Question 1

Automatic transmissions — typical maximum torque multiplication of a torque converter In a passenger-car torque converter, the peak torque multiplication ratio (stall ratio) is typically about:

Accepted Answer

Introduction / Context: A torque converter provides hydrodynamic torque multiplication during launch until turbine speed rises and the stator freewheels. Understanding the stall ratio helps in predicting launch feel and performance. Given Data / Assumptions: Light-duty automotive converter with typical stator and pump/turbine geometry. No exotic high-stall racing units. Peak multiplication occurs at near-zero turbine speed (stall). Concept / Approach: Most OE converters have stall ratios between about 1.8 and 2.8. Higher values would be unusual for standard road cars and bring efficiency penalties after launch. Step-by-Step Solution: Identify typical range for OE converters.Choose the representative mid value: about 2.5. Verification / Alternative check: Spec sheets for common transmissions list stall ratios around 2.0–2.5; performance variants may approach ~3.0. Why Other Options Are Wrong: 10, 25, 40: far beyond hydrodynamic converter capability for automotive applications. Common Pitfalls: Confusing torque multiplication with gear ratio; the converter’s effect is transient and load-dependent. Final Answer: 2.5

Question 2

Carburettor fundamentals — control of mixture quantity and ratio in SI engines Evaluate the statement: “The function of a carburettor is to control the amount and ratio of the air–fuel mixture.”

Accepted Answer

Introduction / Context: Before electronic fuel injection became universal, carburettors were the standard devices for metering fuel and mixing it with intake air in spark-ignition engines across operating conditions. Given Data / Assumptions: Conventional float-type carburettor with jets, venturi, throttle plate, and enrichment circuits. Normal running modes: idle, part load, acceleration, power, and choke for cold start. Concept / Approach: The carburettor creates a pressure drop in the venturi as air flows. This draws fuel through calibrated jets. The throttle controls the total airflow (quantity), while jetting and auxiliary circuits influence the air–fuel ratio to meet engine demands. Step-by-Step Solution: Throttle opening sets airflow and therefore mixture quantity to the engine.Main, idle, and power jets plus air bleeds shape the mixture ratio across speeds and loads.Hence, the statement that a carburettor controls both amount and ratio of mixture is true. Verification / Alternative check: Tuning procedures adjust jet sizes and needle positions to correct mixture across the operating range, confirming control of ratio. Why Other Options Are Wrong: False: contradicts the fundamental operation of carburettors. Common Pitfalls: Confusing throttle-only control (quantity) and forgetting that jets and circuits actively shape air–fuel ratio (quality). Final Answer: True

Question 3

Automotive radiator heat exchange In a water-cooled automobile engine, how does heat transfer from the hot coolant inside the radiator to the surrounding air? Select the most complete combination of modes.

Accepted Answer

Introduction / Context: A radiator is a compact crossflow heat exchanger. Understanding the sequence of heat transfer modes helps diagnose cooling problems and design efficient thermal systems in automobiles. Given Data / Assumptions: Coolant flows inside thin metal tubes with external fins. Ambient air moves across fins due to vehicle motion and/or a fan. Surfaces are metallic and at temperatures modestly above ambient. Concept / Approach: The overall process involves three modes. First, energy moves from the moving coolant to the tube inner wall. Second, it travels through the tube/fin metal. Third, it is released from the outer fin surfaces to the air stream. Radiation always exists between warm fins and surroundings, although it is usually smaller than forced convection in automotive service. Step-by-Step Solution: Inside tubes: convection from coolant to inner wall (forced by water pump).Across metal: conduction through tube wall and into fins.From fins: primarily convection to air; plus net thermal radiation to nearby surfaces and sky.Therefore the correct and complete answer includes conduction, convection, and radiation. Verification / Alternative check: Heat exchanger analysis uses overall heat transfer coefficient U combining inside convection hi, metal conduction, and outside convection ho, with a small radiation term added when needed. This framework confirms all three modes participate. Why Other Options Are Wrong: Radiation only or convection only omit essential steps through the metal wall. Conduction only ignores the fluid-side heat transfer and airside removal. Convection and radiation ignores the necessary conduction path through the tube/fins. Common Pitfalls: Overlooking fouling inside tubes (reduces inner convection), bent/dirty fins (hurts airside convection), or low coolant flow; all degrade overall U more than radiation ever helps. Final Answer: conduction, convection and radiation

Question 4

Engine mechanism — piston-to-rod connection In a reciprocating internal combustion engine, the connecting rod is attached to the piston by which component?

