Metal fatigue in Lycoming engines limiting its TBO?

Is anyone aware of statistical or other data that would indicate what
percentage of engines make it well beyond the factory specified TBO,
and how much longer they can be flown safely? I worry about sudden
engine failure due to metal fatigue.

Many of the small Lyc. engines have a TBO of around 2,000 hours. My
O-320-D3G (TBO 2,000hrs) has now 2,200 hrs since new, it's never been
opened for any reason. Of the above time, 1,100 hrs have been flown in
my RV-6.

I change oil (15W50) and full-flow filter every 50 hrs, cut-open the
filter for inspection, and have the oil analyzed. The compression is
still in the mid-70s.

I plan to continue flying until any of oil analysis/compression/oil
consumption would indicate a noticeable departure from their historic
values.
But the one other thing I worry about is the matter of metal fatigue,
which would not be indicated by any of the factors that I am
observing, but which could lead to engine stoppage.
If you have any data to support using these engines past their TBO it
would be much appreciated.

The parts subject to fatigue (crank and rods) are generally not replace
during overhaul.

Mike
MU-2

"Wolfgang" wrote in message
om...
Is anyone aware of statistical or other data that would indicate what
percentage of engines make it well beyond the factory specified TBO,
and how much longer they can be flown safely? I worry about sudden
engine failure due to metal fatigue.

Many of the small Lyc. engines have a TBO of around 2,000 hours. My
O-320-D3G (TBO 2,000hrs) has now 2,200 hrs since new, it's never been
opened for any reason. Of the above time, 1,100 hrs have been flown in
my RV-6.

I change oil (15W50) and full-flow filter every 50 hrs, cut-open the
filter for inspection, and have the oil analyzed. The compression is
still in the mid-70s.

I plan to continue flying until any of oil analysis/compression/oil
consumption would indicate a noticeable departure from their historic
values.
But the one other thing I worry about is the matter of metal fatigue,
which would not be indicated by any of the factors that I am
observing, but which could lead to engine stoppage.
If you have any data to support using these engines past their TBO it
would be much appreciated.

In rec.aviation.owning Mike Rapoport wrote:
: The parts subject to fatigue (crank and rods) are generally not replace
: during overhaul.

Right. They are inspected (magnafluxed, etc), but not replaced unless flawed.
If they are flawed (read: cracked). A cracked rod/crank/cam is NOT going to live for
2000 hours and then die at 2050 hours. It's going to die much quicker than that. If
it's worn much, it'll show up in the oil.

If the engine isn't abused (long periods of sitting, excessively high temps
cracking cylinders, subject to overly excessive thermal gradients, etc), it should run
for a good while.

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

"Wolfgang" wrote in message
om...
Is anyone aware of statistical or other data that would indicate what
percentage of engines make it well beyond the factory specified TBO,
and how much longer they can be flown safely? I worry about sudden
engine failure due to metal fatigue.

Many of the small Lyc. engines have a TBO of around 2,000 hours. My
O-320-D3G (TBO 2,000hrs) has now 2,200 hrs since new, it's never been
opened for any reason. Of the above time, 1,100 hrs have been flown in
my RV-6.

I change oil (15W50) and full-flow filter every 50 hrs, cut-open the
filter for inspection, and have the oil analyzed. The compression is
still in the mid-70s.

I plan to continue flying until any of oil analysis/compression/oil
consumption would indicate a noticeable departure from their historic
values.
But the one other thing I worry about is the matter of metal fatigue,
which would not be indicated by any of the factors that I am
observing, but which could lead to engine stoppage.
If you have any data to support using these engines past their TBO it
would be much appreciated.

IMHO, piston engines will most often fail gracefully in that they give good
indications of ill health well before outright failure. No guarantees, of
course. But, it's pretty hard to find a generally smooth running engine with
low oil consumption and good compression that has failed catastrophically.

The above does not extend to accessories like magnetos and fuel systems
which do fail suddenly and can result in an engine stoppage. It also
assumes that you know the history of this particular engine and that it has
enjoyed excellent maintenance without suffering any trauma like a prop
strike.

Wolfgang wrote:
Is anyone aware of statistical or other data that would indicate what
percentage of engines make it well beyond the factory specified TBO,
and how much longer they can be flown safely? I worry about sudden
engine failure due to metal fatigue.

Hours are not a good measure of the condition of an engine. I can
tell you from having a relatively low time Lycoming blow on me in
flight and seeing other engines go way past TBO even when subjected
to student flight training.

It's all a matter of how regularly it is flown and maintained.

The club I was in had a 172 with something like 2400 SMOH on it
(and it was over twice that much total time). The owner finally
relented and had it overhauled because the flying club president
was worrying too much.

Remember that while the engine may still be going strong, the
accessories (Bendix mags and the like) probably need more frequent
attention. There comes a point when you got to take it down anyhow
so you get the "might as wells" and open it up.

In article ,
Ron Natalie wrote:

Wolfgang wrote:
Is anyone aware of statistical or other data that would indicate what
percentage of engines make it well beyond the factory specified TBO,
and how much longer they can be flown safely? I worry about sudden
engine failure due to metal fatigue.

