Diesel Mechanic Trade (ALP)

Diesel Mechanic trade covers diesel engines, fuel systems, cooling, electrical.

Diesel engine basics:

• 4-stroke: intake, compression, power, exhaust.
• 2-stroke: less common in railway use.
• Compression ignition (no spark plug).
• Compression ratio: 14:1 to 22:1 (much higher than petrol).

Engine components:

• Cylinder block: main body.
• Pistons + rings: seal combustion chamber.
• Crankshaft: converts reciprocating → rotation.
• Camshaft: opens/closes valves.
• Valves: intake + exhaust.
• Connecting rod: piston to crankshaft.
• Flywheel: smooth power output.

Fuel system:

• Tank → filter → pump → injectors.
• Mechanical injection (older).
• Common rail direct injection (CRDI): modern, electronic.
• Fuel injection pressure: 1500-2000+ bar in modern engines.

Cooling system:

• Air-cooled (small engines, motorcycles).
• Liquid-cooled (most automotive, railway diesel locos).
• Components: radiator, water pump, thermostat, fan.

Lubrication system:

• Oil sump → pump → filter → galleries → returns.
• Oil grade: SAE 10W-30, 15W-40, etc.
• Functions: reduce friction, cool, clean, seal.

Electrical system:

• Battery: 12V (cars), 24V (trucks, locos).
• Alternator: charges battery, runs accessories.
• Starter motor: cranks the engine.
• Glow plug: helps cold-start in diesel.
• Sensors: temperature, pressure, RPM.

Diesel Locomotive specifics:

• WDM-3A, WDP-4: common Indian diesel locos.
• Power output: 3000-4000 HP.
• Diesel-Electric transmission: diesel engine → DC generator → DC traction motors.
• Marhowra factory (Bihar): builds modern diesel locos.

Common faults:

• Hard starting → fuel filter, glow plugs.
• Low power → injectors, air filter.
• Overheating → coolant level, thermostat, radiator.
• Excessive smoke → fuel, injectors.

Maintenance:

• Daily checks: oil level, coolant, fuel.
• Periodic: filter change, valve adjustment, injector cleaning.

Tools:

• Spanners (open, ring), socket set, torque wrench, multimeter, compression tester, injector tester, micrometer.

Safety:

• Diesel is flammable; no smoking.
• Hot engine: wait to cool.
• Battery: avoid shorts.

RRB ALP focus: 4-stroke cycle, engine components, diesel-electric transmission for locos.