Accepted Answer

Introduction / Context: The piston-to-connecting-rod joint must transmit high alternating forces while allowing oscillation as the rod swings on the crankpin. Knowing the correct component name avoids confusion during overhauls. Given Data / Assumptions: Piston has a pin bore (gudgeon-pin boss). Connecting rod has a small-end eye with a bush or bearing. Retainers (circlips) may prevent axial pin movement. Concept / Approach: The cylindrical member passing through the piston bosses and the small-end eye is called the piston pin (also gudgeon pin or wrist pin). It provides a journal for oscillation and transmits gas and inertia loads. Step-by-Step Solution: Identify joint type: pin joint between piston and rod small end.Name of load-carrying member: piston pin (gudgeon pin).Select the option that correctly names this member. Verification / Alternative check: Workshop manuals and parts catalogs label this as piston pin/wrist pin; circlips or spirolocks retain but do not form the primary joint. Why Other Options Are Wrong: Cap bolt and rod cap belong to big-end assembly at the crankpin, not the piston end. Cap roller bearing is not the standard term nor the correct location. Circlips are retainers, not the joint component itself. Common Pitfalls: Installing pins without correct clearance or lubrication causes scuffing; incorrect circlip seating risks catastrophic pin walk. Final Answer: piston pin

Question 5

Brake faults — consequence of vapour lock in hydraulic brakes What is the primary effect of vapour locking on vehicle brake performance?

Accepted Answer

Introduction / Context: Vapour lock occurs when brake fluid boils in lines or calipers, creating compressible vapour pockets. Understanding the symptom is critical for safety and maintenance. Given Data / Assumptions: Hydraulic service brakes using glycol ether or silicone-based fluid. High temperature from heavy braking or dragging brakes. Possible moisture contamination lowering fluid boiling point (wet boiling point). Concept / Approach: Hydraulic systems rely on near-incompressible fluid to transmit force. When vapour forms, it compresses under pedal force, absorbing stroke without generating sufficient line pressure at the calipers/wheel cylinders. The consequence can range from severe sponginess to complete loss of braking force. Step-by-Step Solution: Heat raises local fluid temperature above its boiling point → vapour bubbles form.Vapour compresses when the pedal is pressed → large pedal travel, little clamp force.In extreme cases, pedal goes to the floor with negligible braking → functional failure. Verification / Alternative check: Field reports and testing show dramatic loss of deceleration during fade with vapour lock; recovery may occur after cooling as vapour condenses. Why Other Options Are Wrong: More effective braking is impossible with compressible vapour present. Delayed operation (option c) can occur early, but the dominant hazard is near-total loss under sustained pressure. No effect is incorrect; the effect is severe. Common Pitfalls: Using old contaminated fluid (low wet boiling point); inadequate cooling; resting foot on pedal causing drag; failing to flush fluid at recommended intervals. Final Answer: brakes fail completely

Question 6

Hydraulic brake system — role of the master cylinder In a typical passenger-car hydraulic braking system, what is the primary function of the master cylinder?

Accepted Answer

Introduction / Context: The master cylinder is the heart of a hydraulic brake system. Knowing its function helps in diagnosing issues such as a sinking pedal, internal leaks, or air in lines. Given Data / Assumptions: Conventional systems may include a vacuum booster (servo), proportioning valves, and ABS modulator. The master cylinder contains a reservoir and primary/secondary pistons with seals and ports. Concept / Approach: When the driver presses the pedal, mechanical force is transmitted (often through a booster) to the master-cylinder pistons. These pistons displace brake fluid and generate hydraulic line pressure that actuates calipers or wheel cylinders using Pascal’s principle. Step-by-Step Solution: Pedal force → pushrod → master piston(s).Piston motion closes compensation ports → pressure builds in circuits.Pressure transmitted via lines/hoses to calipers/wheel cylinders → brake force at discs/drums. Verification / Alternative check: Pressure gauges placed at outlets rise proportionally with pedal force; leaks or bypassing seals show reduced or unstable pressure, confirming the master’s purpose. Why Other Options Are Wrong: Free play adjustment is a mechanical linkage task, not the master’s core function. Boosting is the vacuum/ hydraulic booster’s role, not the master cylinder's. Equalization is handled by proportioning/ABS logic; equal pressure is not always desired. The reservoir stores fluid, but the master’s key role is pressure generation. Common Pitfalls: Air in the master or lines prevents pressure buildup; wrong pushrod length can block ports causing drag. Final Answer: convert the driver’s pedal force into hydraulic pressure

Question 7

Diesel fuel system — injector function In a compression-ignition (Diesel) engine, what is the principal function of the fuel injector?

