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Nelson conducted a compression test on a four-cylinder petrol engine and found that the engine has low compression in one of the cylinders - NSC Mechanical Technology Automotive - Question 5 - 2019 - Paper 1
Question 5
Nelson conducted a compression test on a four-cylinder petrol engine and found that the engine has low compression in one of the cylinders. 5.1.1 Name TWO types of ... show full transcript
Worked Solution & Example Answer:Nelson conducted a compression test on a four-cylinder petrol engine and found that the engine has low compression in one of the cylinders - NSC Mechanical Technology Automotive - Question 5 - 2019 - Paper 1
Step 1
5.1.1 Name TWO types of compression tests Nelson can perform on the engine.
Answer
Nelson can perform the following two types of compression tests on the engine:
- Wet Test: This involves adding a small amount of oil to the cylinder to check if compression improves, which indicates worn piston rings or cylinder walls.
- Dry Test: This test measures the engine’s compression without any oil added and checks the basic condition of the cylinder and piston rings.
Step 2
5.1.2 Give TWO possible reasons for low compression in the cylinder.
Answer
Two possible reasons for low compression in the cylinder are:
- Worn Cylinder Walls: Over time, the cylinder walls may wear down, leading to insufficient sealing and low compression.
- Leaking Piston Rings: If the piston rings are worn or damaged, they can fail to create a proper seal, allowing combustion gases to escape.
Step 3
5.2 Explain how static imbalance of a wheel is corrected using a wheel balancing.
Answer
Static imbalance of a wheel can be corrected by:
- Applying Weights: A small mass or weight is placed on the wheel rim at the location directly opposite the heavy spot until the wheel is balanced.
- Checking Balance: The wheel is re-checked to ensure that it rotates evenly without vibrations.
Step 4
5.4 Give TWO reasons for a high CO reading.
Answer
Two reasons for a high CO reading are:
- Too Rich Mixture: An imbalance in the air-fuel mixture where there is not enough air can cause incomplete combustion, leading to higher CO emissions.
- Faulty Injectors: Clogged or malfunctioning fuel injectors can deliver excess fuel, contributing to elevated CO levels.
Step 5
Step 6
5.5.2 Explain how to take a caster reading on the wheels of a motor vehicle using the wheel alignment equipment in FIGURE 5.5.
Answer
To take a caster reading, follow these steps:
- Ensure that the wheels are straightened and the turntables are on zero.
- Fit the gauge to the centre of the wheel.
- Turn the front of the wheel 20° inwards.
- Zero the castor scale.
- Turn the wheel through 40° in the opposite direction and take the reading on the castor scale.
Step 7
5.6 Which information is required by the diagnostic scanner before a diagnostic test can be conducted on an internal combustion engine?
Answer
The information required by the diagnostic scanner includes:
- Vehicle Identification Number (VIN): This helps identify the specific vehicle model and engine specifications.
- Make and Model of the Vehicle: Necessary for compatibility with the diagnostic tool.
- Engine Type: To ensure that the correct diagnostics procedures are followed.