gear pairs. Final driven gear refers to the ring gear in the differential that drives the axle shafts (driveshafts/half-shafts). Concept / Approach: The engine sends torque to the clutch; when engaged, torque enters the gearbox input and is transferred to the countershaft. The selected gear on the mainshaft meshes with the countershaft gear, delivering torque to the output. The propeller shaft transmits torque to the differential, where the final driven (ring) gear turns the differential case and, via side gears, the driveshafts to the wheels. Step-by-Step Solution: Engine → clutch → gearbox input (drives countershaft).Countershaft → selected gear mesh → mainshaft (output).Mainshaft → final drive (ring gear) in differential.Ring gear → half-shafts (driveshafts) → wheels. Verification / Alternative check: Workshop manuals depict the countershaft driven continuously by the input, while the mainshaft is powered through engaged gears, confirming the chosen sequence. Why Other Options Are Wrong: (a) puts driveshafts before the clutch—a physical impossibility. (b) swaps the order of countershaft and mainshaft relative to the clutch. (d) places the clutch after gearbox shafts. (e) includes a torque converter (automatic transmission), not applicable here. Common Pitfalls: Confusing terminology: some texts call the gearbox input the main/input shaft and the output the mainshaft; the functional order still places countershaft before output. Final Answer: engine - clutch - countershaft - mainshaft - final driven gear - driveshafts - wheels

Question 16

V-type multi-cylinder engines — typical bank angle In most common automotive 'V' engines, the two rows (banks) of cylinders are typically arranged at which bank angle for smooth operation and packaging?

Accepted Answer

Introduction / Context: The bank angle in a V-type engine is the included angle between the two cylinder banks. It influences primary and secondary balance, firing intervals, engine height/width, and the feasibility of even firing without split-pin crankshafts. Given Data / Assumptions: General question about typical V-engine practice, not a specific V6 or narrow-angle variant. Many classic V8 engines adopt a right-angle configuration. Even firing and balance considerations are key selection factors. Concept / Approach: While some V6 engines commonly use 60° for compactness and smoother firing, the widely recognized and historically standard bank angle for V8 engines is 90°. The question asks for a general typical arrangement in V-engines, and 90° is the conventional textbook answer, especially for V8 designs that dominate many applications. Step-by-Step Solution: Identify common architectures: V8 → 90°, V6 → 60° (common), narrow-angle V → smaller angles.Select the best-known general angle for V-type engines across classic designs.Answer: 90°. Verification / Alternative check: Automotive engineering texts cite 90° as the standard for conventional cross-plane V8 for balance and even firing with shared crank pins. Why Other Options Are Wrong: 45° is too narrow for most V layouts. 60° is common for V6, but the question is general; 90° is more broadly cited. 130° is excessively wide for typical vehicle engines and used rarely. Common Pitfalls: Assuming one angle fits all V engines; engineers choose angle based on cylinder count, firing order, and packaging. However, for a general exam context, 90° is the standard reference. Final Answer: 90°

Question 17

Automotive electricals — main function of the battery In a conventional passenger car, what is the primary duty of the storage battery within the electrical system?

Accepted Answer

Introduction / Context: The automotive battery and alternator form a complementary pair. Knowing their roles helps in diagnosing starting problems and charging faults. Given Data / Assumptions: Vehicle uses a standard 12 V lead-acid battery (or equivalent chemistry) and an alternator with a regulator. Engine-driven alternator supplies power once the engine is running. Power demand during cranking is high for a short duration. Concept / Approach: The battery's primary function is to deliver high current to the starter motor to crank the engine from rest. It also buffers voltage, powers accessories with engine off or at idle, and bridges transient loads. However, when the engine is running above idle, the alternator normally supplies most electrical power and recharges the battery. Step-by-Step Solution: Identify starting requirement: starter motors may draw hundreds of amperes.Only the battery can supply this instantaneous current at engine standstill.Once running, alternator takes over load and charges battery.Therefore, the battery's main task is to power the starter during engine start. Verification / Alternative check: Service manuals specify cold-cranking amps (CCA) as the key battery rating, underscoring its primary role in starting. Why Other Options Are Wrong: The alternator supplies electricity to the vehicle when running, not the reverse. The battery does stabilize voltage but that is secondary to starting duty. Continuous powering during normal running is alternator's job. Voltage regulation is handled by the alternator's regulator, not the battery. Common Pitfalls: Misattributing charging issues to the battery when the alternator or regulator is faulty; ignoring parasitic drains that deplete the battery between starts. Final Answer: Provide a large burst of power to crank the starter motor when starting the engine

Question 18

Tyre maintenance — when to check inflation pressure At what temperature condition should tyre inflation pressure be checked to obtain an accurate ''cold'' reading for road vehicles?