Accepted Answer

Introduction / Context: Diesel engines rely on compression-ignition. The injector's spray quality and timing dominate combustion efficiency, emissions, and noise. Given Data / Assumptions: Air-only is compressed; fuel is injected near the end of compression. Injector may be mechanical or electronically controlled (common-rail). High-pressure atomization is required for rapid mixing with hot air. Concept / Approach: The injector meters, times, and atomizes fuel into fine droplets with an appropriate spray pattern and penetration so that self-ignition occurs due to the high temperature of compressed air. It does not intentionally pre-mix fuel with air before compression nor provide spark. Step-by-Step Solution: High-pressure pump/rail supplies injector.Injector opens per control signal/pressure → atomized spray enters cylinder.Spray interacts with hot, compressed air → auto-ignition and combustion. Verification / Alternative check: Engine starts and runs without spark system; combustion phasing tracks injection timing, confirming injector’s primary role. Why Other Options Are Wrong: Mixing before compression is a petrol engine carburation/port injection concept. Diesels do not use a spark or separate flame front provider. Fuel return lines exist but are not the injector’s principal function. Common Pitfalls: Poor atomization (worn nozzles) causes smoke and rough running; incorrect timing elevates noise and NOx. Final Answer: spray atomized fuel into the cylinder at the correct timing

Question 8

Detonation in spark-ignition engines — primary consequence Which of the following is a significant effect of detonation (knock) during engine operation?

Accepted Answer

Introduction / Context: Detonation is the auto-ignition of end-gas after spark, producing pressure waves that ring the combustion chamber. It is harmful to performance and components. Given Data / Assumptions: Spark-ignition petrol engine under high load or advanced timing. Low-octane fuel or high intake temperature. No pre-ignition assumed (a different fault). Concept / Approach: Knock disrupts controlled flame propagation, reducing effective mean pressure and forcing the ECU (if present) to retard timing, both of which reduce power. Prolonged knock also increases thermal and mechanical stresses, risking overheating and damage. Step-by-Step Solution: End-gas auto-ignites → pressure oscillations → unstable combustion.Engine control retards ignition to avoid knock → lower torque output.Net result: noticeable loss of power and drivability. Verification / Alternative check: Dyno testing with induced knock shows reduced brake mean effective pressure once timing is pulled back. Why Other Options Are Wrong: Ignition delay refers to time before combustion starts; knock is not a delay but abnormal rapid combustion. Overheating can occur but is a secondary consequence; the primary immediate effect felt by a driver is power loss. Overcooling and improved economy are incorrect. Common Pitfalls: Confusing detonation with pre-ignition; using too low octane; excessive intake air temperature; carbon deposits elevating compression. Final Answer: loss of power

Question 9

Brake fluids — essential characteristics Which of the following are fundamental requirements for an automotive brake fluid?

Accepted Answer

Introduction / Context: Brake fluid transmits pressure, lubricates components, and must withstand extreme temperatures. Choosing the right fluid prevents vapour lock, corrosion, and seal failure. Given Data / Assumptions: Typical DOT 3/4/5.1 glycol-ether fluids or DOT 5 silicone in special cases. Hydraulic brakes with rubber seals and mixed metals. Operating conditions include cold starts and repeated hard stops. Concept / Approach: High boiling point prevents vapour formation under heavy braking. Low viscosity ensures rapid valve actuation (ABS) and good flow at low temperatures. Chemical compatibility with elastomers and metals avoids swelling, softening, or corrosion. Step-by-Step Solution: Property 1: Dry and wet boiling points must exceed service temperatures.Property 2: Viscosity must remain within specification over wide temperature range.Property 3: Additive package must protect seals and metal parts from corrosion and wear.Therefore, the correct selection is “all of these”. Verification / Alternative check: Standards (e.g., DOT) specify minimum boiling points, viscosity limits, pH range, and corrosion tests, confirming all listed properties are required. Why Other Options Are Wrong: Any single property alone is insufficient; lacking one compromises safety or durability. “None of these” is clearly false. Common Pitfalls: Mixing incompatible fluids (e.g., DOT 5 with DOT 3/4/5.1), ignoring fluid change intervals causing low wet boiling point, or using contaminated containers. Final Answer: all of these

Question 10

Clutch construction — fastening of friction facings Clutch facings (friction linings) are commonly attached to the clutch plate by which fasteners?

