Each shard of metal is ever so slightly curved. There are dozens of them lying on the table. I push them around with my fingers, getting burnt, black, nasty oil on my hands. A bit at a time, like assembling a jig saw puzzle, I recreate the ring of metal the shards once formed.
“Yep,” says the mechanic cheerfully, “I’d say that was your problem.”
Myself, I’m somewhere between horrified and relieved. I’m horrified that this string of broken pearls came from inside my engine; while I’m relieved that approving an expensive cylinder replacement wasn’t money wasted.
Remember that weird oil thing I wrote about a few weeks ago? Right after that Tess went in for major maintenance, and my crew could find nothing wrong. But within four hours of writing that rather large check for preventative maintenance, I was making another quasi-emergency landing with redline oil pressure. Followed by another. You can read all about that adventure over at General Aviation News, but in a nutshell, things went from fine to worse in record time.
Hidden under the cowl, deep inside the front right cylinder, the piston rings were giving out. At my annual, right before this flight, all the cylinders had compressions in the 70s, which is regarded as healthy. Six hundred miles later, the front-right was at 30 and was pronounced dead on arrival by the lead mechanic at Springfield Flying Service. It gave virtually no advanced warning. It just died.
The autopsy actually raised more questions than it answered. Two of the four rings were fractured, allowing oil to flood up into the cylinder. That said, other than the oil loss, there was little to show for it. Against all odds, the cylinder was still working and the plugs weren’t fouled, which they should have been, given the 1.5 quarts of oil per hour the cylinder was guzzling. The innards of the cylinder showed exposure to extreme heat, the parts being “cooked,” according the mechanics. But I’ve never abused the engine. And if it were cooked in the past, how did it last so long? Questions without answers.
But speaking of questions and answers, laid bare and torn open, I was able to see more of Tessie’s engine than ever before. And more. I got a guided tour through her inner workings while serving as official wrench holder for the mechanic replacing the cylinder. I spent an entire day giving what (little) help I could—hold this, please hand me that… no, the one to the left—and learning. I got to meet the push rods. Saw the cams. Touched the valves.
I’ll never be a mechanic. I don’t have the right kind of mind for it. But this one day of mechanic school opened my eyes in a new way to what’s happening under the hood.
And that will make me a better pilot.