Mechanical Technology Fitting and Machining Memo 1 (English)

May-June 2025 — Grade 12 / Matric — Mechanical Technology

Memo 2025 Grade 12 English

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1.1During the marking of multiple choice questions, only ONE possible answer can be accepted. If the candidate indicated two or more responses, ONLY the first response will be recognised/ acknowledged and marked according to the marking guidelines.

1.2

1.3If question numbering of sub questions is not correct according to the question paper sequence, the responses can be accepted if a sequence pattern can be identified.

1.4Attention must be given to mark allocation in questions where two (2\ marks were allocated for one response, e.g ( Any 1 x 2

1.5There must be ONE tick allocated for each mark awarded.

1.6An unanswered question must be indicated with a cross (X\

1.7All blank pages in an ANSWER BOOK must be crossed out to indicate that the pages have been seen by the marker.

1.8Attention must be given to questions where the candidate did not complete the question and continued answer(s\ on subsequent pages in the ANSWER BOOK . Continue marking such questions and award marks, if applicable.

1.9During calculation marking, pay attention to the position of the tick mark(s\.

1.10If a candidate skipped a step where a tick mark is allocated in the marking guidelines and the final answer is correct, the total amount of tick marks must be indicated by the marker to indicate full marks awarded for the

1.11If the unit required for calculations is specified in the question, the final answer can be considered correct without explicitly stating the unit, provided that the numerical value match es the unit specified or used in the question.

1.12If an incorrect unit is stated in the candidate's answer during calculations, the answer will be marked incorrect ev en if the value itself is correct.

1.13Attention must be given to calculation type questions when different methods are used by candidates to obtain the correct answer.

1.14Attention must be given to special marking instructions to the marker which are stated for specific questions in the marking guidelines.

1.15A red line must be drawn by the marker to indicate the end of each question.

1.16Marks of sub question totals must be indicated on the outside margins of the ANSWER BOOK pages and NOT on the inside margins.

1.17Marks of sub question totals, when indicated on the outside margins, must be in line with the sub questions and must NOT circled.

1.1Total marks of a question must be indicated on the red line drawn by the marker and circled as to indicate marks for particular questi ons. The marker must transfer the marks to the cover page and ensure

Q1— Section header —

1.1[6] Me ch6

Q2— Section header —

2.1Manual guillotine: Blade guard or back of the machine to catch the cut material must be fitted. Cut material must be allowed to fall to the floor to be collected when safe to do so. The guillotine must never be adjusted during operation.

2.2Examination procedures for First Aid Visible signs Visible symptoms Indicators to diagnosis Vital functions (Any 3 x 1 \ (3\

2.3Acetylene cylinders key: So that the valve can be quickly closed. /In case of an emergency. Product layout or a process layout

2.4.1Process layout [10] Me ch10

Q3— Section header —

3.1Heat treatment: Work piece size Quenching rate

3.2Machining test:

3.2.1Easy to cut Annealing: To relieve internal stresses of the steel Soften steel to allow for easy machining Make steel ductile Refine grain structure Reduce brittleness (Any 1 x 1\ (1\

3.4Normalising:

3.4.1above Rapid cooling: To increase the hardness of the metal. To produce fine grain structure. To maximise tensile strength. To minimise ductility. (Any 1 x 1\ (1\

3.6Processes which cause internal stress: Machining Forging Welding Bending/Rolling Twisting Extreme/rapid heating Flame/plasma cutting Hardening

Q4— Section header —

4.1(1\

4.2[14] Me ch14

Q5— Section header —

5.1Engine faults detected on cylinder leakage test only but not compression test Leaking exhaust valves Leaking inlet valves Cracked cylinder head Blown head gasket

5.2Conduct compression test:

5.2.1Place connected: Spark plug hole (1\

5.2.2Unit of measure: Bar/kPa (1\

5.2.3Reason spark plugs removed: To allow engine to crank ( swing with minimal resistance. (1\