Accepted Answer

Introduction / Context: Clutch plates employ friction facings that must be secured without damaging mating surfaces. The choice of fastener material influences wear of the flywheel and pressure plate and the serviceability of the assembly. Given Data / Assumptions: Organic or sintered facings riveted to a steel core plate. Service conditions: high temperature, vibration, and repeated engagement. Compatibility with cast iron or steel mating surfaces is important. Concept / Approach: Soft non-ferrous rivets (brass or copper) are preferred because, in the event of wear-through, they are less likely to gouge the flywheel or pressure plate compared to hard steel rivets. They also ease riveting and reduce the risk of cracking the facing material. Step-by-Step Solution: Identify requirement: secure facings with minimal damage risk.Evaluate options: brass rivets are soft and sacrificial; steel rivets are too hard; screws are uncommon on friction facings.Select brass rivets as the standard practice. Verification / Alternative check: OEM and aftermarket clutch specifications frequently list copper/brass rivets; performance clutches may use different retention but rivets remain common. Why Other Options Are Wrong: Steel rivets/screws can score mating surfaces if exposed. Aluminium screws lack strength at temperature. Adhesive-only designs are rare in high-temperature automotive clutches. Common Pitfalls: Incorrect rivet length or setting pressure can loosen facings; always follow torque and staking procedures. Final Answer: brass rivets

Question 11

Piston rings — classification Automotive pistons typically employ two categories of rings. Identify the correct pair.

Accepted Answer

Introduction / Context: Piston rings provide gas sealing and oil regulation. Most engines use a combination of upper compression rings and lower oil-control assemblies for reliable operation. Given Data / Assumptions: Typical ring pack: two compression rings and one oil-control ring (three-piece). Cylinder made of cast iron or liners in aluminum blocks. Normal lubrication and honing crosshatch present. Concept / Approach: Compression rings seal combustion gases and transfer heat from the piston to the cylinder wall. The oil-control ring meters oil film, scraping excess and returning it through drain holes to the crankcase. Step-by-Step Solution: Top rings: provide primary gas seal and heat path.Oil ring: controls oil, often with expander and side rails.Thus, the two classes are compression rings and oil-control rings. Verification / Alternative check: Service literature labels rings as compression (top/second) and oil-control; other names are colloquial. Why Other Options Are Wrong: “Sliding seal,” “pressure,” “sealing,” or “relief” rings are nonstandard terms. “Oil scrapper” is an informal synonym but paired with oil-control duplicates function while omitting compression rings. Common Pitfalls: Improper ring end gaps, wrong orientation, or carboned drain holes cause oil burning and poor sealing. Final Answer: compression and oil-control rings

Question 12

Parking brake actuation — method used in vehicles In standard passenger vehicles, the parking (hand) brake is normally actuated by which method?

Accepted Answer

Introduction / Context: The parking brake provides a secure hold when stationary and serves as an emergency backup. Regulations often require an independent actuation method from the service brake hydraulic circuit. Given Data / Assumptions: Conventional cars with cable-operated handbrakes or foot-operated parking pedals. Some modern vehicles use electric parking brakes that actuate a mechanical mechanism. Primary service brakes are hydraulic. Concept / Approach: Parking brakes are typically mechanical via cables or screw/lever mechanisms acting on rear discs (integrated drum-in-hat or caliper mechanism) or rear drums. This independence ensures parking capability even if hydraulic pressure is lost. Step-by-Step Solution: Identify regulatory intent: independent, fail-safe actuation.Common implementation: lever/pedal → cables/gear → rear brakes.Therefore, the method is mechanical actuation. Verification / Alternative check: Vehicle manuals illustrate cable routing to rear brake mechanisms; electric parking brakes still drive a mechanical clamp or drum via motors. Why Other Options Are Wrong: Hydraulic actuation would not be independent and could leak down; pneumatics are used on heavy trucks, not typical cars. “None of these” is false; a clear standard method exists. Common Pitfalls: Corroded cables and misadjusted mechanisms reduce holding force; always test on slopes after service. Final Answer: mechanically

