Metal fatigue in Lycoming engines limiting its TBO?

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.