Engines and Engine Systems

Motors and Engine Systems

This chapter covers all the knowledge required for the Red Seal exam as an agricultural equipment technician, specifically on diesel and gasoline engines, their auxiliary systems, diagnostic procedures, and applicable Canadian standards. You must master operating principles, tolerances, torque specifications, tune-up procedures, and performance calculations.

Diesel Engine Operating Principles

Four-Stroke Diesel Cycle

The modern agricultural diesel engine operates on the four-stroke cycle, invented by Rudolf Diesel. The four phases are:

Key point for the exam: Fuel injection occurs before TDC, with a typical advance of 10° to 25° of crankshaft rotation. The ignition delay is the time between the start of injection and the actual start of combustion.

Two-Stroke Cycle

Some high-power agricultural diesel engines (e.g., articulated tractors) use the two-stroke cycle. Each crankshaft revolution produces a power stroke. The distinctive feature is the use of a scavenging blower to expel burned gases and admit fresh air. The compression ratio is similar, but volumetric efficiency is harder to maintain.

Diesel vs. Gasoline Engine Comparison

Engine Mechanical Components

Cylinder Block and Liners

The cylinder block, made of gray cast iron or aluminum alloy (lightweight engines), supports all mechanical stresses. Liners are classified into two types:

Measurement procedure: Use a dial bore gauge to measure ovality and taper. The maximum wear tolerance is generally 0.05 mm to 0.10 mm depending on the manufacturer. Beyond that, reboring or replacement is required.

Pistons, Rings, and Wrist Pins

The aluminum alloy piston must withstand temperatures of 300 °C to 400 °C at the crown. The rings perform three functions:

Ring end gap: Ring end gap must be measured by inserting the ring into the cylinder, pushed with an inverted piston to keep it perpendicular. Typical values: 0.20 mm to 0.45 mm for the compression ring. Excessive gap indicates cylinder wear.

Piston-to-liner clearance: Measured at the piston skirt, perpendicular to the pin axis. Typical value: 0.05 mm to 0.15 mm. Insufficient clearance causes seizure; excessive clearance causes knocking and oil consumption.

Crankshaft and Bearings

The forged steel crankshaft converts linear motion into rotation. Main bearings and connecting rod bearings are steel shells coated with an anti-friction alloy (babbit, copper-lead, aluminum-tin).

Torque specifications: Always consult the manufacturer's manual. Connecting rod bolts are often angle-tightened (e.g., 60 N·m + 60° + 30°). Never reuse connecting rod bolts after loosening — they are torque-to-yield (plastic deformation) fasteners.

Bearing clearance: Measured with Plastigage. Typical value: 0.025 mm to 0.075 mm for a main bearing. Excessive clearance reduces oil pressure; insufficient clearance causes seizure.

Cylinder Head and Head Gasket

The cylinder head, made of cast iron or aluminum, contains the valves, injectors, and coolant passages. The head gasket must withstand high combustion pressures and thermal variations.

Cylinder head flatness: Check with a straightedge and feeler gauges. The maximum allowable deformation is 0.05 mm over 150 mm of length. Resurfacing can be performed, but respect the minimum head height specified by the manufacturer.

Head bolt tightening: Follow the spiral sequence from the center outward, in several passes (e.g., 40 N·m, then 80 N·m, then 120 N·m, then an angular tightening of 90°). Torque-to-yield (TTY) head bolts must be replaced systematically.

Diesel Fuel Injection System

Injectors and Pumps

The injection system must deliver fuel at very high pressure, at the right time, in the right quantity, and with perfect atomization. The main types:

Common rail: The high-pressure pump feeds an accumulator (rail) common to all injectors. The injectors are electronically controlled by solenoid valves. Injection timing and injection duration are precisely controlled, allowing pilot injections (pre-injection) to reduce noise and emissions.

Injector testing: On a test bench, check the opening pressure (e.g., 220 bar ± 5 bar), sealing (no dripping at 100 bar below opening pressure), and spray pattern (regular cone, no streams).

Governor

The governor maintains constant engine speed despite load variations. Types:

Maximum speed adjustment: The maximum no-load speed (high idle) must be set according to manufacturer specifications, generally 3,600 to 4,200 RPM for small engines, 2,200 to 2,500 RPM for large ones. The rated speed (full load) is approximately 100 to 200 RPM lower.

Injection Timing

Timing determines the precise moment of injection relative to TDC. Incorrect timing causes:

Timing procedure: Remove the timing cover, rotate the engine to the timing mark on the flywheel, and verify that the mark on the pump aligns with the one on the mounting bracket. Use a dial indicator to measure pump lift at the injection point.

Cooling System

Components and Functions

The cooling system maintains engine temperature between 80 °C and 95 °C. Components:

Coolant

Coolant is a mixture of water, ethylene glycol (or propylene glycol), and corrosion inhibitors. The recommended ratio is 50/50, providing protection down to -37 °C and a boiling point of 108 °C at atmospheric pressure.

