Question 39 3AE01 - Third Assistant Engineer

The Correct Answer is D ### Explanation of Correct Option (D) **D) Overheated motor windings:** When an auxiliary diesel engine fails to start and the starting system is repeatedly engaged, the electric starting motor draws very high currents. This repeated, high-load operation without sufficient cooling causes the motor windings to rapidly heat up. As the temperature of the copper windings increases, their electrical resistance significantly rises. According to Ohm's Law ($V = IR$), increased resistance for a given battery voltage ($V$) reduces the current ($I$) that the motor can draw. Since the torque produced by a DC starting motor is directly proportional to the current it draws, the reduction in current leads to a substantial loss of torque and power, causing the engine to crank very slowly. ### Explanation of Incorrect Options **A) Low lube oil viscosity:** Low viscosity (thin oil) would actually reduce the friction and resistance within the engine, making it easier for the starting motor to crank the engine, potentially leading to faster, not slower, cranking speeds. **B) Low compression pressure:** Low compression pressure (due to worn rings or leaking valves) makes the engine easier to turn over, as the starting motor expends less energy overcoming the compression resistance. While low compression is a major reason for the engine *failing* to start (ignition issue), it would not cause the starting motor itself to crank the engine slowly; if anything, it might allow the motor to crank *faster*. **C) Ring gear with broken teeth:** Broken teeth on the ring gear (or starter pinion) would lead to intermittent engagement or a complete failure to engage/transfer torque when the pinion hits the damaged section. It would result in a sudden clunk or grinding noise and no rotation, but it would not cause a continuous, consistent, *slow cranking speed* after the engine is engaged.