Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Contact breaker point replacement
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Contact breaker point replacement
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Subject: Auto Electrical Works
Class: Senior Secondary 2
Term: 2nd Term
Week: 2
Theme: Ignition System
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Remove Contact points. Reconditionimpairedpoints. Couple new or recovered Contact points. Adjust to correct gap in the in stalled Contact point.
transmission in neutral (manual) or park (automatic).
2. Disconnect Battery: Remove the negative (-) battery terminal.
3. Locate Distributor: Identify the distributor, typically found on the side of the engine block, with spark plug wires leading from its cap.
4. Remove Distributor Cap: Unclip or unscrew the two retaining clips/screws on the distributor cap and carefully lift it off. Note the orientation for correct reinstallation.
5. Remove Rotor: Gently pull the rotor off the distributor shaft. It is usually a friction fit.
Step 2: Removing Old Contact Points
1. Identify Point Assembly: Locate the contact breaker point assembly inside the distributor.
2. Disconnect Primary Lead: Carefully disconnect the thin primary lead wire from the terminal on the moving contact arm. This wire usually connects to the condenser and then to the primary side of the coil. Note how it is routed.
3. Unscrew Fixed Contact: Loosen and remove the small screw(s) holding the fixed contact base to the distributor base plate. There may be one or two screws.
4. Remove Moving Contact Assembly: Once the fixed contact is free, the entire moving contact arm assembly can usually be unclipped or lifted off its pivot point. Remove both the fixed and moving contacts.
5. Remove Condenser (Optional but Recommended): If replacing the condenser, unscrew its retaining screw and pull it out. Note its orientation and connection point.
Step 3: Reconditioning Impaired Points (If applicable) (This step is performed if the decision is to recondition rather than replace)
1. Inspect Points: Examine the contact surfaces for pitting, burning, or carbon deposits. Light pitting can be reconditioned. Heavy damage or deep pitting necessitates replacement.
2. Use Point File/Emery Cloth: Using a specialized point file or a piece of very fine-grade emery cloth/sandpaper (e.g., 400-600 grit), gently file or sand the contact surfaces until they are clean, flat, and smooth.
3. Clean Surfaces: Wipe off any metallic dust or debris from the reconditioned surfaces with a clean, lint-free cloth. Ensure no abrasive particles remain.
4. Assess Wear: Check the fibre heel for excessive wear. If the heel is significantly worn, reconditioning is futile; replacement is required.
Step 4: Installing New or Recovered Contact Points
1. Install New Condenser (If applicable): If replacing, install the new condenser, securing its retaining screw and connecting its lead wire appropriately.
2. Install Moving Contact Assembly: Place the moving contact arm onto its pivot pin and ensure it moves freely without excessive play.
3. Install Fixed Contact: Secure the fixed contact base to the distributor base plate using its screw(s). Do not fully tighten yet, as some designs allow for slight adjustment during gap setting.
4. Connect Primary Lead: Connect the primary lead wire to the terminal on the moving contact arm. Ensure the connection is secure and not shorting against the distributor body.
Step 5: Adjusting the Contact Point Gap This is a critical step for ignition timing and performance.
1. Rotate Engine to Max Opening: Manually rotate the engine crankshaft (using a spanner on the crankshaft pulley bolt) or momentarily "bump" the starter motor until the fibre heel of the moving contact arm is resting on the highest point (lobe) of the distributor cam. This ensures the points are at their maximum open position.
2. Select Feeler Gauge: Choose the correct feeler gauge blade for the specified point gap (refer to the vehicle's service manual or a reliable auto-data source for the exact specification, e.g., 0.015-0.019 inches or 0.38-0.48 mm, but typically 0.015" or 0.40mm).
3. Insert Feeler Gauge: Insert the correct feeler gauge blade between the fixed and moving contact surfaces. It should slide in with a slight drag – not too loose, not too tight.
4. Adjust Gap: If the gap is incorrect: Loosen the small screw that secures the fixed contact base (if it wasn't fully tightened). Use a screwdriver or a dedicated adjusting tool to slightly move the fixed contact base in or out until the feeler gauge slides with the correct drag. Once adjusted, tighten the retaining screw for the fixed contact base securely, being careful not to alter the gap during tightening. Recheck the gap with the feeler gauge Introduction to Contact Breaker Points Contact breaker points (also known as points or breaker points) are electromechanical switches found in the distributor of a conventional (Kettering) ignition system. Their primary function is to interrupt the primary circuit of the ignition coil at precise timings, leading to the collapse of the magnetic field in the coil and inducing a high voltage in the secondary circuit, which then fires the spark plugs. Components of a Contact Breaker Point Assembly:
1. Fixed Contact: A stationary metallic contact point mounted on an insulated base.
2. Moving Contact: A movable metallic contact point that pivots on a spring-loaded arm.
3. Heel (Cam Follower): A fibre or plastic block attached to the moving contact arm, designed to ride on the distributor cam.