Maintenance: Test the pH (must be between 7.5 and 9.0), glycol concentration (refractometer), and inhibitors (test strips). Replace the coolant according to the manufacturer's interval (often 2 years or 4,000 hours).

Common Problems

Lubrication System

Oil Circuit

The circuit includes: oil pan, oil pump (gear or rotor type), filter, oil cooler, and lubrication passages. Typical oil pressure is 2 to 5 bar when hot, at operating speed.

Pump types:

Oil filter: The full-flow filter filters all the oil. The bypass filter filters a portion of the oil continuously, providing finer filtration.

Engine Oils

Oils are classified according to API (American Petroleum Institute) and ACEA (Association des Constructeurs Européens d'Automobiles) standards. For agricultural diesel engines, common classes are:

SAE viscosity: Viscosity is indicated by a code (e.g., 15W-40). The first number (15W) indicates cold viscosity, the second (40) hot viscosity. The choice depends on ambient temperature:

Oil analysis: Spectrometric analysis detects wear metals (iron, copper, lead, aluminum), contaminants (silica, glycol, fuel), and additive condition. It is an essential predictive maintenance tool.

Intake and Exhaust System

Turbocharger

The turbocharger uses exhaust gas energy to compress intake air. It increases engine power by 30% to 50% without increasing displacement.

Components: Turbine (hot side), compressor (cold side), center shaft with floating bearings, and wastegate.

Lubrication: The shaft is lubricated by engine oil under pressure. A cool-down period of 1 to 2 minutes at idle before shutdown is recommended to prevent oil coking in the bearings.

Common problems:

Charge Air Cooler (CAC)

The charge air cooler (intercooler) lowers the temperature of compressed air from 120 °C to 150 °C down to 40 °C to 60 °C. Denser air contains more oxygen, improving combustion and reducing emissions.

Leak test: Pressurize the intake circuit to 1.0 to 1.5 bar and listen for leaks. A leak causes power loss and black smoke.

Exhaust System and Aftertreatment

Modern engines are equipped with aftertreatment systems to meet emissions standards:

Canadian standards: Off-road engines (including agricultural) must comply with the Off-Road Engine Emissions Regulations under the Canadian Environmental Protection Act (CEPA). The standards are aligned with US EPA Tier 4 standards.

Electrical and Electronic System

Batteries and Starting

Agricultural batteries are typically 12 V, with a capacity of 600 to 1,000 Ah (C20). Starting a diesel engine requires high current: 300 to 600 A at -18 °C.

Starting power calculation: The required power is approximately 0.1 kW per liter of displacement at normal temperature, and 0.2 kW per liter at -20 °C. A 6 L engine therefore requires 0.6 kW when hot and 1.2 kW when cold.

Glow plugs: Glow plugs heat the combustion chamber to 800 °C to 1,000 °C in 5 to 10 seconds. Their typical resistance is 0.5 to 1.0 Ω. A resistance test with an ohmmeter can detect a faulty glow plug.

Sensors and Actuators

Modern engines use many sensors:

OBD diagnostics: Agricultural engines use the ISO 11783 (ISOBUS) or J1939 protocol for communication. A diagnostic tool (e.g., multi-brand diagnostic electronics) allows reading fault codes (DTCs) and live data.

Diagnostic and Maintenance Procedures

Compression Test

The compression test measures the pressure in each cylinder. Procedure:

Typical values: 25 to 35 bar for a diesel engine in good condition. The difference between cylinders must not exceed 10%. Low pressure in one cylinder indicates ring wear, valve issues, or a faulty head gasket.

Leak-Down Test

The leak-down test identifies the source of compression loss. You apply air pressure (6 to 7 bar) into the cylinder at TDC and listen:

Exhaust Smoke Analysis

Smoke color is a diagnostic indicator:

Engine Tune-Up

A complete tune-up includes:

Canadian Standards and Regulations

Canadian Electrical Code

The Canadian Electrical Code, Part I (CE Code) applies to electrical installations, including those on agricultural equipment. Rule 8-200 concerns the calculation of electrical load for motors. For a single-phase motor, the rated current is used; for a three-phase motor, the current is calculated using the formula:

I = P / (√3 × U × cos φ)

Where:

Rule 28-100: Motor overload protection. The protection device must be set at 125% of the rated current for motors with a service factor of 1.15.

CSA B149.1

The CSA B149.1 - Natural Gas and Propane Installation Code applies to engines operating on propane or natural gas. Key requirements:

Occupational Health and Safety Regulations

The Occupational Health and Safety Act and its regulations require technicians to use appropriate personal protective equipment (PPE), including safety glasses, chemical-resistant gloves, and hearing protection. Lockout/tagout procedures are mandatory before any intervention on a running or energized engine.

Common Pitfalls to Avoid

Summary