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Jack conducted a compression test on a four-cylinder petrol engine - NSC Mechanical Technology Automotive - Question 3 - 2016 - Paper 1
Question 3
Jack conducted a compression test on a four-cylinder petrol engine. He found that the engine has low compression. 3.1.1 Name TWO types of compression tests Jack can... show full transcript
Worked Solution & Example Answer:Jack conducted a compression test on a four-cylinder petrol engine - NSC Mechanical Technology Automotive - Question 3 - 2016 - Paper 1
Step 1
3.1.1 Name TWO types of compression tests Jack can perform on his car's engine.
Answer
Jack can perform the following two types of compression tests on his car's engine:
- Wet Compression Test: This test involves adding a small amount of oil to each cylinder before performing the compression test, which helps determine if the low compression is due to worn piston rings or cylinder walls.
- Dry Compression Test: In this test, the engine is cranked without any oil added, and it measures the baseline compression level in the cylinders.
Step 2
3.1.2 Give TWO reasons for low compression in the engine.
Answer
Two possible reasons for low compression in the engine are:
- Worn Piston Rings: Over time, piston rings can wear out, leading to a loss of compression as they fail to seal the combustion chamber effectively.
- Leaking Valve: If an intake or exhaust valve is leaking, it can cause loss of the compression, as the combustion gases escape instead of being contained in the cylinder.
Step 3
Step 4
3.3 Explain, in point form, the procedure when the cooling-system pressure tester is used to test the pressure in the cooling system.
Answer
The procedure for using a cooling-system pressure tester is as follows:
- Remove the Radiator Cap: Start by safely removing the radiator cap and fitting the tester.
- Pump Air into the System: Introduce air at the prescribed pressure into the cooling system.
- Note the Reading: Monitor the gauge reading; if it drops, it indicates a leak in the system.
- Testing for Leaks: To check for a leaking cylinder-head gasket, start the engine.
- Monitor Pressure while Running: Observe the pressure reading while the engine is operating; an increase in pressure suggests a leaking cylinder-head gasket.