In observing and selling in the GA field for nearly 20 years, Ive come to the conclusion that even though it bombed in the market, Porsche got one thing right when it teamed up with Mooney on the PFM: Even though they had an engine that would have sailed to 2000 hours and beyond, they proclaimed that it should be topped at mid-life. They even built that into the price and provided the overhaul nearly for free.
In spite of the airplanes other shortcomings, this approach to engine longevity did wondrous things for PFM owners mentality. It relieved them from having to worry about an engine mid-life crisis.
And it got Porsche out from under the inevitable bellyaching about how that lousy German engine developed soft cylinders well before its time, leaving the owner stuck in Tijuana spitting out valves and pieces of rings while belching oil down the belly at 1400 hours. Talk to any PFM owner and youre not likely to hear much bitching about the engine itself.
The wisdom here for all owners is this: Rather than constantly worrying about whether your engine will make it to TBO without cylinder work, ease the strain by simply planning for it. The fact is, the majority of engines need some kind of mid-life jug work before they reach TBO and some need a lot more than others.
In my experience, this applies about equally to Lycoming and Continental engines. Oddly, with no aviation experience to speak of, the nimrods at Porsche kind of figured out the mandated top TBO on their own, an idea that seems to have escaped Mobile and Williamsport.
We can argue endlessly about why engines dont make it to TBO without new jugs. You need only hang around the average busy maintenance shop for a few weeks or take any experienced A&P to lunch to learn how tender the top end of the typical airplane engine really is.
Cylinders crump for any number of reasons, some beyond the pilots control. Whipsawing the throttle spikes the CHTs, too much or too little leaning does the same or causes the engine to run over rich, leading to valve deposits that probably cause the typical Lycoming morning sickness. That sort of stuff you can avoid. But what about the cylinder that goes soft or cracks because of an unseen metallurgical inclusion? Or a piston ring that parts for no apparent reason? It happens.
Best case, the various components in an aircraft engine wear at different rates. The upper end will normally always wear faster than the bottom end. And thats good. For when the bottom end goes, it spews parts all over the real estate below and rather than looking for re-conditioned jugs, you might be looking for a new airplane.
In the case of Porsche, the cost of a mid-life overhaul was built into the cost of the engine itself, more or less. What would it cost if you did the same for your own airplane, by merely budgeting for the top ahead of time? Lets take the IO-360 used in the Mooney 201. A first-rate overall will cost about $16,000, including removal and re-install, although a cut-rate shop might do it for less.
Over a 2000-hour TBO, that works out to $8 per operating hour for engine maintenance. Although not everyone does it, the smarter way to manage costs is to pay as you go, establishing an engine and maintenance fund based on actual costs.
Now some IO-360s make it to TBO without a top, some dont. If you budget $5000 for the top, youd have more than enough to recondition the cylinders at mid-time and youd only add $2 to your hourly engine budget. When a valve crunches or a jug cracks, you can simply have the work done and write the check, because you expected it. And if you dont need the top? Lucky you. Put the windfall toward a new interior, a paint job or an IFR GPS.
The need for a top overhaul is not determined entirely by chance. You already know the formula: Fly as often as possible, at least 150 hours a year. Change the oil frequently, certainly at least every 50 hours. Dont be too afraid of shock cooling but dont hammer the jugs with chopped-throttle power management, either. Common sense applies.
And if none of that works? Plan for the top overhaul and have it done when the airplane is in for annual. Thatll minimize your down time and lessen the worry of having to do it when you least expect it. You cant ask for much more than that.
by Coy Jacob
Coy Jacob owns the Mooney Mart and is an Aviation Consumer contributing editor.