Question 13

Automotive clutches — recommended free pedal play In passenger cars, the typical free pedal play (free travel at the clutch pedal top before release mechanism begins to act) is approximately:

Accepted Answer

Introduction / Context: Correct clutch pedal free play is essential for smooth engagement, avoiding clutch slip, and preventing premature release bearing wear. Free play is the small movement at the pedal before the release mechanism starts to act on the pressure plate. This question checks standard service-interval knowledge for typical passenger cars. Given Data / Assumptions: Conventional single-plate dry clutches used in most cars. Healthy linkage or hydraulic system with no abnormal wear. Measurement is at the pedal pad edge, engine off, vehicle on level ground. Concept / Approach: Manufacturers specify a nominal free play band to ensure the clutch fully engages without the release bearing riding on the pressure plate. Too little free play risks slip and heat; too much makes disengagement difficult and can cause gear clash. A widely accepted nominal value for many cars is about 25 mm at the pedal top (often a range around 20–30 mm). Step-by-Step Solution: Identify standard service data: typical car clutch free play ≈ 25 mm.Compare with options: 15 mm (too small), 40–60 mm (too large).Select the nearest standard nominal value: 25 mm. Verification / Alternative check: Workshop manuals commonly quote free play around 20–30 mm at the pedal or 3–5 mm at the release fork clearance. This validates 25 mm as a representative figure. Why Other Options Are Wrong: 15 mm can leave insufficient clearance, causing bearing drag. 40 mm and 60 mm are excessive and can prevent full disengagement, causing gear grinding and poor shift quality. Common Pitfalls: Measuring with carpets interfering; ignoring self-adjusting mechanisms on some hydraulic systems; adjusting without checking release fork or cable wear. Final Answer: 25 mm

Question 14

Two-stroke engine process terminology The expulsion of burnt gases from the cylinder by the incoming fresh charge from the crankcase is called:

Accepted Answer

Introduction / Context: In two-stroke engines, intake and exhaust processes overlap. Proper terminology distinguishes critical processes that affect power, emissions, and efficiency. This question targets recognition of the process by which exhaust gases are displaced by the fresh charge. Given Data / Assumptions: A crankcase-scavenged two-stroke engine. Transfer ports feed fresh mixture while exhaust ports release burnt gases. No valves; port timing controls gas exchange. Concept / Approach: Scavenging is the process of sweeping out exhaust gases by the fresh charge. The quality of scavenging determines residuals, temperature, and next-cycle filling. Different scavenging methods include cross-flow, loop, and uniflow. Terms like priming, cleaning, and detonation refer to other concepts and are not correct here. Step-by-Step Solution: Identify the described action: burnt gases being pushed out by fresh charge.Recall the textbook term for this displacement: scavenging.Choose the term matching the definition: scavenging. Verification / Alternative check: Engine cycle diagrams show transfer port opening shortly after exhaust port opening, with fresh charge flow patterns designed for efficient scavenging. Why Other Options Are Wrong: Cleaning is a generic word, not the technical process. Priming refers to preparation of fuel or pumps. Detonation is abnormal combustion in spark-ignition engines, unrelated to gas exchange. Common Pitfalls: Confusing scavenging with supercharging; assuming four-stroke valve overlap is the same as two-stroke scavenging. Final Answer: scavenging

Question 15

Hydraulic brake actuation path — sequence of force transmission When the driver depresses the brake pedal, the correct sequence of components transmitting force to the pads/shoes is:

