Waypoints

Here's the scenario: You're on vacation. The phone rings. It's the shop manager who has been working on your airplane. You can bet he's not calling to wish you luck on your golf game. Once he delivers the news that you need a new engine, do you: a) Thank him profusely for delivering the news — glad that you hadn't suffered a catastrophic engine failure, and then go about your vacation without a fret or worry, or b) Kick the lawn chair, curse under your breath, and spend the rest of your one week a year off staring into space trying to remember what accessories should be overhauled and whining into the cell phone to any engine guru you can think to call?

Thank you for thinking that I would choose option a. I confess it was not the case. No lawn chairs were hurt in the making of this story. It was easily bent back into service.

You may recall that back in the March issue in this column I mentioned that the cylinder head temperatures on the number four cylinder on my engine had gone cold during a takeoff (see " Waypoints: The Value Equation," March Pilot). I had several similar incidents over the next few months. Most of the time the temps would stabilize even before I could react, but on a couple of occasions the engine ran noticeably rough on takeoff and the temperatures didn't stabilize, causing me to abort the takeoff. Checking the spark plugs, ignition harness, and fuel injectors revealed nothing. Sometimes the mere act of checking those items would cause the engine to run just fine upon startup.

Meanwhile, the engine oil analysis over the last couple of oil changes had shown increasing levels of aluminum, chrome, nickel, and iron. The reports were not high enough to demand immediate attention, but the trend was definitely upward and reaching the caution level. Engine oil analysis — when done consistently by the same lab — can be a valuable tool in evaluating the health of an engine. However, short of massive chunks of metal in the oil or oil filter, seldom will oil analysis tell you exactly what is wrong or how bad things are. There are a lot of things inside an engine made of aluminum, chrome, nickel, and iron and it's tough to decide where to start based on that information alone.

But combine the oil analysis trends with information from cylinder compression checks, engine analyzer results, changes in oil and fuel consumption, and true airspeed variations and you can begin to get a better picture of what's happening inside that big slug of metal out front.

In my case, I had definitely seen an increase in oil consumption over the last six months. The engine had consistently burned a quart about every 10 to 12 hours for a couple of years. But recently, consumption had increased to about a quart every seven hours. Fuel burn actually seemed down slightly. Likewise, true airspeed seemed to be down by a couple of knots. Whereas I once counted on a consistent 170 to 172 kt true, I was seeing speeds closer to 165 kt in recent months.

The slight decrease in performance and increase in oil consumption are consistent with an engine reaching midlife. In this case, though, the increase in oil consumption was not gradual, but abrupt. The engine was almost 12 years old and had almost 1,200 hours on it on a recommended time between overhaul intervals of 1,700 hours. The previous owners had not flown the airplane much in the first nine years of the engine's life. I have flown it consistently in the three years I have owned it.

In trying to analyze the symptoms, I became a bit like a doctor trying to diagnose an illness. Could be this; could be that. Meanwhile, most flights occurred without any significant symptoms at all. The engine ran fine. Blackstone Laboratories, which does the engine oil analysis, recommended I keep on flying but sample the oil more frequently — a sound strategy. I would have followed that advice had the increasing wear metals been the only symptom.

But I wasn't content to keep flying it when occasionally the application of full power for takeoff caused decreasing temperatures in cylinder four and roughness. Frederick Aviation, the maintenance shop, not wanting to waste my money troubleshooting in the dark, suggested I keep flying until the problem manifested itself more often or more clearly. But when I fly, I typically have a destination to get to — a meeting or commitment — often with passengers on board. I didn't like the idea that the engine might or might not perform as expected on a given day.

In digging deeper into the problem, I took a look again at the data from the engine analyzer. As I've mentioned before, the airplane is equipped with a JP Instruments EDM-800 multi-probe engine analyzer. The display is what initially tipped me off to the cool cylinder temperature on takeoff. I've always paid close attention to the display on takeoff — usually reassured by the sight of steadily increasing temperatures during the takeoff roll.

I nabbed another download of data from the instrument. JPI recently developed its own analysis software that works much better than any off-the-shelf spreadsheet. In looking at data from the first incident where the engine ran rough on takeoff, the staff at JPI had suggested that it might be caused by a valve problem. More recent data samples paralleled the early reports.

In an act of sheer desperation I actually read the manual for the engine analyzer. In its troubleshooting section, the book described and depicted a variety of problems that might show up on the display and what might cause such depictions. One of the depictions looked remarkably like what I had seen. The book, too, suggested that it might be caused by a valve problem.

Tired of the unknown, I finally asked the shop to pull the number four cylinder to see what was going on. The airplane went into the shop on a Friday afternoon, the day before the start of my long-scheduled vacation. And so it was the following Monday that I received the not-so-welcome call from the shop with the news that the lobe on the camshaft that actuates the intake valve for the number four cylinder was all but worn away. Likewise, the corresponding tappet to the lobe was chipped and battered (spalled in A&P parlance) and generally a mess. At least we knew where the metal was coming from. The eroded lobe only partially actuated the valve, causing incomplete combustion in that cylinder — a situation that was particularly apparent during high power settings, such as takeoff. The incomplete combustion would also explain the slight decrease in fuel consumption and the lagging true airspeeds. Suddenly all of the pieces fit together.

At a minimum, I needed a new camshaft. That's not good news, because in order to replace the camshaft, the engine must be removed from the airplane and the case split. Once the case is opened to replace the camshaft — an expensive part itself — the engine shop will most likely find a few items beyond normal wear limits on an engine with 1,200 hours on it, such as mine. Those items would need to be replaced before the engine was closed again for reinstallation. The labor for such an effort would be the same whether I was patching up an old engine or installing an overhauled one. In the end, I would end up spending about half the price of an overhauled engine to patch up mine. Once put back together, an engine with 1,200 hours on it doesn't owe you much. It wouldn't be unusual for cylinders to start demanding attention in another 100 hours or so.

Rather than throw good money after bad, I decided to go ahead and overhaul the engine despite the fact that my checkbook wasn't quite ready for such a big divestiture. A call to the AOPA Aircraft Loan Program brought a flurry of paperwork my way to refinance the aircraft loan to include the bill for the engine overhaul. Oh, but the new interest rate is lower, I console myself.

As I write this, the engine case is in Zyglo inspection at Penn Yan Aero in New York. The airplane is stuffed forlornly in the corner of the maintenance shop with a stand under its tail, a gaping emptiness where the engine once sat.

Seeing airplanes flying overhead, I feel somehow left out and disconnected. I miss the airplane. The kids wanted to visit their cousins this weekend. It seemed like a good idea and I was thinking ahead to the flight when one of them reminded me that we were grounded.

For the price of a new car (which I now won't be buying), I'll be flying again soon — but not soon enough.

E-mail the author at [email protected].