Cracked cylinder: Typical cause?

What would be the most likely reason a cylinder in a high-time engine
would crack, old-age or poor temperature management on a descent?

--
Peter

Neither


"Peter R." wrote in message
...
What would be the most likely reason a cylinder in a high-time engine
would crack, old-age or poor temperature management on a descent?

--
Peter

kage ) wrote:

Neither

Sorry for asking a close-ended question. If you could expand on your
"neither," this rather inexperienced poster could learn something.

--
Peter

Lousy Continental engineering.

Jim

Peter R.
shared these priceless pearls of wisdom:

-What would be the most likely reason a cylinder in a high-time engine
-would crack, old-age or poor temperature management on a descent?



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Peter R. wrote:
: What would be the most likely reason a cylinder in a high-time engine
: would crack, old-age or poor temperature management on a descent?

Pull power, full rich, shove nose over. Guy parked next to me has an
Archer, flies maybe 100 hours/year. Goes through at least one cylinder/year,
sometimes 2 or 3. That's his secret: at the top of descent he pulls power
to idle, goes to full rich, and shoves the nose over. Please note that
the full rich bit is required to properly master cylinder cracking. If you
leave the mixture alone until level-off you'll not have any trouble. Better
yet if you leave both the throttle and mixture alone.

You should have heard this guy going on at Oshkosh. He visited each cylinder
vendor that he's tried and they all suggested that he leave the mixture leaned.
He wasn't interested in their viewpoint, he just wanted to beat them up
about lousy quality.
--
Aaron Coolidge

The answer is primarily "metal fatigue" and design margins.

For steel if the stress is below about 15% of ultimate yield then it
does not fatigue. However the lower fatigue limit for aluminum is
ZERO. Aluminum always fatigues no matter what the stress level is.
Every time the cylinder fires the steel barrel and the aluminum head
gets a stress cycle. The stress is proportional to the peak cylinder
pressure which varies with power output of the engine. The number of
cycles to failure verses stress level is not linear. Since it is non
linear if you design a part that is subject to cyclic stress then
half the stress it will last much more than two times as long before
it cracks.

If you buy a rebuilt cylinder you do not know if it has 500 hours or
5000 hours. You also can not always tell if it has already cracked
and been welded.

In my opinion flying through a rain storm would shock cool a cylinder
MUCH faster than a sudden power reduction.

(This is my opinion and I am sticking to it until I have test data to
indicate otherwise.)
John


On Sat, 2 Oct 2004 10:35:36 -0400, Peter R.
wrote:

What would be the most likely reason a cylinder in a high-time engine
would crack, old-age or poor temperature management on a descent?

"kage" wrote in message ...
Neither


Oh, come on. Cylinders suffer from age-related thermal damage
just like any other metal machinery that's subjected to heat.
Detonation can also be a factor in such cases.

Dan


"Peter R." wrote in message
...
What would be the most likely reason a cylinder in a high-time engine
would crack, old-age or poor temperature management on a descent?

--
Peter

If you buy a rebuilt cylinder you do not know if it has 500 hours or
5000 hours. You also can not always tell if it has already cracked
and been welded.

Why in the world would anyone buy a rebuilt cylinder nowadays?

The price differential between new and used is so small -- and the risks are
just too great.

Heck, I wouldn't put a rebuilt cylinder on my CAR (not that any such thing
is ever necessary on modern automobiles), let alone an airplane.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Why in the world would anyone buy a rebuilt cylinder nowadays?

The price differential between new and used is so small -- and the risks
are
just too great.

Heck, I wouldn't put a rebuilt cylinder on my CAR (not that any such thing
is ever necessary on modern automobiles), let alone an airplane.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"


On a similar note, if a cylinder compression was low, would you rebuild it,
or buy a new one?

Adam

Peter R. wrote
What would be the most likely reason a cylinder in a high-time engine
would crack, old-age or poor temperature management on a descent?

While both are possible, neither is most likely.

When considering what causes an aviation problem, you need to consider
what aspect is most under the control of the FAA. That will be the
biggest problem.

In this case, the FAA controls design (through the awarding of a type
certificate or STC or writing the TSO) and manufacturing/quality
control (through the awarding of a production certificate or PMA) so
those are in fact the two most likely reasons for cylinder cracking -
poor design and poor QC.

Michael