MARKING GUIDELINE

QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC)
1.1 Cย  (1)
1.2 Aย  (1)
1.3 Bย  (1)
1.4 Dย  (1)
1.5 Aย  (1)
1.6 Cย  (1)ย  ย  ย [6]

QUESTION 2: SAFETY (GENERIC)
2.1 Reason for wearing a helmet:

  • Protects your eyes from ultra violet rays and infra-red rays.ย (2)

2.2 Angle grinder safety:

  • Safety guard must be in place before grinding.ย 
  • Protective shields must be placed around the object being ground to protect passers-by.ย 
  • Use the correct grinding disc for the job.
  • Do not use excessive force while grinding and cutting.
  • Make sure there are no excessive force while grinding and cutting.
  • Make sure there are no cracks on the disc before you start a job.
  • Protective clothing and eye protection are essential. (Any 2)ย  ย  ย  ย  (2)

2.3 Maximum gap โ€“ bench grinder:

  • 3 mmย (1)

2.4 Band saw safety:

  • Wear safety glasses or a face shield.ย 
  • Wear protective footwear when required.ย 
  • Make sure all guards are in place.ย 
  • Check for correct tension on the blade.
  • Use blades that are sharp, properly set and suitable for the job.
  • Keep the floor clean and free of obstructions or clutter. (Any 3)ย  (3)

2.5 Gas cylinder safety precautions:

  • Always store and use gas cylinders in an upright position.ย 
  • Never stack cylinders on top of one another.ย 
  • Do not bang or work on the cylinders.
  • Never allow cylinders to fall.
  • No oil and grease should come into contact with gas cylinders or fittings.
  • Keep the caps on the cylinders for protection. (Any 2)ย  (2)ย  ย  ย  [10]

QUESTION 3: MATERIALS (GENERIC)
3.1 Quenching:

  • Quenching means to cool the heated material rapidly.ย 
  • Cooling the material to room temperature.
  • Water is normally used for low and medium carbon steels.ย 
  • Oil is used on high carbon and alloy steel.
  • Extreme cooling brine is used. (Any 3) (3)

3.2 Difference between brine and salt water:

  • Brine hardens steels better than fresh water, salt inhibits the water from dissolving into atmospheric gas.ย 
  • Salt water does not vaporise as quickly as fresh water.ย  (2)

3.3 Purpose of case-hardening:

  • It hardens the surface.ย 
  • It provides a wear resistant surface.ย 
  • Strengthens core to withstand applied loads.ย  (3)

3.4 Methods of case-hardening:

  • Mild steel can be surface hardened by heating to its critical range and immersing in case hardening compound. Carbon is absorbed into surface layer of steel.ย 
  • Mild steel can be heated in an atmosphere of nitrogen called Nitriding.ย (Any 1 x 2) (2)

3.5 Difference between annealing and normalising:

  • Annealing requires steel to cool down over an extended period thus resulting in an internal structural change in the steel, making it softer.ย 
  • Normalising merely removes work-related stresses.ย  (4)ย  ย  ย  ย ย [14]

QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC)
4.1 C ๐Ÿ—ธ
4.2 B ๐Ÿ—ธ
4.3 A ๐Ÿ—ธ
4.4 A ๐Ÿ—ธ
4.5 C ๐Ÿ—ธ
4.6 D ๐Ÿ—ธ
4.7 D ๐Ÿ—ธ
4.8 B ๐Ÿ—ธ
4.9 D ๐Ÿ—ธ
4.10 D ๐Ÿ—ธ
4.11 C ๐Ÿ—ธ
4.12 C ๐Ÿ—ธ
4.13 B ๐Ÿ—ธ
4.14 A ๐Ÿ—ธ (14 x 1) [14]

QUESTION 5: TOOLS AND EQUIPMENT (SPECIFIC)
5.1
5.1.1

  • Periscope optical alignment gauge ๐Ÿ—ธ OR (1)
  • Dunlop gauge optical alignment ๐Ÿ—ธ

5.1.2

  • 1 โ€“ Contact ๐Ÿ—ธ
  • 2 โ€“ Mirror gauge ๐Ÿ—ธ
  • 3 โ€“ Periscope ๐Ÿ—ธ
  • 4 โ€“ Periscope gauge ๐Ÿ—ธ
  • 5 โ€“ Height slot/Height bar ๐Ÿ—ธ
  • 6 โ€“ Toe gauge ๐Ÿ—ธ
  • 7 โ€“ Calculator ๐Ÿ—ธ
  • 8 โ€“ Stand ๐Ÿ—ธ (8)