5.3Setup of cylinder leakage test:

5.3.1Precaution before spark plug removed: Blow dirt away from around the spark plug. (1\

5.3.2Reasons piston is at TDC: To ensure both /all alves are closed. (2\

5.4Difference between static and dynamic wheel balancing: STATIC BALANCING DYNAMIC BALANCING (2\ Check where the wheel stops. Done while wheel rotates. Corrects wheel bounce

5.5Functions of the wheel weight hammer: Remove balancing weights. Fit balancing weights To cut weight if one cannot get correct weight. Clean foreign matter from treads (Any 2 x 1\

5.6Wheel alignment tool:

5.6Identify tool: Bubble gauge Angles measured with bubble gauge: Camber Caster Functions of the turn tables:

Q6— Section header —

6.1Importance of correct firing order for crankshaft: Reduced torsional stress Reduced vibrations/ improve smooth running Reduced chance of over twisting

6.2Engine terms:

6.2.1Rotating mass: The crankpin and the lower two thirds of the connecting rod. (2\

6.2.2Reciprocating mass: The pistons and the upper third of the connecting rod. (2\

6.3Types of vibration dampers: Friction face Combined rubber and friction disc Rubber type (Any (2\

6.4Balancing the crankshaft dynamically: Drill holes (remove mass\ in crank webs (2\

6.5Engine layout

6.5ngine cylinder layout engine (1\ Advantages of this engine cylinder layout Shorter overall length Can fit into smaller engine compartment Lighter mass

6.6Power strokes:

6.6One cylinder, two stroke engine: One Eight cylinder, four stroke engine Four Me

6.7Turbo charger:

6.7Labels: Compressor mpeller wheel/blade Compressor Compressor/Impeller housing/casing Turbine housing/casing Turbine blade /wheel

6.7Turbo charger drive: Exhaust gas (1\

6.8Limiting boost pressure: Waste gate Vanes Dump valve (Any 2 x 1\ (2\

6.9Twin charging system:

6.9Labels: Supercharger Intercooler Turbo charger /Turbine Advantages twin charging over super

Q7— Section header —

7.1Definitions:

7.1.1Swept 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\

7.1.2Mechanical efficiency: The relationship between the theoretical power (IP\ and actual power (BP\ developed by the engine. (2\

7.2Methods to lower the compression ratio: Fit thicker gasket between cylinder block and cylinder head. Fit a shim between cylinder block and cylinder head. Fit piston with suitable lower crowns. Fit shorter connecting rod.

7.3Calculations:

7.3.1Swept volume: (3\

7.3.2Clearance volume (3\ ch 13

7.3.3New bore diameter: CV= CR-1 SVCVCR1 56,51121 621,61cm SVL SV4 621,614

7.4Engine calculations:

7.4.1Torque: BP2NT whereN 50r/s 161000 250 50,93 (4\ Me

7.4.2Indicated power in kW: strokes/se firing Area PLANn (7\

7.4.3Mechanical efficiency: ME100 19,48 82,14% (2\ [32] Me ch32

Q8— Section header —

8.1Gas Analysis: LTS EFECTS\ SIBLE COR ECTIVE

8.1.2roc ing Excessive unburned fuel Reset fuel mixture. Improper timing Check and reset ignition system. Vacuum leak

8.1.4ygen ing Too lean air fuel ratio. Reset fuel mixture. Ignition problems. Check and reset ignition system. Vacuum leaks.

