MECHANICAL TECHNOLOGY: AUTOMOTIVE
GRADE 12
NATIONAL SENIOR CERTIFICATE EXAMINATIONS
MEMORANDUM
MAY/JUNE 2019

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

QUESTION 2: SAFETY (GENERIC)
2.1 Angle grinder:

• Do not use excessive force while grinding. ✓
• Ensure that the sparks do not endanger co-workers. ✓
• Keep hands clear from grinding disc. ✓
• Maintain a firm grip on the angle grinder. ✓
• Grinding disc fitted will not turn faster than the manufactures recommendation. ✓
• Make sure that there is no cracks or chips on the grinding disc
• Safety guard must be in place. ✓
• PPE must be worn.✓
• Beware of lockable switches in the on position when the machine is plugged in and switched on. ✓
• Check for defective cables. ✓
• Secure work piece properly. ✓
• Grinding angle to be away from body to prevent sparks directly on clothing. ✓
• Make sure disc does not wobble during cutting. ✓
  (Any 2 x 1) (2)

2.2 Welding goggles:

• To protect your eyes from the spatter / sparks. ✓
• To protect your eyes from the harmful rays / UV rays. ✓
• To ensure proper vision of the process. ✓
  (Any 2 x 1) (2)

2.3 PPE – Bench grinder:

• Overall ✓
• Safety goggles / face shield ✓
• Safety shoes ✓
• Safety gloves ✓
  (Any 2 x 1) (2)

2.4 Process and product workshop layout:

• The product layout ensures that the machines are arranged in the sequence of the manufacturing process of a product. ✓
• The process layout is based on the type of manufacturing process needed in the making of the product. ✓ (2)

2.5 Employer’s responsibility – equipment:

• They must provide and maintain equipment. ✓
• Ensure that the equipment is safe to use by employees.✓
• Provide safe storage for equipment. ✓
• Provide proper training of employees in the use of the equipment. ✓
• Enforce safety measures/ OHS acts and Regulations. ✓
• Employer must provide proper personal protective equipment (PPE) for the specific machines. ✓
  (Any 2 x 1) (2)

[10]

QUESTION 3: MATERIALS (GENERIC)
3.1 Tests to distinguish between metals:

• Bending test: ✓ hit with hammer. ✓
• Filing test ✓ file material. (colour and ease) ✓
• Machining test ✓ machine material. (type of shaving, ease and colour) ✓
• Sound ✓drop on floor. (high or low frequency) ✓
• Spark test. ✓Shape and colour of sparks. ✓
  (Any 4 x 2) (8)

3.2 Heat-treatment:
3.2.1 Tempering:
After hardening, the steel must be tempered.

• To relieve the strains induced.✓✓
• To reduce brittleness. ✓✓
  (Any 1 x 2) (2)

3.2.2 Normalising:
To relieve the internal stresses. ✓✓ (2)
3.2.3 Hardening:

• To produce extremely hard steel. ✓✓
• To enable it to resist wear and tear. ✓✓
  (Any 1 x 2) (2)

[14]

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

QUESTION 5: TOOLS AND EQUIPMENT (SPECIFIC)
5.1 Compression test:
5.1.1

• Wet test✓
• Dry test ✓ (2)

5.1.2 Reasons for low compression:

• Worn cylinders ✓
• Worn piston rings ✓
• Worn piston ✓
• Leaking inlet valve ✓
• Leaking exhaust valve ✓
• Leaking cylinder head gasket ✓
• Cracked cylinder ✓
• Cracked piston ✓
  (Any 2 x 1) (2)

5.2 Static imbalance:
A small mass or weight✓ is applied to the wheel rim diametrically opposite the heavy spot until the wheel is in balance. ✓ (2)
5.3 Cylinder leakage tester:
5.3.1 Components of cylinder leakage tester:

• Spark plug adapter / connector ✓
• Meter / gauge ✓
• Flexible air hose ✓
• Compressed air coupling ✓
• Control valve / knob ✓(5)

5.3.2 Cylinder leakage test reasons:

• Loss in power. ✓
• Low compression. ✓
• To determine if the cylinder head gasket has blown. ✓
• Oil consumption due to excessive leakage past the oil piston rings. ✓
• To identify leaking valves. ✓
  (Any 2 x 1) (2)

