Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Dismantling and assembling
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Dismantling and assembling
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Subject: Auto Electrical Works
Class: Senior Secondary 2
Term: 3rd Term
Week: 1
Theme: Starting System
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This topic covers the fundamental practical skill of dismantling and assembling starter motors. Understanding the internal components and their functions is crucial for diagnosis, repair, and maintenance of automotive electrical systems. Proficiency in this area directly contributes to the employability and entrepreneurial potential of learners in the automotive repair sector across Nigeria.
Performance Objectives: At the end of this lesson, students will be able to: Identify the main components of a starter motor. Correctly list the sequence for dismantling a starter motor. Correctly list the sequence for assembling a starter motor.
field casing over the armature and brush holder assembly, aligning it with the drive end housing. Ensure the field windings are not pinched.
5. Install Commutator End Housing (Rear Housing): Carefully align the commutator end housing with the field casing and armature shaft. Guide the armature shaft into the bushing in the end housing. Ensure the brushes seat correctly on the commutator.
6. Install Through Bolts: Insert the long through bolts through the drive end housing, field casing, and commutator end housing. Hand-tighten the nuts initially, then use a socket wrench to tighten them evenly and securely. Do not overtighten.
7. Install Solenoid Switch: Position the solenoid onto the drive end housing, ensuring the plunger correctly engages with the engagement lever (yoke). Install and tighten the solenoid mounting screws/nuts. Reconnect the copper strap from the solenoid to the field winding terminal, ensuring a tight connection. Reconnect the small control wire terminal nut and washer.
8. Final Inspection: Manually rotate the pinion gear to ensure smooth movement and proper engagement/disengagement. Check all connections and bolts for tightness. Conduct continuity tests with a multimeter (if trained) to ensure internal electrical connections are correct. --- Bolts: Locate the two or more long through bolts that pass through the entire length of the starter motor. Using the appropriate socket or spanner, loosen and remove these bolts.
4. Separate the Commutator End Housing (Rear Housing): Gently tap the commutator end housing (opposite the drive end) with a rubber mallet if it's stuck. Carefully pull the commutator end housing away from the motor casing, being mindful of the brushes and brush springs. Remove the brush holder assembly if it comes off with the housing. Note the position of the brushes.
5. Remove the Field Casing (Motor Casing) and Armature: With the commutator end housing removed, the field casing (containing the field windings) can be pulled off the armature. Carefully slide the armature out of the drive end housing, taking care not to damage the commutator or shaft.
6. Remove the Brush Holder Assembly (if not already removed): If the brush holder assembly remained with the field casing or armature, gently slide it off, noting how the brushes are seated. Compress the brush springs if necessary.
7. Remove the Drive End Housing and Overrunning Clutch Assembly: At this point, the armature, overrunning clutch (Bendix drive), and engagement lever (yoke) are likely still within the drive end housing. Carefully slide the engagement lever off its pivot points. Inspect the retaining clip/stop collar that secures the overrunning clutch to the armature shaft. Using appropriate tools (e.g., a small punch and hammer), tap the stop collar down to reveal the C-clip or circlip. Carefully remove the C-clip/circlip. This usually requires a special tool or careful prying with a small screwdriver. Slide the stop collar, overrunning clutch, and any thrust washers off the armature shaft. Note their order. Inspection and Cleaning during Dismantling: Clean all components thoroughly using a wire brush and suitable solvent (e.g., petrol or kerosene, used with caution and adequate ventilation). Inspect the commutator for wear, burns, or excessive runout. Check armature windings for shorts or opens (can be done with a multimeter). Inspect brushes for wear (replace if less than half their original length). Check brush springs for proper tension. Inspect the overrunning clutch for free movement and engagement. It should spin freely in one direction and lock in the other. Check bearings/bushings in both end housings for wear. Examine field windings for signs of burning or damage. Sequence of Assembling a Starter Motor (Step-by-Step): Assembly is essentially the reverse of dismantling, with careful attention to lubrication and component alignment.
1. Prepare for Assembly: Ensure all components are clean, inspected, and any worn parts have been replaced. Lightly lubricate the armature shaft and bushings/bearings with a thin coat of high-temperature grease.
2. Install Overrunning Clutch and Drive End Housing: Slide any thrust washers onto the armature shaft, followed by the overrunning clutch (ensure correct orientation). Slide the stop collar onto the shaft. Install the C-clip/circlip into its groove on the armature shaft. Use a punch or suitable tool to tap the stop collar securely over the C-clip. Insert the armature with the overrunning clutch into the drive end housing. Position the engagement lever (yoke) correctly onto its pivot points and around the overrunning clutch.
