FAA Powerplant Written Practice Test

What is a primary purpose of the run-in procedure after overhauling a piston engine?

1. To improve fuel flow

2. Seating the piston rings

3. Increasing engine temperature

4. Inspecting for leaks

The correct answer is: Seating the piston rings

The primary purpose of the run-in procedure after overhauling a piston engine is to seat the piston rings. This is crucial because properly seated piston rings create a good seal between the combustion chamber and the crankcase, which enhances engine efficiency and performance. During the run-in, the engine is operated under controlled conditions, allowing the rings to wear slightly against the cylinder walls to achieve optimal contact. This process helps to prevent oil consumption, blow-by, and ensures the engine operates effectively at full capacity. While improving fuel flow, increasing engine temperature, and inspecting for leaks are all important maintenance considerations, they are not the main objective during the run-in procedure specifically aimed at ensuring the longevity and performance of the piston rings.