Ask Paul: What’s the TBO on my engine?

Q: I have obtained a 1978 Bellanca 7GCBC with a Lycoming 0-320-A2B engine manufactured in 1977. I am attempting to learn more about this engine, including why the log book contains an entry at the 1,200 hour mark showing the engine as being “on condition” but I have been unable to determine why.

Is the 1,200 hour entry correct for this year and model engine and if so and I were to have it overhauled, what route could I take to make it a 2,000 hour O/H engine — or is this possible?

I also understand the -27A at the end of the serial number indicates it is a wide deck engine. Is this correct?


A: Mike, I think I can brighten your day, but you’d better read this to the end. If your engine is, in fact, an O-320-A2B manufactured in 1977 by Lycoming, it does have a 2,000 hour TBO time as set forth in Lycoming Service Instruction 1009AV. Where the confusion may come stems from earlier revisions to this Service Instruction, where it was perceived that any engine not reaching its recommended TBO time within a 12-year period should be overhauled.

The reasoning, which I feel is still valid — to a point — was that if the engine did not reach its recommended TBO in that time period, it certainly had suffered extended periods if inactivity, which may prove harmful to the internal components as a result of corrosion. Other negative factors of these extended periods of inactivity, such as deteriorating fuel and oil hoses, carburetor and fuel injector components, including fuel pumps, are just some of the things we are concerned with.

Experiencing problems with any of these or other major components could possibly reduce the performance of the engine or, in a worse case scenario, lead to a premature engine failure.

Mike, I suspect the logbook entry at the 1,200 hour point was done simply to continue the engine in service at that time. There was some confusion regarding the 12-year limit in the past, so putting an engine “on condition” was a simple way to continue it in service since it reflected the condition of the engine at that particular time. All of the engine’s vital signs, such as hot differential compression check data, oil filter and or pressure screen inspection for any signs of metal contamination, oil consumption, etc. should have been noted in the engine logbook for future reference. During the next regular scheduled maintenance event the previous recorded data would be compared with the information collected at this point and, if nothing had changed, continue the engine in service.

NOTE: There is a caveat, however, which may apply to your aircraft. In Lycoming Service Instruction 1009AV, it clearly states in one of the “Notes” for the O-320 series engines, that if the engine was modified to incorporate an inverted oil system for aerobatic maneuvers, the engine TBO time then must be determined in the same manner as an AEIO aerobatic engine. If this applies to your engine, then the recommended TBO would be 1,600 hours. I’d strongly suggest you contact your maintenance facility and have them review Lycoming S I 1009AV, which they should have on file. With the information you provided here, they should be able to determine exactly which TBO applies to your engine.

Yes, the -27A in the engine serial number does indicate it is a wide deck engine configuration. Just to clear up any confusion, all O-320-A2B wide deck engines have a 2,000 hour TBO right out of the Lycoming factory, except those mentioned above regarding the inverted oil system.

There isn’t much else I can say about the O-320-A2B except for the fact that it’s probably one of the best engines Lycoming ever produced and has been around forever. If it’s flown frequently and has regular oil and filter changes, it’ll probably outlive you and I both with little or no problems.

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