Engine Systems and Repair Flashcards

What is the primary purpose of the crankshaft in an internal combustion engine?

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.

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?

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.

What is the correct method for measuring crankshaft journal wear?

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.

What does excessive blue smoke from the exhaust at startup indicate?

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.

What is the function of the harmonic balancer on a crankshaft?

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.

During a cylinder leakage test, air is heard escaping from the tailpipe. What component is most likely at fault?

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.