MECHANICAL TECHNOLOGY: AUTOMOTIVE
GRADE 12
NATIONAL SENIOR CERTIFICATE EXAMINATION
MEMORANDUM
MAY/JUNE 2021

QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC)
1.1 B ✓(1)
1.2 A ✓ (1)
1.3 C ✓ (1)
1.4 C ✓(1)
1.5 D✓ (1)
1.6 A ✓ (1)
[6]

QUESTION 2: SAFETY (GENERIC)
2.1 First aid basic treatment:

• Examination ✓
• Diagnosis ✓
• Treatment ✓ (3)

2.2 Drill press (Already been switched on):

• Never leave the drill unattended while in motion.✓
• Switch off the drill when leaving. ✓
• Use a brush or wooden rod to remove chips. ✓
• When reaching around a revolving drill, be careful that your clothes do not get caught in the drill or drill chuck. ✓
• Don't stop a revolving chuck with your hand. ✓
• Don't adjust the drill while working. ✓
• Don't open any guard while in motion. ✓
• Keep hands away from action points. ✓
• Do not force the drill bit into the material.✓
• Apply cutting fluid if required. ✓
  (Any 2 x 1) (2)

2.3 Isolation of electrode holder:
To prevent electric shock. ✓ (1)
2.4 Disadvantages of the process layout:

• Production is not always continuous. ✓
• Transportation costs between process departments may be high. ✓
• Additional time is spent in testing and sorting as the product moves to the different departments. ✓
• Damage to fragile goods may result from extra handling. ✓
  (Any 2 x 1) (2)

2.5 Advantages of the product layout:

• Handling of material is limited to a minimum.✓
• Time period of manufacturing cycle is less. ✓
• Production control is almost automatic. ✓
• Control over operations is easier. ✓
• Greater use of unskilled labour is possible. ✓
• Less total inspection is required. ✓
• Less total floor space is needed per unit of production. ✓
  (Any 2 x 1) (2)

[10]

QUESTION 3: MATERIALS (GENERIC)
3.1 Heat-treatment:

• Heat the metal slowly to a certain temperature. ✓
• Soak the metal for a certain period to ensure a uniform temperature. ✓
• Cool the metal at a certain rate to room temperature. ✓ (3)

3.2 Quenching mediums:

• Water ✓
• Brine✓
• Liquid salts ✓
• Oil ✓
• Soluble oil and water ✓
• Sand ✓
• Molten lead ✓
• Air ✓
• Lime ✓
  (Any 3 x 1) (3)

3.3 Annealing:

• To relieve internal stresses of the steel ✓
• Soften steel to make machining possible ✓
• Make steel ductile ✓
• Refine grain structure ✓
• Reduce brittleness ✓
  (Any 1 x 1) (1)

3.4 Carbon steels:

• Low carbon steel ✓
• Medium carbon steel ✓
• High carbon steel ✓ (3)

3.5 Iron-carbon equilibrium diagram:

1. Percentage carbon / carbon content ✓
2. Temperature in °C ✓
3. AC3 line / Higher critical temperature ✓
4. AC1 line / Lower critical temperature ✓ (4)

[14]

QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC)
4.1 C ✓(1)
4.2 C ✓(1) 
4.3 D ✓(1)
4.4 B✓(1)
4.5 C ✓(1)
4.6 C✓(1)
4.7 B✓(1)
4.8 A ✓(1)
4.9 C ✓(1)
4.10 A ✓(1)
4.11 A ✓(1)
4.12 D✓(1)
4.13 C ✓(1)
4.14 D ✓(1)
[14]

QUESTION 5: TOOLS AND EQUIPMENT (SPECIFIC)
5.1 Compression tester labels:

1. Pressure gauge/Pressure meter ✓
2. Pressure release valve ✓
3. Air hose/Pipe/Flexible pipe ✓
4. Spark plug connector/Adapter ✓(4)

5.2 Function of Cylinder Leakage Tester:

• To check where the combustion chamber/cylinder leaks gases ✓ during compression stroke/power stroke. ✓
• To determine the percentage ✓ pressure loss ✓ from the combustion chamber.
  (Any 1 x 2) (2)

