The purpose of the engine run-in is to permit newly installed parts to burnish or wear in piston rings to seat against cylinder walls, and valves to become seated.

The purpose of the engine run-in is to permit newly installed parts to burnish or wear in piston rings to seat against cylinder walls, and valves to become seated.

• A. Test for leaks
• B. Shorten the run duration
• C. Engine run-in
• D. Improve fuel economy

Answer: (C)

The main concept is that an engine run-in is performed to seat newly installed parts by allowing burnishing wear where they contact each other. When rings are first installed, the mating surfaces of the piston rings and cylinder walls aren’t perfectly smooth or matched yet. Through controlled operation, the rings wear just enough to form a proper seal against the cylinder walls, and the valve faces seat against their seats so combustion occurs efficiently. This seating reduces blow-by, improves compression, and helps ensure reliable operation as the components finish mating. The statement that matches this purpose is the one describing engine run-in itself. It isn’t about testing for leaks, which is done with separate checks; it isn’t about shortening the run to save time—insufficient run-in can leave poor seating; and while fuel economy may improve after proper seating, the run-in’s primary goal is to achieve correct seating and sealing of rings and valves.

The main concept is that an engine run-in is performed to seat newly installed parts by allowing burnishing wear where they contact each other. When rings are first installed, the mating surfaces of the piston rings and cylinder walls aren’t perfectly smooth or matched yet. Through controlled operation, the rings wear just enough to form a proper seal against the cylinder walls, and the valve faces seat against their seats so combustion occurs efficiently. This seating reduces blow-by, improves compression, and helps ensure reliable operation as the components finish mating.

The statement that matches this purpose is the one describing engine run-in itself. It isn’t about testing for leaks, which is done with separate checks; it isn’t about shortening the run to save time—insufficient run-in can leave poor seating; and while fuel economy may improve after proper seating, the run-in’s primary goal is to achieve correct seating and sealing of rings and valves.