3. Install Brush Holder Assembly: If the brush holder was separate, install it onto the armature's commutator end. Carefully guide the brushes over the commutator segments, compressing the springs as needed. Ensure brushes are correctly seated.
4. Install Field Casing (Motor Casing): Carefully slide the field casing over the armature and brush holder assembly, aligning it with the drive end housing. Ensure the field windings are not pinched.
5. Install Commutator End Housing (Rear Housing): Carefully align the commutator end housing with the field casing and armature shaft. Guide the armature shaft into the bushing in the end housing. Ensure the brushes seat correctly on the commutator.
6. Install Through Bolts:** Insert the long through bolts through the drive end housing, field casing, and commutator end housing. * Hand-tighten the nuts initially, then use a A starter motor is an electric motor used to rotate the internal combustion engine to initiate the engine's operation under its power. It converts electrical energy from the battery into mechanical energy to crank the engine.
Main Components of a Starter Motor:
1. Solenoid Switch (Starter Relay): An electromagnetic switch that performs two functions: Connects the battery directly to the starter motor windings. Engages the pinion gear with the engine's flywheel ring gear.
2. Armature: The rotating part of the motor, consisting of a shaft, a core (laminations), and windings. When current flows through the windings in a magnetic field, it produces torque.
3. Field Windings: Coils of thick wire wound around soft iron pole shoes, typically housed in the motor casing. They create a strong magnetic field when current passes through them.
4. Brushes: Carbon blocks that ride on the commutator, transmitting electrical current from the field windings to the armature windings.
5. Commutator: A segmented copper cylinder mounted on the armature shaft, connected to the armature windings. It reverses the current direction in the armature windings to maintain continuous rotation.
6. Drive End Housing (Front Housing): Supports the armature shaft and houses the overrunning clutch/pinion gear assembly. It bolts to the engine bell housing.
7. Commutator End Housing (Rear Housing): Supports the rear end of the armature shaft and houses the brushes and brush holder assembly.
8. Overrunning Clutch (Bendix Drive): A mechanism that allows the pinion gear to engage the flywheel and transmit torque, then disengage once the engine starts, preventing the engine from driving the starter motor at excessive speeds.
9. Pinion Gear: A small gear on the overrunning clutch assembly that meshes with the flywheel ring gear.
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0. Through Bolts: Long bolts that hold the drive end housing, field casing, and commutator end housing together. Safety Precautions during Dismantling and Assembly: Always disconnect the vehicle battery before working on the starter motor. Wear appropriate Personal Protective Equipment (PPE) such as safety goggles and gloves. Use the correct tools for each task to prevent damage to components or injury. Work on a clean, stable surface. Handle components carefully, especially the delicate armature and commutator. Note the orientation and position of all parts during dismantling to aid correct reassembly.
Tools Required: Assorted spanners (combination, ring, open-end) Socket wrench set with extensions Screwdrivers (flat-head and Phillips) Hammer (plastic or rubber mallet may be needed) Pliers (combination, needle-nose) Wire brush (for cleaning components) Multimeter (for testing components, if part of the task) Bench vise (to secure the starter motor) Cleaning rags/cloths Parts tray/container (to organize disassembled parts) Grease/lubricant (for assembly) Sequence of Dismantling a Starter Motor (Step-by-Step):
1. Preparation: Secure the starter motor firmly in a bench vise, taking care not to damage the casing. Clean the exterior of the starter motor with a wire brush and rag to remove dirt and grime. Gather all necessary tools and a parts tray.
2. Remove the Solenoid Switch: Disconnect the battery cable from the solenoid's main terminal (if applicable, though typically done when removing from vehicle). Remove the small control wire terminal nut and washer. Carefully detach the copper strap connecting the solenoid to the motor body (field windings). Note its orientation. Remove the solenoid mounting screws/nuts (usually two) that secure it to the drive end housing. Gently pull the solenoid away from the drive end housing, ensuring the plunger is free. Be careful not to bend the engagement lever (yoke).
3. Remove Through Bolts: Locate the two or more long through bolts that pass through the entire length of the starter motor. Using the appropriate socket or spanner, loosen and remove these bolts.
