Most aircraft piston engines have at least one soft spot, preventing them from being 100-percent reliable over time. With big-bore Continentals, it’s often cylinder wear. Small-bore Lycomings, on the other hand, can be susceptible to premature camshaft wear. Of course, run any engine long enough and hard enough in any machine and it will ultimately fail. In aviation, though, an engine’s long-term reliability is by no means assured. That’s a lesson I learned the hard way.
The Cessna 210 I owned for a while was in overall good shape, with a mid-time engine. For the first couple of years I had it, I spent a lot of time going through it, often with an experienced A&P/IA, replacing worn screws, bolts and bushings, and cracked plastic, repainting small components, plus cleaning and inspecting various items, including the spark plugs.
One day, while working with the A&P/IA, we tackled the fuel injectors. We removed them, cleaned them and reinstalled them per the manufacturer. Though I was familiar with torque wrenches, I had never used the “clicker” style version, and ended up applying way too much torque to the #5 cylinder’s injector. Once the error was discovered, we removed and reinstalled it with the correct torque specification.
A few years later, I was en route when my engine monitor went nuts, indicating high cylinder head temperature (CHT) on that same #5 cylinder; above 500 degrees F. I immediately reduced power and enrichened the mixture to cool the cylinder and made a precautionary landing. Although my right-seater on that flight happened to be an A&P, we had no tools and no way to inspect it. We kept a close eye on it all the way home, ultimately concluding it was a one-time issue with the system. I kept flying it as-is.
A few months after that episode, that same #5 cylinder swallowed its intake valve, which created all sorts of havoc. As it happened, I had another A&P in the right seat that day. Once on the ground, the reason for the cylinder’s failure was obvious: A crack at the fuel injector port that wasn’t there when we took off allowed the intake valve seat to get loose, destroying the valve. We knew that because we both looked over the engine closely before takeoff.
I’m positive my overenthusiastic application of the torque wrench years earlier not only resulted in the high CHT episode—possible detonation?—but also the crack.
I still make mistakes when tinkering with my new airplane, but applying too much torque to fuel injectors isn’t one of them.
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