Lycoming SL1481B local copy states
Clearly the engine does not become illegal to install after this time. You just lose the warranty.
There is an additional 1 year limit
and on my reading this cannot be extended. This has come up before e.g. when Socata were assembling the last TB aircraft (c. 2002) they tried hard to make sure the engines were fitted to the aircraft no more than 365 days from when Lycoming shipped them. For example, my engine was shipped by Lycoming on 24/2/2001 and was installed by Socata 8/1/2002. Some other aircraft had the dates much closer to 365 days.
Some years later when I was looking at doing the crank swap AD I talked to Socata about purchasing one of these old “new” engines (they had 14 in stock) and they said they cannot be sold unless they are overhauled. And others told me that after the 1 year the engine is not legally airworthy no matter how preserved. One would think that practically this can’t be right because e.g. you could fill it completely with oil, but actually oil seals and o-rings etc will still have a finite life.
Are there any definitive rules on the above i.e. is there really a 1 year “hard limit”?
And if there is, surely it would apply equally to an aircraft that has been sitting in a hangar for 1 year, too.
Not that I am aware of for part 91 N registered aircraft.
For Annex II aircraft in Sweden you do a corrosion check every five years to stay airworthy. I would guess that it deals with this issue. No corrosion is good for airworthiness.
What about maintenance actions (e.g. inspections) which can render an engine unairworthy once somebody becomes aware of something?
I spoke to one UK engine builder a few days ago about this. Here’s a short list of potential unairworthy-upon-external-inspection items:
I made the point that #1 would render most turbocharged engines unairworthy after a few hundred hours (a little crack around the exhaust port) and he laughed 
But at least you can fix that one by replacing the cylinder (and burning a load of extra avgas while bedding in the new rings).
None of the above are time-related however. So merely leaving a plane to sit for a few years does not make the engine unairworthy, provided it does not breach any of the above. If it is full of rust (quite likely) then the cam followers will disintegrate, damage the camshaft, and within a few hundred hours you have metal in the oil. However, if the engine was not yet installed in the aircraft, it would become unairworthy because of breaching the storage time limits (which are packaging dependent; typically 1 year max).
Once an engine is opened up, e.g. to fix a crankcase seam leak, that opens a new can of worms e.g.
Peter wrote:
any corrosion found has to be fixed
Yes, corrosion inside engines is not a good thing and is removed any time the engine is apart, although outside of the U.K. or similar climate corrosion does not occur in storage with quite the ferocity you describe.
Peter wrote:
any parts outside overhaul limits need replacing
‘Need’ is a funny word. Often replacing more than is legally required provides additional value for the same amount of labor. However from a regulatory point of view if the engine is simply being disassembled and reassembled for some reason it is not an overhaul and visual inspection of unaffected parts is adequate. An overhaul takes it one step further, everything is measured when disassembled and brought at minimum within service limits (i.e. not completely worn out), and ideally within new limits.
As a slight diversion from the regulations and into the “real” world of what actually works, I read that Lycoming once ran an engine on a dyno for thousands of hours. This engine was stopped from time to time and the cylinders were filed away so it had really awful compressions. It still developed something like 95% (or was it 98%) of the original power. It makes perfect sense as how can much of that exploding gas (at 2,400 RPM) escape down the side of a piston? Apart from increased crank case pressure, most must still be converted into power
I read this years ago and the above is from memory so the exact details might be wrong. However, if the cam is still good and the valves are lifting and sealing properly then it will develop (almost) full power. If it has worn pistons and is burning loads of oil then it is probably still fine. I actually think that the old air compression test should be junked in favour of Borescopes which I believe is now Lycoming’s official advice.
(1) if it fails a compression test then run the engine for 30 min or so
(2) do the compression test again
(3) if it still fails then borescope the engine and believe the borecope
Correct me if I’m wrong on any of this- it was a long time ago I read all of this.
Also statistically a 3,000 hour engine in good condition which is not making any metal is probably safer than an engine between 0-400 hours old. There is one plane on the airfield which is used 3 times a week and the engine has done about 2,800 hours. I’d trust that plane over a long water stretch much more than some of the engines which are well below TBO (in time and hours) and go out less than 6 times a year.
Archer-181 wrote:
so it had really awful compressions
My first car was an 850 Mini (which was already over 20 years old when I got it). At some point it burned a valve – it actually happened quite quickly – and I had to go to my parents house nearly 100 miles away to work on it, since I didn’t have any off-street parking and they had a garage (and I was a penniless 18 year old student at the time, much of the penilessness was caused by owning a car, I may add). Once the car was up to some speed, you wouldn’t know there was a problem at all. At 60 mph it would run smooth as anything and if I kept the revs up it made good power (well, good for an 848cc A series engine at least).
When I took the head off it, one of the exhaust valves had a pea-sized hole in it.
There was an accident here in Switzerland where an O360 was in doubt of having produced enough power. Take Off in fairly high density altitude, the pilot “felt” the plane did not climb and crashlanded about 500 m after the runway end. Airplane ruined, prop bent.
When they went through the docs, some interesting stuff emerged.
The airplane was stored for over 13 years and still had the original engine on at the time of the accident. It had been overhauled once and had 1750 hrs approx since the overhaul which had happened before the storage. No conservation had been applied. Various deficiencies were found such as The exhaust pipe flange on cylinder no. 3 was defective, the baffles inside the exhaust muffler were damaged, the rubber engine mounts were severely cracked, the flexible oil return tubes were severely cracked and the rubber sleeves of the manifold pipes to the individual cylinders were cracked. After the storage, both magnetoes and the carburettor were overhauled, otherwise no maintenance was done.
They put the engine onto a test stand and found it produced full power. After the test, they checked compressions and found them between 72-75/80. Boroscoping showed corrosion in the cylinders, yet the engine produced full power. It was found that the engine was likely no factor in the accident.
https://www.sust.admin.ch/inhalte/AV-berichte/2289_e.pdf
It is amazing what abuse these engines apparently can take.
