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5.1 Describe how a wet compression test is done on an internal combustion engine - NSC Mechanical Technology Automotive - Question 5 - 2022 - Paper 1
Question 5
5.1 Describe how a wet compression test is done on an internal combustion engine. 5.2 Explain the functions of the following tests done on an internal combustion en... show full transcript
Worked Solution & Example Answer:5.1 Describe how a wet compression test is done on an internal combustion engine - NSC Mechanical Technology Automotive - Question 5 - 2022 - Paper 1
Step 1
Describe how a wet compression test is done on an internal combustion engine.
Answer
To perform a wet compression test, follow these steps:
- Remove the spark plug from the cylinder being tested.
- Pour or squirt a small amount of oil into the cylinder through the spark plug hole to help seal any potential leaks.
- Insert a compression gauge into the spark plug hole.
- Turn the engine over using the starter motor while keeping the throttle wide open to get an accurate reading.
- Record the reading on the gauge.
- Compare the results with the dry compression test results to assess the condition of the piston rings and cylinder walls.
Step 2
Explain the functions of the following tests done on an internal combustion engine: 5.2.1 Compression test
Answer
The compression test measures the pressure inside the cylinder created by the piston. This test helps in identifying the health of the piston rings and cylinder walls. If the pressure is low, it may indicate wear or damage that could affect engine performance.
Step 3
Explain the functions of the following tests done on an internal combustion engine: 5.2.2 Cylinder leakage test
Answer
The cylinder leakage test determines the percentage of air leakage from the cylinder. It indicates the presence of worn piston rings, valve issues, or gasket failures. By identifying where the leakage occurs, mechanics can pinpoint specific problems that need to be addressed.
Step 4
State FOUR precautions to be taken when using a gas analyser.
Answer
- Ensure the inlet hose is not stepped on.
- Confirm that hose connections are airtight and valves are closed properly.
- Avoid allowing exhaust leaks during the measurement process.
- Make sure the area is well-ventilated to prevent gas build-up.
Step 5
Explain how the optical alignment gauges are used to measure wheel alignment after they have been calibrated.
Answer
To measure wheel alignment using optical alignment gauges, you should:
- Center the steering on the car before testing.
- Position the tracking gauge against each front wheel.
- Use the periscope to identify the alignment mark.
- Adjust the triangle on the periscope for accurate readings of toe-in and toe-out.
Step 6
Describe how you would conduct a computerised diagnostic test on a vehicle using the on-board diagnostics (OBD-II) scanner.
Answer
To conduct a computerized diagnostic test:
- Plug the OBD-II scanner into the vehicle's diagnostic port.
- Turn on the vehicle's ignition without starting the engine.
- Start the diagnostic scan using the scanner.
- Retrieve the trouble codes, read the diagnostic data, and analyze any issues indicated by the codes.
Step 7
Name TWO methods used to balance the wheels of a motor vehicle.
Answer
- Dynamic balance: This method involves spinning the wheel and measuring the imbalance to adjust weights accordingly.
- Static balance: This method positions the wheel on a flat surface, allowing any heavy spots to settle at the bottom, indicating where to add weights.