4. Spring: Provides tension to keep the moving contact closed against the fixed contact until opened by the cam.
5. Primary Lead Wire: A wire connecting the moving contact assembly to the ignition coil's primary terminal.
6. Condenser (Capacitor): Although often replaced alongside the points, the condenser is electrically connected across the points. Its role is to absorb the spark that forms across the points as they open, preventing burning and pitting, and to quickly discharge current to aid in the rapid collapse of the coil's magnetic field.
Operation of Contact Breaker Points: As the engine runs, the distributor shaft rotates, driven by the camshaft. The distributor shaft has a cam (typically with lobes equal to the number of engine cylinders). As each lobe of the cam rotates and pushes against the heel of the moving contact arm, it forces the moving contact away from the fixed contact, thereby opening the points. When the cam lobe passes, the spring tension closes the points again. This opening and closing action precisely switches the primary circuit of the ignition coil. Why Replace or Recondition Points? Over time, due to the high current switching and electrical arcing, the contact surfaces of the points can: Pitting: Small craters forming on one contact and corresponding build-up on the other. This occurs due to material transfer (tungsten).
Burning/Oxidation: Discoloration and carbon deposits due to excessive arcing, often exacerbated by a faulty condenser or incorrect gap.
Wear: The fibre heel can wear down, leading to an incorrect point gap and subsequent ignition timing issues.
Spring Weakness: The spring can lose tension, causing point bounce at higher RPMs. These issues lead to poor spark, engine misfires, reduced power, increased fuel consumption, difficult starting, and eventual engine failure. Regular inspection and replacement/reconditioning are crucial for conventional ignition systems. Tools and Materials Required for Replacement/Reconditioning: Screwdrivers (flat-head and Phillips) Distributor spanner (for holding the distributor shaft or loosening clamp) Feeler gauge (for measuring point gap) Point file or fine-grade emery cloth/sandpaper (for reconditioning) Clean rag or shop towel New contact breaker points (if replacing) New condenser (highly recommended to replace alongside points) Timing light (for final ignition timing check, not directly for point replacement but essential for system calibration). * Multimeter (optional, for checking primary circuit continuity).
Safety Precautions:
1. Disconnect Battery: Always disconnect the negative (-) terminal of the battery before working on electrical components to prevent accidental shorts and electric shock.
2. Avoid Hot Engine: Allow the engine to cool down before handling distributor components.
3. Handle Components Carefully: Ignition components can be delicate.
4. Cleanliness: Ensure work area and components are clean to prevent dirt contamination. Detailed Step-by-Step Procedure for Contact Breaker Point Replacement and Adjustment: Step 1: Preparation and Access
1. Park Vehicle Safely: Engage parking brake, place transmission in neutral (manual) or park (automatic).
2. Disconnect Battery: Remove the negative (-) battery terminal.
3. Locate Distributor: Identify the distributor, typically found on the side of the engine block, with spark plug wires leading from its cap.
4. Remove Distributor Cap: Unclip or unscrew the two retaining clips/screws on the distributor cap and carefully lift it off. Note the orientation for correct reinstallation.
5. Remove Rotor: Gently pull the rotor off the distributor shaft. It is usually a friction fit.
Step 2: Removing Old Contact Points
1. Identify Point Assembly: a slight drag – not too loose, not too tight.
4. Adjust Gap: If the gap is incorrect: Loosen the small screw that secures the fixed contact base (if it wasn't fully tightened). Use a screwdriver or a dedicated adjusting tool to slightly move the fixed contact base in or out until the feeler gauge slides with the correct drag. Once adjusted, tighten the retaining screw for the fixed contact base securely, being careful not to alter the gap during tightening. Recheck the gap with the feeler gauge to confirm accuracy.
5. Clean Contacts (Final): After adjustment, slide a clean, lint-free paper or business card between the points and pull it out to remove any residue from the feeler gauge.
Step 6: Reassembly and Final Checks
1. Reinstall Rotor: Gently push the rotor back onto the distributor shaft, ensuring it seats correctly.
2. Reinstall Distributor Cap: Place the distributor cap back onto the distributor, aligning it with the locating notches, and secure it with its clips/screws.
3. Reconnect Battery: Reconnect the negative (-) battery terminal.
4. Start Engine: Start the engine and listen for smooth operation.
5. Check Ignition Timing (Crucial Follow-up): After replacing/adjusting points, it is highly recommended to check and adjust the ignition timing using a timing light. The point gap adjustment directly affects ignition timing. This step ensures the engine runs efficiently and prevents potential damage. (While timing adjustment is a separate skill, the teacher should emphasize its importance as a follow-up to point replacement.)