Accepted Answer

Introduction / Context: Tyre pressure recommendations assume a 'cold' tyre, meaning the tyre has been parked long enough to return to ambient temperature. Checking at the correct condition ensures load capacity, handling, wear, and fuel economy meet design targets. Given Data / Assumptions: Ambient (surrounding) temperature may vary by climate and season. Vehicle has been stationary for several hours or driven less than a few kilometers at low speed. Gauge measures absolute or gauge pressure consistently. Concept / Approach: Tyre pressure rises with temperature due to gas expansion. OEM placard pressures are specified for 'cold' conditions at the current ambient, not at a fixed laboratory temperature. Therefore, the correct condition is to measure at ambient temperature with tyres cooled to that temperature. Step-by-Step Solution: Park the vehicle and let tyres cool to ambient (typically 2–3 hours).Measure pressure and adjust to placard values.If measured hot, apply manufacturer hot-to-cold correction or recheck later. Verification / Alternative check: Ideal gas relation indicates pressure increase as temperature rises; after highway driving, measured pressure will be higher than the cold specification. Why Other Options Are Wrong: Fixed temperatures like 20°C, 25°C, or 35°C are not universally applicable; placards are not tied to a single fixed temperature in real-world use. Checking at 50°C (hot) gives misleading readings relative to cold specification. Common Pitfalls: Bleeding air from hot tyres to match cold specs (leads to underinflation when tyres cool); ignoring seasonal changes that warrant adjustments. Final Answer: ambient temperature

Question 19

Automotive tyres — region of maximum flexing Which part of a pneumatic automobile tyre experiences the greatest flexing during service and is therefore most critical for heat buildup and fatigue?

Accepted Answer

Introduction / Context: Tyre durability depends on how different regions deform under load and rotation. Flexing generates heat, which accelerates material fatigue and can lead to sidewall cracking or ply separation if poorly managed. Given Data / Assumptions: Radial or bias-ply pneumatic tyres on passenger vehicles. Typical pressures and normal road operation. No structural damage or extreme underinflation assumed. Concept / Approach: The sidewall spans between the bead and the tread/belt region and must accommodate cyclic radial and lateral deflections as the contact patch enters and leaves the road. This region undergoes the largest strain amplitude per revolution, leading to the greatest flexing and heat buildup. Step-by-Step Solution: Identify deformation regions: tread block deformation vs. sidewall bending.Recognize that belts under the tread constrain flex, while sidewalls remain compliant to absorb deflection.Therefore, sidewall is the area of maximum flexing. Verification / Alternative check: Thermography and strain gauging show higher cyclic strain and temperature rise in sidewalls, especially under low inflation or high load. Why Other Options Are Wrong: Bead is relatively rigid and anchored to the rim. Shoulder and tread flex but are reinforced by belts; flexing is less than in the sidewall. Belt package is stiff by design to stabilize the tread. Common Pitfalls: Underinflation increases sidewall flexing excessively; overloading or prolonged high-speed driving without proper inflation can overheat and damage sidewalls. Final Answer: Side wall

Question 20

Starter motor drive — method of transmitting torque to the engine flywheel In a typical automotive starting system, the starter motor turns the engine via which type of drive engagement?

Accepted Answer

Introduction / Context: Cranking the engine requires a compact, high-torque transmission from the electric starter motor to the flywheel ring gear. The drive must engage only during starting and disengage afterward to prevent overspeeding the starter. Given Data / Assumptions: Conventional 12 V starter with a pinion (Bendix or solenoid-shift mechanism). Flywheel has a hardened ring gear. Engagement is temporary during cranking. Concept / Approach: The starter uses a small pinion gear that meshes with the large ring gear on the flywheel. This gear drive provides a large speed reduction and torque multiplication needed to overcome engine compression and friction at low cranking speeds. Step-by-Step Solution: Starter solenoid actuates → pinion moves to mesh with ring gear.Motor energizes → torque transmitted through gear mesh.Engine starts → pinion retracts or overruns via a one-way clutch. Verification / Alternative check: Service diagrams show the pinion-to-ring gear mesh as the standard mechanism; no belts or chains are used. Why Other Options Are Wrong: Belts and chains are unsuitable for brief, high-torque intermittent engagement and would require tensioning mechanisms. Friction rollers would slip and wear quickly under cranking loads. Common Pitfalls: Worn ring gear teeth or misadjusted pinion throw cause grinding; weak batteries or bad solenoids hinder engagement. Final Answer: gear drive

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