Question 1

Battery state-of-charge indicator What is the typical specific gravity (at 25°C) of the electrolyte in a fully charged automotive lead–acid battery?

Accepted Answer

Introduction / Context: Specific gravity of the electrolyte (sulphuric acid solution) is a quick indicator of the state of charge in conventional serviceable lead–acid batteries. Given Data / Assumptions: Temperature near 25°C (hydrometer readings are temperature-dependent). Battery in good condition without stratification. Concept / Approach: As a lead–acid battery charges, sulphuric acid concentration increases, raising specific gravity. A fully charged battery typically reads about 1.26–1.28. Discharged batteries approach 1.12–1.18 depending on design. Step-by-Step Solution: Recognize full-charge SG range ≈ 1.26–1.28.Select the value within common specification for a fully charged unit.Therefore, 1.28 is the correct nominal figure. Verification / Alternative check: Service manuals and hydrometer charts show green/good zone around 1.26–1.28 at 25°C. Why Other Options Are Wrong: 1.00: distilled water; fully discharged is much higher than this. 1.82 or 2.81: far too high; such acid strength is unsafe and not used in batteries. 1.10: indicates deep discharge or defective cell. Common Pitfalls: Ignoring temperature correction; cold temperatures lower readings, and hydrometers may require adjustment. Final Answer: 1.28

Question 2

Crankshaft counterweighting — inline four-cylinder engines A typical in-line four-cylinder automotive crankshaft commonly uses how many counterweights (balance weights)?

Accepted Answer

Introduction / Context: Counterweights on a crankshaft reduce bearing loads and vibration by balancing rotating and partially balancing reciprocating masses. The number and placement depend on engine design. Given Data / Assumptions: Modern, production in-line four-cylinder passenger car engine. Four crank throws, 180° apart. Concept / Approach: An inline-4 typically has four crankpins. Many designs use two counterweights per crank throw (leading and trailing), resulting in a total of eight counterweights to reduce bending moments and improve smoothness. Step-by-Step Solution: Count crank throws: 4.Assign two counterweights per throw in common practice.Total counterweights = 4 * 2 = 8. Verification / Alternative check: Crankshaft photos and parts catalogs for common inline-4 engines (1.5–2.5 L) show 8 counterweights, though some lightweight or older designs may use fewer as a compromise. Why Other Options Are Wrong: 4: used in some older or cost-reduced designs but not typical for modern refinement. 12 or 16: excessive for an inline-4, more typical in multi-throw engines with different architecture. 0: two-stroke small engines may omit, not automotive inline-4. Common Pitfalls: Confusing balance shaft usage (to address secondary imbalance) with crank counterweights; they serve different purposes. Final Answer: 8

Question 3

In automotive maintenance, when should the engine oil level be checked for an accurate reading? Select the best practice considering that oil needs time to drain back to the sump after the engine is switched off.

Accepted Answer

Introduction / Context: Checking engine oil level correctly is a foundational automotive maintenance task. An accurate reading protects the engine from lubrication failures, excessive wear, and overheating. This question tests best practice around when to read the dipstick so that the oil has fully returned to the sump. Given Data / Assumptions: The vehicle has been running before the check. Oil is circulating in galleries and on engine surfaces while running. We want a stable, repeatable reading on the dipstick. Concept / Approach: Engine oil must drain back to the sump to give a true level. Immediately after shutdown, some oil remains in passages and on components (head, crankcase walls, timing area). Waiting a short period allows capillary films and pooled oil to return by gravity, reducing reading error. Step-by-Step Solution: Step 1: Park on level ground and switch off the engine.Step 2: Wait a few minutes so oil can drain to the sump for a steady level.Step 3: Pull the dipstick, wipe, reinsert fully, then pull and read between MIN and MAX marks.Step 4: Top up only if below the recommended mark, using the specified grade. Verification / Alternative check: A cold, overnight-soaked engine also gives a valid reading because oil has fully drained. Many manufacturers specify checking after several minutes warm soak or cold before start; either method avoids reading while oil is still distributed in the engine. Why Other Options Are Wrong: Immediately after switch-off: level is artificially low because oil has not drained back. While running: oil is being pumped; the dipstick level is meaningless. At high-idle speed: same problem as running; turbulence increases error. Common Pitfalls: Checking on a slope causes false high/low readings. Not fully seating the dipstick before reading leads to errors. Overfilling beyond MAX can cause foaming and crank windage losses. Final Answer: Check the engine oil level a few minutes after switching off, allowing oil to drain back to the sump for an accurate reading.

