Mechanical Technology May June 2023 (Automotive) MG Eng hlayiso.com

Downloaded from hlayiso.com SENIOR CERTIFICATE EXAMINATIONS/ NATIONAL SENIOR CERTIFICATE EXAMINATIONS MECHANICAL TECHNOLOGY: AUTOMOTIVE 2023 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 21 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 2 DBE/2023 SC/NSC – Marking Guidelines QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 C (1) 1.2 A (1) 1.3 A (1) 1.4 C (1) 1.5 B (1) 1.6 A (1) [6] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 3 DBE/2023 SC/NSC – Marking Guidelines QUESTION 2: SAFETY (GENERIC) 2.1 Safety rule after the work procedures: Switch off the machine.  (1) 2.2 Space between the tool rest and the emery wheel:  To prevent the work piece from jamming between the wheel and tool rest.   Prevents the wheel from being damaged.   Prevents the work piece from being damaged.   Prevent injury.  (Any 2 x 1) (2) 2.3 Workshop layouts: 2.3.1 Process layout.  (1) 2.3.2 Product layout.  (1) 2.4 Hydraulic press:  Safety goggles   Safety gloves   Safety shoes   Overall  (Any 1 x 1) (1) 2.5 Safety guard on the portable angle grinder:  To protect one against sparks/metal particles.   To protect one from a breaking disc.   To protect your hand from coming into contact with the disc.  (Any 1 x 1) (1) 2.6 Shearing/Guillotine machine:  Follow the manufactures recommendations.   Keep hands away from action points.   Do not exceed the maximum material thickness.   Ensure that all guards are in place and secure.   Report defects immediately.  (Any 1 x 1) (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 4 DBE/2023 SC/NSC – Marking Guidelines 2.7 Storing gas cylinders:  Upright position   Stored at 20°C / cool area   Empty cylinders stored separately from full cylinder.   Never store cylinders on top of each other.   Oxygen cylinders separate from fuel cylinders.   Secure gas cylinders.   Ensure that cylinders are properly closed.   Stored away from sparks / flammable material/ electrical switches.   Stored in a well-ventilated area.   Safety signs should be displayed.   Keep cylinders clearly labelled (Full/Empty).  (Any 2 x 1) (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 5 DBE/2023 SC/NSC – Marking Guidelines QUESTION 3: MATERIALS (GENERIC) 3.1 Purpose of tempering:  To relieve  strain / brittleness.   To increase  the toughness of the steel.   To refine  grain structure.  (Any 1 x 2) (2) 3.2 Heat treatment processes: 3.2.1 Case hardening:  To obtain a wear-resistant surface  and at the same time be tough enough internally at the core  to withstand the applied loads.  For a hard case over a tough core.  (Any 1 x 2) (2) 3.2.2 Annealing:  To relieve  internal stresses.   To soften  steel.   Facilitate  the machining processes.   Increase  the steel’s ductility.   Reduce  brittleness.  (Any 1 x 2) (2) 3.3 Spark test:  Hold steel against grinding wheel.   Observe the spark pattern to identify the type of steel.  (2) 3.4 Tests: 3.4.1 Filing test: File on the tip or near the edge  of the material. The bite will determine the hardness.  (2) 3.4.2 Bend test:  Metal is subjected to deformation by bending.   Observe the rupture of the metal.  (2) 3.5 Sound test on steel: 3.5.1 Low carbon steel (LCS): Dull (low pitch) sound. (1) 3.5.2 High carbon steel (HCS): Loud and clear (high pitch)  sound. (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 6 DBE/2023 SC/NSC – Marking Guidelines QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 C (1) 4.2 B (1) 4.3 A (1) 4.4 C (1) 4.5 B (1) 4.6 C (1) 4.7 B (1) 4.8 C (1) 4.9 A (1) 4.10 B (1) 4.11 D (1) 4.12 A (1) 4.13 C (1) 4.14 C (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 7 DBE/2023 SC/NSC – Marking Guidelines QUESTION 5: TOOLS AND EQUIPMENT (SPECIFIC) 5.1 Engine cylinder compression test: 5.1.1 Reasons for compression test:  To determine the amount of compression loss  from a specific cylinder.   To determine if the compression rings  are worn.  (Any 1 x 2) (2) 5.1.2 Type of compression test:  Dry test   Wet test  (2) 5.1.3 Reasons for low compression:  Worn / cracked cylinders   Worn / broken piston rings   Worn / broken piston   Leaking inlet valve   Leaking exhaust valve   Worn / cracked / bent valve assembly   Leaking cylinder head gasket  (Any 2 x 1) (2) 5.2 Cylinder leakage tester: 5.2.1 Labels for cylinder leakage tester: A – Pressure control valve / - knob / - regulator  B – Gauge / Meter  C – Compressor hose / - air hose / -pipe  D – Spark plug connector / - adapter / - hose / - pipe  (4) 5.2.2 Reason for pressurised air: To determine the …  percentage pressure leakage  from the cylinder.   location  of the cylinder leakage.  (Any 1 x 2) (2) 5.3 Precautions when performing the exhaust gas analysis:  The inlet hose must not be stepped on or restricted in any way.   The hose connections must be airtight.   There should be no leaks in the exhaust, manifolds or vacuum systems.   Condensate must be blown out of the hoses and pickup probe.   The condenser must be drained after each test.   When the paper filter becomes light grey, it should be replaced.   Test must be done in a well-ventilated area.   Ensure the tester is connected to the battery correctly.  (Any 3 x 1) (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 8 DBE/2023 SC/NSC – Marking Guidelines 5.4 Systems scanned by on-board diagnostic scanner:  Powertrain (PCM)   Transmission (TCM)   Brakes (ABS)   Body (BCM)   Engine (ECM)   Humidity, ventilation and air conditioning (HVAC)   Air bags (SRS)  (Any 3 x 1) (3) 5.5 Faults on the wheel established during dynamic wheel balancing:  The extent of the imbalance   The run-out of the tyre   The run-out of the wheel assembly  (Any 2 x 1) (2) 5.6 Perform dynamic wheel balancing:  Start the balancer and allow wheel to spin.   Obtain the imbalance readings and its locations on the rim.   Fit the correct weights.  (3) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 9 DBE/2023 SC/NSC – Marking Guidelines QUESTION 6: ENGINES (SPECIFIC) 6.1 Crankshaft: 6.1.1 Crankshaft  (1) 6.1.2 Function: To convert the reciprocating motion of the pistons  into rotary motion.  (2) 6.1.3 Crank web / counterweight  (1) 6.1.4 Static balance: The crankshaft is in static balance when the mass in all directions  from the centre of rotation is equal while it is at rest.  (2) 6.2 Vibration damper: 6.2.1 Crankshaft  (1) 6.2.2 Function: To smooth/dampen out the engine vibrations.  (1) 6.3 Engine cylinder configurations:  Inline / straight   V  W  Flat / horizontal   Radial / X-Engine   U-Engine   K-engine   Delta  (Any 3 x 1) (3) 6.4 Power strokes intervals:  To reduce engine vibrations.   To ensure smooth running of the engine.   To reduce the wear rate on the engine components.  (Any 2 x 1) (2) 6.5 Determine the firing order:  Read from the vehicle specifications.   It may be written on the tappet cover.   Check the order in which the valves rock.   Check the order in which the sparks are distributed from the distributor.  (Any 3 x 1) (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 10 DBE/2023 SC/NSC – Marking Guidelines 6.6 Turbocharger: 6.6.1 Boost: The increasing of manifold pressure  above the normal atmospheric pressure.  (2) 6.6.2 Types:  Variable Geometry Turbocharger (VGT)   Non-variable Turbocharger  (2) 6.7 Supercharger: 6.7.1 Reasons for fitting:  To increase cylinder pressure / compression pressure.   To increase the volumetric efficiency.   To increase the engine output / performance.   Increase fuel efficiency.  (Any 2 x 1) (2) 6.7.2 Mechanical drive:  Belt   Gears   Chain   Shaft  (Any 2 x 1) (2) 6.8 Twin-charging:  A combination of a turbocharger  and a supercharger.   Two turbochargers  are combined on the same engine.   Two superchargers  are combined on the same engine.  (Any 1 x 2) (2) 6.9 Advantages of twin-charging:  Outstanding fuel economy.   Reduce/eliminates lag at low revolutions.   Increased power and torque across the entire power band.   Reduced power required (sapping effect) by the supercharger pulley from the engine.  (Any 2 x 1) (2) [28] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 11 DBE/2023 SC/NSC – Marking Guidelines QUESTION 7: FORCES (SPECIFIC) 7.1 Swept volume:  Total volume  when the piston moves from bottom dead centre to top dead centre.   Total volume  displaced during a stroke.  (Any 1 x 2) (2) 7.2 Method to increase compression ratio:  Remove shims between the cylinder block and cylinder head.   Fit thinner cylinder head gasket.   Machine metal from cylinder head.   Skim metal from cylinder block.   Fit a piston with a higher crown.   Fit a crankshaft with a longer stroke.   Increase the bore of the cylinders / bigger pistons.  (Any 3 x 1) (3) 7.3 Calculation: 7.3.1 Swept volume:   D2 SV  L 4    (9 2 )   10  4  636,17 cm 3  (3) 7.3.2 Original clearance volume: SV CV  CR  1 636,17   10,5  1   66,97 cm3  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 12 DBE/2023 SC/NSC – Marking Guidelines 7.3.3 New bore diameter: SV New compression ratio  1 CV SV  (CR  1)(CV)  SV  (11 1)(66,97)  SV  669,7 cm 3    D2 SV  L 4 SV  4 D   L 669,7  4     10  9,234 cm   92,34 mm  (7) 7.4 Prony brake calculations: 7.4.1 Indicated power in kW: P =900  103 Pa 86 L= 1000 = 0,086 m    D2 A= 4   0,0842  = 4 = 5,542×10-3 m2  2000 N=  60  1 = 33,33 power strokes / sec  n = 2 cylinders IP=PLANn = (900  103 )(0,086)(5,542 10 -3 )(33,33)(2)  = 28593,86 W = 28,59 kW  (7) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 13 DBE/2023 SC/NSC – Marking Guidelines 7.4.2 Brake power in kW: Torque  Force  radius   (25  10)(0,4)   100 Nm  BP  2  NT  2    33,33  100   20941,85663 W  20,94 kW  (5) 7.4.3 Mechanical efficiency: BP   100 IP 20,94   100  28,59  73,24 %  (2) [32] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 14 DBE/2023 SC/NSC – Marking Guidelines QUESTION 8: MAINTENANCE (SPECIFIC) 8.1 Gas Analysis: FAULTS POSSIBLE CAUSES CORRECTIVE (DEFECTS) MEASURES 8.1.1 8.1.2 High oxygen Too lean air-fuel ratio.  Reset fuel mixture.  (O2) Ignition problems.  Check and reset ignition reading system.  Vacuum leaks.  Repair vacuum leaks.  Catalytic converter not Check and repair the working.  catalytic converter.  (Any 1 x 1) (Any 1 x 1) 8.1.3 8.1.4 High Excessive unburned fuel.  Reset fuel mixture.  hydrocarbon Improper timing.  Check and reset ignition (HC) system.  reading Vacuum leak.  Repair vacuum leaks.  Faulty air management Check and repair the air system.  management system.  (Any 1 x 1) (Any 1 x 1) (4) 8.2 Compression test: 8.2.1  Prevent distribution of high voltage.   To prevent electrical shock.   To gain access to the spark plugs.  (Any 1 x 1) (1) 8.2.2  To prevent fuel entering the exhaust system.   To prevent fuel from entering the tester.  (Any 1 x 1) (1) 8.2.3  To obtain the correct amount of air entering the cylinder.   To obtain a correct reading.  (Any 1 x 1) (1) 8.2.4  To compare reading to the specifications.   To check if the pressure is correct or not.  (Any 1 x 1) (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 15 DBE/2023 SC/NSC – Marking Guidelines 8.3 Cylinder leakage test: FAULTS POSSIBLE CAUSES CORRECTIVE MEASURES (DEFECTS) 8.3.1 Hissing sound at Leaking inlet valves.  Replace or reseat valves.  the air intake Gasket blown between Replace head gasket.  adjacent cylinders.  (Any 1 x 1) (Any 1 x 1) (2) 8.3.2 Hissing sound at Worn piston rings.   Overhaul engine.  the dipstick  Fit new rings.  Worn piston.   Fit new pistons.   Overhaul engine.  (Any 1 x 1) (Any 1 x 1) (2) 8.4 Causes of a high oil pressure reading:  Blocked oil passages   Too little crankshaft bearing clearances   Dirty or contaminated oil   Oil viscosity is too high   Pressure relief valve stuck in closed position.  (Any 3 x 1) (3) 8.5 Fuel pressure test: 8.5.1 Manufacturer's specifications for fuel pressure test:  Fuel pressure after the fuel pump.   Fuel pressure when the engine is idling.   Fuel pressure on high revolutions.  (Any 2 x 1) (2) 8.5.2 Placement of fuel pressure tester: Fit the fuel pressure tester to the fuel line.  (1) 8.5.3 Perished rubber pipe of fuel pressure tester:  Fuel / pressure will leak from the pipe.   The tester will give inaccurate results.   Fire hazard.  (Any 1 x 1) (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 16 DBE/2023 SC/NSC – Marking Guidelines 8.6 Causes of cooling system pressure drop: Coolant leaks from …  between gaskets/seals of the cooling system.   water hoses.   blown cylinder head gasket.   the water pump.   radiator.   