Question 7 MODE01 - Chief MODU Engineer

The Correct Answer is C **Explanation for C (Correct Option):** Option C, "The piston has a replaceable crown," is correct because illustration MO-0067 typically depicts a large, built-up, or composite piston used in heavy-duty or marine diesel applications. These pistons are designed in two primary sections: a steel or high-strength alloy crown (top section) bolted to a cast iron or aluminum skirt (lower section). This built-up construction allows the highly stressed crown, which manages combustion heat and ring wear, to be replaced independently of the skirt, saving maintenance costs and time. The defining characteristic of this type of piston architecture is the **replaceable crown**. **Explanation for Incorrect Options:** **A) The piston has five compression rings.** This is typically incorrect. While some older or specialized engines might use more rings, modern heavy-duty engines generally minimize friction and aim for high efficiency, usually utilizing only two or three compression rings. Five compression rings would be excessive and inefficient for most modern diesel designs represented by such technical illustrations. **B) The piston has one oil scraper ring.** This is a specific numerical detail that may or may not be true depending on the exact engine model shown. Many large trunk pistons use two oil control or scraper rings for effective oil management, or they might integrate the scraper function into the lowest compression ring groove. Since the presence of a replaceable crown is a fundamental architectural certainty for this class of component, specific ring count details like "one" are less universally accurate than the structural design itself. **D) All of the above.** Since options A and B are incorrect, option D cannot be correct.