Question 4

In a four-wheel-drive (4WD) vehicle drivetrain, how many gearboxes are typically used (counting the main transmission and the separate transfer case)?

Accepted Answer

Introduction / Context: A 4WD drivetrain must split torque between front and rear axles. This requires more than a single gearbox. The question probes understanding of the components that provide speed ratios and torque distribution in a typical 4WD layout. Given Data / Assumptions: Conventional longitudinal engine and 4WD layout. Driver-selectable or full-time 4WD via a transfer case. Counting distinct torque-processing housings. Concept / Approach: The main gearbox (transmission) provides multiple speed ratios for the vehicle. A separate transfer case (often called a secondary gearbox) splits power to front and rear propeller shafts and may provide high/low ranges. Together, these are commonly described as two gearboxes in 4WD systems. Step-by-Step Solution: Identify the main transmission: provides gear ratios (1st, 2nd, …, reverse).Identify the transfer case: splits torque to front and rear, offers high/low range.Total counted gearboxes = 1 (transmission) + 1 (transfer case) = 2. Verification / Alternative check: Service manuals and parts diagrams list both a transmission and a transfer case as separate assemblies, each with its own housing, shafts, and gears—confirming two gearboxes in standard 4WD layouts. Why Other Options Are Wrong: 1: Ignores the transfer case. 3 or 4: Overcounts; differentials are not classified as gearboxes. Common Pitfalls: Confusing differentials (front/rear) with gearboxes. Differentials manage wheel speed differences, not driving ranges. Assuming AWD crossovers without a separate low range; many still have a power take-off/transfer unit distinct from the transmission. Final Answer: 2

Question 5

Valve train maintenance: If the valve clearances are excessively large, which listed problem is most accurate among the options below?

Accepted Answer

Introduction / Context: Correct valve lash (clearance) ensures that valves open to the designed lift and duration and also fully seat for heat transfer and sealing. This question examines the effect of excessively large clearance and asks you to pick the closest accurate statement among the choices given. Given Data / Assumptions: Overhead valve or overhead cam engine with specified cold lash. Clearance is larger than specification. We evaluate the provided options for the most accurate outcome. Concept / Approach: Large valve clearance delays opening and hastens closing. The valve achieves less lift and shorter open duration. Typical effects: tapping noise, reduced volumetric efficiency, loss of power, rough idle, and slightly higher emissions. However, larger clearance still allows the valve to close firmly on its seat, promoting heat transfer from valve to seat. Step-by-Step Solution: Effect 1: Opening occurs later, closing occurs earlier → less air/fuel intake or exhaust scavenging.Effect 2: Reduced lift → flow restriction → power loss and roughness.Effect 3: Seating remains reliable → not typically incomplete closure; overheating from loss of heat transfer is more a risk with too-small lash.Effect 4: Spark plug fouling relates more to mixture, oil control, or ignition, not directly to large lash. Verification / Alternative check: Workshop manuals stress that too small lash risks valves not seating fully, causing burning and overheating of valves. This is essentially the opposite of the condition posed here (too large lash). Why Other Options Are Wrong: Overheating of the engine: large lash does not directly cause general engine overheating. Incomplete valve closure: more typical of lash that is too tight (too small), not too large. Spark plug fouling: not a primary symptom of large lash. Common Pitfalls: Mixing up symptoms of tight vs. loose lash. Assuming any abnormal lash automatically causes plug fouling or gross overheating. Final Answer: none of these

Question 6

Engine oils are graded by SAE viscosity numbers. Among SAE 30, SAE 40, SAE 70, and SAE 80, which oil is the most viscous (thickest at operating temperature)?