8.2Perform wet compression test: Squirt oil into cylinder onto piston. Fit compression tester. Open throttle valve fully. Crank

8.3Cylinder leakage test faults:

8.3.1Bubbles in radiator: Repair /Replace cylinder head. Replace cylinder head gasket. Repair/Replace cylinder block. Replace cylinder sleeves. (Any 1 x 1\

8.3.2Hissing sound at the exhaust pipe: Rep lace exhaust valve seat exhaust valve. Repair/Replace valve seats. (Any 1 x 1\

8.3.3Hissing sound at the dipstick: Replace piston rings. sleeve cylinders. bore cylinders. Replace damaged piston. (Any 1 x 1\ (1\

8.4Oil pressure test:

8.4.1Change the oil: Oil is dirty/ contaminated. Incorrect oil viscosity/Oil is too thick /Oil too thin (Any 1 x 1\

8.4Clean the oil pick up screen: Blocked oil pump screen in sump. (1\

8.4Replace the oil pump Worn/ broken oil pump. (1\

8.4place oil filter: Oil filter is dirty/ contaminated. (1\

8.5Manufacturer s specification Fuel pressure after the injector pump or fuel pump. Fuel pressure when the engine is idling. Precautions for cooling system pressure test Top up the water level. Do not put more pressure i

Q9— Section header —

9.1Difference between gearbox

9.1.1Type of clutch The manual gearbox has a dry clutch. Type of gear system The automatic gearbox uses an epicyclic gear system. Torque converter: Lock up clutch torque converter

9.3omponents of the torq ue converter

9.3.1Pump/ Impeller picyclic gear system

9.4Labels: Sun gear Planetary gear Annulus/ ring gear Planet carrier Output shaft (5\

9.4Advantages of epicyclic gear trains: Provides a variation in torque. Higher reduction ratio is achieved. Changes the direction of rotation. s compact in design. Gears are in constant mesh. Reduce vibration.

9.5Function of automatic gearbox components

9.5.1Valve body: To direct oil to components. (2\

9.5.2Oil pump: Circulates /Pumps the oil (2\ [18] Me ch18

Q10— Section header —

10.1Wheel alignment pre checks: Kerb mass against the manufacturer s specifications Kerb height (riding height\ Tyre pressures Tyre wear Tyre sizes

10.2Negative caster: x 1 labels\ (4\ Front of Vehicle Perpendicular line Negative caster Centre line

10.3ensors

10.3.1Manifold a bsolute pressure sensor (MAP\: Air intake system (1\

10.3.2Camshaft position sensor (CMP\: Cylinder head (1\

10.3.3Lambda (oxygen\ sensor: Exhaust system (1\

10.4Basic functions of sensors: Detect engine operating conditions.

10.5Coil on plug (COP\ ignition:

10.5.1Labels: Spark plug Control module Ignition switch Crank position sensor (CPS\ (4\

10.5.2Conventional ignition: Common coil HT leads Distributor (Any 2 x 1\ (2\

10.6Environmentally friendly ga Water vapour/mist/steam Nitrogen Carbon dioxide (Any 2 x 1\ (2\

10.7Advantages of the adaptive speed control system: Adapt the vehicle speed. Maintain a safe distance from the vehicle in front. Provide a warning if there is a risk of a collision. It can take control of the brakes.

10.8Rotor:

10.8.1Labels: Slip ring Brushes Pole pieces (3\

10.8.2Function: o provide electromagnet Induces current into the stator. (Any 1 x 2\ (2\

10.9Advantages of an electric fuel pump: Immediate supply of fuel when the ignition switch is turned on. operation noise. Less discharge pulsation of fuel. Compact design.

10.10Functions of a check (one way\ valve: It maintains the pressure in the fuel line to prevent vapour lock. It ensures better start ability. Prevents back flow /Allows the fuel to flow in one direction. (Any 2 x 1\

Topics Identified

CircuitsMaterialsConstruction

Mark Allocation

Total200 marks

Sections6 + 10 + 14 + 14 + 23 + 28 + 32 + 23 + 18 + 32 = 200 marks

Paper information

SubjectMechanical Technology

Year2025

SessionMay-June

TypeMemo

PaperPaper 1

LanguageEnglish

Pages20

Downloads9

Examination context

Decade2020s

Years ago1y

Season—

Start day—

Exam period—

Days since exam—

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