Question 25 3AE01 - Third Assistant Engineer

The Correct Answer is D **Why Option D is Correct:** During normal operation, the piston rings travel up and down the cylinder liner. The top ring, which reverses direction just below the top of the liner, wears away the liner material in the area of its travel. However, a small portion of the liner above the highest point of the top ring's travel remains untouched and retains its original diameter. This difference in diameter creates a wear ridge (or carbon ridge, depending on the engine type and operating conditions) at the very top of the liner. When the piston is being removed during maintenance, the top piston ring (which is generally larger in diameter due to wear and expansion than the unworn bore at the top) encounters this ridge. If the ridge is not removed, forcing the piston through it can cause the rigid top ring to be severely compressed or bent, leading to the **breaking of the rings, ring lands (the grooves on the piston that hold the rings), or both**. **Why the Other Options are Incorrect:** * **A) Excessive ring wear during the seating period:** The seating period occurs primarily when new rings are installed, and they adapt to the cylinder bore profile. While the ridge might slightly complicate the seating of *new* rings, its primary danger lies in piston removal, not excessive wear during the seating process itself. * **B) Excessive lubrication of the top ring:** The wear ridge is a mechanical obstruction and does not directly cause excessive lubrication. Lubrication is managed by the oil control rings and the cylinder lubrication system. * **C) Improper coating of lubrication on the cylinder wall:** While the uneven surface created by the ridge may affect oil film continuity slightly, it is a localized issue at the very top of the stroke. The primary function of providing lubrication is not severely impaired by this ridge, and the immediate, critical danger remains the mechanical interference during disassembly.