ITI Mechanic Diesel Viva Questions and Answers
In the mechanic diesel practical, you usually dismantle, check or adjust part of an engine, and the examiner then asks how a diesel engine works and why you did each step. These are the questions asked most often, with short answers.
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Correct tools and sequence, measurements against specifications, and your understanding of the four-stroke cycle, the fuel system and engine faults.
Diesel mechanic viva questions with answers
Engine basics
What are the four strokes of a diesel engine?
Suction (only air), compression (air compressed and heated), power (fuel injected, ignites by heat of compression) and exhaust.
Why does a diesel engine not need a spark plug?
It is a compression-ignition engine: air is compressed so much (compression ratio about 15:1 to 22:1) that its temperature ignites the injected fuel.
What is the firing order of a four-cylinder engine?
Commonly 1-3-4-2 (some engines use 1-2-4-3).
What is tappet clearance and why is it needed?
The gap between the rocker arm and valve stem when the valve is closed. It allows for heat expansion so the valve closes fully. Set it on a cold engine as per the manual using a feeler gauge.
Fuel system
What is bleeding of a diesel fuel system?
Removing air from the fuel lines, filter and pump by loosening bleed screws and operating the primer pump until fuel flows without bubbles. Air in the system stops the engine from starting.
What does a fuel injector do?
Sprays fuel into the combustion chamber at high pressure as a fine atomised spray at the correct time.
Name the parts of the fuel system in order.
Fuel tank, feed (lift) pump, fuel filters, injection pump (or common-rail pump and rail), high-pressure pipes and injectors, with return lines.
Cooling, lubrication and faults
What does a thermostat do?
It keeps the coolant flowing in the engine until the engine reaches working temperature, then opens to send coolant to the radiator.
Why is engine oil used?
To reduce friction and wear, cool parts, clean, seal piston rings and prevent rust.
What does black smoke from a diesel engine indicate?
Incomplete combustion: excess fuel or too little air, such as a choked air filter, faulty injectors or overloading.
What do white and blue smoke indicate?
White: unburnt fuel at start or water/coolant entering the cylinder. Blue: engine oil burning, often from worn rings or valve guides.
Safety
What safety steps do you take before working under a vehicle?
Park on level ground, apply the hand brake, chock the wheels, support the vehicle on stands (never only on a jack) and disconnect the battery for electrical work.
Why should you never check injector spray with your hand?
The high-pressure fuel can pierce the skin and cause serious injury.
Your opening answer to practise
Copy the lines that are true for you, replace every [bracket] and delete the rest. Every number should be one you can repeat in a practical test.
Opening answer for the Mechanic Diesel viva
- My name is [name], roll number [number], trainee of ITI Mechanic Diesel, [ITI name], session [year].
- Today my practical job was [e.g. tappet setting on a four-cylinder engine and bleeding the fuel system].
- I followed the safety steps: [PPE worn], [tools checked], [area cleaned after work].
- The result: [measurement / test reading / output], within [tolerance / expected value].
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Common questions
What questions are asked in the ITI diesel mechanic viva?
Four-stroke cycle, compression ignition, firing order, tappet clearance, fuel-system bleeding, injectors, cooling and lubrication, smoke colours and workshop safety.
Which question is asked most often?
How a diesel engine ignites without a spark plug, and how to bleed the fuel system.
Do I need to remember specifications?
Know where to find them (the workshop manual) and the common ones for the engine you worked on, such as tappet clearance.
Can I get these viva questions as a PDF?
Open the page, choose Print in your browser menu, then Save as PDF. The page prints without menus.
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