5.3 Cylinder leakage test procedure:

• Turn the crank shaft until both valves, on the cylinder to be tested, are closed. ✓
• Remove the HT leads / spark plugs ✓
• Connect the spark plug adaptor (tester) to the spark plug hole. ✓
• Lock the crankshaft pulley so that it cannot turn. ✓
• Couple the compressed air pipe to the tester and calibrate the tester. ✓
• Couple the spark plug adapter hose to the cylinder leakage tester. ✓
• Note the results and location of gas leakage occurring in the combustion chamber. ✓
  (Any 6 x 1) (6)

5.4 Exhaust gas analyser:

• Hydrocarbon (fuel and oil vapour) / HC ✓
• Carbon dioxide / CO₂ ✓
• Sulphur dioxide / SO₂ ✓
  (Any 2 x 1) (2)

5.5 Exhaust gas analysis test precautions:

• Always calibrate the exhaust gas analyser with the pick-up hose removed. ✓
• The pick-up hose must not be stepped on or restricted in any way. ✓
• The pick-up hose connections must be airtight. ✓
• The vehicle being tested should have no leaks in the exhaust, manifolds or vacuum systems. ✓
• Must be conducted in a well-ventilated area.✓
• Take good care when handling the equipment. ✓
  (Any 3 x 1) (3)

5.6 Function of Turn-tables:
To make it possible ✓ to turn the front wheels in and out / side to side ✓ when checking the wheel alignment angles. (2)
5.7 Use of optical alignment gauge:
To measure / check the toe-in and toe-out of the vehicle. ✓ (1)
5.8 Functions of OBD scanner:

• Scan for faults (diagnostics). ✓
• Programme the ECU. ✓
• Reset fault codes. ✓
• Programme the keys to vehicle's ignition system. ✓
  (Any 3 x 1) (3)

[23]

QUESTION 6: ENGINES (SPECIFIC)
6.1 Correcting static imbalance:

• By fitting balance mass pieces to the crank webs. ✓
• By removing metal from the crank webs. ✓
• By arranging the crank pins of the crankshaft. ✓
  (Any 2 x 1) (2)

6.2 Crankshaft balancing:
6.2.1 Dynamic balancing:
Balancing in all directions✓ while crankshaft is rotating. ✓ (2)
6.2.2 Reciprocating mass:
The mass of the pistons, gudgeon pins ✓ and the upper third of the connecting rod. ✓(2)
6.3 Features to improve engine balance:

• Connecting rods and pistons are kept as light as possible / static balanced. ✓
• Flywheel is carefully balanced. ✓
• Counterweights on the crankshaft. ✓
• The firing order is reconfigured. ✓ (4)

6.4 Types of vibration dampers:

• Friction face-type ✓
• Combined rubber and friction disc ✓
• Rubber type ✓
• Inertia ring type ✓
  (Any 2 x 1) (2)

6.5 Different types of cylinder arrangements:

1. Inline type / Straight arrangement ✓
2. V-type ✓
3. W-type / double-V type ✓(3)

6.6 Three-cylinder inline engine:

Marking:
Labelling power impulse angle 120°. ✓
Drawing position of crankpins. ✓
Numbering of crankpins. ✓ (3)
6.7 Types of superchargers:

• Roots ✓
• Twin-screw ✓
• Centrifugal and ✓
• Vane ✓
  (Any 3 x 1) (3)

6.8 Advantages of using a turbocharger:

• More power is obtained from an engine with the same engine capacity. ✓
• A turbocharger is driven by the exhaust gases of the engine and therefore there is no power loss✓
• It gives improved fuel consumption in proportion to engine capacity. ✓
• The effect of height above sea level on power is eliminated.✓
• Improve volumetric efficiency. ✓
  (Any 3 x 1) (3)

6.9 Turbocharger:

1. Intercooler/air cooler ✓
2. Compressed air flow ✓
3. Turbine/Turbine housing/Turbocharger ✓
4. Exhaust gas flow/exhaust system/exhaust manifold✓ (4)

