Old engines
 

Elsewhere, it was mentioned, and not for the first time, that some pilots are not confident that "old" engines provide power as they would have when they were new. I resist this notion.

The engine does not know its age, it knows how it has been maintained. If it is maintained well, it will produce its rated power. It's simple physics. If an owner lets its condition deteriorate, it will produce less power at full open throttle, until eventually, it scares someone into knowing it needs maintenance.

If you believe that the engine you're flying will not meet the flight manual performance standards, then you have made the determination that the engine is not airworthy, and you should not fly the plane. It could not be more simple. For many fixed pitch prop airplanes, the Type certificate data sheet will specify a minimum and maximum RPM to be achieved static on the ground. This is an excellent way for a pilot to quickly assess engine condition and performance (assuming an accurate tach!). CS prop engines are not quite so straight forward in that regard.

I've owned my O-200 for nearly 31 years. In that time, I've put more than 3000 hours on it. It produces the same power now, as it did when I first bought it (well, probably a little more, I bought it as a near to TBO engine). I have maintained it over the years, and it has rewarded me with dependable power the entire time, with the only exception being a stuck exhaust valve once. Otherwise, perfect reliability and performance.

We cannot control the age of our engines, other than replacing with new, but we can control the condition. The performance will be based upon condition - so let's not blame age!

Agreed, the theory originates with car engines which can get very low on power in a worn out old banger. If you just drive it until it dies, never have it properly serviced, never change the oil etc then you will get low compression due to worn rings and bores etc.
Aircraft engines have specified service intervals and if properly maintained and overhauled according to the book they should last almost forever.

It's a long time since I hung up my licences but in those days every aircraft was required to have two-year or three-year C of A overhaul and inspection, depending on schedule. Once put together the aircraft was test flown fully loaded and had to attain its scheduled climb performance, from memory Tiger Moth 580 ft/min, C150 620 ft/min, PA28R-180 970 ft/min. If they failed on climb it was usually due to poor compression due engine wear.
In support of Ancient Geek we had several Lycoming 'fours' running perfectly after 3,000 hours 'on condition' and one IO-360 with over 4000 SMOH. Of course we changed oil regularly, with spectro-analysis every 100 hours and results recorded on graphs (no computers then!) We also differential compression tested every 100 hours, again keeping graphs to build a long-term picture.

It's a simple job to have the cylinder compressions tested every once in a while. This is a good and reliable indicator of general engine health.

Agreed, but please NOT 'every once in a while'. The tests must be regular (as I said, 100 hrs) and must be recorded to build a maintenance picture which will show a trend in time for action to be taken.

Compression makes very little difference to power out. Cam wear makes the biggest difference and a big problem on low usage lycomings due to poor design placement of it on top of the crankcase and according to them the I0360 needs to be flown 40 hours a month to make TBO, this keeps the cam oiled. Even so I am very surprised any 10360 or O360 makes it as such a design mess.

I believe Oxford ran their Cherokee engines for up to 5000 hours provided they were only used for Airways training. Maybe they still do?

Yes ok but, it does depend on how the engine is used. 100 hrs per year - fine. 100 hrs in five years - not so fine !


I don't know about cam wear. I do know that if your compressions are down on even just one or two cylinders, You'll struggle at MAUW or even less, to separate yourself from the runway.

Compression does not tell anything on power, only on wear and oil consumption. Does anybody have the link handy to the publication on how they tried to study the effect and still had almost full power even with compression rings removed?

...But compression does tell us a lot about the general health of an engine, and a higher compression ratio = bigger bang = more power.


Haven't heard of that article but I'd be interested to read it. Not sure I'd like to run it for very long without the rings...

here is the answer to the 80% Power without piston rings question:
check-out Youtube "All About Cylinders (with callouts)" a seminar with Mike Bush

The Lycoming IO360 as used on a Cessna172S is the best general aviation aircraft engine ever made. Florida flight schools run them to 4000 hours, and replace the cylinders every 2000 hours with new ones. There is nothing wrong with rebuilt jugs by the way. Many schools use AvBlend oil additive to stop valves sticking.

