A ploy to sell more engines?

Q: While TBO is recommended as 2,000 hours or 12 years, whichever comes first, the brokers trying to sell me a used plane always belittle that second limitation, chalking it up to Lycoming wanting to sell more rebuilds. Can you clear the air on this one?


A: The text of Lycoming Service Instruction 1009AT, which addresses “Recommended Time Between Overhaul Periods,” has always been a controversial issue. While it lists the recommended hours for each engine, it also includes a rather profound caveat that has become a point of discussion by many: “All engines that do not accumulate the hourly period of time between overhauls specified in this publication are recommended to be overhauled in the 12th year.”

While it was generally thought to be a ploy by the engine manufacturers to sell more parts or factory overhauled or rebuilt engines, this was not the case.

Both Lycoming and Continental offer factory exchange engines as an alternative to a field overhauled engine at competitive prices. This has generated many engines being sold on an exchange basis, while providing both manufacturers with a realistic learning curve about their engines that have been in service under various conditions and times over a period of years.

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What to do about a ‘slightly’ rough running engine

I always look forward to hearing what you have to say, so here is my question: I fly a 1954 Piper PA-22/20 with an O-320 (no suffix) Lycoming, with about 975 hours since major. I fly it 150 to 175 hours per year, and keep up with all the maintenance an old ship requires. The engine runs beautifully, takes about 1/2 quart of oil between changes, has no leaks and has good compression. However, when I pull back the power for a long descent (2,300 to 2,100 rpm), I get a “”slightly”” rough running engine. If I reduce further, to 1,500 or so, it smooths out. I had the prop statically balanced at a reputable shop and it seemed to help a little, but I was wondering if dynamic balancing would be the next place to look, or is there another direction?

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