Comments on: Engine Overhauls – Arbitrary or Necessary?

By: winterhawk

winterhawk — Fri, 04 Dec 2009 19:37:18 +0000

TBO is a concept that the airlines and military moved away from years ago and went to ‘condition’ maintenance, so why does GA cling to such an outmoded concept? It appears that TBO, like some ADs, are based on secret data and likely a lawyer’s opinion. Add that one can replace all but the engine data tag with new parts and it is still considered a repair unless the work is done by the manufacturer and the term “overhaul’ takes on a certain level of silliness in search of a counterfeit data tag, so lets move away from both the term and the concept and learn to speak of ‘IRAN’, which is Inspect and Repair As Necessary. This is condition driven maintenance and it avoids euthanizing good engines and repairs bad ones while avoiding both needless infant mortality of new parts and maintenance induced failures. But it requires data collection and analysis.

I suggest learning to collect your own data using such tools as a data-recording engine monitor, oil filter inspection and oil analysis. When a component fails, ask why? Inspect those things that can be inspected and try to find pass/fail criteria. Get educated and dabble in the black art of analyzing the data: Advanced Pilot Seminars from GAMI and Savvy Owner Seminars from Mike Busch are on line, inexpensive, data driven and teach what you need to know or where to look for answers. Join a type club and look for data-driven experiences. Aviation Consumer also has a wealth of information on their web site. When all else fails, google it. You’ll be amazed at the discussions going on out there. Most blogs are opinions, but a few are data driven and very good.

Think about the things that can kill you and proceed accordingly: The lack of spark, fuel, air and oil are going to ruin your day, so magneto, fuel, air and oil system conditions are critical to long-term happiness. Unfortunately, many owners lump them into TBO when they should be inspected and maintained on condition.

Constant speed propellers are a special case in my opinion. Their TBO is based on worse case, but If the aircraft is hangared, oil changed often and prop inspected and dynamically balanced, an overhaul is a waste of money. Instead, ask for an ‘inspect and reseal,’ which gives experts the option of fixing what’s broke and reusing what’s serviceable. Asking for an overhaul means they have to follow the overhaul manual, which mandates replacing parts and grinding blades regardless of condition. It’s important to know that there are only so many grinds in a blade before it is scrap. If it isn’t necessary why do it?

There are some things that have not improved in 40 years and we need to look for alternatives. Dry vacuum pumps fail randomly and insidiously. Why do we keep using them? Lycoming exhaust valves stick so often they have an SB called the valve wobble test, yet Continentals rarely suffer from stuck valves. Why can’t Lycoming fix that? I might add that a stuck valve might have resulted in a broken follower or damaged the cam, but there’s no SB for that. Why? Likewise, magneto ignition in an era of breakerless ignition is a crime, but the options are few. Why is that? Engine and airframe manufacturers set high cylinder temp limits that are murder on metals and oil. Aluminum alloys like cylinder heads can only withstand so many heat cycles, and higher temps translate directly into shorter cylinder life. Why not design cooling systems so the cylinders run cooler so they last longer?
Finally, there is lean of peak operation: LOP is easy using GAMI injectors on a properly instrumented engine, but carburetted and engines can do it too, which results in cleaner burning, cooler running engines. GAMI offers irrefutable data on it’s benefits, and Continental has slowly warmed to the idea. Unfortunately Lycoming continues to resist the concept. Go with the data!

By: Bob Davidson

Bob Davidson — Fri, 04 Dec 2009 17:55:44 +0000

The engine in my 81 172P was torn down and inspectedat 1500 hrs that engine is now at 2000 hr TBO. I have been told not to due the overhaul but do 50 hr oil tests and keep flying until metal show up then do the OV. What’s your take?

By: Thomas Olsen

Thomas Olsen — Mon, 24 Aug 2009 20:27:44 +0000

The FAA allows air carriers who have the appropriate programs to extend overhauls beyond the required TBO, but they must have appropriate monitoring programs, and they generally build up to the increased TBO’s in increments.

I don’t know how that translates to General Aviation Operations, but even during the days of the large, round piston engines, there were some carriers who were allowed to increase the overhaul interval beyond the manufacturer’s recommended TBO because they had a program to watch the engines to keep them on the wing as long as possible.

By: Don Lovett

Don Lovett — Sat, 08 Aug 2009 00:57:59 +0000

I replaced the engine in my 1966 Cherokee 180 with a new one in 1979. About 1650 hours on it now. I never use the primer to start it. Change the oil frequently (hourwise, at least). Do not abuse the engine. Slow descents. Shallow climbs. Installed a 4 cylinder EGT over 20 years ago. The compression at the most recent annual was not lower than 74 pounds in any cylinder. At its best, it is so smooth the Turn and Bank needle looks to be glued in place. Get 8 hours per quart. As long as oil and filter analysis do not indicate to the contrary, I will fly her just like I always have. I too believe in not fi\xiing that which isn’t broken.

