258 – C’mon Does Valve Lapping Really Work?!
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In this episode of the Airplane Owner Maintenance Podcast, host Dean Showalter dives deep into the controversial yet effective practice of valve lapping, responding to listener questions and sharing a detailed personal story from a recent annual inspection on a turbocharged Bonanza with a Tornado Alley system. The episode begins with a heartfelt update on a previous fix for a rough-running Aerostar engine, followed by a gripping listener story about a near-emergency landing due to a failing magneto in a Stinson 108. Dean emphasizes the importance of in-flight mag checks and situational awareness. He then transitions into the core topic: valve lapping. Using a real-world example where cylinder one showed low compression (44/80), Dean explains his meticulous process—changing the rotocoil, installing new springs, lapping the exhaust valve aggressively with minimal compound, and performing a thorough cleanup with avgas and compressed air. After reassembly, compression jumped to 65/80, proving the method’s effectiveness. Dean defends valve lapping against skeptics, citing years of successful applications and the importance of proper technique and cleanup. He also shares how a mechanic’s resistance to learning new methods led a pilot to seek his help, reinforcing the value of continuous learning in aviation maintenance. The episode closes with a reflection on the joy of flying, including a recent King Air 350 flight to Charlotte.
Valve lapping is a highly effective, non-invasive method to improve compression and fix exhaust valve leaks in Continental engines when done correctly.
Always replace the rotocoil and consider new springs when lapping an exhaust valve—these are low-cost, high-impact upgrades.
Thorough post-lapping cleanup with avgas, compressed air, and a microfiber cloth is critical to prevent debris from causing damage.
Compression testing, when done with precision and consistency, remains a valuable diagnostic tool for cylinder health.
Proactive maintenance like bore scoping and compression testing can prevent in-flight emergencies and avoid premature cylinder removal.
…and 2 more takeaways available in PodZeus
Welcome & Episode Preview
Dean welcomes listeners to the podcast, introduces the episode's theme—whether valve lapping really works—and previews the story of a recent inspection on a turbocharged Bonanza with low compression.
Listener Story: Stinson 108 Mag Failure
“Had I done a mag check in flight, I could likely have flown it back home on one mag and spared some follow-up drama.”
Aerostar Engine Fix & Listener Feedback
Dean updates listeners on the successful resolution of a rough engine in an Aerostar, attributing it to cleaning fuel injector airlines. He shares several appreciative emails from listeners, including one about a family flight in a Stinson and another about visiting the Pensacola Naval Aviation Museum.
The Valve Lapping Story: Low Compression Diagnosis
“I ran the engine for the annual inspection... I could only get it up to 44 out of 80. I was not at all concerned about the operation of this engine... but the compression number was a red flag.”
The Lapping Process & Best Practices
“I just put on like a tiny bit, tiny bit at a time... Way too much. I just put on like a tiny bit, tiny bit at a time.”
“Had I done a mag check in flight, I could likely have flown it back home on one mag and spared some follow-up drama.”
“After I put everything back together... I was able to get a good solid 65 out of 80. So I was super happy with that, and that was even before I ran the engine.”
“If people don't want to learn and change, that's their decision. But for me, I want to continue learning all I can all along the way.”
Host
Dean Showalter
person
Airplane Owner Maintenance Podcast
media
Aerostar
other
Bonanza
other
Rotocoil
other
Valve Lapping Compound
product
Avgas
other
Stinson 108
other
Tim Barnes
person
Justin
person
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