Accepted Answer

Introduction / Context: SAE viscosity grades indicate the resistance to flow of engine oils. Higher numbers generally mean thicker oil at the reference temperature. Selecting the correct grade ensures proper lubrication, film strength, and cold-start performance. Given Data / Assumptions: Single-grade SAE numbers are being compared (no W winter designation here). All oils are evaluated at their standard test temperature for kinematic viscosity. Concept / Approach: For single-grade oils, a larger SAE number corresponds to a higher viscosity range at 100°C. Therefore, among the listed options, the largest number is the most viscous at operating temperature. Step-by-Step Solution: Compare numeric grades: 30, 40, 70, 80.Identify the highest number: 80.Conclude the most viscous oil among the options is SAE 80. Verification / Alternative check: Viscosity charts from standards bodies (e.g., SAE J300) show viscosity ranges increasing with grade number for non-W oils, confirming the conclusion. Why Other Options Are Wrong: SAE 30, SAE 40, SAE 70: each has lower viscosity than SAE 80 at the specified test temperature. Common Pitfalls: Confusing multigrade designations (e.g., 10W-40) with single grades; the logic still holds at operating temperatures for the second number. Assuming thicker is always better; excessively thick oil can reduce flow and efficiency. Final Answer: SAE 80

Question 7

Automotive glass safety: A heat-treated (tempered) glass used in vehicles usually shatters into what form upon cracking, in order to reduce injury risk?

Accepted Answer

Introduction / Context: Vehicle side and rear windows are commonly made from tempered safety glass to reduce injury risk in collisions or impacts. Understanding how tempered glass fails is important for safety engineering and repair decisions. Given Data / Assumptions: The glass is properly tempered (heat-treated), not laminated. Upon critical stress or impact, the glass fails as designed. Concept / Approach: Tempered glass is created by heating followed by rapid quenching to build compressive surface stresses and tensile core stresses. This stored energy causes the pane, when fractured, to disintegrate into many small, relatively blunt particles instead of large sharp shards. Step-by-Step Solution: Tempering process → compressive skin and tensile core.Crack initiation → release of internal stresses.Result → the pane crumbles into small pellets, not daggers. Verification / Alternative check: Contrast with laminated windshield glass, which uses layers and PVB interlayer to hold shards together, typically preventing full shattering and ejection. Why Other Options Are Wrong: Sharp edged fragments: typical of ordinary annealed glass, not automotive tempered glass. Common Pitfalls: Confusing tempered and laminated glass roles in vehicles (windshields are typically laminated; side/rear often tempered). Assuming every automotive glass behaves the same upon impact. Final Answer: small particles

Question 8

Lead–acid battery technology: A “maintenance-free” automotive battery typically uses which plate-grid alloy to minimize water loss and reduce servicing needs?

Accepted Answer

Introduction / Context: Maintenance-free automotive batteries aim to minimize electrolyte loss and reduce or eliminate topping-up. The alloying of the lead grids has a major impact on gassing, water loss, and corrosion behaviour. Given Data / Assumptions: Typical 12 V lead–acid automotive battery. Closed/sealed with pressure relief, not service-removable caps in most designs. Concept / Approach: Lead–antimony grids promote gassing during charge and thus water loss, necessitating periodic topping up. Switching to lead–calcium grids greatly reduces gassing, improving water retention and enabling “maintenance-free” labeling when paired with proper separators and sealing. Step-by-Step Solution: Identify key difference: antimony vs. calcium alloying.Lead–calcium → reduced gassing → lower water consumption → minimal maintenance.Therefore, maintenance-free batteries commonly employ lead–calcium plate grids. Verification / Alternative check: Manufacturer datasheets describe “Ca–Ca” (calcium–calcium) technology for maintenance-free batteries due to lower self-discharge and gassing rates. Why Other Options Are Wrong: Lead–antimony grids: used in serviceable batteries; higher water loss. “Does not contain acid” and “does not contain water”: incorrect—these are still lead–acid cells with electrolyte; they are sealed/maintenance-reduced, not empty. Common Pitfalls: Confusing AGM, EFB, and flooded chemistries; all are lead–acid but vary in construction. Assuming maintenance-free means no electrolyte present. Final Answer: lead-calcium plate grid

Question 9

Clutch engagement state: When a vehicle is stationary and the driver is not pressing the pedal (engine idling in neutral), is the clutch normally in the engaged or disengaged position?

