248 - Mark's Cessna T210 Exhaust Valve Story

Last Monday, I lapped the #5 exhaust valve on a Continental engine. But more importantly, I met the owner / pilot of a Turbo Centurion, and now I’m happy to call him a good friend! Thanks for flying all the way up here Mark! Here’s the story: Mark had been a little concerned about the #5 exhaust valve, not because he was having any particular trouble with it, but because the borescope photo showed a slightly irregular appearance. And being proactive, Mark decided to do some research. That’s when he found me, and some of the information I’ve published to help airplane owners understand borescoping, exhaust valve lapping, and other useful pieces of information you often won’t find in the “maintenance manual.” Mark’s local shop had indicated it would be a good idea to keep an eye on the #5 exhaust valve, and if it continued to be a problem, the cylinder may need to be removed for a repair or replacement. Some years ago, I would have had similar thoughts. But not today. In the past 5 years, I’ve rescued many cylinders from premature removal, especially on large bore Continentals… and I was hopeful we could remedy Mark’s situation as well. Instead of removing cylinders in situations where the exhaust valve is showing beginning signs of burning, or the compression is dropping into the 50’s and 40’s and below, I now consider the first option of LAPPING THE EXHAUST VALVE WITHOUT REMOVING THE CYLINDER, AND INSTALLING A NEW ROTOCOIL. Mark was interested to learn about this process, so we agreed on a plan for him to fly his airplane from North Carolina to the Shenandoah Valley of Virginia for some not-so-invasive surgery on his airplane engine. Soon after Mark landed, we rolled his Cessna T210 in the shop and got to work. I won’t bore you in this post with all the details, but we lapped the exhaust valve and were both pleased with the progress along the way and with the end result. Take a look at some photos showing the lapping compound at work, and the nice, shiny sealing band that’s developing on the edge of the valve.