By: Rodger Tracy

Rodger Tracy — Sat, 08 Aug 2009 00:03:01 +0000

In 1996 I bought a C-205 with a friend. After a couple of years we were forced to do an overhaul due to jet-fuel contamination of our fuel – unknown to us and many others. We had a high end overhaul done at a very very reputable shop – and paid more for it. Within the first 100 hours we had a major oil leak and the engine had to be pulled and repaired because of a missing seal done during the overhaul. Fortunately, the problem was not catastrophic – just messy. As a result I do not trust even the best of OH’s, FREMAN’s, or even new engines.

In 2002 I bought a 1970 C-206 with a fairly high time FREMAN Gold Seal engine that had been very well cared for. I am now over TBO and log every quart of oil I add. I have an Air Wolf filter that gets changed with the oil every 35 hours. I do an oil analysis and cut the filter open every 35 hours. At annual we do a borescope and compression. I have averaged 6 hours/quart over the seven years I have owned the aircraft, and the oil useage has gradually gotten better over time – it started at 4 hours/quart and my last oil change is up to 7 hours/quart. I am a CPA member and have studied Mike Busch’s recommendations carefully. I fly the engine very conservatively and carefully. I have not had a single engine problem of any kind in the seven years I have owned the aircraft. I will continue to fly the aircraft and do what I have been doing. I feel MUCH safer with this engine which is now 29 years since FREMAN and just beyond TBO of 1,700 hours on the IO-520F than I would with either a factory new or FREMAN. Mike Bush’s studies indicate your greatest danger of catasrophic failure is during the first 500 hours. I have been sharing the aircraft with a missionary aviation pilot friend who is also my mechanic who has flown the aircraft all across the US with no problems. We have changed out serveral accessories over these seven years at the first indication of any problem. The aircraft has a Sportsman STOL kit, BAS shoulder harnesses, and many other saftey improvements in case I have to land it off field. My airline pilot – flight instructor son puts me through the ringer every two years on my four hour bi-annual.

By: Dean A. Fawley

Dean A. Fawley — Fri, 07 Aug 2009 16:55:23 +0000

I find it interesting that in your email article, August 7, 2009, you have an entry about YET another AD issued for cylinders on Continental Engines. It really is dissheartening that an owner should tear down a perfect running engine in the interest of safety and then to have another costly AD issued for that newly overhauled engine.
The Coast Guard Auxilliary is also mandating the TBO rule. My IA says there is no reason to crack open my engine. We have had several instances of “bad” overhauls in our unit. My IA suggested to me that I just ignore the TBO and use the overhaul money to fly more, outside of the Coast Guard Auxilliary. The Coast Guard does not pay enough for me to manage an expensive AD.

By: SM

SM — Fri, 07 Aug 2009 15:25:39 +0000

Aviation has become a game of CYA and blame someone else. Unfortunately we, the pilots, pay the price in this game. TBO’s, Service Bulletins, AD’s and regulations are ways of shifting the blame to someone else. When we climb into an airplane we are PIC and are “responsible for and the final authority” for that flight. We take the risk. Wether you fly a low time engine or one over TBO, if you are not prepared for an emergancy, either one can bite you. When it happens you the pilot are alone. The lawyers, insurance companies, FAA and the last A&P(IA) to do your annual are not there. They just figure out who is paying and who is making money afterwards.

By: Lebor Thorvaaldski

Lebor Thorvaaldski — Fri, 07 Aug 2009 13:24:44 +0000

I don’t know how you can have an intelligent discussion of this subject without a thorough analysis of the data manufacturers use to set TBO’s. Seems to be some big secret, doesn’t it? Before we start mandating that charitable groups force compliance with TBO’s, maybe we should force manufacturers to prove that TBO’s mean something. Better yet, the TBO limit should be set by an organization independent of manufacturers, as the latter have an obvious conflct of interest.

We need actual data on the risk introduced by overhauling an engine that is currently running fine. Finally, we need better diagnostics. For example, compression testing is widely known to be a poor guage of health, yet many people rely on these numbers.

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By: Jeffrey J. Sacks

Jeffrey J. Sacks — Mon, 13 Jul 2009 21:57:00 +0000

What does the AOPA Insurance Carrier for one say about coverage when private aircraft engine goes over TBO ? Are there technical requirements that need to be supplied to insurance carrier to continue beyond TBO or is going beyond TBO a no-go with carrier ?

jeff