5.1.3 To check the toe-in and toe-out of a vehicle. ๐Ÿ—ธ (1)
5.2 Safety rules when using emission gas analyser:

  • The inlet hose must not be constricted in anyway. ๐Ÿ—ธ
  • The hose connection must be airtight and the condenser valve closed. ๐Ÿ—ธ
  • There must be no leaks on the exhaust. ๐Ÿ—ธ
  • The condensate must be blown out of the hose regularly. ๐Ÿ—ธ
  • The hoses must be disconnected from the analyser so that the pump will not be damaged. ๐Ÿ—ธ
  • The condenser must be drained after each use. ๐Ÿ—ธ
  • The paper filter must be changed when turned light grey. ๐Ÿ—ธ
  • The fuel filter on the condenser must be changed regularly. ๐Ÿ—ธ (Any 4 x 1)ย  ย  ย (4)

5.3 Set-up procedure for card type compressor tester:

  • Remove the spark plug ๐Ÿ—ธ
  • Put a new card in the tester ๐Ÿ—ธ
  • Depress the throttle valve and crank the engine for at least four revolutions ๐Ÿ—ธ
  • Activate the tester and move to cylinder 2 ๐Ÿ—ธ
  • Do the same for all cylinders ๐Ÿ—ธ
  • Remove the card and compare with specification ๐Ÿ—ธย  ย  ย  (6)

5.4 The main purpose of the following automotive workshop tools:
5.4.1 Gas analyser: To analyse the gas coming out of the exhaust of a motor vehicle. ๐Ÿ—ธย (1)
5.4.2 Wheel balancer: To balance the wheel of a vehicle for static and dynamic balance. ๐Ÿ—ธย (1)
5.4.3 Compression tester: To measure the pressure the piston will create during compression stroke. ๐Ÿ—ธย (1)ย  ย  ย  ย ย [23]

QUESTION 6: ENGINE (SPECIFIC)
6.1 Purpose of a vibration damper:

  • Vibration dampers are fitted to the front of the crankshaft ๐Ÿ—ธ to smooth out the engine vibrations. ๐Ÿ—ธ(2)

6.2 Types of vibration dampers:

  • Friction face-type ๐Ÿ—ธ
  • Combined rubber and friction disc ๐Ÿ—ธ(2)

6.3 Factors responsible for crankshaft vibration:

  • Action of unbalance forces upon the shaft ๐Ÿ—ธ
  • Torsional effect of power stroke ๐Ÿ—ธ(2)

6.4 Factors that determine engine configuration:

  • Number of cylinders ๐Ÿ—ธ
  • Position of the cylinders ๐Ÿ—ธ
  • Engine layout ๐Ÿ—ธ
  • Firing order ๐Ÿ—ธ
  • Position where the engine is located and how it is mounted ๐Ÿ—ธ(Any 3 x 1) (3)

6.5 Types of engine cylinder configurations:

  • In-line engine ๐Ÿ—ธ
  • V-type engine ๐Ÿ—ธ
  • Horizontally opposed ๐Ÿ—ธ
  • W-engine ๐Ÿ—ธ (Any 3 x 1) (3)

6.6 Principle of operation of a working turbocharger:

  • The turbine is driven by the exhaust gases, ๐Ÿ—ธ the compressor forces more air into the inlet manifold ๐Ÿ—ธ while the centre hub assembly contains the bearing, lubrication, cooling and shaft that connect the turbine and the compressor ๐Ÿ—ธย (3)

6.7 Disadvantages of a turbocharger:

  • Can have turbo lag problems ๐Ÿ—ธ
  • It tends to heat up the compressed air ๐Ÿ—ธ
  • Over revving must be controlled by waste gate ๐Ÿ—ธ
  • Shut-down procedure must be adhered to in-line with the product specification. ๐Ÿ—ธ (Any 3 x 1)ย  ย  (3)

6.8 Difference between turbocharger and supercharger

  • Turbocharger is driven by exhaust gases ๐Ÿ—ธ while supercharger is driven by a belt and pulley system ๐Ÿ—ธย (2)