[28]

QUESTION 7: FORCES (SPECIFIC)
7.1 Terms:
7.1.1 Power:
Power is the rate ✓ at which work is done. ✓
7.1.2 Compression Ratio:
It is the ratio between the total volume of a cylinder when the piston is at bottom dead centre (BDC) ✓ to the volume in a cylinder when the piston is at top dead centre (TDC).✓ (2)
7.2 Calculation of compression ratio:
7.2.1 Swept volume:= πD² x L
                                     4
 π7² x 7.5
  4
SV = 288,6³ cm

7,2.2 Original clearance volume:
CV =   SV    
               CR - 1
= 288.63
   9.5 - 1
=288.63
     8.5
CV = 33,96 cm

7.2.3 New bore diameter:
Compression ratio = SV +CV
                                     CV
= SV  + 1
   CV
SV = CV(CR 1)
= 33,96(10 - 1)
SV = 305,64 cm³
SV =πD² x L
         4
Diameter =√SV x 4
                     π x L
D = 305,64 4
        π x 7,5
D = 7,203 cm
D = 72,03 mm (6)

7.3 Power calculations:
7.3.1 Torque:
Torque = Force x Radius
= (25 x 10) x  420  
                     1000
= 250 x 0,42
= 105 N.m

7.3.2 Indicated power:
P = 900kPa = 900 x 10³Pa
L = 86mm =   86    = 0.086m
                    1000
D = 84mm
=   84    = 0,084m
  1000
A = π x D² 
         4
= π x 0.084² 
         4
= 5,54 x 10^-3 m²

OR
A = π x D² 
         4
= π x 84² 
       4
= 5541,77mm²
=5541,77 x 10^-6m² 

N = 2000r/min =  2000   = 16,667 power stroke/sec
                           60 x 2
n = 4 cylinders

Related Items

IP = PLANn
= (900 x 10³) x 0,086 x 5541,77 x 10^-6 x 16,667 x 4
= 28596W
= 28,60 kW

OR
N = 2000r/min =2000= 33,333 r/sec
                            60
n = ⁴/₂ = 2 power strokes
IP = PLANn
= (900 x 10³) x 0,086 x 5541,77 x 10^-6 x 33.333 x 2
= 28600W
= 28,60 kW (8)

7.3.3 Brake power:
Brake Power = 2πNT
= 2 x π x 2000 x 105
                 60
= 21991,149 W
= 21,99 kW (3)

7.3.4 Mechanical efficiency:
Mechanical efficiency = BP x 100
                                      IP
= 21.99 x 100
   28.60
= 76.89%
(NO UNIT, NO MARK FOR FINAL ANSWER) (2)
[32]

QUESTION 8: MAINTENANCE (SPECIFIC)
8.1 Cooling system pressure test:
8.1.1 Repair or replace water hose or clamp. ✓(1)
8.1.2 Cylinder head gasket blown. / Cylinder head warped. ✓(1)
8.1.3 Replace Welch or core plug. ✓(1)
8.1.4 Replace radiator cap with suitable replacement. ✓(1)
8.2 Function of the radiator cap:

• Regulates the pressure in the cooling system. ✓
• Allows coolant to return to the radiator from the expansion tank. ✓
• The radiator cap seals / close the cooling system. ✓
  (Any 2 x 1) (2)

8.3 Exhaust gas readings causes:
8.3.1 Possible causes of high carbon monoxide (CO) reading:

• Too rich mixture ✓
• Ignition misfire✓
• Dirty or restricted air filter ✓
• Improper operation of the fuel delivery system. ✓
• Faulty thermostat / stuck in open position or coolant sensor ✓
• Non-functioning PCV valve system ✓
• Catalytic converter not working ✓
  (Any 2 x 1) (2)

8.3.2 Possible causes high nitrogen oxide (NOx) reading:

• Lean fuel mixture ✓
• Improper spark advance ✓
• Malfunctioning EGR valve ✓
• Malfunctioning catalytic converter ✓
  (Any 2 x 1) (2)

