Engine Performance & Tuning Flashcards
7 cards from real MTC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Engine Performance & Tuning flashcards as text
When performing a cylinder leak-down test on a marine engine, what does a reading of 25% leakage indicate?
Answer: Excessive leakage requiring investigation
Leak-down readings above 20% generally indicate excessive leakage from worn rings, bad valves, or head gasket failure requiring further diagnosis.
What is the correct procedure for setting valve clearance on an overhead cam marine engine?
Answer: Set clearance with the cam lobe pointing away from the follower
Valve clearance must be set when the cam lobe points away from the follower (valve fully closed) so the clearance is measured at the base circle.
A two-stroke marine engine produces excessive power loss. Air-cooled reeds are found worn and not sealing. What is the likely result of this condition?
Answer: Loss of crankcase compression and poor scavenging
Worn reed valves allow air/fuel mixture to escape back into the intake, reducing crankcase pressure and scavenging efficiency, causing significant power loss.
Which of the following best describes volumetric efficiency in a marine engine?
Answer: The ratio of actual air/fuel mixture drawn in vs. theoretical cylinder volume
Volumetric efficiency is the ratio of actual air volume inducted into the cylinder compared to the theoretical displacement volume, expressed as a percentage.
On a marine engine with electronic fuel injection, a MAP sensor reading lower than actual manifold pressure would cause the ECM to:
Answer: Lean the fuel mixture
If the MAP sensor reads lower pressure than actual, the ECM calculates less air entering the engine and commands less fuel, causing a lean condition.
What is the primary function of a harmonic balancer on a marine engine crankshaft?
Answer: Dampen torsional vibration in the crankshaft
A harmonic balancer absorbs and dampens torsional vibration (twisting forces) generated by combustion pulses in the crankshaft to prevent fatigue failure.
A marine technician observes that engine oil pressure drops significantly at operating temperature but is normal when cold. The MOST likely cause is:
Answer: Worn main and rod bearings
Worn bearing clearances allow increased oil flow and pressure loss; hot oil is thinner, making the pressure drop more pronounced at operating temperature.