310S Engine Systems and Repair 1 — Questions and Answers
Question 1: What is the primary purpose of the crankshaft in an internal combustion engine?
- To open and close the valves
- To convert reciprocating motion into rotational motion (Correct answer)
- To compress the air-fuel mixture
- To circulate coolant through the engine
Correct answer: To convert reciprocating motion into rotational motion
The crankshaft converts the reciprocating (up-and-down) motion of the pistons into rotational motion that can be transmitted to the drivetrain.
Question 2: A compression test on a four-cylinder engine shows cylinders 1, 2, and 4 at 150 psi, but cylinder 3 reads 90 psi. What should the technician do next?
- Replace the head gasket immediately
- Perform a wet compression test on cylinder 3 (Correct answer)
- Replace the piston rings on cylinder 3
- Condemn the engine block
Correct answer: Perform a wet compression test on cylinder 3
A wet compression test adds oil to the cylinder. If compression rises significantly, the rings are worn. If it stays low, the issue is likely valves or a head gasket leak.
Question 3: What is the correct method for measuring crankshaft journal wear?
- Feeler gauge between the journal and bearing
- Outside micrometer at multiple points on the journal (Correct answer)
- Dial indicator on the flywheel flange
- Vernier caliper across the journal diameter
Correct answer: Outside micrometer at multiple points on the journal
An outside micrometer is used to measure crankshaft journals at multiple points to check for out-of-round and taper conditions, which indicate wear.
Question 4: What does excessive blue smoke from the exhaust at startup indicate?
- Coolant leaking into the combustion chamber
- Worn valve stem seals allowing oil to seep into the cylinders (Correct answer)
- A rich fuel mixture condition
- Catalytic converter failure
Correct answer: Worn valve stem seals allowing oil to seep into the cylinders
Blue smoke at startup typically indicates worn valve stem seals. Oil pools on top of the valves when the engine is off and burns on the next startup.
Question 5: What is the function of the harmonic balancer on a crankshaft?
- To balance the weight of the flywheel
- To dampen torsional vibrations in the crankshaft (Correct answer)
- To drive the timing chain or belt
- To seal the front of the crankcase
Correct answer: To dampen torsional vibrations in the crankshaft
The harmonic balancer (vibration damper) absorbs and reduces torsional vibrations generated by the power pulses of the engine, preventing crankshaft fatigue and failure.
Question 6: During a cylinder leakage test, air is heard escaping from the tailpipe. What component is most likely at fault?
- Intake valve
- Exhaust valve (Correct answer)
- Head gasket
- Piston rings
Correct answer: Exhaust valve
Air escaping from the tailpipe during a leak-down test indicates that the exhaust valve is not sealing properly, allowing pressurized air to pass into the exhaust system.
310S Engine Systems and Repair 1
What is the primary purpose of the crankshaft in an internal combustion engine?