Accepted Answer

Introduction / Context: Clutches use spring force to press the friction disc between the flywheel and pressure plate. Understanding the default (rest) state helps diagnose driveline noises and engagement behaviour at stops. Given Data / Assumptions: Manual transmission vehicle. Engine idling, transmission in neutral, driver foot off the clutch pedal. Concept / Approach: With the pedal released, the pressure plate springs clamp the clutch disc to the flywheel, so the clutch is engaged. Power is not transmitted to the wheels in neutral because no gear is selected even though the input shaft turns. Step-by-Step Solution: Pedal up → springs apply → disc clamped → engaged.In neutral → gearbox input rotates, output stationary → vehicle does not move.Pedal down → release mechanism lifts pressure plate → disc free → disengaged. Verification / Alternative check: Workshop procedures call the pedal-released state “engaged” and pedal-depressed state “disengaged,” matching how clamping force is applied by the spring pack. Why Other Options Are Wrong: “Incorrect” would imply the clutch is disengaged at rest without the pedal depressed, which contradicts pressure-plate spring design and normal operation. Common Pitfalls: Assuming “vehicle not moving” means “clutch disengaged”; neutral prevents motion despite an engaged clutch. Riding the clutch at stops leads to premature release-bearing wear. Final Answer: Correct

Question 10

Powertrain calculation: A car engine produces 125 N·m at 2700 r.p.m. in second gear (gear ratio 1.75) with a final drive ratio of 4.11. If the overall transmission efficiency is 90%, what torque is available at the driving wheels?

Accepted Answer

Introduction / Context: Wheel torque determines tractive effort and acceleration. Gear ratios multiply engine torque, while drivetrain losses reduce it. This question practices the fundamental multiplication of torque by gear and final drive ratios with efficiency applied. Given Data / Assumptions: Engine torque T_engine = 125 N·m at 2700 r.p.m. Gear ratio (second gear) = 1.75. Final drive ratio = 4.11. Overall efficiency η = 0.90. Concept / Approach: Total torque multiplication equals gear ratio * final drive ratio. The effective wheel torque also includes efficiency losses. Use: T_wheel = T_engine * gear_ratio * final_drive * η Step-by-Step Solution: Step 1: Multiply by gear ratio → 125 * 1.75 = 218.75 N·m.Step 2: Multiply by final drive → 218.75 * 4.11 = 899.0625 N·m.Step 3: Apply efficiency → 899.0625 * 0.90 = 809.15625 N·m.Step 4: Round sensibly → 809.1 N·m (matches option). Verification / Alternative check: Sanity check: Multiplication factor is 1.75 * 4.11 ≈ 7.1925. Then 125 * 7.1925 ≈ 899.1; after 10% loss, ≈ 809.2. The result is consistent. Why Other Options Are Wrong: 8.091 N·m and 80.91 N·m: off by factors of 100 and 10; ignore the large ratio multiplication. 8091 N·m: off by factor of 10; ignores efficiency and decimal placement. Common Pitfalls: Forgetting to include final drive ratio. Applying efficiency before multiplication or using percentage wrongly. Final Answer: 809.1 N-m

Question 11

Wheel alignment and stability: Toe-in is set on a vehicle's front axle. What is the principal benefit of toe-in as stated here?

