The service life of a worn aluminum piston for an auxiliary diesel, for which no spares are readily available, can be extended by __________.

Correct Answer: Option A — knurling the piston skirt surface

Knurling an aluminum piston skirt raises ridges of metal via mechanical displacement, effectively expanding the outer diameter and creating microscopic pockets that retain lubricating oil. This approved salvage technique restores proper operational clearance within the cylinder liner for worn auxiliary components.