What is the main purpose of engine run-in?

What is the main purpose of engine run-in?

• A. To condition the lubrication system
• B. To verify ignition timing
• C. To burnish piston rings and seat valves
• D. To test for leaks

Answer: (C)

During engine run-in, the main goal is for the moving friction surfaces to mate and form proper seals. Piston rings must wear against the cylinder walls to create a gas-tight seal, and the valve faces must seat against their seats to stop leakage on compression and exhaust strokes. This initial, controlled wear smooths the roughness of those surfaces so combustion gases stay in the cylinder and oil isn’t sucked into the combustion chamber. While the lubrication system and general reliability improve during the run-in, the central purpose is establishing these seals. Verifying ignition timing or performing a leak check may be done as part of broader checks, but they are not the primary objective of the run-in itself.

During engine run-in, the main goal is for the moving friction surfaces to mate and form proper seals. Piston rings must wear against the cylinder walls to create a gas-tight seal, and the valve faces must seat against their seats to stop leakage on compression and exhaust strokes. This initial, controlled wear smooths the roughness of those surfaces so combustion gases stay in the cylinder and oil isn’t sucked into the combustion chamber. While the lubrication system and general reliability improve during the run-in, the central purpose is establishing these seals. Verifying ignition timing or performing a leak check may be done as part of broader checks, but they are not the primary objective of the run-in itself.