Q: I have a ’69 Skyhawk with 2,500 hours on the engine. Good compression, no metal, one quart oil burn every eight hours. Should I get a top overhaul or a complete engine overhaul or just keep flying until an indication of a problem?
TED HALL, Upperco, Md.
A: Well, I must tell you that with 2,500 hours of operation since 1969, this engine certainly doesn’t owe you anything! If this is the original engine in this aircraft and after providing you reliable service for 45 years, I’d say you got your money’s worth.
You stated the engine has over 2,500 hours, but you didn’t specifically say it was the original engine in the aircraft. Because of that, my response will be based on both scenarios — that this is the original engine or a replacement engine that has accumulated 2,500 hours on it. This way, we’ll have all the bases covered.
There are a couple of ways to look at your situation, but the final decision must rest in your lap. From what you mentioned, the important items we normally look closely at in order to determine an engine’s health all appear to be fine. Since no specifics were provided other than the oil consumption, which is excellent, I believe I’d continue to fly the aircraft.
However, that being said, I’d feel much better knowing exactly what the entire maintenance history has been on this engine. If you have maintained this engine over the years with frequent oil and filter changes, hot differential compression checks, etc., and have no indications of anything that would alert you to impending problems, it would appear this engine still has some good life remaining. Please remember that I’m only making the above comments based on the very simple information you provided.
Getting back to your main question, I’d certainly not recommend doing a top overhaul if the information you mentioned is correct. If the oil consumption, differential compression checks, and nothing shows up in the oil filter or oil pressure screen, then I’d feel confident in continuing the engine in service.
I would recommend that you keep a close tab on its operation, especially if the oil consumption begins to increase or compression checks begin to decline. Be certain to closely inspect the oil pressure screen or the oil filter element, whichever you have, for any indications of foreign materials.
Again, I only based my response on the information you provided, and this in no way applies to the many other Lycoming engines out there with operating times well beyond the Lycoming recommended TBO time.
My Warrrior had 2950 SMOH and only had one cylinder replaced during those hours. I got it majored this year as oil consumption was down to 1 quart every 3 hours, and was taking another long trip in her. Go Lycoming and go Millenium Superior cylinders!
I helped on a C180 which had 4000 TT. The owner complained of the engine making heat in climb, and I concluded that the bearings must have been worn and that the engine was making heat in climb due to wear since in cruise it was normal, as well as descent. The compressions were good. No oil analyses had been performed. I recommended a complete overhaul due to (presumed) internal wear.
The owner had bought the plane at 2000TT on the belief that it had completed an engine overhaul.
When we opened up the engine the main bearings were worn down and we concluded that, at 2000 hours, that the engine had merely been topped and that no overhaul of the main part of the engine had been performed. This was a shock to all, yet is a testament to the durability of Lycoming engines (provided they are properly flown and maintained). We concluded that the engine had 4000 since new with no actual overhaul.
How does this relate to the high time engine in the example? It shows that while cylinders may be handling the time in use well, that there is no assurance that the internals are doing likewise. Regular oil analyses show if internal wear is present. If oil analyses have not been performed the owner has no knowledge of the internal condition of the engines and so if exposing himself to real risk since he has a very high time engine and has no knowledge of its condition.
Further, I had an IO320B1A that had 71 and 73 over 80 compressions, yet had some vibration at 1800 SMOH. I knew the engine was making metal (from oil inspection) so I started by pulling cylinders and I found that three out of four had broken rings – yet the compressions were all in good range. This prompted an engine overhaul. The point being that just having good compressions is not a definitive guide to engine condition.
A few years ago I bought a Cessna 150 from the original owner. The engine had never been worked on other than normal maintenance.
It had over 3300 hours on it, good uniform compression, used than a quart of oil between changes, and didn’t mark it’s territory with leaks.
I flew it for about a year and sold it with nearly 3400 hours!
Charlie