LEARNING OUTCOME 1

Major Engine Components

Crankshaft:

Visual: Located at the bottom of the engine block, it's a large, heavy shaft with offset journals (crank pins). You may see its pulley or flywheel externally. When exposed, it has rounded journals for the connecting rods to attach.

Aural: When rotating, a healthy crankshaft produces a smooth, consistent whirring sound. Irregular noises like knocking or clanking indicate potential problems.

Camshaft:

Visual: Located in the cylinder head (overhead cam engines) or within the engine block (pushrod engines). It has lobes (cams) that actuate the valves. In overhead cam engines, it is visible when the valve cover is removed.

Aural: A properly functioning camshaft produces a smooth, rhythmic ticking sound. Excessive ticking or tapping can indicate wear or damage.

Pistons and Connecting Rods:

Visual: Pistons are cylindrical components inside the cylinders. Connecting rods connect the pistons to the crankshaft. They are not visible without disassembling the engine. However, signs of problems can be external, such as excessive blow-by (exhaust gases escaping around the pistons).

Aural: Piston slap (a knocking sound) can indicate worn pistons or cylinders. Rod knock (a deep, heavy knocking sound) suggests connecting rod bearing issues.

Gudgeon Pins (Wrist Pins):

Visual: These pins connect the pistons to the connecting rods. They are internal and not visible without disassembly.

Aural: A loose gudgeon pin can produce a sharp, metallic clicking or knocking sound.

Valves:

Visual: Located in the cylinder head, they control the intake and exhaust of gases. You can see the valve stems and valve springs when the valve cover is removed.

Aural: A light, rhythmic ticking sound is normal. Excessive ticking or tapping can indicate valve lash problems or worn components. Whistling sounds can be caused by leaking valves.

Cylinder Head:

Visual: The top part of the engine, it houses the valves, camshaft (in overhead cam engines), and spark plugs or injectors. It is a large metal component bolted to the top of the engine block.

Aural: Head gasket leaks can produce hissing or bubbling sounds, especially when the engine is running.

Engine Block:

Visual: The main body of the engine, it contains the cylinders, crankshaft, and coolant passages. It is a large, heavy metal casting.

Aural: Cracks or leaks in the engine block can produce hissing or gurgling sounds, especially when the engine is hot.

Valve Springs:

Visual: Located around the valve stems, they close the valves after they are opened by the camshaft. They are coiled springs.

Aural: Broken or weak valve springs can produce a rattling or clattering sound, and misfires.

Minor Engine Components

Bearings:

Visual: These are located at points where rotating components meet stationary ones (e.g., crankshaft bearings, camshaft bearings). They reduce friction. They appear as smooth metal surfaces or rollers.

Aural: Worn bearings can produce a rumbling, grinding, or whining sound.

Sump (Oil Pan):

Visual: The lowest part of the engine, it holds the engine oil. It's a metal or plastic pan bolted to the bottom of the engine block.

Aural: Damage to the sump can lead to oil leaks, which may not produce a sound but will result in visible oil dripping.

Covers (Tappet and Front):

Visual: Tappet covers (valve covers) seal the top of the cylinder head, preventing oil leaks. The front cover protects the timing gears or chains. They are typically metal or plastic covers.

Aural: Leaks from these covers can result in hissing or dripping sounds.

Gears:

Visual: These are toothed wheels that transmit motion between shafts (e.g., timing gears, oil pump gears). They are visible when covers are removed.

Aural: Worn or damaged gears can produce a whining or grinding sound.

Belts:

Visual: These are flexible bands that transmit power between pulleys (e.g., serpentine belt, timing belt). They are usually made of rubber.

Aural: Worn or loose belts can produce a squealing or chirping sound.

Chains:

Visual: These are metal links that transmit power between sprockets (e.g., timing chain). They are stronger than belts.

Aural: Worn or loose chains can produce a rattling or slapping sound.

Engine Cycles and Types

Four-Stroke (Otto) Cycle:

This cycle completes one power stroke in four piston strokes (two crankshaft revolutions).

• Crankshaft: Converts reciprocating motion of pistons to rotary motion.
• Camshaft: Controls the opening and closing of valves.
• Pistons: Move up and down in the cylinders, creating compression and power.
• Valve Train: Consists of valves, valve springs, pushrods (if applicable), and rocker arms, which control valve operation.

The four strokes are:

1. Intake: Intake valve opens, piston moves down, drawing in air fuel mixture.
2. Compression: Both valves closed, piston moves up, compressing the mixture.
3. Power: Mixture ignites, piston moves down, producing power.
4. Exhaust: Exhaust valve opens, piston moves up, expelling exhaust gases.

Two-Stroke Cycle:

This cycle completes one power stroke in two piston strokes (one crankshaft revolution).