8.3.3 Possible causes high oxygen (O₂) reading:

• Too lean air-fuel ratio ✓
• Ignition problems ✓
• Vacuum leaks✓
• Malfunctioning catalytic converter ✓
  (Any 2 x 1) (2)

8.4 Safety requirements when setting up the oil tester:

• Ensure the tester can read the expected pressures of the engine. ✓
• Clean the sender unit area before fitting the tester. ✓
• Ensure that the rubber hoses of the tester are not perished.✓
• Keep the tester away from moving engine parts when conducting the test.✓
  (Any 3 x 1) (3)

8.5 Fuel-pressure test/manufacturers' specifications:

• Fuel pressure (suction) before the fuel pump. ✓
• Fuel pump delivery pressure (after the fuel pump). ✓
• Fuel-line pressure at idle speed. ✓
• Fuel-line pressure at high revolutions. ✓
• Fuel pressure in the common rail (at injectors). ✓
  (Any 4 x 1) (4)

8.6 Compression test:
8.6.1 High tension leads:

• The ignition system will be disabled. ✓
• Prevent electrical shock✓
• To have access to the spark plugs in order to remove them. ✓
  (Any 1 x 1) (1)

8.6.2 Throttle valve fully open:

• To ensure maximum amount of air enters the cylinder.✓
• To obtain a correct reading.✓
  (Any 1 x 1) (1)

8.6.3 Recording the readings:

• Compared to the specifications reading.✓
• To note the differences in readings between the cylinders.✓
  (Any 1 x 1) (1)

8.7 Increase in compression after wet test:

• Piston ring / Compression ring✓
• Cylinder (sleeve / walls)✓
  (Any 1 x 1) (1)

[23]

QUESTION 9: SYSTEMS AND CONTROL (AUTOMATIC GEARBOX) (SPECIFIC)
9.1 Differences between an automatic gearbox and a manual gearbox:

• Manual – clutch pedal operated.✓
  Automatic – no clutch pedal operated. ✓
• Manual – Gears selected manually with gear lever. ✓
  Automatic – Gears selected automatically by the gearbox. ✓
  (Any 1 x 2) (2)

9.2 Function of torque converter:

• Multiplies engine torque automatically according to road and engine speeds✓
• Transfers drive from the engine to the transmission. ✓
• Acts as a Flywheel to keep the engine turning during the idle strokes.✓
• Slips during initial acceleration and while stopping to prevent stalling.✓
• Dampens torsional vibrations of the engine✓
• Drives the Transmission oil pump.✓
  (Any 2 x 1) (2)

9.3 Lockup clutch:
To overcome slip✓ that occurs inside the torque converter. ✓ (2)
9.4 Stall speed:

• The condition when the impeller of a torque converter rotates at maximum speed ✓ and the turbine is almost stationary.✓
• When the pump has reached the highest velocity ✓ and the turbine is at stall (standing still). ✓
• When the vehicle is stationary✓ just before it starts moving / while the engine is idling. ✓
  (Any 1 x 2) (2)

9.5 Single epicyclic gear system:
9.5.1 Epicyclic gear train:

1. Sun gear✓
2. Annulus / Ring gear ✓
3. Planet gear ✓
4. Planet carrier ✓ (4)

9.5.2 Advantages of an epicyclic gear train:

• The input shaft and output shaft have the same axis of rotation. ✓
• Load is distributed to several planetary gears.✓
• Many transmission-ratio options from ONE or a combination of several gear trains.✓
• Longer service life compared to traditional gearboxes for similar load. ✓
• Epicyclic gearbox has the ability to transmit higher torque. ✓
• It has less inertia. ✓
• Used to obtain higher gear ratios.✓
• Compact in size.
• All the gears are constantly in mesh. ✓
  (Any 2 x 1) (2)

9.6 Function of the valve body:

• It detects the load ✓ and adjust the gear ratio according to the torque requirements.✓
• It directs the oil pressure ✓ to the correct hydraulic actuator. ✓
  (Any 1 x 2) (2)