I own a Lycoming O320. I change the oil and filter every 25 hours. I always use CamGuard oil additive, and Marvel’s Mystery Oil fuel additive. l fly it most weeks, but nowhere near 40 hours a month. Maybe 40 a quarter, but I still expect my zero timed engine to last indefinitely. Always fly at least once a month, for at least one hour, to keep it lubed up and condensation free.

Camshaft wear is caused by corrosion which forms on the lifters, causing them to pit. This then acts as sandpaper on the camshaft. 20w50 oil stays on a camshaft for about seven weeks, whilst SAE 40 or 50 lasts about five. 5% Camguard will prevent any corossion forming even in infrequently used engines.
The Lycoming engine design is not a mess. They make a great product. Just realize that an aircraft is designed to be flown. Use it or lose it. It is after all a tool, not a toy.

Mike Busch. I assume

Russ

In the 80s I attended a GAMTA Working Group meeting regarding JAA and engine lives. The German LBA stated that as the manufacturer recommended 2000hr or 10 years then that was all they could approve, no variation nor extension. It wasn't a question of condition more of public liability. The late Dick Stratton of CSE stated that they, with the approval of the CAA, ran the engines on their training fleet to 5,000 HR with cylinder changes at I think 1,000 HR. The problem was more with the specification of the oil as at that time multi grades were in their infancy and the specifications were based on technology that was then 50+ years old. Sadly we still suffer from such attitudes.

I've always wondered how the manufacturer determine these times. The required certification block test is a 150 hour run test - no longer.

Ah, oil, my favorite subject.

Multi grade oils are great, but they are not the ‘be all, and end all’ - ‘one size fits all’.
I use both Phillips XC20W50 and AeroShell 15w50 in Winter.
The W does stand for Winter after all.
The AeroShell along with the Exxon Elite brand are semi-synthetics.
The Phillips isn’t but it is much cheaper.
Does it make a difference, no not really.
But once my stock of Phillips XC is used up, I’m unlikely to buy more.
I get my oil from a distributor at the same price an airport would pay.
And a Twenty spot isn’t going to break the bank, so I upgrade to the semi.
Which brings me to, where and when I’d use multi weight.
US in Winter time, and likely all year round in Northern Europe.
But not in Summer in Southern Europe or the US.
In these conditions a straight weight oil is better.
I use Phillips Victory W100 and AeroShell 80 Plus depending on temperature.
The Phillips has the Lycoming additive in it.
The AeroShell has the Plus.
Exactly what the Plus is, I”m not sure.
But I’m not taking any chances.
I still use 5% CamGuard as a precautionary measure.

Obviously seals and gaskets dry up with age.
But CamGuard is also a conditioner.

I zero timed my engine.
Now I or somebody with my last name is going to run the thing out again.
Come he’ll or high water, I’ll drag it kicking and screaming to at least TBO.
And most likely far beyond.
I own two cars. One has 240,000 and the other 155,000 miles.
With correct maintenance they will do a whole lot more.

Flight schools do not change their oil but every 50 hours, and run leaded AvGas.
Personally I much prefer unleaded AutoGas.
I don’t think I’ll have any valve problems.

The next advancement will be semi synthetic straight weight oils.
Can’t wait !

So with the advent of modern lubricants, why can’t recommended TBO’s go to 3000 hours and 15 years?

A. not all old engines runs well on modern lubricants
B. somebody has to talk to troglodytes in administration
C. the engine manufacturer has to actively throw money for recertification of engines they don't want to survive - all below 5xx displacement is PITA to make profit from

My little 1974 Grumman AA1B has 2440 hrs total time on the original engine (Lycoming O-235 C1C). All 4 cylinders were replaced with new at 1800 hrs and I fully expect the engine will last longer than my flying career.

It flies 50 to 60 hrs airtime a year, but it never sits more than 2 weeks between flights and the oil is replaced at 25 hrs or 6 Months, which ever comes first. Regular use is the secret to engine longevity.

Continental disagree with you there.This link is interesting to read, I prefer to use a combination of oil analysis, compression tests in combination with a borescope examination to tell me how my engine is running. Compressions alone can be misleading.

PilotDAR mentions the static RPM test as a good indicator of engine performance. This AAIB report explains what this simple test may catch...