MTC Engine Performance & Tuning 3

Question 1

When performing a cylinder leak-down test on a marine engine, what does a reading of 25% leakage indicate?

Accepted Answer

Excessive leakage requiring investigation

Answer

Leak-down readings above 20% generally indicate excessive leakage from worn rings, bad valves, or head gasket failure requiring further diagnosis.

Question 2

What is the correct procedure for setting valve clearance on an overhead cam marine engine?

Accepted Answer

Set clearance with the cam lobe pointing away from the follower

Answer

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.

Question 3

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?

Accepted Answer

Loss of crankcase compression and poor scavenging

Answer

Worn reed valves allow air/fuel mixture to escape back into the intake, reducing crankcase pressure and scavenging efficiency, causing significant power loss.

Question 4

Which of the following best describes volumetric efficiency in a marine engine?

Accepted Answer

The ratio of actual air/fuel mixture drawn in vs. theoretical cylinder volume

Answer

Volumetric efficiency is the ratio of actual air volume inducted into the cylinder compared to the theoretical displacement volume, expressed as a percentage.

Question 5

On a marine engine with electronic fuel injection, a MAP sensor reading lower than actual manifold pressure would cause the ECM to:

Accepted Answer

Lean the fuel mixture

Answer

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.

(MTC) Marine Technician Certification Practice Test

(MTC) Marine Technician Certification Practice Test

MTC Engine Performance & Tuning 3