9.7 Methods of cooling the automatic transmission oil:

• By using a special oil cooler alongside the engine cooling radiator ✓ and circulating transmission fluid through it. ✓
• Circulating transmission fluid ✓ through a radiator✓
• The transmission oil sump ✓ is designed with fins to assist with cooling. ✓
  (Any 1 x 2) (2)

[18]

QUESTION 10:SYSTEMS AND CONTROL (AXLES, STEERING GEOMETRY AND ELECTRICITY) (SPECIFIC)
10.1 Requirements of a well-planned steering mechanism:
It must be …

• light and easy to control. ✓
• free from vibration and road shocks.✓
• as direct as possible without needing too much driver attention or effort.✓
• self-centring. ✓
• able to operate without being unduly affected by the action of the suspension or braking systems.✓
  (Any 3 x 1) (3)

10.2 Wheel alignment angles:
10.2.1 Function of Positive camber:

• Less steering effort ✓
• The vehicle mass being carried by the larger inner front wheel bearing. ✓
  (Any 1 x 1) (1)

10.2.2 Function of Ackermann's angle:
It allows for variable toe-out to the front wheels on turns. ✓(1)
10.3 Caster:
10.3.1 Wheel alignment angle: C
Negative ✓ caster ✓angle (2)
10.3.2 Negative caster angle purpose:
Negative caster ensures easier turning ✓ and provides better cornering to the vehicle. ✓ (2)
10.3.3 Caster angle labels:
A. King pin / Steering axis ✓
B. Perpendicular line ✓
D. Centre line of kingpin / Steering axis ✓ (3)
10.4 Engine management system:
10.4.1 Function of sensor:

• It detects the engine operating conditions. ✓✓
• It gives the input information to the ECU. ✓✓
  (Any 1 x 2) (2)

10.4.2 Function of actuators:

• It gets the output information / signal from the ECU.✓✓
• It makes the necessary adjustments. ✓✓
  (Any 1 x 2) (2)

10.5 Requirements to make the catalytic convertor function effectively:

• The convertor working temperature must not exceed 600 °C. ✓
• Unleaded petrol must be used. ✓
• Prevent persistent misfire. ✓
• Prevent burnt engine oil from melting the ceramic monolith. ✓
• The lambda sensor must function properly. ✓
  (Any 2 x 1) (2)

10.6 Lambda sensor:
The lambda sensor is fitted on the exhaust system.  (1)
10.7 Adaptive speed control:

• Maintain a speed as set by the driver.✓
• Adapt the speed to maintain a safe distance from the vehicle in front. ✓
• Provide a warning if there is a risk of a collision. ✓
• Prevent driver fatigue. ✓
• Improve fuel economy. ✓
• A constant controlled speed setting prevents speeding fines. ✓
  (Any 3 x 1) (3)

10.8 Diode:
10.8.1 Diode ✓ (1)
10.8.2 Function of the diode:

• The function of the diode is used to change alternating current ✓ into direct current. ✓
• It allows the current flow in the circuit in one direction only ✓ and blocks it from flowing in the opposite direction. ✓
  (Any 1 x 2) (2)

10.9 Function of components in the alternator:
10.9.1 Rectifier:
Converts alternating current (AC) to direct current (DC). ✓ (1)
10.9.2 Stator:

• To provide a core ✓that concentrates the magnetic lines of force onto the stator windings. ✓
• To provide a coil ✓ into which a voltage is induced which is used to charge the battery.✓
• Converts the rotating magnetic field ✓ to electric current to charge the battery.✓
  (Any 1 x 2) (2)

10.9.3 Rotor:

• Provides a rotating ✓ electro-magnet. ✓
• Induces an electric voltage ✓ into the stator windings. ✓
• Fitted with slip rings ✓ to allow for a moving electrical connection. ✓
  (Any 1 x 2) (2)

10.10 Functions of the check valve in the electric fuel pump:

• It ensures the pressure in the fuel line is maintained. ✓
• It allows the fuel to flow in one direction only from the fuel tank.✓ (2)

[32]
TOTAL:200