5.4 Reasons for a high CO reading:

• High idle speed ✓
• Too rich mixture ✓
• Ignition misfire ✓
• Clogged air filter ✓
• Improper operation of the fuel supply system ✓
• Faulty choke (choke stuck in closed position ✓
• Faulty injectors ✓
• Faulty thermostat/coolant sensor ✓
• Non-functioning PCV vale system ✓
• Faulty catalytic converter ✓
  (Any 2 x 1) (2)

5.5 Wheel alignment gauge:
5.5.1 Bubble gauge ✓ (1)
5.5.2 Caster reading:

• Ensure that the wheels are straighten and the turntables are on zero. ✓
• Fit the guage to the centre of the wheel. ✓
• Turn the front of the wheel 20° inwards. ✓
• Zero the castor scale.✓
• Turn the wheel through 40° in the opposite direction. ✓
• Take the reading on the castor scale.✓
• Do the same for the other wheel. ✓ (5)

5.6 Diagnostic scanner:

• The vehicle identification number (VIN). ✓
• The make and the model of the vehicle. ✓
• The engine type.✓
  (Any 2 x 1) (2)

[23]

QUESTION 6: ENGINES (SPECIFIC)
6.1 Balancing of engine:
6.1.1 Engine crankshaft:

• Static balance ✓
• Dynamic balance ✓ (2)

6.1.2 Methods to balance a crankshaft:

• Static balance: By fitting balance mass pieces to the crank webs or by removing metal from the crank webs. ✓
• Dynamic balance: Vibration is reduced by removing metal from certain parts orfrom parts of the crank webs. ✓ (2)

6.1.3 Factors that cause vibration:

• Mechanical unbalance caused by unbalanced moving parts. ✓
• Power unbalancing caused by uneven pressure on the pistons and crankshaft. ✓
• The crankshaft and flywheel assembly is not statically balanced. ✓
• The crankshaft and flywheel is not dynamically balanced. ✓
  (Any 2 x 1) (2)

6.2 Firing order factors:

• The position of the cranks on the crankshaft. ✓
• The arrangement of the cams on the camshaft. ✓
• The number of cylinders. ✓
  (Any 2 x 1) (2)

6.3 Vibration damper:
It is a mass fitted to the crankshaft ✓on the opposite side of the flywheel to counteract the torsional vibration of the crankshaft. ✓ (2)
6.4 Supercharger:
6.4.1 Type of supercharger:
Centrifugal type✓ (1)
6.4.2 Supercharger parts:

1. Air inlet port ✓
2. Air outlet port ✓
3. Rotor (impeller) ✓
4. Vane (fins) ✓(4)

6.5 Advantages of engine with supercharger:

• More power is developed compared to a similar engine without a supercharger. ✓
• An engine with a supercharger is more economical per given kilowatt output.✓
• Less fuel is used compared to engine mass. ✓
• Power loss above sea level is eliminated. ✓
• Do not suffer lag. ✓
• Cheaper, easier to install, service and maintain. ✓
• Increases volumetric efficiency. ✓
  (Any 2 x 1) (2)

6.6 Operation of the turbocharger:

• The exhaust gases from the engine are routed to the turbine wheel to enable the turbine wheel to spin at a very high speed.✓
• The gases are then channelled out of the housing and wheel assembly into the normal exhaust system.✓
• As the turbine wheel spins, it turns a common shaft, which in turn spins the compressor wheel. ✓
• The compressor draws air in through the compressor inlet.✓
• It delivers the compressed air through the outlet and the induction port then into the cylinders. ✓
• This boosted pressure delivered to the cylinders increases the volumetric efficiency of the engine. ✓
• Then it also increases the engine’s performance. ✓ (7)

6.7 Turbo charger disadvantage against a super charger:

• Require lubrication. ✓
• Suffers from lag. ✓
• Tend to heat the air, reducing density. ✓
• Needs to be controlled from over-revving by the waste gate. ✓
• Some turbochargers require a special shut-down procedure before the ignition can be switched off. ✓
• More expensive to install. ✓
  (Any 2 x 1) (2)

6.8 High altitude:
At high altitude less oxygen is available for combustion ✓ and therefore the performance will be weaker than at sea level. ✓ (2)
[28]