heater radiator.   corroded welch or core plugs.   components not fitted correctly.  (Any 4 x 1) (4) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 17 DBE/2023 SC/NSC – Marking Guidelines QUESTION 9: SYSTEMS AND CONTROL (AUTOMATIC GEARBOX) (SPECIFIC) 9.1 Solutions for an automatic gearbox: 9.1.1  Remove the propeller / drive shaft.   Use a flatbed tow-truck.   Use a mobi-jack / lift the drive wheels off the ground.  (Any 1 x 1) (1) 9.1.2  Use a lock-up clutch.   The torque converter needs to be replaced.   The torque converter to be repaired.   Top-up fluids/oil.  (Any 1 x 1) (1) 9.1.3  Identify the cause of the problem and repair.   Use an oil cooler.   Top-up/replace fluids/oil.  (Any 1 x 1) (1) 9.1.4 Ensure the lever is shifted to:  Park (P)   Neutral (N)  (Any 1 x 1) (1) 9.1.5 Use automatic transmission fluid (ATF).  (1) 9.2 Components of the torque converter: 9.2.1  Pump   Impeller  (Any 1 x 1) (1) 9.2.2 Turbine  (1) 9.2.3 Stator  (1) 9.3 Manual valve  (1) 9.4 Advantages of epicyclic gear trains:  Provides a variation in torque.   Changes the direction of rotation.   It's compact in design.   Gears are in constant mesh.  (Any 2 x 1) (2) 9.5 Gear system of an automatic gearbox: 9.5.1 Double epicyclic gear system  (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 18 DBE/2023 SC/NSC – Marking Guidelines 9.5.2 Obtain reverse gear:  The brake band locks the annulus 1.   The input shaft (engine) drives the sun gears.   Planet gear 1 walks around the sun gear 1 in a reverse direction.   Planet gear 1 turns the planet carrier in a reverse direction.   Planet carrier turns the output shaft.  (5) 9.6 Oil pump  (1) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 19 DBE/2023 SC/NSC – Marking Guidelines QUESTION 10: SYSTEMS AND CONTROL (AXLES, STEERING GEOMETRY AND ELECTRONIC) (SPECIFIC) 10.1 Well-designed steering system:  Light and easy to control   Free from vibration and road shocks   As direct as possible without much drivers effort.   Self centering   Not unduly affected by the suspension or braking system operation  (Any 2 x 1) (2) 10.2 Wheel alignment angle: 10.2.1 Label A-C: A. Axle centre  B. Rear axle  C. Steering arms  (3) 10.2.2 Angle D: Ackermann's angle  (1) 10.2.3 It gives variable toe-out  to the front wheels on turns.  (2) 10.3 Unbalanced wheels drawings: 10.3.1 Wheel bounce (hop):   OR  Bounce (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 20 DBE/2023 SC/NSC – Marking Guidelines 10.3.2 Wheel wobble (shimmy):  Wobble  (2) 10.3.3 Difference between wheel wobble and wheel bounce:  Wheel wobble is the side to side movement (vibration) of a wheel.   Wheel bounce is the up and down movement (vibration) of a wheel.  (2) 10.4 Materials coating the monolith:  Aluminium oxide   Platinum   Rhodium   Palladium  (Any 2 x 1) (2) 10.5 Functions of sensors: 10.5.1 Lambda sensor:  The sensor measures the oxygen content in the flow of the exhaust gas.   Sends the information to the electronic control unit (ECU).  (2) 10.5.2 Throttle position sensor (TPS) sensor:  Detects the position of the throttle.   Sends the information to the electronic control unit (ECU).  (2) 10.5.3 Mass Air Flow (MAF) sensor:  To measure the air flow to the engine.   To measure the air flow temperature.   Sends the information to the electronic control unit (ECU).  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 21 DBE/2023 SC/NSC – Marking Guidelines 10.6 Operation of common rail direct injection (CRDI):  The high pressure pump transfers the fuel under high pressure to the common rail.   The common rail holds and distributes the pressurised fuel to the injectors.   The injectors spray the fuel directly into the cylinder.  (3) 10.7 Current is generated:  If a magnetic field is moved across a conductor , a voltage is induced across the ends of the conductor , which will cause a current to flow   Convert mechanical energy  into electrical energy  by electro- magnetic induction.  (Any 1 x 3) (3) 10.8 Alternator stator tests:  Continuity   Leakage  (2) 10.9 Positions electrical fuel pump is placed:  Inside the fuel tank   External – anywhere on the fuel line.  (2) [32] TOTAL: 200 Copyright reserved