Wear and friction are not less because the power output is
reduced at altitude. Bearing wear increases clearances and
oil pressure will decrease. You can detect some of the wear
by careful inspection of an assembled engine. There are
some things that can't be checked without engine
disassembly. If you tear the engine down, you might as well
complete the overhaul.
TBO is only mandatory in commercial operations. Because of
the cost of being sued, most FBO do overhauls at TBO because
juries decide. Private owners are free to do what they
want. Compression can be checked and since aircraft engines
use individual cylinders, rings and valves can be repaired
one cylinder at a time as required. That does not alter TBO
time.
Overhaul includes all components and accessories, such as
magnetos. A freshly overhauled engine [or a new one] is
suspect for the first 100 hours.


--
James H. Macklin
ATP,CFI,A&P


"gman" wrote in message
ups.com...
| Hello All,
| Where I fly, the density altitude on the tarmac is
typically more than
| 7000ft even on cold days (9000ft on hot days). As a
result, non-turbo
| engines cannot develop any more than 70% of rated power.
|
| The consensus around here is that as long as the engines
are blessed by
| the mechanics and checked for compression, one can exceed
the
| recommended TBO sometimes by a factor of 2x.
|
| My question is this: Is this practice safe? What about
material fatigue
| in the engine components (i.e. crank shaft, pistons, rods,
valves etc)?
| Would this practice make the chances of an engine failure
more likely?
|
| Thanks.
|