QUESTION 7: FORCES (SPECIFIC)
7.1 Compression Ratio
Is the ratio between the total volume of a cylinder when the piston is at bottom dead centre ✓ to the volume of the charge in a cylinder when the piston is at top dead centre. ✓ (2)
7.2 Compression ratio calculations:
7.2.1 Swept Volume = πD² x L 
                                     4
= π(8,4)² x 9.0
      4
= 498,76cm³(3)
7.2.2 Compression Ratio =  SV + CV  
                                                CV
CV =   SV   
        CR - 1
= 498,76 
   8,5 - 1
= 498,76 
      7.5
= 66,50cm³ (3)
7.2.3 New bore diameter:
Compression Ratio= SV  + 1
                                 CV
9,5 - 1 =   SV   
              66.50
πD² x L = 66,50 x 8.5
  4
D² = 66.50 x 8.5 x 4
               π x 9
= 79.97cm³
D = √79.97
= 8.94 cm
= 89.4 mm (6)
7.3 Power calculations:

7.3.1 Force =(125 x 10)
= 1250 N
Torque = Foce x radius
 1250 x 0.3
= 375 Nm (3)
7.3.2 Indicated Power = P x L x N x n
P = 950 kPa
L = 140 
     1000
= 0.14m
=  π D²
     4
= 11.31 x 10^-3m
N =  2400  
       60 x 2
= 20 power stroke/sec
n = 4 cylinders

Indicated Power = P x L x N x n
= 950 x 0.14 x 11.31 x 10^-3 x 20 x 4
120.34 kW (9)

7.3.3 Brake Power = 2π x N x T
= 2π40 x 375 W
= 94247.78W  (3)

7.3.4 Mechanical Efficiency = BP  x 100%
                                                IP
= 94.25  x 100%
  120.34
= 78.32%(3)
[32]

QUESTION 8: MAINTENANCE (SPECIFIC)
8.1 Oil pressure test - Manufacturers’ specification:

• Oil pressure at engine idle speed. ✓
• Oil pressure when the engine is cold. ✓
• Oil pressure when the engine is hot. ✓
• Oil pressure on high revolutions. ✓
  (Any 3 x 1) (3)

8.2 Exhaust pressure test:

• Determine if the catalytic converter is blocked✓
• Determine if silencer is blocked. ✓
• Decrease in power output. ✓
• Lack of high speed power. ✓
• Poor fuel consumption. ✓
• Overheating. ✓
• A leaking exhaust system. ✓(2)

8.3 Radiator cap test:

• Install the cap on the cooling system pressure tester. ✓
• Increase the pressure in the tester while watching the pressure gauge. ✓
• The pressure cap should release air at a rated pressure stamped on the cap. ✓
• Cap should hold pressure for at least one minute. ✓ (4)

8.4 Fuel-pressure test – manufacturers' specifications:

• Fuel pressure before fuel pump. ✓
• Fuel pressure before the carburettor. ✓
• Fuel pressure at idle speed. ✓
• Fuel pressure at high revolutions. ✓
• Fuel pressure before the injectors pump. ✓
• Fuel pressure after the injectors pump. ✓
  (Any 4 x 1) (4)

8.5 Compression test:
8.5.1 High tension lead:
The ignition system will be disabled ✓ to prevent electrical shock. ✓ (2)
8.5.2 Fuel injectors disconnected:

• To prevent unburned fuel entering the exhaust system ✓ and from entering the tester. ✓
• To prevent fuel from entering ✓ the cylinders and causing oil dilution. ✓
  (Any 1 x 2) (2)

8.5.3 Throttle valve fully open:
To obtain the correct amount of air entering the cylinder ✓ and to obtain a correct reading. ✓ (2)
8.5.4 Recording the readings:
The reading obtained during the compression test can be compared to the specification reading ✓ to check if the pressure is correct or not. ✓ (2)
8.6 Wet test-procedure:

• Add oil to that cylinder which has a low reading. ✓
• Carry out compression test as for dry test, if the reading increases it indicates that the piston rings are worn. ✓ (2)

[23]

QUESTION 9: SYSTEMS AND CONTROL (AUTOMATIC GEARBOX) (SPECIFIC)
9.1 Methods of cooling the automatic transmission:

• By using a special oil cooler alongside the engine cooling radiator and circulating transmission fluid through it. ✓
• Circulating transmission fluid through the bottom radiator tank. ✓ (2)

