Grade 10 power mechanics Engines – use illustrations to explain four-stroke and two-stroke engine cycles. Notes

1. (a) Identify & outline the sub-sub-strands:
   • Identification of engine components
   • Sketching of engine components
   • Functions of engine components
   • Measurement of engine components
   • Importance of engine components
2. (b) Identify components of an engine
3. (c) Sketch components of an engine
4. (d) Describe functions of engine components
5. (e) Perform measurements on engine components
6. (f) Appreciate the need for engine components

Simple explanation (short)

- A four-stroke engine completes one power cycle in four piston movements: intake, compression, power (expansion) and exhaust. It uses valves to control flow.
- A two-stroke engine completes a power cycle in two piston movements (one crankshaft revolution). It uses ports in the cylinder walls for intake and exhaust; some actions are combined (scavenging + intake with compression).

Illustrations

Key engine components (identify & outline)

• Piston — moves up/down inside the cylinder.
• Cylinder — guides piston; has ports (two-stroke) or valves (four-stroke).
• Connecting rod — links piston to crankshaft.
• Crankshaft — converts up/down motion to rotation.
• Valves (intake & exhaust) — control gas flow (four-stroke).
• Ports — openings in cylinder wall for two-stroke intake/exhaust.
• Spark plug (petrol) — ignites air-fuel mixture.
• Carburettor or fuel injector — mixes fuel & air.

Functions (simple)

1. Piston: compresses mixture and transmits force to crankshaft.
2. Cylinder: provides sealed space for combustion.
3. Connecting rod: transmits piston force to crank.
4. Crankshaft: provides rotational power to wheels or machine.
5. Valves/ports: allow controlled entry and exit of gases.
6. Spark plug: starts combustion in petrol engines.

Sketching & simple drawing tasks (for learners)

- Draw a cross-section of a cylinder and label piston, rings, connecting rod, crankshaft, valve/port and spark plug.
- Practice quick 1-minute sketches showing each of the four strokes and label them.
- For two-stroke: sketch piston at top and bottom showing ports and arrowed gas flow.

Measurement activities (simple and safe)

Give learners hands-on tasks using common measuring tools:

• Measure piston diameter (bore) using a vernier caliper — record in mm.
• Measure stroke length (distance piston moves) using a ruler or caliper on a model — record in mm.
• Measure connecting rod length (centre-to-centre) with a tape or ruler — record in mm.
• Measure valve clearance (on a stationary engine with teacher supervision) using feeler gauge — explain why clearance is needed.

Safety note: Measurements on hot or running engines must not be done. Always use cold, stationary engines or models. Supervise tools.

Importance / appreciation

• Correct parts (piston, rings, valves) make the engine efficient and reduce fuel use.
• Good measurements and fits prevent leakage and wear — increasing engine life.
• Understanding cycles helps diagnose problems (e.g., poor compression → low power).
• Kenyan context: small engines (generators, boda-bodas, pumps) rely on correct parts and maintenance.

Suggested learning experiences (classroom & practical)

1. Starter demonstration: Show a short video or teacher demonstration of a cutaway engine model (4-stroke & 2-stroke) — pause to point out strokes/ports/valves.
2. Group sketching: In pairs, students draw the 4 strokes and the 2 positions of a two-stroke; label components. Teacher circulates and corrects.
3. Hands-on measurement: Using a dismantled small engine (or clear model), pupils measure bore, stroke, rod length and record results.
4. Role play: Four students act out the four strokes (Intake, Compression, Power, Exhaust) to remember sequence and role of valves.
5. Local application: Visit a nearby workshop (if possible) to see motorcycle or generator engines; identify whether engines are two- or four-stroke and why.
6. Assessment: Short quiz where students match component names to functions, draw cycles and compute simple compression ratio (using bore & stroke measured).

Class task example (45-minute lesson plan)

1. Introduction (5 min): Ask, "What makes a car or generator run?" Brief recap of combustion.
2. Explain cycles with diagrams (10 min): Show four-stroke and two-stroke images above and narrate.
3. Group activity (15 min): Sketch + label components + measure parts on model.
4. Share & discuss (10 min): Groups present one thing they learned and one safety point.
5. Wrap up (5 min): Short quiz question: "Why would a mechanic prefer a four-stroke for a car and sometimes a two-stroke for a small generator?"

Assessment ideas

- Short labeled drawing of a cylinder and piston (identify parts).
- Describe each stroke of a four-stroke engine in two sentences.
- Practical: measure bore and stroke and calculate a simple compression ratio: CR = (cylinder volume at bottom + clearance volume) / clearance volume (use teacher-provided numbers for clearance).