Accepted Answer

Introduction / Context: Modern hydraulic brake systems commonly include a vacuum servo (brake booster) to reduce pedal effort. Understanding the order of components ensures correct diagnostics and system comprehension. Given Data / Assumptions: Typical passenger car hydraulic brakes with a vacuum booster. Master cylinder converts mechanical input to hydraulic pressure. Brake lines convey pressure to calipers/wheel cylinders. Concept / Approach: The driver’s foot acts on the pedal, which is mechanically linked to a vacuum servo. The servo multiplies force and directly actuates the master cylinder. The master cylinder pressurizes fluid, sending it through rigid lines and flexible hoses to calipers or wheel cylinders that clamp pads or expand shoes. Step-by-Step Solution: Pedal applies input to booster (servo) first.Booster amplifies force into the master cylinder pushrod.Master cylinder generates hydraulic pressure into brake lines.Lines deliver pressure to calipers/shoes at the wheels. Verification / Alternative check: Vehicle schematics show pedal linkage entering the booster can, with the master cylinder bolted to the booster’s front face, confirming the physical order. Why Other Options Are Wrong: Options placing the master cylinder before the booster ignore real layout. Starting with brake lines is impossible without pressure. Putting the servo after lines is incorrect. Common Pitfalls: Confusing ABS modulator placement (it fits in the hydraulic path but after the master); forgetting that booster aids force, not pressure source. Final Answer: brake pedal - vacuum servo mechanism - master cylinder - brake lines - brake pads

Question 16

Engine capacity and swept volume per cylinder A four-cylinder engine has a total swept volume (capacity) of 2.4 litres. The swept volume of one cylinder is:

Accepted Answer

Introduction / Context: Engine capacity is the sum of the swept volumes of all cylinders. Converting between litres and cubic centimetres and dividing by cylinder count are routine but essential skills in automotive calculations. Given Data / Assumptions: Total capacity = 2.4 litres. Number of cylinders = 4. 1 litre = 1000 cm3. Concept / Approach: Swept volume per cylinder = total swept volume / number of cylinders. A simple unit conversion to cm3 is often requested to match service data tables and specification sheets. Step-by-Step Solution: Convert total capacity: 2.4 litres = 2.4 * 1000 = 2400 cm3.Divide by cylinder count: 2400 / 4 = 600 cm3.Match to options: 600 cm3. Verification / Alternative check: As a quick check, 2.0 L four-cylinder is 500 cm3 per cylinder; 2.4 L should be a bit higher: 600 cm3. This sanity check aligns with the computed result. Why Other Options Are Wrong: 400 cm3 corresponds to a 1.6 L engine. 1200 cm3 would be two-cylinder equivalent, not one. 2400 cm3 is the total, not per cylinder. Common Pitfalls: Forgetting litre-to-cm3 conversion; mixing swept volume with total engine displacement including clearance volume. Final Answer: 600 cm3

Question 17

Tilt steering construction In vehicles equipped with tilt steering, the steering column is pivoted at the:

Accepted Answer

Introduction / Context: Tilt steering allows drivers to adjust the steering wheel angle for comfort and ergonomic alignment. Knowing the pivot component helps in service and troubleshooting mechanisms within the steering column assembly. Given Data / Assumptions: Standard tilt steering column found in passenger vehicles. Locking pawl or detent positions determine tilt angles. Pivot point must be robust and centrally located within the tilt mechanism. Concept / Approach: The tilt function is realized by a pivoting joint commonly called the tilt bracket. The column housing and steering shaft pass through this bracket, which allows angular adjustment while maintaining column integrity and wiring routing (e.g., clockspring harness). Step-by-Step Solution: Identify the dedicated component controlling pivot: the tilt bracket.Relate bracket function to column angle change while keeping mounting points intact.Select the option naming the tilt bracket as the pivot location. Verification / Alternative check: Exploded diagrams of steering columns label the hinge-like element as the tilt bracket, where the locking mechanism engages incremental positions. Why Other Options Are Wrong: Upper/lower brackets may secure column to the dash but are not the pivot component. A steering yoke joint refers to universal joints in the shaft, not the cabin tilt pivot. Common Pitfalls: Confusing telescopic adjustment (axial movement) with tilt; assuming the universal joint provides the cabin-side tilt, which it does not. Final Answer: tilt bracket

Question 18

Automotive refinishing — role of thinner in paint application In vehicle painting, thinner (reducer/solvent blend) is added primarily to:

