Question 16 AEL01 - Assistant Engineer - Limited

The Correct Answer is B **Explanation for why Option B (knurling the piston skirt surface) is correct:** Knurling is a specific repair technique used to temporarily increase the effective diameter of a worn piston skirt, particularly when replacement parts are unavailable. The knurling process uses a specialized tool to displace metal on the skirt surface, creating a crisscross pattern of raised ridges. These raised ridges compensate for the wear (loss of diameter) that has occurred. This expansion restores the necessary clearance between the piston and the cylinder liner, improving lubrication retention and reducing piston slap, thereby extending the service life of the worn component until proper replacement can be sourced. **Explanation for why the other options are incorrect:** * **A) turning down the piston skirt to concentric values:** This process involves removing material, which would decrease the piston diameter, exacerbating the clearance issues caused by wear and increasing piston slap. This would significantly shorten the service life. * **C) building up the piston skirt with a liquid epoxy material and then re-machining:** While building up the skirt diameter is the goal, using liquid epoxy for highly stressed, high-temperature components like diesel pistons is unsuitable. Epoxy materials lack the necessary mechanical strength, heat resistance, and wear characteristics to survive the operational environment of a diesel engine, leading to rapid failure and potentially catastrophic engine damage. * **D) increasing the dimensions of the ring land grooves:** The ring lands (the areas where the piston rings sit) are critical for sealing and heat transfer. Increasing their dimensions (usually depth or width) addresses ring wear, not piston skirt wear. Furthermore, improperly modifying these dimensions can compromise the structural integrity of the piston or negatively affect ring sealing and function.