Teacher Activities: Introduction (10 mins): Begin by asking questions about engine starting problems students might have observed or experienced (e.g., "Engine cranking but not starting," "engine missing"). Introduce the topic of contact breaker points as a key component in solving some of these problems, especially in older vehicles. Briefly outline the learning objectives for the session.
Conceptual Explanation (20 mins): Use diagrams, charts, or an actual distributor assembly (if available) to illustrate the components of the contact breaker points and their location within the distributor. Explain the function of each component and how the points open and close in synchronization with the engine's operation. Discuss the reasons for wear and tear (pitting, burning, wear of the heel) and their consequences on engine performance. Emphasize safety precautions before commencing any practical work. Demonstration of Removal and Reconditioning (20 mins): Live Demonstration (Preferred): Using a functional or mock-up distributor (on a stand or a vehicle in the workshop), demonstrate the step-by-step process of: Accessing the distributor (removing cap and rotor). Disconnecting the primary lead. Unscrewing and removing the fixed and moving contact points. Demonstrate how to recondition lightly pitted points using a point file or fine emery cloth. Explain when reconditioning is feasible versus when replacement is necessary.
Visual Aids (If no live demo): Use large, clear images or a video demonstration if a physical distributor isn't available. Narrate the steps clearly. Demonstration of Installation and Adjustment (25 mins): Continue the demonstration by showing students how to: Install new or reconditioned contact points and reconnect the primary lead. Crucially, demonstrate how to rotate the engine (or distributor shaft) to find the maximum point opening. Demonstrate the correct use of a feeler gauge to measure the gap. Show how to adjust the gap precisely by loosening and tightening the retaining screw. Emphasize the "slight drag" principle. Reinstall the rotor and distributor cap. Interactive Q&A and Clarification (15 mins): Encourage students to ask questions throughout the demonstrations. Address any misconceptions and reinforce key steps and safety practices. Quiz students verbally on tool identification and procedural steps. Supervised Practical Session (Remaining time, or separate practical period): Divide students into small groups (2-3 per group). Provide each group with a distributor assembly (preferably on a mock engine or test bench), the necessary tools, and either new points or old points suitable for reconditioning. Circulate among the groups, observing their work, providing immediate feedback, correcting errors, and ensuring safety. Encourage peer learning and troubleshooting within groups.
Student Activities: Active Listening and Note-Taking: Students will listen attentively to the teacher's explanations and demonstrations, taking detailed notes on procedures, tools, and safety precautions.
Observation: Closely observe the teacher's demonstrations of point removal, reconditioning, installation, and gap adjustment.
Questioning: Actively ask questions to clarify doubts and deepen understanding during and after demonstrations.
Practical Application (Hands-on): In groups, students will practice removing existing contact points from a distributor. Students will practice reconditioning impaired points using the appropriate tools. Students will install new or reconditioned points into the distributor. Students will use a feeler gauge to accurately adjust the contact point gap to the specified measurement. Students will reassemble the distributor components (rotor, cap).
Peer Collaboration: Students will work together in groups, assisting each other, discussing steps, and verifying measurements.
Safety Adherence: Strictly follow all safety guidelines provided by the teacher, especially concerning battery disconnection and careful handling of tools and components.
Entrepreneurship and Local Economy (Roadside Mechanics/Workshops): Many older vehicles in Nigeria, such as classic Peugeot models, older Volkswagen Beetles, and various commercial buses/taxis (e.g., some Toyota Hiace models), still rely on conventional ignition systems with contact breaker points. Students who master this skill can readily find employment or establish their own small auto repair shops ("mechanic village" style) in their communities. This offers a direct pathway to self-employment and contributing to the local informal economy by servicing vehicles that form the backbone of local transportation.
Vehicle Maintenance and Cost Savings: For vehicle owners in Nigeria, understanding and being able to replace/recondition contact points can lead to significant cost savings. Instead of paying a mechanic for a relatively simple procedure, individuals can maintain their own vehicles, prolonging engine life and improving fuel efficiency. This is particularly relevant given fluctuating fuel prices and the desire to keep vehicles running optimally for daily commutes or commercial activities (e.g., 'Okada' motorcycle maintenance, or small commercial van upkeep).
Problem Solving and Diagnostic Skills: Learning about contact breaker points enhances students' diagnostic abilities. When an older vehicle experiences hard starting, misfires, or poor performance, a student trained in this area can quickly identify if faulty contact points are the culprit. This builds a foundational problem-solving mindset essential for any technical profession, especially in environments where advanced diagnostic tools might not always be available, and hands-on troubleshooting is key.