Accepted Answer

Introduction / Context: Toe-in and toe-out are alignment settings affecting tire wear, steering stability, and straight-line tracking. Manufacturers specify a slight toe-in on many vehicles to compensate for compliance and dynamic forces. Given Data / Assumptions: Statement: Toe-in ensures parallel rolling, stabilizes steering, and helps prevent side slip and excessive tire wear. Normal road speeds and typical front suspension compliance. Concept / Approach: Under forward motion, wheel bearing and bushing clearances plus lateral forces tend to spread the front wheels, reducing static toe-in to near-zero. Starting slightly toe-in thus yields near-parallel rolling during driving, enhancing straight-line stability and wear. Step-by-Step Solution: Static toe-in is set slightly positive.Driving forces deflect linkages outward.Net result at speed: wheels roll nearly parallel, minimizing scrub and stabilizing steering. Verification / Alternative check: Alignment specs in service manuals include small positive toe values; test drives confirm reduced wander and uniform tread wear with correct toe settings. Why Other Options Are Wrong: Marking the statement “Incorrect” would contradict established alignment practice for many road vehicles where slight toe-in is recommended. Common Pitfalls: Confusing toe with camber or caster; each affects handling differently. Setting toe-in too large causes rapid tire feathering and drag. Final Answer: Correct

Question 12

Compare compression ratios: Is the compression ratio in Diesel engines lower or higher than in petrol (spark-ignition) engines?

Accepted Answer

Introduction / Context: Compression ratio (CR) strongly influences efficiency, power characteristics, and combustion. Diesel engines use compression ignition, requiring high temperature from compression alone, whereas petrol engines use spark ignition and are limited by knock resistance of the fuel. Given Data / Assumptions: Typical petrol engine CR ≈ 8 to 12 (modern high-efficiency designs may be slightly higher). Typical Diesel engine CR ≈ 14 to 22 (some heavy-duty higher). Concept / Approach: Diesel relies on heat of compression to ignite fuel; thus CR must be higher than petrol. This directly contradicts the statement that Diesel CR is less than petrol CR. Step-by-Step Solution: Identify claim: “Diesel CR < petrol CR”.Compare typical CR ranges (Diesel > petrol).Conclude the statement is false. Verification / Alternative check: Thermal efficiency trends show higher CR increases theoretical efficiency (per ideal cycles), consistent with Diesel engines having higher CR to achieve self-ignition and high efficiency. Why Other Options Are Wrong: Choosing “Agree” would misstate fundamental engine design differences and fuel ignition methods. Common Pitfalls: Confusing boost pressure in turbocharged petrol engines with static CR. Overgeneralizing from specific models; the general rule remains Diesel CR > petrol CR. Final Answer: Disagree

Question 13

Automobile engineering — measurement tools Which instrument is specifically used to measure valve tappet (valve lash) clearance during engine maintenance?

Accepted Answer

Introduction / Context: Correct valve tappet clearance (also called valve lash) is critical in internal combustion engines. Too much clearance causes noise and reduced valve lift; too little clearance can lead to valves not seating fully, overheating, and loss of compression. Measuring this small gap precisely is a routine yet vital servicing task. Given Data / Assumptions: The gap to be measured is very small, typically in the range of 0.05 mm to 0.40 mm depending on engine and whether the valve is intake or exhaust. Measurement is taken with the cam lobe on its base circle (valve fully closed) or at the specified crank angle. Ambient workshop conditions; no special electronics assumed. Concept / Approach: The industry-standard tool for gauging small, known clearances is the feeler gauge, a set of calibrated steel blades of known thicknesses. The correct blade should slide with a slight drag between the rocker/adjuster and the valve stem tip (or cam and bucket/shim in overhead cam designs). Other listed instruments are not intended for such tiny, in-situ gap checks. Step-by-Step Solution: Ensure the engine is at the specified temperature (often cold) and the valve is fully closed.Select a feeler gauge blade matching the manufacturer’s specified clearance.Insert the blade between the contact faces; feel for light resistance (“go”) and check that the next thicker blade does not enter (“no-go”).Adjust using the locknut/screw (if applicable) until the specified feel is achieved; recheck after tightening. Verification / Alternative check: Confirm by trying one size thinner (should be easy) and one size thicker (should not enter). Record values for all valves. Why Other Options Are Wrong: Screw pitch gauge measures thread pitch, not clearance. Engineering scale cannot resolve such small gaps reliably. Vernier caliper and micrometer measure external/internal dimensions, not an in-assembly clearance with correct tactile feedback. Common Pitfalls: Measuring on the cam lobe instead of base circle; mixing metric and inch blades; not accounting for hot lash specifications where required; over-tightening the locknut and changing the setting. Final Answer: feeler gauge