Accepted Answer

Introduction / Context: Paint application quality depends on proper viscosity for atomization, flow, and leveling. Thinners (reducers) are solvent blends matched to paint chemistry and ambient conditions. This question addresses the main purpose of adding thinner. Given Data / Assumptions: Automotive primer, basecoat, or clearcoat systems. Air, HVLP, or electrostatic spray methods. Ambient temperature within recommended reducer range. Concept / Approach: Thinner adjusts the viscosity so the paint atomizes correctly at the gun and flows out on the panel, avoiding orange peel, runs, or dry spray. While solvents do help wet pigments and resins, the principal control variable is viscosity suited to the nozzle, pressure, and temperature. Hardness of the dried film is determined by resin crosslinking and curing, not the thinner itself (except through evaporation rate influencing film formation). Step-by-Step Solution: Identify paint application requirement: correct viscosity for sprayability and leveling.Relate thinner function to reducing viscosity.Select the option focused on optimizing viscosity. Verification / Alternative check: Technical data sheets specify reducer ratios and temperature ranges to hit target viscosity seconds in a Ford or Zahn cup, affirming the goal is viscosity control. Why Other Options Are Wrong: Mixing pigments and resin is part of formulation and stirring; thinner aids but is not the primary reason in the booth. Film hardness comes from resin chemistry and curing agents; thinner does not 'harden' the paint. Common Pitfalls: Using fast reducer in high heat causing solvent pop; over-thinning leading to sags; ignoring flash times between coats. Final Answer: optimise its viscosity

Question 19

Rotational energy smoothing in engines The component that smooths out cyclic power impulses from the engine crankshaft is the:

Accepted Answer

Introduction / Context: Reciprocating engines produce pulsating torque because each cylinder only fires intermittently. A device is needed to store energy during power strokes and release it during compression/exhaust strokes to smooth rotation. Given Data / Assumptions: Conventional four-stroke engine with discrete firing events. Rigid crankshaft and drivetrain. A heavy rotating mass attached to the crankshaft. Concept / Approach: The flywheel provides rotational inertia, storing kinetic energy (E = 0.5 * I * omega^2). During power strokes it accelerates slightly; during non-power strokes it decelerates, evening out speed. Other components serve different roles: clutch disengages drive, differential splits torque left-right, torque converter fluid-couples the engine to the transmission in automatics but is not used on manuals and is not the primary smoothing device on the crank itself. Step-by-Step Solution: Identify the need: smooth angular velocity.Recall the part providing inertia: flywheel.Select 'flywheel' as the correct answer. Verification / Alternative check: Engines with lightweight flywheels exhibit more speed fluctuation at idle; multi-cylinder engines require smaller flywheels due to more frequent firing, confirming the effect. Why Other Options Are Wrong: Clutch couples/decouples power flow; differential distributes torque to wheels; torque converter adds hydrodynamic coupling but the core smoothing of crank pulsations is by the flywheel. Common Pitfalls: Confusing NVH damping with inertia; assuming torque converters are present on manuals; overlooking dual-mass flywheels designed to further isolate torsional vibrations. Final Answer: flywheel

Question 20

Wheel imbalance symptoms during vehicle operation An out-of-balance wheel typically causes the wheel–tyre assembly to:

Accepted Answer

Introduction / Context: Wheel balance affects ride quality and tyre wear. Understanding the typical motion from imbalance helps diagnose whether static or dynamic balancing is needed. Given Data / Assumptions: Passenger car with pneumatic tyres. Highway speeds where imbalance effects are noticeable. Suspension components otherwise healthy. Concept / Approach: Static imbalance causes up-and-down (vertical) hop, while dynamic imbalance (couple imbalance) causes a side-to-side wobble when viewed from front/rear. Both present as vibrations at certain speeds (shimmy) and can be corrected by adding weights at appropriate positions on the rim. Step-by-Step Solution: Relate imbalance to centrifugal forces acting off the rotation axis.Identify motions: vertical bounce (static) or lateral wobble (dynamic).Choose the option that describes these real-world motions. Verification / Alternative check: Balance machines display correction planes for static and dynamic components; road tests show speed-specific vibrations that disappear after proper balancing. Why Other Options Are Wrong: 'Heavy point hits the road surface' is not how tyres behave; longitudinal deflection is not the typical symptom; standing waves relate more to high-speed carcass flex at extreme speeds, not ordinary imbalance. Common Pitfalls: Confusing imbalance with out-of-round tyres or bent rims; overlooking worn suspension bushings that exacerbate symptoms. Final Answer: bounce vertically or deflect from side to side (as seen from front or rear)

Automobile Engineering Questions