• It eliminates separate intake and exhaust strokes, using ports in the cylinder walls.
• It is simpler but less efficient than the four-stroke cycle.
• It is common in small engines (e.g., lawnmowers, motorcycles).
• Intake and exhaust happen during the compression and power strokes.

Compression Ignition Engines (Diesel Engines):

These engines use compression to ignite the fuel.

• Air is compressed to a high temperature, and fuel is injected into the hot air, causing it to ignite.
• They are more efficient than spark ignition engines.
• They are common in trucks, buses, and heavy equipment.
• They do not use spark plugs.
• They use high pressure fuel injection.

Lubrication System

The lubrication system is critical for the smooth operation and longevity of an engine. Its primary functions are:

• Reducing Friction: Engine components move at high speeds, generating friction. Lubrication creates a thin film of oil between these parts, minimizing friction and wear.
• Cooling: Oil absorbs heat from engine components and carries it away, helping to regulate engine temperature.
• Cleaning: Oil carries away contaminants, such as metal particles and combustion byproducts, preventing them from causing damage.
• Sealing: Oil helps to seal the gaps between piston rings and cylinder walls, maintaining compression.
• Corrosion Prevention: Oil forms a protective barrier on metal surfaces, preventing corrosion.

Key Components of a Lubrication System

• Oil Pan (Sump): Stores the engine oil.
• Oil Pump: Circulates oil throughout the engine.
• Oil Filter: Removes contaminants from the oil.
• Oil Passages: Channels through which oil flows to various engine components.
• Oil Pressure Sensor/Switch: Monitors oil pressure and alerts the driver to low pressure.
• Oil Control Valves: In modern engines, these valves control oil flow to various parts of the engine.

Changing Engine-Related Filters and Oil: A Lubrication System Maintenance Task

Regular oil and filter changes are essential for maintaining the lubrication system's effectiveness.

• Oil Change:
  • Old oil becomes contaminated and loses its lubricating properties.
  • Draining the old oil and replacing it with fresh oil ensures optimal lubrication.
• Oil Filter Change:
  • The oil filter traps contaminants, preventing them from circulating through the engine.
  • Replacing the filter regularly prevents it from becoming clogged and ineffective.

Why it matters:

• By changing the oil and filter, you remove abrasive particles, and sludge that can cause excessive wear.
• Fresh oil will have the correct viscosity, and additives to protect the internal engine parts.
• A clean oil filter will ensure proper oil flow.

Engine Tune-Up

An engine tune-up aims to restore optimal engine performance by addressing various factors, including the valve train, engine timing, and ignition timing.

Valves:

Purpose: Valves control the intake of air-fuel mixture and the exhaust of combustion gases. Proper valve operation is essential for efficient engine performance.

Tune-up Procedures:

• Valve Lash Adjustment: Adjusting the clearance between the valve stem and the rocker arm or tappet. Incorrect valve lash can lead to noise, reduced performance, and valve damage.
  • This is done by using feeler gauges to measure the clearance, and then adjusting the set screws or shims to obtain the correct clearance.
• Valve Inspection: Visually inspecting valves for wear, damage, or carbon buildup.
• Valve Stem Seal Replacement: Replacing worn valve stem seals to prevent oil leakage into the combustion chamber.
• Compression Test: a compression test can be used to determine if the valves are sealing correctly.

Importance:

Properly adjusted valves ensure proper cylinder sealing, optimal combustion, and efficient engine operation.

Engine Timing:

Purpose: Engine timing refers to the coordination of the crankshaft and camshaft(s). It ensures that valves open and close at the correct times relative to piston movement.

Tune-up Procedures:

• Timing Belt/Chain Inspection: Inspecting the timing belt or chain for wear, damage, or proper tension.
• Timing Belt/Chain Replacement: Replacing worn or damaged timing belts or chains to prevent engine damage.
• Camshaft Timing Adjustment: Adjusting the camshaft timing to ensure proper valve timing. Modern engines use variable valve timing, which is adjusted by the engine control unit.
• Crankshaft position sensor and camshaft position sensor checks: These sensors provide the engine control unit with information about the engine timing, and should be checked.

Importance:

Correct engine timing is crucial for optimal engine performance, fuel efficiency, and emissions control.

Ignition Timing:

Purpose: Ignition timing refers to the timing of the spark plug firing in relation to piston position. It ensures that the air-fuel mixture ignites at the optimal moment for efficient combustion.

Tune-up Procedures:

• Distributor Inspection/Adjustment (Older Engines): Inspecting and adjusting the distributor to ensure proper spark timing. Modern vehicles do not use distributors.
• Ignition Timing Check (Modern Engines): Checking the ignition timing using a scan tool or timing light. Modern engines control ignition timing electronically.
• Spark Plug Inspection/Replacement: Inspecting and replacing worn or fouled spark plugs.
• Ignition Coil Inspection: Checking the ignition coils for proper operation.

Importance:

Correct ignition timing ensures complete combustion, optimal power output, and reduced emissions.