MTC Transmission & Drivetrain Systems 3

Question 1

What causes a propeller shaft to vibrate excessively at higher RPM on an inboard vessel?

Accepted Answer

Shaft misalignment or a bent/damaged propeller

Answer

A bent shaft or damaged propeller creates an unbalanced rotating mass that produces vibration that worsens as RPM increases.

Question 2

What is the purpose of a cutlass bearing on an inboard propeller shaft?

Accepted Answer

Supports and lubricates the rotating shaft using water

Answer

The cutlass bearing is a water-lubricated rubber bearing in the strut or stern tube that supports the propeller shaft's outboard end.

Question 3

When bleeding air from a hydraulic marine transmission control system, the technician should:

Accepted Answer

Start at the highest point in the system and work downward to the actuator

Answer

Air rises, so bleeding from the highest point first ensures all trapped air is purged progressively down to the actuator.

Question 4

A stern drive unit that steers but does not trim is MOST likely caused by:

Accepted Answer

Hydraulic leak in the trim cylinder or low hydraulic fluid

Answer

The trim function relies on hydraulic pressure; a cylinder leak or low fluid level will disable trim while steering (mechanical) remains functional.

Question 5

What is the correct method for measuring propeller shaft runout?

Accepted Answer

Mount a dial indicator against the shaft and rotate it one full revolution

Answer

A dial indicator measures total indicated runout (TIR) as the shaft rotates, revealing bends or eccentricity that cause vibration.

(MTC) Marine Technician Certification Practice Test