Two and Three Wheeler Vehicle Servicing

Automotive Mechanics Level-II Study Notes

• This module focuses on the skills and knowledge needed for minor servicing of two and three-wheeler vehicles.
• Key aspects include task preparation, fault identification, component replacement, and post-service checks.
• It also covers documentation.

Key Units Covered:

• Preparing for work on two and three-wheelers.
• Removing, disassembling, checking, and testing system assemblies.
• Replacing or reassembling system assemblies.
• Cleaning the work area and maintaining equipment.

Module Instructions Emphasize:

• Reviewing learning objectives.
• Following instructions
• Reading of info sheets.
• Completing self-checks.
• Performing operation sheets.
• Completing the LAP test.

Unit 1: Preparing to Service Two and Three Wheelers

• This unit introduces electrical and mechanical components of two/three-wheelers.
• It discusses the use of workshop manuals.

Introducing Electrical/Mechanical Elements

• Three-wheelers are vehicles with three wheels, sometimes classified as motorized tricycles or motorcycles.
• In many countries, auto rickshaws serve as essential urban transport, including in developing countries like Ethiopia.

Two/Four-Stroke Gasoline/Diesel Engines

• The primary difference between 2-stroke and 4-stroke engines lies in the speed of the combustion cycle.
• This is determined by how many times the piston moves.

4-Stroke Engines

• In a 4-stroke engine, the piston makes two strokes per revolution, including compression and exhaust strokes.
• Spark plugs ignite fuel once every other revolution.
• These engines have separate oil compartments and don't require pre-mixing fuel and oil.

2-Stroke Engines

• In a 2-stroke engine, the combustion cycle concludes with one piston stroke.
• The spark plugs ignite fuel every single revolution.
• Two-stroke engines require pre-mixing oil with the fuel.

Component Parts of 2-Stroke Engine:

• Key components include cylinder, combustion chamber, exhaust port, and crankcase.
• It also includes reed valve, connecting rod, piston, crankshaft, intake port, and transfer port.

4-Stroke vs 2-Stroke Engine Advantages and Disadvantages:

Four-Stroke Engine

• Power developed every two crankshaft revolutions.
• Torque is not uniform.
• A heavy flywheel is needed.
• Air or air/fuel mixtures directly enter the cylinder.
• One power stroke occurs in two revolutions, using less lubricant/coolant.

Two-Stroke Engine

• Power is developed in each crankshaft revolution.
• Torque is more uniform.
• A lighter flywheel is needed.
• Charges enter the crankcase first, then the cylinder.
• Power produces each revolution, requiring greater cooling/lubrication.

Four-Stroke and Two-Stroke Comparisons

• Four-stroke engines do not have a scavenging process; two-stroke engines do.
• Four-stroke engines produce less noise, while two-stroke engines produce more.
• Four-stroke engines have more power output but higher maintenance costs.
• Four-stroke engines require more space and are harder to start.
• Two-stroke engines are simpler, easier to start, and need less space.
• Four-stroke engines are more robust with higher thermal efficiency and initial cost.
• Volumetric efficiency is higher in four-stroke engines due to greater intake capacity.
• Volumetric efficiency is lower in two-stroke engines due to less charge in the cylinder.

Engine Systems

• Engines convert heat from burning fuel into useful work, transforming thermal energy into mechanical energy.

Engine Classification

Combustion-Based:

• External combustion engines use steam generated outside the engine cylinder.
• Internal combustion engines burn fuel inside the cylinder.

Fuel-Based:

• Diesel engines use diesel.
• Petrol engines use petrol.
• Gas engines use propane, butane, or methane.

Ignition-Based:

• Spark ignition engines use carburetors.
• Compression ignition engines use fuel injectors.

Spark Ignition Engines

• Air and fuel are mixed and drawn into the cylinder, ignited by a spark plug.
• This combustion is "constant volume combustion" (CVC).

Compression Ignition Engines

• Air enters the cylinder during suction, and high temperature ignites the fuel.
• Compressed air reaches 700-900°C to ignite the fuel.

Working Cycle-Based:

• Four-stroke cycle engines need two crankshaft revolutions per cycle.
• Two-stroke cycle engines need one crankshaft revolution per cycle.

Construction of an IC Engine

• The engine converts piston motion into rotary crankshaft motion with a connecting rod.
• Cylinders are bored into the cylinder block, sealed with gaskets to prevent leakage.
• Combustion occurs at the top of the cylinder head.

Cylinder Block

• It is the largest engine part, usually cast from iron or aluminum.
• It has passages for lubricants and coolant.

Cylinder Head

• Attached to the cylinder block, it forms the combustion chamber.
• Engine combustion occurs here.

Piston

• Transforms heat energy into mechanical energy.
• Heat energy does work on its enclosed top.

Piston Rings

• They are metallic split rings in grooves on the piston's outer diameter, providing a seal.
• There are generally 3 - 4 rings used in an IC engine.
• They seal burnt gasses from the crankcase.
• Rings conduct heat from the piston crown to cylinder walls.
• Rings control oil flow and prevent gas intermixture in the combustion chamber.