Hours are not a good measure of the condition of an engine. I can
tell you from having a relatively low time Lycoming blow on me in
flight and seeing other engines go way past TBO even when subjected
to student flight training.

It's all a matter of how regularly it is flown and maintained.

The club I was in had a 172 with something like 2400 SMOH on it
(and it was over twice that much total time). The owner finally
relented and had it overhauled because the flying club president
was worrying too much.

Remember that while the engine may still be going strong, the
accessories (Bendix mags and the like) probably need more frequent
attention. There comes a point when you got to take it down anyhow
so you get the "might as wells" and open it up.


The big problem on Lycomings is not fatigue, but corrosion of the #1 &
#2 cam lobes on engines infrequently flown. Moisture collects in the top
of the forward part of the crankcase, which is where the cam is located;
#1 & #2 cam lobes are right therre to get the moisture.

Very often you will see those cam lobes worn down more than the others
at overhaul. The engine will run, but power and smoothness will be
degraded.

"Orval Fairbairn" wrote in message
news
The big problem on Lycomings is not fatigue, but corrosion of the #1 &
#2 cam lobes on engines infrequently flown. Moisture collects in the top
of the forward part of the crankcase, which is where the cam is located;
#1 & #2 cam lobes are right therre to get the moisture.

Prop acting as a heatsink? Cooler at the front due to airflow?

Paul

Wellll...

The engine in our 172 was pulled this spring 'cause some
metal started coming of the rear most cam lobe...

2740 hrs...

All but the last 80 hrs were in flight training, (running
whenever the sun shone over a period of 4 yrs)..

Was a shame, running very smooth & strong, compression in high
70's....great oil press...

The inspections required for running it "on condition" were a
cost factor tho... so we yanked it at the 1st sign of (confirmed)
metal...

There was a certian amount of comfort in flying behind an
engine subjected to such rigorous attention that is required during
"on condition" time...

Fly it...and pay attention to it,, especially the
accessories, THEY seldom go the distance whereas the "engine"
probably will.. (at least a 320)

Dave


On 3 Nov 2004 10:25:09 -0800, (Wolfgang) wrote:

Is anyone aware of statistical or other data that would indicate what
percentage of engines make it well beyond the factory specified TBO,
and how much longer they can be flown safely? I worry about sudden
engine failure due to metal fatigue.

Many of the small Lyc. engines have a TBO of around 2,000 hours. My
O-320-D3G (TBO 2,000hrs) has now 2,200 hrs since new, it's never been
opened for any reason. Of the above time, 1,100 hrs have been flown in
my RV-6.

I change oil (15W50) and full-flow filter every 50 hrs, cut-open the
filter for inspection, and have the oil analyzed. The compression is
still in the mid-70s.

I plan to continue flying until any of oil analysis/compression/oil
consumption would indicate a noticeable departure from their historic
values.
But the one other thing I worry about is the matter of metal fatigue,
which would not be indicated by any of the factors that I am
observing, but which could lead to engine stoppage.
If you have any data to support using these engines past their TBO it
would be much appreciated.

For corrosion and other reasons stated by other posters, there is also
a time limit of 12 years that Lycoming suggests as TBO. If the engine
has not been torn down and inspected for 20 years, relying on hours
only is risky.

The limiting factor isn't generally crank/rod/ or other major
component fatigue (especially in those bullet-proof O-320s)but is
probably corrosion and cam/lifter spalling. Oil analysis might catch
either one. I doubt the factory has any info beyond that they would
or even could release.

From a strictly cumulative fatigue analysis standpoint there could
have been an innocent relatively short term event in the engine life
such as simply max throttle on a bitterly cold winter day that has
done most of the fatigue damage. Or it could simply be long term
operation at a wrong RPM where the crankshaft & prop are resonant.

This type of "abuse" exists, but the wise ones (i. e. the certifiers)
have decided and found that there is enough metal in this engine that
it seems to be able to handle it. Hence for example there is no
prohibited RPM range. Certainly the operating experience of a large
fleet helps reinforce this. Whether that is true for precisely all
supposedly identical engines and all conditions is impossible to say,
but the history on this engine series is probably the best in the
business. But engineering is an art, not a science. As one
(mechanical) I can understand why the factory is reluctant to say to
keep operating it.

I have an O-320 E2D in a 172M last assembled over 29 years ago, & now
at 1700 hrs TTSN. It has been opened only slightly for the oil pump
gear AD, but otherwise it has shown no deterioration in compression,
smoothness, or oil consumption over its lifetime. I'd like to think I
have run it pretty carefully, but I realize I am running a slight
chance. On the other hand, seeing the occasional AD show up on newly
manufactured parts scares me too. The comfort I have is that I
personally know the entire history of its operation. My decision is
to keep operating it.

Our IA once mentioned a Citabria in fish spotting duty out over the
Atlantic that had 3800 hrs on it without overhaul.

Unfortunately the limits of technology has to make it your call. But
others are doing it too.