Question 14

Fuels and knocking resistance A petrol (gasoline) that detonates easily in a spark-ignition engine is referred to as what?

Accepted Answer

Introduction / Context: Detonation (knock) is spontaneous, uncontrolled end-gas combustion in a spark-ignition engine, producing pressure waves that can damage components and reduce efficiency. The fuel’s resistance to knock is quantified by its octane rating. Given Data / Assumptions: Spark-ignition (petrol) engine operating with fixed compression ratio. Octane number indicates knock resistance under standardized test conditions. Other descriptors (unleaded, premium) may correlate with additives and marketing but are not strict measures of knock resistance unless a number is specified. Concept / Approach: Lower octane fuels auto-ignite more readily under pressure and temperature, promoting detonation. Higher octane fuels can withstand higher compression and advanced ignition timing without knocking. Therefore, a petrol that “detonates easily” is low octane petrol. Step-by-Step Solution: Identify property controlling detonation: octane rating.Relate “detonates easily” to “low knock resistance.”Low knock resistance corresponds to a low octane rating.Thus, the correct description is “low octane petrol.” Verification / Alternative check: Engines designed for high octane fuel often knock when run on lower octane; ECU knock sensors may retard timing to protect the engine, demonstrating dependence on octane. Why Other Options Are Wrong: High octane petrol resists knock; it does not detonate easily. Unleaded refers to absence of tetraethyl lead, not directly to knock behavior unless octane is specified. Blended or “premium” fuels may have higher octane, but the term alone is not definitive. Common Pitfalls: Confusing “power” or “energy content” with octane; octane rating does not measure energy per litre but knock resistance. Assuming all premium fuels are the same across regions despite differing octane scales (RON, MON, AKI). Final Answer: low octane petrol

Question 15

Four-stroke engine cycle — firing frequency In a four-cylinder inline, four-stroke engine, how many firing (power) strokes occur during one revolution of the crankshaft?

Accepted Answer

Introduction / Context: Understanding the relationship between cylinder count and firing frequency helps diagnose vibration, misfire patterns, and gearbox input torque pulsations. In a four-stroke engine, each cylinder completes the full cycle (intake, compression, power, exhaust) over two crankshaft revolutions. Given Data / Assumptions: Four-stroke operating principle: one power stroke per cylinder every 2 revolutions. Four cylinders in-line, evenly phased for smoothness. Constant speed steady operation without misfire. Concept / Approach: Number of power strokes per revolution equals total cylinders divided by 2 (for four-stroke engines). For a 4-cylinder: 4 / 2 = 2 power strokes per single crank revolution, evenly spaced. Step-by-Step Solution: Each cylinder fires once every 720 degrees of crank rotation.During 360 degrees (one revolution), only half of the cylinders fire.With 4 cylinders, half is 2; hence 2 firing strokes per revolution. Verification / Alternative check: Typical firing orders (e.g., 1-3-4-2) show two firings per revolution when plotted over 720 degrees; strobing at the crank confirms 2 pulses per rev at the flywheel. Why Other Options Are Wrong: 1 and 3 do not match the 4/2 rule. 4 would imply every cylinder fires each revolution, which is two-stroke behavior. 0 is incorrect because in any given single revolution there are indeed power events. Common Pitfalls: Confusing two-stroke and four-stroke firing frequencies; overlooking that multi-cylinder phasing spreads torque pulses to reduce vibration. Final Answer: 2

Question 16

Brake system diagnostics — warning indicator In a hydraulic brake system, the dashboard brake warning light primarily alerts the driver to which fault condition?