Piston Ring types include

• Compression rings and Oil control rings.

Connecting Rod

• Its main use is connecting the piston and crankshaft, moving reciprocal motion from the piston to the crank pin.
• The rod consists of a shank, small end (connected to the piston via the 'gudgeon pin'), and a big end connected to the crankshaft.

Crankshaft

• The crankshaft is the power transmission system element that converts piston reciprocating motion to rotating motion.
• It comprises crankpins, crank webs, balancing weights, and main journals.

Flywheel

• It balances the engine, reducing vibrations from offset pistons.
• Gear teeth are attached to a starter motor for engine start.
• It provides inertia, keeping the crankshaft spinning between piston firings.
• The flywheel's weight affects the engine's performance.

Camshaft

• This provides force to open the valves.
• A shaft with egg-shaped lobes extends through the cylinder block.
• A gear mechanism rotates the camshaft once for every two crankshaft revolutions in a four-stroke cycle engine.

Valves

• Valve mechanisms open and close intake/exhaust valves.
• This ensures proper timing for air-fuel mixture input and exhaust gas output.
• Pear-shaped cams on the camshaft drive this.
• The inlet valve enables air-fuel mixture into the cylinder.
• The exhaust valve allows spent gases to escape.

Two/Three-Wheeler Ignition Systems

• An ignition system ignites compressed air-fuel mixture in the engine.
• A 12V system increases voltage to 20,000-30,000V needed for the spark plugs in the chamber.

Battery Coil Ignition System Components:

Primary Circuit includes

• a 6 or 12V battery, ammeter, ignition switch, and primary winding of 200-300 turns of 20 SWG wire.

Secondary Circuit includes

• A secondary winding consisting of 21,000 turns of 40 SWG wire.

Magneto Ignition System

• This system uses a self-contained generator to provide high voltage to the engine through spark plugs.
• A magnet spins near a wire coil, which generates a "held back" magnetic force.

Electronic Ignition System

• Electronic ignition systems provide a stronger spark for igniting leaner fuel mixtures.

Kick and Self-Starter Systems

• A kick start begins an internal combustion engine, especially in motorcycles or off-road vehicles without an electric system.
• In the past, motorcycles exclusively used kick start systems which are now replaced by electric starters

Self-Start System involves

• Rotating the crankshaft by means of a starter motor to start the engine.

Lighting and Auxiliary Electrical Systems

• The focus is on various indicators and switches found on motorbikes.

Indicators and Switches:

• Turn signal indicator lights flash when the turn signal switch is active.
• Neutral indicator lights up when the transmission is in neutral.
• High beam indicator shows when the headlight's high beam is on.
• Oil level warning light indicates when the engine oil is low.
• Coolant temperature warning light warns of engine overheating, requiring immediate cool down.

Chassis and Subsystems on multi-wheelers

• Key parts consist of the frame, suspension, wheels, and brakes.

Frame

• It acts as a skeleton for mounting the gearbox and engine, maintaining wheel alignment.
• Frame is constructed of steel, aluminum, or alloy.

Suspension System

• The shock absorbers keep both those on the vehicle from feeling road shocks.
• Suspension is either front or rear.
• It ensures consistent ground contact for control.
• Front suspension guides the front wheel for steering, springing, dampening, and braking.

Wheels

• It is a circular object with an axle that enables motion by rolling.
• It consist of the rim and spokes, it should be properly aligned due to its direct influence to driving.
• Aluminium and steel rims and spokes are generally used for wheels.

Drive Layouts and Control Systems

• Shifting gears: Close the throttle during clutch press, shift to the following appropriate gear, and release the cluth.

Clutch, Gearbox, Transmission

• The clutch is a mechanical device to control the amount of motion and power from one element to another, being engaged/disengaged amount in amount and time.

Gearbox/Transmission

• A gearbox functions using a mechanical method of transferring energy from one device to another.
• Its main use is to increase torque while decreasing speed.
• Motorcycle gear boxes contain gears in various sizes that lock together during gear switching to gear the transmision.
• Motorcycle gear box is component of the transmission that makes the ratio between the transmission and driving wheels.

Motorcycle Gear Box Types:

• Horizontally split (seam on horizontal plane).
• Vertically split (seam on the vertical plane).
• Cassette type (gears load in from one side).

Sourcing and Using Workshop Manuals

Work shop manual Provides

• Detailed instructions for repair, dismantling, testing, and rebuilding vehicle components.

Owner's Manual Includes:

• Operating instructions, fluid information, and specs for the vehicle and its accessories.

Auto Manufacturers' Service Manuals Includes:

• Repair and specification information for various vehicles written for technicians.
• Divided into sections covering chassis, suspension, engine, brakes, etc.

Finding Information in Service Manuals:

• Identify the system you're working on.
• Use the VIN (vehicle identification number). Select the correct manual, locate the appropriate section.
• Read and study the diagrams, follow all steps, and adhere to specifications.

Specifications Must Include:

• Price for services, day/hourly/all-inclusive rates, quality, quantity, required supplier experience, dimensions, performance and installation/maintenance/servicing/warranty.