9.2 Advantages of automatic transmission:

• It reduces driving fatigue. ✓
• Greater reduction of wheel spin under bad road conditions. ✓
• The vehicle can be stopped suddenly without the engine stalling.✓
• The system dampers all engine torsional vibrations. ✓
  (Any 2 x 1) (2)

9.3 Purpose of automatic gearbox:
To relieve the driver of clutch ✓ and gear shift operation. ✓ (2)
9.4 Gear ratio on torque:
The higher the gear ratio the lower the torque transferred ✓ and the lower the gear ratio the higher the torque transferred✓ (2)
9.5 Advantages of torque converter:

• Torque increases automatically. ✓
• Smooth transfer of torque. ✓
• Minimum servicing is required.✓
• To absorb shocks. ✓
  (Any 2 x 1)(2)

9.6 Automatic gearbox:
9.6.1 Brake band ✓ (1)
9.6.2 Brake band labels:

1. Lever shaft✓
2. Lever ✓
3. Strut ✓
4. Brake band ✓
5. Anchor ✓
6. Band adjuster ✓ (6)

9.6.3 Brake bands function:
To enable the annulus to come into a stationary position to change to another ratio. ✓ (1)
[18]

QUESTION 10: SYSTEMS AND CONTROL (AXLES, STEERING GEOMETRY AND ELECTRONICS) (SPECIFIC)
10.1 Preliminary wheel alignment check:

• Kerb mass against the manufacturers specifications.✓
• Uneven wear on the tyres.✓
• Tyre pressure. ✓
• Run-out on the wheels. ✓
• Correct preload on the wheel bearings. ✓
• Kingpins and bushes. ✓
• Suspension ball joints for wear, locking and lifting. ✓
• Suspension bushes for excessive free movement. ✓
• Steering box play and whether secure on chassis. ✓
• Tie-rod ends. ✓
• Sagged springs, which include riding height. ✓
• Ineffective shock absorbers. ✓.
• Spring U-bolts. ✓
• Chassis for possible cracks and loose cross-members. ✓
  (Any 5 x 1) (5)

10.2 Toe-out on turns:
This toe-out effect in a turn gives a true rolling motion to the front wheels ✓ in a corner without scuffing. ✓ (2)
10.3 Dynamic balance of the wheel and tyre assembly:
Dynamic balance of the wheel and tyre assembly refers to the equal distribution of all weights around the axis of rotation in all rotation parts. ✓ (1)
10.4 Reasons of the speed control system:

• The speed control system is to control the throttle opening electronically. ✓
• To keep the vehicle speed constant. ✓ (2)

10.5 Disadvantages of the speed control:

• The system is expensive. ✓
• High maintenance costs if the system becomes faulty. ✓ (2)

10.6 Diode:
The function of the diode is to permit current to flow in only one direction ✓ and to block it from flowing in the opposite direction. ✓(2)
10.7 Advantages of an electric fuel pump:

• Immediate supply of fuel when the ignition switch is turned on. ✓
• Low operational noise. ✓
• Less discharge pulsation of fuel. ✓
• Compact and light design.✓
• Prevents fuel leak and vapour lock.✓
  (Any 2 x 1) (2)

10.8 Aspects that an injector needs to fulfil:

• Precise fuel flow rate ✓
• Good linearity ✓
• Wide active range ✓
• Good spray characteristics ✓
• No leakage ✓
• Silent operation✓
• Durability✓
• To cope with different needs for different engines 
  (Any 2 x 1) (2)

10.9 Ackerman principle:
10.9.1 Ackerman angle steering principle / geometry. (1)
10.9.2 Parts:

1. – Rear axis 
2. – Longitudinal axis 
3. – Steering arms 
4. – Front wheels 
5. – Extended centre lines from steering arms ✓
6. - Intersection  (6)

10.9.3 If the centre lines of the steering arms are extended ✓ they will intersect on the longitudinal axis of the vehicle. ✓ (2)
10.10 Alternator:
10.10.1 Rotor assembly ✓ (1)
10.10.2 Parts:

1. – slip ring ✓
2. – brushes ✓
3. – pole pieces ✓ (3)

10.10.3 The function of the rotor assembly is to provide a rotating electro-magnet to generate current. ✓(1)
[32]
TOTAL: 200