4. Separate the Commutator End Housing (Rear Housing): Gently tap the commutator end housing (opposite the drive end) with a rubber mallet if it's stuck. Carefully pull the commutator end housing away from the motor casing, being mindful of the brushes and brush springs. Remove the brush holder assembly if it comes off with the housing.
Note Teacher Activities: Introduction (5 minutes): Teacher reviews previous lesson on starter motor principles. Teacher introduces the topic of dismantling and assembling starter motors, highlighting its practical importance in auto repair. Teacher states the lesson objectives clearly. Key Concept Explanation and Demonstration (20 minutes): Teacher displays a complete starter motor (if available) or detailed diagrams/cutaway models. Teacher systematically identifies and explains each major component (solenoid, armature, field windings, brushes, commutator, drive/commutator end housings, overrunning clutch) and its function. Teacher explains the purpose of dismantling and the common faults that necessitate it (e.g., worn brushes, faulty solenoid, damaged Bendix drive). Teacher demonstrates the proper use of required tools for dismantling/assembly. Teacher emphasizes safety precautions.
Dismantling Demonstration (30 minutes): Teacher performs a step-by-step live demonstration of dismantling a starter motor, narrating each step and explaining the rationale. Teacher verbally highlights potential challenges and common mistakes. Teacher uses a parts tray to organize components as they are removed, labeling them if necessary. Teacher involves students by asking them to identify parts as they are removed and to name the next logical step.
Assembly Demonstration (30 minutes): Teacher performs a step-by-step live demonstration of assembling the starter motor, emphasizing correct component alignment, lubrication, and tightening procedures. Teacher ensures students observe closely, pointing out critical connection points and potential pitfalls. Teacher conducts a brief functional check (e.g., checking for free rotation of pinion) after assembly.
Guided Practice Facilitation (20 minutes): Teacher divides students into small groups (e.g., 3-4 students per group). Teacher provides each group with a starter motor (if available) or detailed diagrams/worksheets. Teacher guides students through the dismantling and assembly process, providing close supervision and immediate feedback. Teacher circulates among groups, addressing questions and correcting errors.
Student Activities: Active Listening and Observation (Introduction & Demonstration phases): Students listen attentively to the teacher's explanations and observe the demonstrations. Students ask clarifying questions during the demonstration. Students take notes on component identification, dismantling/assembly sequences, and safety procedures. Component Identification Practice (During/After demonstration): Students identify components on the displayed starter motor or diagrams as prompted by the teacher. Students verbally recall functions of different parts.
Tool Identification: Students identify and name the tools demonstrated by the teacher.
Group Practical Work (Guided Practice): Working in assigned groups, students follow the teacher's instructions to practice dismantling and then assembling a starter motor. Students collaboratively identify parts, discuss the sequence, and assist each other in the practical tasks. Students document the sequence of steps and tools used in their notebooks.
Reporting and Discussion: Each group briefly reports on their progress, challenges encountered, and key learnings. Students participate in a class discussion, sharing observations and problem-solving strategies. ---
Automotive Repair and Entrepreneurship: In Nigeria, the demand for skilled auto mechanics is consistently high due to the large number of vehicles on the road (new and fairly used) and the challenging road conditions that often lead to wear and tear. A thorough understanding of starter motor dismantling and assembly directly equips learners for employment in garages, dealerships, and independent workshops.
Furthermore, it empowers them to start their own auto-electrical repair businesses, providing essential services to vehicle owners in their communities and contributing to the local economy. This skill can be applied to repairing cars, buses, commercial motorcycles (Okada), and tricycles (Keke Napep). Preventive Maintenance and Troubleshooting: Knowledge of starter motor components and their typical failure modes allows individuals to perform basic diagnostics and preventive maintenance. For instance, a vehicle owner or technician who understands that worn brushes or a sticky solenoid can cause starting issues might identify and address these problems before they lead to complete starter motor failure. This saves vehicle owners money on costly replacements and ensures vehicle reliability, which is critical for commercial drivers (e.g., taxi drivers, haulage operators) whose livelihood depends on their vehicle's operational status.
Appliance Repair (Transferable Skills): While specifically focused on auto electrical, the principles of dismantling, inspecting, and assembling electro-mechanical devices are transferable. The systematic approach, tool usage, and understanding of electrical-to-mechanical conversion learned here can be applied to troubleshooting and repairing other electrical motors found in home appliances (e.g., blenders, fans, washing machines) or industrial equipment. This broadens the learner's skill set and potential for diversification in technical fields beyond just automotive. ---