Things I learned when overhauling an engine

I bought my 1973 Piper Cherokee 180 in March of 2019, and have since put over 150 hours on it. The first year of ownership was both some of the most joy I’ve had, and some of the most stress. The Cherokee has been good to me, but it’s old, and has showed its age in interesting ways. First I replaced the attitude indicator, then the transponder went south, and then :scary music: metal in the oil.

When I bought the Cherokee, the engine was already at 1650 hours since major overhaul (SMOH). It’s a standard Lycoming O-360-A4A, with a time between overhaul (TBO) of 2000 hours — so it was not entirely surprising when metal started showing up in my filter and oil analyses.

Annual inspection was in March. The A&P who did the work noted the metal, followed Lycoming procedures for determining next steps, and eventually returned the airplane to service while telling me to change the oil more frequently and keep an eye on the filter. The next oil change was ok. The one following that, not so much, so I started asking around for advice. I started to think about the engine in terms of diagnosing a problem, versus open-heart surgery on the airplane — but I also got recommendations for A&Ps who could do the work, and started looking for estimates.

Everyone warned me — oh, overhaul is the worst thing. I hope you have money set aside for overhaul. Avoid it if you can. And of course, when the engine started making metal, I heard a similar refrain. It was like something tragic had happened. “Oh nooooooo but you just got the airplane!” “Ugh, sorry to hear that, that’s rough.” And while I appreciate the sympathy, and wish I hadn’t needed an overhaul a year and change into ownership, the reality is that major maintenance and repair is all but inevitable. I had squirreled the funds aside, knowing how I planned to fly my Cherokee and that I’d be coming face-to-face with overhaul at some point.

It’s worth noting here that I am pretty risk-averse. The engine was already making me nervous and somewhat reluctant to fly. I definitely didn’t want to go do pattern work at the height of summer on it (though who are we kidding, that’s no fun even with a healthy engine). While I was being continuously reassured that catastrophic failure was not imminent, I didn’t really want to test the theory.

The hardest part of this whole process was figuring out that overhaul was truly necessary, and then being patient while the work was completed. I was fine with the idea, but I definitely didn’t want to do it if it wasn’t necessary yet.

Here’s what I knew when I started calling mechanics for advice:

  • The engine was last overhauled in 1993
  • It was over 1850 hours SMOH
  • “Full power” was no longer quite as “full” as it used to be
  • I had more than a quarter-teaspoon of metal in the oil filter at annual, then again two oil changes later
  • Oil analysis was showing a trend of increasing iron, aluminum, and nickel in the oil, with iron well over the lab’s “green” limits

I went first to Larry Donaldson at Chesapeake Aviation (KANP), hoping he would be able to help me diagnose the issue. Larry very patiently listened to my data points, but as soon as I was done, he was unequivocal in his recommendation to overhaul. That engine is 25 years old, he said. You can try and fix the issue now, but you’ll be back at this decision point in a year.

Larry, it turns out, doesn’t do engine overhauls. He sent me to Steve, at Aero Services of Winchester (formerly, I think, Aero Engines). Steve also very patiently listened to my data points and arrived at the same conclusion as Larry. By this point, between Larry, Steve, and a few friends, I had four different, experienced mechanics independently arriving at the conclusion that the engine needed an overhaul. Steve recommended Valley Aircraft Services in nearby Mount Jackson, VA, to actually do the overhaul. After getting the quote and noting the schedule, I committed to overhaul and crossed my fingers that I’d made the right decision.

The logistics of the thing turned out to be pretty simple. In early October, my CFI kindly ferried the airplane to Winchester, where Steve and his crew uninstalled the engine. They work closely with Valley Aircraft, so they handled the transfer of the engine to the crew performing the overhaul. I didn’t have a great idea of how long this was going to take, nor did I get routine status updates during the process (though to be fair, I didn’t ask for them). I found out that the engine had been removed from the airplane when I called the shop to tack on some avionics work. I found out that the engine had been reinstalled when FlightAware let me know my tail number was flying. And I found out that the overhaul was complete when Steve called me to ask when I wanted to pick the airplane up!

The total elapsed time between when the Cherokee got dropped off, and I picked it up again, was less than six weeks. Picking it up was in itself an adventure: newly-overhauled engines have to be flown hard in order to break them in properly. The shop had done the critical first hour while test flying, but it needed another nine hours or so of full-power, full-rich time in the sky to complete the break-in. Here’s where I learned things that hadn’t shown up in the very, very many articles about engine overhaul on the Internet!

For example, carburetors can be set lean or rich by default in the factory. Mine was set very lean, and will be tweaked richer at the first oil change, because I’ve been seeing absolutely bananas engine temperatures in climb. If I don’t manage the climb carefully, it would be trivial to exceed 500 degrees. Even in cruise, the engine runs hotter than what I was trained to think of as “normal,” hovering around 400 degrees.

After the first couple of flights, I got nervous about the high temps and called the shop for advice. According to the guys who rebuilt the engine and are guaranteeing the work for the first 200 hours, the high temps I’m seeing are to be expected, and will continue to come down as the engine fully breaks in. Between the factory-lean carburetor, and the shiny new very-well-sealed cylinders, the baseline “normal” temperature for carbureted piston engines is expected to be higher than those at the end of their functional lives.

All in all, for something that was always characterized to me as a A Very Bad Day, overhauling my engine — while expensive, and time-consuming — turned out much better than I anticipated. The airplane was down for less time than for annual this year. It flies like a dream now; there’s less vibration and noise, and of course there’s much more power! While I hope I don’t have to go through this again any time soon, I’m happy with the way things went, and that I now have an engine to last me another decade or so. Bonus — I also now have my old camshaft, which was indeed corroded and misshapen, which I’m going to turn into a lamp for my office!