Useful life of a 20 year old engine

[rk]

I am in the market for an early model DA40. Some of the listings I am coming across have still a quite a bit of time left on the original engine. For example, one airplane I am looking into has an engine that's 1200 hours since new. That's 800 hours before TBO, and in theory with 100hrs/year flying I should be able to use it for 8 more years.

However, these are 20 year old engines, and they might also haven't been flown that often. So is it realistic to expect that the engine will last till TBO?

 

[mandm]

There’s really no way to know, but there are things that you can check to improve your chances. I’m not a mechanic and these are just my opinions.

1) Compression check (Lycoming engines should be in the 70s out of 80)
2) Age of cylinders (Date last replaced)
3) Frequency of oil change and oil filter change too!
4) Oil analysis reports
5) Oil burn rate

If a recent cylinder overhaul then your compressions might be higher, this kind of buys you some time till your next overhaul too. Provided no other issues with your engine (such as making metal or burning too much oil).

I have an older engine too, but still some time before TBO (hours wise), compressions are good, it’s not burning too much oil (0.5-1 quart per 10 tach hours). I’m also hoping to get another 500-700 hours on it, but let’s see. I also don’t want to have my engine quit on me either.

 

[Country Flier]

 

[Kenny Phillips]

Certainly get it 'scoped, or even get one of the cheapy electronic cameras and look in the plug holes. If you see pitting or rust rings on the cylinders, it sat for a while. Ours did, so we opted for an overhaul and calculated that when we bought it. Ah, the good old days of $14K field overhauls.

 

[Checkout_my_Six]

Everything you quoted with respect to TBO and calendar months....means nothing. The engine needs to be inspected. It could be fine. Mine was last overhauled in 1994....and it looks great inside. Here's what an old engine can look like inside....

 

[Let'sgoflying!]

Buy one that is run-out, and factor in an overhaul (downtime and purchase price $).

I can't count how many times someone bought an airplane with their calculations of 'how many years it would last'; only to have that engine apart in the first two years. There should be a meme for it.

Next best is to buy an airplane with an overhaul/replacement that was done 200 hours ago by a good name.

 

[frfly172]

Only a good inspection will give you an idea of the condition of the engine. An engine that hasn’t been run often and hasn’t had good preventative maintenance can be more problems than you need.

 

[Vance Breese]

Lycoming Service Instruction No. 1009AS

Engine deterioration in the form of corrosion (rust) and the drying out and hardening of composition materials such as gaskets, seals, flexible hoses and fuel pump diaphragms can occur if an engine is out of service for an extended period of time. Due to the loss of a protective oil film after an extended period of inactivity, abnormal wear on soft metal bearing surfaces can occur during engine start. Therefore, all engines that do not accumulate the hourly period of time between overhauls specified in this publication are recommended to be overhauled in the twelfth year.

Food for thought.

 

[Dan Thomas]

And every post misses the most common factor in short engine life: short runs, or ground-runs.

Combustion of a gallon of gasoline produces nearly a gallon and a half of water. Most of that goes out the exhaust as water vapor, but some gets past the rings, especially in a cold engine, and into the crankcase, where it condenses and mixes with the oil to form nitric, sulfuric and hydrochloric acids that eat that engine from the inside. The owner who makes a circuit or two and puts the airplane away, or who goes to the airport and runs it for ten or 15 minutes, thinking he's saving the engine, is ruining it. It is not a car. It is an aircooled engine with large clearances when cold so that it doesn't seize at operating temperatures far above car engines. It has no PCV system to scavenge blowby gases from the crankcase, since manifold pressures are too high (low vacuum) at typical aircraft operating power levels. PCV needs vacuum to work.

Both Lycoming and Continental have recommendations against ground runs. Lots of engine rebuilders see the results of it.

Far too much emphasis is placed on atmospheric moisture, and yet engines that have sat for many years without being run are just fine inside.

We replaced the engine on a newer 172 that had less than 300 hours on it. The owner had quit flying but was running it up on the ground. We found it badly corroded inside, nowhere near safe.

From https://www.lycoming.com/content/frequency-flight-and-its-affect-engine



From https://www.lycoming.com/content/low-time-engine-may-not-mean-quality-and-value

The point of this discussion is simple. A low-time engine may not add value to an aircraft, and the buyer should be aware of all factors which may affect the condition and value of the engine. An engine which is not flown frequently is subject to deterioration as a result inactivity. When the engine does not achieve flight operating temperatures on a regular basis, the moisture and acids that form as a result of combustion and condensation are not vaporized and eliminated through the exhaust and crankcase breather. As moisture and acids collect in the engine, they contribute to the formation of rust on the cylinder walls, camshaft and tappets.

I underlined the important stuff.

 

[Klaus M]

Everything you quoted with respect to TBO and calendar months....means nothing. The engine needs to be inspected. It could be fine. Mine was last overhauled in 1994....and it looks great inside. Here's what an old engine can look like inside....

OR, it can look like this 1300 hour 2005 Factory Overhauled O-540...

 

[EdFred]

Mine was OHed in 81 and the lower still looks amazing

 

[MooneyDriver78]

OR, it can look like this 1300 hour 2005 Factory Overhauled O-540...
View attachment 117913

Is that rust or a coating on the cam shaft, given the texture I assume the latter.

 

[catmandu]

I purchased a plane with a 30 yr SNEW engine, 800 hours. It truly was a deathtrap after all that time, just waiting to kill me and my loved ones, and my offer to the seller reflected that. They agreed, and a deal was made.

I inspected the engine closely with my mechanic, and then flew it for another 500 hours, before selling the airplane for a nice profit.

Food for thought.

 

[Checkout_my_Six]

Oh....and that pic I showed was also a couple hundred hours from TBO.

 

[Klaus M]

Is that rust or a coating on the cam shaft, given the texture I assume the latter.

There is a very thin layer of nitrited harden steel on the surface of the cam lobes and followers. Rust will cause pitting through that hardened surface and expose the much softer steel. About 200 hours later the metals are grinding down rapidly. If this engine ran for another 100 hours the lobe would be totally gone.

 

[Dan Thomas]

Is that rust or a coating on the cam shaft, given the texture I assume the latter.

It's a coating. A brand-new Continental camshaft looks the same:

 

[Dan Thomas]

There is a very thin layer of nitrited harden steel on the surface of the cam lobes and followers. Rust will cause pitting through that hardened surface and expose the much softer steel. About 200 hours later the metals are grinding down rapidly. If this engine ran for another 100 hours the lobe would be totally gone.

The camshaft doesn't look too bad, but I'm wondering about the lifter behind it. Spalling?