Nasa Icing courses

"Jay Honeck" wrote in message news:
And mechanical failures should have simple explanations, no? WHY did
one of the cam lobes fail? Why didn't ALL of the cam lobes fail?

Timeless issue. www.aviationconsumer.com has hours of reading on the
subject. The common factor is infrequent flying.

I suppose the *real* issue should be: Why do camshafts work at all? When
you sit down and rationally analyze what is happening inside your engine,
the danged thing should just throw itself to pieces in the first ten
minutes of operation.

Yet, most of them don't.

Some, however, like Ray's engine, do -- and in very peculiar ways. (Just
ONE cam lobe went bad?)

I've gone through a couple on one engine and they had those exact symptoms.
One AME suggested that the front lobes wear more quickly since the cam is
slightly elevated at the front so the oil drains off more quickly. There
are as many theories as worn cams, it sometimes seems.

moo

"Happy Dog" wrote in message
...

I've gone through a couple on one engine and they had those exact
symptoms. One AME suggested that the front lobes wear more quickly since
the cam is slightly elevated at the front so the oil drains off more
quickly. There are as many theories as worn cams, it sometimes seems.


Especially when you take your engine to your flight physical! :-)

"Jay Honeck" wrote in message
news:jN8wf.472265$084.362812@attbi_s22...
....
I suppose the *real* issue should be: Why do camshafts work at all? When
you sit down and rationally analyze what is happening inside your engine,
the danged thing should just throw itself to pieces in the first ten
minutes of operation.

Yet, most of them don't.

The oil film, when all goes well, prevents actual metal to metal contact.
Just like the plain bearings on the crankshaft.

Google the word "tribology": WEB RESULTS 1 - 10 of about 48,500

--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

The oil film, when all goes well, prevents actual metal to metal contact.
Just like the plain bearings on the crankshaft.


I had to have my engine (Lycoming O-235) overhauled last year at less than
1/2 TBO, partially for cam pitting. Prior to my owning it, it hadn't flown
too much for the past few years.

Now, I'm flying every 2 weeks, at least, if weather permits, and am using
Avblend. This additive is supposed to better impregnate the metal, and
prevent some of this corrosion.

I now have the plane in a hanger, instead of outside in the cold and added
moisture.


The few things I've heard about causing the problems a

Flying too infrequently, with oil seeping off the cam and moisture eating at
the exposed surfaces.

When flying happens, not getting the oil completely hot, so as to eliminate
the moisture from it.

Running the engine too slow at startup. Apparently, the cams in some
engines get lubrication mainly from the oil splashing around inside the
case. In some engines, 1000 RPM may not be sufficient for full lubrication
after startup. My A&P suggested 1100 - 1200 RPM.


I'm certainly hoping that the steps I'm taking will keep the engine in good
shape. I can't afford another overhaul anytime soon.

Paul Missman

"Paul Missman" wrote in message
...

....
The few things I've heard about causing the problems a

Flying too infrequently, with oil seeping off the cam and moisture eating
at the exposed surfaces.

When flying happens, not getting the oil completely hot, so as to
eliminate the moisture from it.

That's one thing that could be changed on aircraft engines that would give a
LOT of bang for the buck - positive crankcase ventilation. Huge reduction in
unburned hydrocarbons (you may or may not care about that), and a lot less
moisture in the crankcase - engines last a lot longer.

The straight up auto style PCV valve probably wouldn't be the way to go,
though. It won't get you much at higher altitudes where you have the
throttle wide open.

Running the engine too slow at startup. Apparently, the cams in some
engines get lubrication mainly from the oil splashing around inside the
case. In some engines, 1000 RPM may not be sufficient for full
lubrication after startup. My A&P suggested 1100 - 1200 RPM.

Anything's possible.


--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

Running the engine too slow at startup. Apparently, the cams in some
engines get lubrication mainly from the oil splashing around inside the
case. In some engines, 1000 RPM may not be sufficient for full
lubrication after startup. My A&P suggested 1100 - 1200 RPM.

Isn't that a stitch? Your A&P says 1000 RPM is too *slow* for proper
lubrication. Jim Macklin (and many others) says it may be too *fast* to
run your engine before proper lubrication has occurred. Who is right?

And my A&P says 1000 RPM or slower, primarily to save your prop on loose
rocks but also to ensure long engine life.

Argh. Wouldn't you think there would be SOME science to this?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:

Argh. Wouldn't you think there would be SOME science to this?

If there is, it's available from Lycoming or Continental for your engine. Not
from "my A&P says...."

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.

"Jay Honeck" wrote in message
news:Hxkwf.474673$084.253721@attbi_s22...

Isn't that a stitch? Your A&P says 1000 RPM is too *slow* for proper
lubrication. Jim Macklin (and many others) says it may be too *fast* to
run your engine before proper lubrication has occurred. Who is right?


Your O-540 is probably better at oil distribution than my O-235. Your
engine is substantially larger and more expensive. They can afford to give
it a better oiling system than exists in a smaller, cheaper engine.

As for trusting Lycoming to tell us: I believe they have a commitment to
safety, but they also make money from parts, like cam shafts. Adding to
that, summer is much different than winter oil at startup, not to mention
cylinder clearances. On startup, do you want the cylinders to wear out
faster, or would you rather protect your cam? You may not be able to have
both in an optimum fashion on some engines. Less RPM may help the
cylinders, but leave the cam with less lubrication. It makes me wish that
all cams had a direct spray oil system, and that there was an electric oil
pump that could be used to lubricate the engine prior to startup.

Paul Missman

Jay Honeck wrote:
Running the engine too slow at startup. Apparently, the cams in some
engines get lubrication mainly from the oil splashing around inside the
case. In some engines, 1000 RPM may not be sufficient for full
lubrication after startup. My A&P suggested 1100 - 1200 RPM.


Isn't that a stitch? Your A&P says 1000 RPM is too *slow* for proper
lubrication. Jim Macklin (and many others) says it may be too *fast* to
run your engine before proper lubrication has occurred. Who is right?

And my A&P says 1000 RPM or slower, primarily to save your prop on loose
rocks but also to ensure long engine life.

Argh. Wouldn't you think there would be SOME science to this?

You'd think so, and maybe there is, but if so it hasn't penetrated the pilot
community. Most of what you read is superstition, collective wisdom, common
sense, anecdotal reports, opinion, experiments run with small sample sizes.
Seems the best you can do is to read all the recommendations and try to do the
things that make sense to you. It's frustrating.

Dave

Jay Honeck wrote:

Some, however, like Ray's engine, do -- and in very peculiar ways. (Just
ONE cam lobe went bad?)

Why?

Once again. When the layer of hardened steel wears through, the rest of the lobe
wears *very quickly*.

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.