Engine Break-In

Monday, November 23, 2020 at 10:57 AM ET

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On The Cover: A new, or freshly overhauled engine - including top overhauls - needs to be broken in. we're primarily concerned with seating the piston rings, but anytime an engine has undergone major work, it's appropriate to treat it as unproven. For more details see the article beginning on Page 16. Image by Patrick Allen/Dreamstime.com.

Key Takeaways:

An overhauled aircraft engine, despite being new or refurbished, carries an initial risk of "infant mortality," meaning new components can have a higher failure rate in their first few hours of operation.
Initial test flights after an overhaul prioritize safety, involving thorough pre-flight inspections, minimal ground time, high-power takeoffs with higher airspeeds for cooling, orbiting the airport, and continuous monitoring of engine instruments for leaks and abnormalities.
The primary goal of engine break-in is to properly seat the piston rings against the cylinder walls, which is best achieved by operating at high power settings and low altitudes to maximize internal cylinder pressures, while carefully managing heat.
The complete break-in period extends for approximately 25 hours, requiring alternating power settings, avoiding low manifold pressures during descent, and multiple oil and filter changes to monitor for wear and ensure stable oil consumption and cylinder head temperatures.

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By the time you read this, my Debonair should have a freshly overhauled engine holding down its nose. The story of how all that came to be is best told with a few adult beverages, but the bottom line is I will soon have a new hole in my wallet and a zero-since-major-overhual IO-520.

This isn’t my first engine overhaul with this plane, but it has been a while, so I sat down recently to review how I handled the previous one, update myself on the various recommendations and develop a plan for the plane’s next few flights. I came away with new appreciation and respect for test pilots.