6.9 Types of supercharger

Related Items

  • Root supercharger ๐Ÿ—ธ
  • Twin-screw supercharger ๐Ÿ—ธ
  • Centrifugal supercharger ๐Ÿ—ธ
  • Eccentric / sliding vane supercharger ๐Ÿ—ธย  ย  ย  (Any 3 x 1)ย  (3)

6.10

  • A โ€“ Inlet ๐Ÿ—ธ
  • B โ€“ Casing ๐Ÿ—ธ
  • C โ€“ Rotor ๐Ÿ—ธ
  • D โ€“ Vane ๐Ÿ—ธ
  • E โ€“ Outlet ๐Ÿ—ธ (5) [28]

QUESTION 7: FORCES (SPECIFIC)
7.1 Definition of compression ratio:

  • It is the relationship between the total volume of a cylinder when the piston is at the BDC to the volume of the charge (combustion chamber) when the piston is at TDC. ๐Ÿ—ธ๐Ÿ—ธ(2)

7.2

  • Swept volume = ๐œ‹D2 x L
    ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย 4
    = ๐œ‹(10,5)2ย x 11,2
    ย  ย  ย  ย  ย 4
    = 969,81 cm3ย  ๐Ÿ—ธ
    Compression ratio = SV + CVย ๐Ÿ—ธ
    ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย CV
    CR = 969,81 + 98
    ย  ย  ย  ย  ย  ย  ย  ย  ย  98
    CR = 10,9 :1ย  ย  ย  ย  ย (6)

7.3

  • Swept volume = ๐œ‹D2 x L
    ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย 4
    = ๐œ‹(11 )2ย x 11,2
    ย  ย  ย  ย  ย 4
    = 1 064,372 cm3ย 
    Compression ratioย = SV + CVย ๐Ÿ—ธ
    ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย CV
    CR = 969,81 + 98
    ย  ย  ย  ย  ย  ย  ย  ย  ย  98
    CR = 11,9 : 1ย ย ย (4)

7.4ย Indicated power (IP):

  • It is a measure to determine the power developed by the burning fuel within the cylinder of an engine. ๐Ÿ—ธ๐Ÿ—ธย (2)

7.5 Brake power testing tools:
7.5.1 Electric dynamometer is an electric current generating mechanism fitted to the engine. As the engine drives the generator and by measuring the amount of electricity produced, it determines the engine brake power in the process. ๐Ÿ—ธ๐Ÿ—ธ๐Ÿ—ธย  (3)
7.5.2 Chassis dynamometer is a measuring tool used at the drive wheels of a vehicle. It consists of two rollers loaded in-line with the specifications of increasing resistance in order to determine the brake power of an engine. ๐Ÿ—ธ๐Ÿ—ธ๐Ÿ—ธย ย (3)
7.6.1

  • P = 1600 000 Pa ๐Ÿ—ธ
    L =ย  ย  ย  ย 92ย  ย  ย  ย ย 
    ย  ย  ย  ย  1 000
    = 0,092 m ๐Ÿ—ธ
    A = ๐œ‹D2
    ย  ย  ย  ย 4
    = ๐œ‹0,099ยฒย ย ๐Ÿ—ธ
    ย  ย  ย  ย  4
    = 7,70 x 10-3 m2 ๐Ÿ—ธ
    N = 4 600
    ย  ย  ย 60 ร— 2
    = 38,33r/s
    n = 4 cyclinders ๐Ÿ—ธ
    Indicated power = PLANn
    = (1600000) x (0,092) x (7,7 x 10โˆ’3) x (38,33) x (4) ๐Ÿ—ธ
    = 173 779,02 W
    = 173,78 Kw ๐Ÿ—ธย  ย  (7)

7.6.2

  • Brake power = 2๐œ‹ x N x T ๐Ÿ—ธ
    = 2ฯ€70 ร— 280 W ๐Ÿ—ธ
    = 123 150,43 W
    = 123,15 Kw ๐Ÿ—ธย  ย (3)

7.6.3

  • Mechanical efficiency = BP x 100%
    ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  ย  IP
    = 123,15 x 100%ย 
    ย  ย 173,78
    = 70,87%ย  ย  ย  ย  ย  (2)ย  ย [32]

QUESTION 8: MAINTENANCE (SPECIFIC)
8.1
8.1.1 Causes of high hydrocarbon (HC) reading:

  • Excessive unburned fuel by incomplete combustion๐Ÿ—ธ
  • Improper timing ๐Ÿ—ธ
  • Vacuum leak ๐Ÿ—ธ
  • Faulty air management system ๐Ÿ—ธ (Any 3 x 1)ย  (3)

8.1.2 Corrective measures:

  • Reset fuel mixture ๐Ÿ—ธ
  • Check and reset ignition system ๐Ÿ—ธ
  • Check and repair vacuum leaks ๐Ÿ—ธ
  • Check and repair faulty air management system ๐Ÿ—ธ (Any 3 x 1) (3)

8.1.3 Exhaust gases that are analysed:

  • Carbon monoxide ๐Ÿ—ธ
  • Carbon dioxide ๐Ÿ—ธ
  • Nitrogen oxide ๐Ÿ—ธ
  • Sulphur dioxide ๐Ÿ—ธ
  • Oxygen ๐Ÿ—ธ (Any 2 x 1)ย  ย  ย  ย (2)

8.2 Carry out wet test on the cylinder ๐Ÿ—ธ (1)
8.3 Cylinder leakage test procedure:

  • Ensure the vehicle is at normal operating temperature ๐Ÿ—ธ
  • Remove the air filter, high tension cables, oil cap, radiator cap, dip stick ๐Ÿ—ธ
  • Unscrew the spark plug ๐Ÿ—ธ
  • Turn the engine until both valves are close on cylinder 1 and keep the crankshaft pulley locked ๐Ÿ—ธ
  • Screw in the cylinder leakage tester to the sparkplug hole ๐Ÿ—ธ
  • Open the relief valve slowly and check the leakage reading ๐Ÿ—ธ
  • Repeat the process on the other cylinders and compare readings with specifications ๐Ÿ—ธย  (7)

8.4

Faultsย  Possible causesย  Corrective measuresย 
Hissing sound in inletย manifold ๐Ÿ—ธ Worn out inlet valve ๐Ÿ—ธ Replace or lap the inletย valve ๐Ÿ—ธ
Hissing sound inย exhaust manifold ๐Ÿ—ธ Worn out exhaustย valve ๐Ÿ—ธ Replace or lap theย exhaust valve ๐Ÿ—ธ
Hissing sound at dip stick or oil filler cap ๐Ÿ—ธ Piston rings are worn out ๐Ÿ—ธ Overhaul the engine and fit in new biggerย piston and rings ๐Ÿ—ธ
Bubble in radiatorย water ๐Ÿ—ธ Blown gasket or crackedย cylinder head ๐Ÿ—ธ Skim the cylinder headย and replace gasket ๐Ÿ—ธ

(Any 2 x 3) (6)
8.5 Reason for conducting radiator cap pressure testing:

  • In order to determine the relief pressure of the radiator cap and compare with specifications ๐Ÿ—ธย (1)ย  ย  ย  ย ย [23]

QUESTION 9: SYSTEMS AND CONTROL (AUTOMATIC GEARBOX) (SPECIFIC)
9.1 Principle of operation of a torque converter:

  • The pump spins, ๐Ÿ—ธ throwing oil outwards into the curved vanes of the turbine. ๐Ÿ—ธ
  • The stator intercepts the oil ๐Ÿ—ธ and redirects the path of the oil to enter the pump smoothly. ๐Ÿ—ธ
  • The torque produced by the redirected oil isย increased when it leaves the pump again to enter the turbine. ๐Ÿ—ธ (5)

9.2 Function of the following components of an automatic transmission system:
9.2.1 Torque converter multiplies the engine torque automatically accordingย to the road and engine speed. ๐Ÿ—ธ๐Ÿ—ธ (2)
9.2.2 Brake bands are placed around the annulus to enable the annulus toย come stationary position in order to change to another gear. ๐Ÿ—ธ๐Ÿ—ธ (2)
9.2.3 Hydraulic pistons control the brake bands or the multidisc clutchesย which allow the change of gear. ๐Ÿ—ธ๐Ÿ—ธ (2)
9.2.4 Oil pumps are built into the transmission in order to control the brakeย bands and the multidisc clutches. ๐Ÿ—ธ๐Ÿ—ธ (2)
9.3 States of torque converter speed:
9.3.1 Stall speed is the point when the pump has reached the highestย velocity but the turbine is still at rest. ๐Ÿ—ธ (1)
9.3.2 Increasing speed is at the point where the turbine begins to turnย and the vehicle starts moving. ๐Ÿ—ธ (1)
9.4 Type of oil used in automatic transmission:

  • Automatic transmission fluid (ATF) ๐Ÿ—ธ (1)

9.5 Methods of cooling oil in automatic transmission system:

  • The use of special oil cooler alongside the engine cooling radiator ๐Ÿ—ธ
  • Oil circulates through a tank built into the bottom of a radiator tank. ๐Ÿ—ธ (2)ย [18]

QUESTION 10: SYSTEMS AND CONTROL (AXLES, STEERING GEOMETRY AND ELECTRONICS) (SPECIFIC)
10.1 Purpose of the following alignment applications in vehicle:
10.1.1 To overcome the tendency of wheels with positive camber to point outwards. ๐Ÿ—ธ๐Ÿ—ธ (2)
10.1.2 To overcome the tendency of wheels with negative camber to point outwards. ๐Ÿ—ธ๐Ÿ—ธ (2)
10.1.3 To enable a vehicle to navigate a circle/curve effectively without skidding. ๐Ÿ—ธ๐Ÿ—ธ
10.2 Camber ๐Ÿ—ธ (1)
10.3 Functions of the following steering angles:
10.3.1 Camber angle brings the contact point of tyre directly on the road inย order to achieve less steering effort. ๐Ÿ—ธ๐Ÿ—ธ (2)
10.3.2 Caster angle gives self-steering action to the steering and keeps theย wheel in the straight-ahead position. ๐Ÿ—ธ๐Ÿ—ธ (2)
10.3.3 Kingpin inclination is designed to bring the front wheel back to the straight-ahead position after rounding a corner without any driverย effort. ๐Ÿ—ธ๐Ÿ—ธ (2)
10.4 Factors to be considered before wheel alignment is checked or adjusted:

  • Kerb mass must be checked against the manufacturerโ€™s specifications ๐Ÿ—ธ
  • Uneven wear on the tyres ๐Ÿ—ธ
  • Tyre pressure ๐Ÿ—ธ
  • Check wheel nuts with torque wrench ๐Ÿ—ธ
  • Correct preload on the hub (wheel bearings) with torque wrench๐Ÿ—ธ
  • Check kingpin and bushes ๐Ÿ—ธ
  • Suspension ball joints ๐Ÿ—ธ
  • Check suspension bushes for excessive movement ๐Ÿ—ธ
  • Steering box play whether secure on chassis ๐Ÿ—ธ
  • Check the tie-rod ends ๐Ÿ—ธ
  • Sagged springs ๐Ÿ—ธ
  • Check shock absorbers ๐Ÿ—ธ (Any 4 x 1) (4)

10.5 Types of wheel imbalance:

  • Dynamic ๐Ÿ—ธ and static imbalance ๐Ÿ—ธ (2)

10.6 Function of electric fuel pump:

  • To pump fuel from the tank to the ejector at a specified pressure ๐Ÿ—ธ๐Ÿ—ธ (2)

10.7 Types of electric fuel pump:

  • External fuel pump ๐Ÿ—ธ
  • In-tank/submerged fuel pump ๐Ÿ—ธย (2)

10.8 Advantages of an electric fuel pump:

  • Low operation noise ๐Ÿ—ธ
  • Les discharge pulsation of fuel ๐Ÿ—ธ
  • Compact and light design ๐Ÿ—ธ
  • They have the ability to prevent fuel leak and vapour lock ๐Ÿ—ธ
  • Immediate supply of fuel as the ignition is switched on ๐Ÿ—ธ (Any 3 x 1)ย  ย  ย  (3)

10.9 Factors that determine injection quantity:

  • The pressure ๐Ÿ—ธ
  • Injection time ๐Ÿ—ธ
  • Injector orifice ๐Ÿ—ธ (3)

10.10 Advantages of an alternator:

  • Higher output to mass ratio ๐Ÿ—ธ
  • High output at low engine speed ๐Ÿ—ธ
  • Highly reliable ๐Ÿ—ธ
  • Small current through brushes and slip rings ๐Ÿ—ธ
  • It has current regulation characteristics ๐Ÿ—ธ
  • Maximum operation speed can be achieved ๐Ÿ—ธ (Any 3 x 1) (3)ย  ย [32]

TOTAL: 200

Last modified on Tuesday, 15 February 2022 07:53