Accepted Answer

Introduction / Context: Modern vehicles include a red brake warning lamp tied to safety-critical sensors. Interpreting what triggers this lamp is essential for correct troubleshooting and avoiding unsafe operation. Given Data / Assumptions: Conventional tandem (dual-circuit) master cylinder layout. Pressure differential switch or fluid-level switch connected to the warning lamp. Parking brake switch may also illuminate the same lamp in some vehicles, often with an additional symbol. Concept / Approach: The key safety function is to warn of hydraulic failure in either circuit (front/rear or diagonal split). A pressure differential switch moves if one circuit loses pressure, closing the warning circuit. Low fluid level (often due to leaks) may also trigger the lamp; both are manifestations of hydraulic system failure risk. Step-by-Step Solution: Identify the lamp: red “BRAKE” or exclamation symbol.Check for pressure differential or reservoir level signal that indicates a failed circuit.Therefore, the lamp primarily signals failure of a primary or secondary hydraulic circuit. Verification / Alternative check: Confirm by scanning the vehicle manual or wiring diagram: the lamp connects to the differential pressure switch and fluid level sensor; test by opening a bleed screw on one circuit and observing lamp behavior. Why Other Options Are Wrong: Water contamination is not directly sensed. Air in lines may cause a soft pedal but is not directly detected by a simple switch. Power-brake (vacuum/booster) failures often have a separate indicator or different symptoms. Parking brake engagement can light the same lamp but is not the primary safety fault referenced in hydraulic warning systems. Common Pitfalls: Ignoring a lit brake lamp due to a slightly engaged parking brake; always verify fluid level and circuit integrity. Do not drive if pedal travel increases or car pulls to one side. Final Answer: failure of the primary or secondary circuit of hydraulic system

Question 17

Automotive tyres — bead construction Bead wires, which anchor the tyre to the rim and maintain shape under pressure, are typically made from which material?

Accepted Answer

Introduction / Context: The tyre bead forms the interface between tyre and rim, securing the tyre under internal pressure, cornering, and braking forces. The bead must be strong, fatigue-resistant, and dimensionally stable. Given Data / Assumptions: Pneumatic tyre with rubber compound, cord plies, bead fillers, and bead wire(s). Operating pressures and loads typical of passenger or commercial vehicles. Rim hardness and geometry per standards (e.g., bead seat taper). Concept / Approach: High-tensile steel wire (often copper- or brass-plated for adhesion) is used for beads because it provides superior tensile strength, stiffness, and durability in a compact cross-section. The wire is wound into hoops, embedded in rubber, and works with bead fillers to maintain sealing and retention. Step-by-Step Solution: Identify the function: resist hoop stress and maintain airtight seal.Match material to requirement: high tensile strength and fatigue resistance → steel.Therefore, bead wire material is steel. Verification / Alternative check: Cutaway tyres and manufacturer datasheets specify steel bead bundles; metal detectors also reveal steel at the bead. Why Other Options Are Wrong: Copper, zinc, and aluminium lack the required combination of tensile strength and cost-effectiveness for bead cores. Nylon is used in plies or cap plies but not as bead wire. Common Pitfalls: Confusing bead wire with reinforcement cords; cords can be polyester, nylon, steel, or aramid, but bead cores remain steel for most applications. Final Answer: steel

Question 18

Flywheel sizing comparison Compared with similar petrol (spark-ignition) engines, Diesel (compression-ignition) engines generally require what size of flywheel to smooth speed fluctuations?

