I’ve mentioned earlier that my club has run an engine well past the overhaul limits by using an owner-declared maintenance programme. Eventually both some club officers and our CAMO got nervous so we decided to overhaul at 3400 hours. By chance, another one of our aircraft had a prop strike at about the same time. As its engine had 1900 hours since overhaul we decided to go for a full overhaul rather than just a chock load test. The insurance company would pay the cost of chock load testing and repairs related to the prop strike. A full overhaul doesn’t cost that much more when you include such things as removing the engine from the aircraft and putting it back.
It is interesting to compare the engines and what happened at the overhaul. Both engines were overhauled by Nicholson-McLaren who (apart from some administrative mistakes) did an excellent job. Both engines had been run on AVGAS 100LL and AeroShell W80 for most of their lives, but the last few years we’ve switched to Hjelmco AVGAS 91/96UL and Aeroshell W80+, later Total XPD80.
Engine 1: A Lycoming IO-360-L2A with 3400 hours since new. It was the engine that came with the plane when it was delivered from the factory in 2006, so it had a known history. It has never had any major work. This engine has always been easy to start, had low oil consumption, performed very close to book figures and was generally well behaved. Since 2000 hours it has had a boroscope inspection and compression check every 100 hours. The overhaul was completed with very few surprises. The overhaul shop reported that the engine was “actually in good condition” when it arrived. There was some minor work required above the basic overhaul for a cost of about GBP 430 + VAT.
Engine 2: A Lycoming O-360-A4M with 1900 hours since overhaul. This engine was bought newly overhauled from an engine shop in 2009 so its history is unknown, except that it was originally an O-360-A4K that had been modified. In the documentation from the 2009 overhaul, the total time is also given as “unknown”. The engine required some major work in 2012 — the crankshaft was repaired and the camshaft and two pistons replaced. The engine was notoriously difficult to start and had an annoyingly (although not alarmingly) high oil consumption. During the overhaul several defects were discovered, the most important being corrosion on the crankshaft that could not be removed as the crankshaft dimension was already near limits. Instead we had to buy a new crankshaft. There was also severe fretting on the crankcase bearing saddles requiring reboring. Extra work above the basic overhaul was about GBP 6700 + VAT. The overhaul took about a month longer than expected as the crankcase had to be sent to the US for the repair work.
So what are the lessons learned from this? I guess three things:
In the past my club has always replaced an engine with a newly overhauled one rather than sending it for overhaul. In that way we’ve saved one or two months of downtime. This time we elected to keep the IO-360-L2A since it was clearly in very good shape. The O-360-A4M had to be kept for insurance reasons. In the future it is likely that we will not replace the engines even though it will mean the aircraft will be out of service for a longer time.
I don’t have much direct experience, but intuitively, I would completely agree with you.
Always keep a “known history” engine. The best (but also very expensive) engines are factory new ones All other engines are “unkown” to some degree.
If I ever have to overhaul the engine in the Cirrus (13 years and 1200 flight hours since new) I will have it overhauled by a good shop, even though it will mean some downtime.
I have some limited experience with engine overhauls. Unfortunately the bottom line seems to be:
- There is no way to get reliable good quality. The shops have limited turnaround on specific engine types and also the manufacturers have limited turnaround on parts and engines. Thus every single engine is a gamble on quality. There is no one to blame. On such small numbers with those prices there is probably no other way to do it.
- Even factory new engines don’t seem much better because they are built by hand from the same parts supply as the overhauled ones.
- The only part where “new” is probably better than overhauled are the cylinders due to material fatigue.
- Most engine damage is done by lack of use. Therefore some high time low power aeroclub engines actually do rather well.
- Remember that the engine is just a data plate. I did have one engine overhauled and in the end it was put together from so many parts that the only thing which justified it was still the same engine was the data plate.
- Every time I had the engine overhauled I had a good feeling because I went though all the details with the engine shop and they really worked with me as a customer. I thought I had done the maximum to get a good product etc. But a few years later I have to conclude that even this does not assure a reliable engine.
The conclusion of all this was to buy a share in a turbine airplane…
I agree with all above, except:
)Also every case of a premature engine issue that I have ever heard of involved an engine with a “gap” in its history. One might have the owner swearing blind that it was flown once a week but when you ask more carefully you always find a gap (during which, circumstantially, it very likely sat around and corroded away). Unfortunately most planes for sale have sat around for a long time.
Also I have never seen evidence supporting the often asserted “Lycoming metal is crap nowadays”. One owner even had his disintegrated camshaft and cam followers tested by a metallurgical lab and they turned out to be perfectly to spec. The engine was prob99 trashed during a gap in its history during which it presumably got corroded. I did try to get this guy to allow publication of the report but he never got his syndicate to agree to it (or never asked them, etc). I have the report but can’t post it. The plane was recently written off (gear up landing) so there should not be a problem now… it would be very educational.
A search here on e.g.
overhaul or exchange
digs out several good threads – example example example with some passionately expressed views 
Airborne_Again wrote:
Engine history is everything. When you buy an overhauled engine you have no idea what you actually get or what the time in service is for the various parts.
Mostly superstition IMO. These things are really only applicable if you know your engine inside out, like rebuilding the engine between each other race or something in that category of maintenance. On the other hand, there are only so many things that can go wrong, and when fixing the errors you reach a point when there are “nothing” more that can go wrong, until things get worn or old/corroded. If nothing has happened to the engine, if it’s running OK, this only means something eventually will happen at any point in time, it does not mean it’s an “above average” engine. A Lycoming/Continental is not a turbine quality machinery, or a modern automobile engine quality.
Sebastian_G wrote:
The conclusion of all this was to buy a share in a turbine airplane…
Starting to make more and more sense too me too. Financially is it a huge difference for you?
The other half of the problem there are the less than stellar engine shops
But they have a captive market, because schools (and indeed most private owners too) don’t want to do anything complicated and just want to pop the engine in the back of a van, on top of some car tyres, and drive it to the nearest engine shop.
Whether financially a big difference, I assume also depends on which type Sebastian opted to get in to.
Would be interesting to know which next plane you actually stepped up to. The TBM/PC12/Meridian/Jetprop discussion has taken place many times here already, but would be interesting to hear which one you actually stepped into (which is a result of many variables ranging from available options in vicinity to mission profile and finances), and your view of turbine flying.
As I’m getting older, kids are growing and one becomes more risk avert and want less hassles and easier (travel) flying, I’m starting to look into the turbine options too…