Accepted Answer

Introduction / Context: The flywheel stores rotational energy and smooths crankshaft speed fluctuations between firing strokes. Differences in combustion characteristics and operating speeds between Diesel and petrol engines influence flywheel mass selection. Given Data / Assumptions: Diesel engines operate at higher compression ratios and often lower rated speeds. Combustion pressure rise and torque pulsations can be larger in Diesels. Objective: limit cyclic speed variation to acceptable values for drivability and NVH. Concept / Approach: Required flywheel inertia J depends on torque irregularity and target speed fluctuation (delta omega). For the same power, a slower-turning Diesel with stronger pulse amplitudes benefits from a larger inertia to equalize angular velocity. Hence, Diesels typically use heavier (bigger) flywheels than comparable petrol engines. Step-by-Step Solution: Identify torque ripple: Diesel > petrol (generally).Relate inertia to smoothing: greater J reduces speed fluctuation.Conclusion: choose a bigger flywheel for the Diesel to meet NVH criteria. Verification / Alternative check: Compare parts catalogs: Diesel variants often list heavier dual-mass flywheels versus petrol single-mass options in the same vehicle platform. Why Other Options Are Wrong: Smaller or lighter flywheels worsen fluctuations. “Same size” ignores typical differences in torque ripple and speed. All piston engines require some flywheel effect; “no flywheel” is incorrect for road engines. Common Pitfalls: Overlooking modern dual-mass flywheels that separate torsional damping from inertia; confusing crankshaft balance weights with flywheel inertia. Final Answer: bigger flywheel

Question 19

Engine lubrication — filter components Which part of an automotive oil filter actually traps and prevents the passage of metal particles and sludge?

Accepted Answer

Introduction / Context: Clean engine oil is essential to minimize wear. Full-flow oil filters protect bearings and cam surfaces by removing particulates. Knowing each component’s role aids correct diagnosis when oil pressure warnings or dirty oil appear. Given Data / Assumptions: Spin-on or cartridge-type full-flow filter. Oil pump maintains flow; pressure measured after the filter in many systems. Typical filter includes media element, anti-drainback (check) valve, and bypass (relief) valve. Concept / Approach: The filter element (media) is the functional barrier that captures contaminants. Media may be cellulose, synthetic fiber, or blended, designed for a target micron rating and dirt-holding capacity. Valves serve support roles: the relief valve protects flow in cold starts or clogging; the check valve prevents drainback in mounted orientations; the case and base plate provide structure and sealing. Step-by-Step Solution: Identify which component provides filtration: the porous media (element).Recognize the other parts are hydraulic control or housing features.Therefore, the correct answer is “element.” Verification / Alternative check: Cut open a used filter: debris will be trapped within the pleats of the element; valves and housing remain clean. Why Other Options Are Wrong: The relief valve bypasses flow when pressure differential is high; it does not filter. The check valve maintains prime and prevents drainback; it does not filter. The case and base plate are structural and sealing components only. Common Pitfalls: Assuming higher micron ratings always better; balance flow and filtration. Replacing filters late risks bypass operation, allowing unfiltered oil to circulate. Final Answer: element

Question 20

Vehicle geometry — wheelbase definition In automotive terminology, what is meant by the wheelbase of a vehicle?

Accepted Answer

Introduction / Context: Wheelbase is a core dimensional parameter influencing ride comfort, high-speed stability, turning radius, and cabin packaging. It is routinely cited in vehicle specifications and used in alignment equipment setup. Given Data / Assumptions: Standard road vehicle with front and rear axle centers. Measurements taken on level ground with specified tyre pressures. No special steering angles applied during measurement. Concept / Approach: Wheelbase is specifically the longitudinal distance between the front axle centerline and the rear axle centerline, effectively the distance between the centers of the front and rear wheels on the same side (or averaged across). It is distinct from track width (lateral distance between left and right wheels on an axle) and overall vehicle length. Step-by-Step Solution: Identify the two axle centerlines (front and rear).Measure the longitudinal distance between these lines.That measurement defines the wheelbase. Verification / Alternative check: Consult manufacturer specifications; wheel alignment machines request wheelbase and track for geometry calculations. Why Other Options Are Wrong: Option b and c define track (front or rear), not wheelbase. Option d is overall length, a different specification. Option e again is track width, not wheelbase. Common Pitfalls: Confusing wheelbase with the distance between wheel centers on opposite sides; misinterpreting staggered axle positions on specialty vehicles or trailers. Final Answer: distance between the centres of the front and rear wheels

Automobile Engineering Questions