Nasa Icing courses

Strictly my opinion -

Your bad lobe is one of the cam lobes that operates two lifters, so it,
or its companion will be the first to go in a marginal lubrication
situation. The lobes depend on oil thrown from the crankshaft cheeks -
some thing that I don't think happens for a couple of minutes after a
cool start - and especially with a cold engine.

It isn't a question of how quickly does the oil pump get oil get to the
cam bearings as journal bearings will retain enough oil to allow them
to be starved for a minute or two and oil gets there in a few seconds
anyway.

More critical though is how quickly does the crankcase develop that
general fog/spray of oil to finally lubricate all the miscellaneous
(and expensive) surfaces such as cam lobes and cylinder bores. The cam
is at the top of the engine & the lobes are the last thing to get lube.
Possibly if the crank is turning too slow, gravity is such that thrown
blobs of oil can't even make it to the lobes until the oil; gets really
thin. Remember that a new engine will inherently have considerably
less oil leakage from the bearings.

That's why preheat is so important to a Lycoming engine. It isn't as
though it is someting that should be done (usually). It is something
that must be done religiously every time (especially with summer weight
oil) as once cam surfaces are scratched, failure isn't far away. The
longer an engine has been sitting, the more the need for preheat. The
newer the engine, the more the need for preheat too. When and how
much? Who knows.

Also - thick oil reduces the flow demand of the engine, and more of it
will simply blow over the relief valve. Oil that is bypassed this way
has no access to the heat of the engine. Oil warmup will be slow even
if the CHT is getting into an operating range.

My guess is that there was a cold start or cool start with summer oil
combination somewhere in its history although you indicated you always
preheated. Or maybe the cam which is supposed to be case hardened
isn't as hard as it should be. You might check the cam hardness with a
new file on another lobe. It should not be able to bite into it. If
it does, get a hardness test done on it.

On Sat, 07 Jan 2006 22:55:41 GMT, "John R. Copeland"
wrote:

"Scott Draper" wrote in message ...
You mean, Like you just did?

My reply went to every group, because his did (my newsreader did
that.).


Is it true that Forte Agent won't let you adjust the groups you reply to?
I knew it wasn't perfect, but I didn't know it was *that* defective.

Agent (and Free Agent) prompts after hitting reply - first box at the
top of the screen is the list of newsgroups the reply will be copied
to.

Even a 1000 rpm could be a little higher than ideal. It is
hard to say what causes problems sometimes. There are
manufacturing defects, there is a possibility that an oil
passage is partially plugged. Sometimes the mechanic who
assembled the engine can have missed getting assembly lube
on the cam or journal. If it is on a cam and or lifter,
even valve spring tension will effect the load on the wear
surfaces.

Best you can do is follow the engine manufacturer's
recommendations about starting and shutdown, oil changes,
etc and save money for the unexpected work.


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

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Ray Andraka" wrote in message
news:mQ2wf.41528$Mi5.36676@dukeread07...
| Jim Macklin wrote:
|
| Start with the throttle 1/2 open, zero rpm to 1800 with
no
| oil pressure. Etc.
|
|
|
| No, I don't start mine like that. On shut down, I set the
throttle for
| 1000 RPM and lock it. The throttle doesn't move again
until the engine
| is warmed up. I preheat religiously below 30F, and I
don't leave the
| preheater plugged in.
|
| Also, if it were corrosion that got mine, why only one cam
lobe?? My
| mechanic tells me there have been a rash of problems with
newer cams
| with flaws in the case hardening. I haven't seen evidence
to prove it
| though.

Check for valve sticking on that cylinder, that would raise
the pressure on the lifter/cam.


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

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Mark Hansen" wrote in message
...
| On 1/8/2006 5:51 AM, Jay Honeck wrote:
|
| 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?)
|
| Why?
|
| I wonder if this was the first cam lobe to actually fail.
Have they all
| been measured and determined to be within spec?
|
| --
| Mark Hansen, PP-ASEL, Instrument Airplane
| Sacramento, CA

It is to do with air flow, you don't get proper cooling and
crankcase ventilation is very poor on the ground.

After landing, cool down is as important as warm up,
particularly with a turbocharged engine.


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

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"A Lieberman" wrote in message
...
| On Sun, 08 Jan 2006 13:45:12 GMT, Jay Honeck wrote:
|
| Or, put another way, it's four 1-hour hamburger flights
per week, every
| week, all year long...
|
| Is this slightly low Jay? 1/2 hour each way? My
hamburger runs are
| minimum 1 hour each way, which would reduce it to 2
hamburger flights per
| week.
|
| You are right, 200 hours a year is an awful lot of flying.
You had me
| curious for me, how much in a year I fly, and it was as
follows:
|
| 2001 11.7
| 2002 49.5
| 2003 142.2
| 2004 192.9
| 2005 126.4
| 2006 4.0
|
| I try to fly once a week at minimum myself and no less
then one hour air
| time when I fly.
|
| I was told ground runs is one of the worst things you can
do to an airplane
| engine, as it was designed for sustained high RPM
operations, not ground
| run RPMS.
|
| Allen

"Morgans" wrote in message ...

snip

All of this would not be nearly as likely (it seems to me) if aircraft engines were equipped with rollers on the cams.
--
Jim in NC


Yes, the 'new' roller cams finally address this issue...

Low rpm does save the prop, it also keeps the load on the
bearings a little less, throttle jockeying is worst, cold
oil doesn't flow quickly in response to throttle changes.
Also, if you have a constant speed prop, the governor uses
engine oil, so avoid taxing the oil pressure with rpm and /
or prop changes until the oil has had a chance to warm up a
little.

It also came to mind, that a sticking valve will cause more
wear on that cam/lifter assembly, so that can be a problem
to check.

Most engines have the oil pump at one end and oil pressure
is measured from a point on the other end, probably a cam
shaft gallery so that you can tell that oil passages are not
blocked. That is one reason for the "shutdown in 30
seconds" if you don't have oil pressure on starting note.

I like to idle an engine for a minute (4-5 minutes with
turbocharged engine) to allow it to cool before shutdown
while still having oil cooling. This would be at
1,000-1,200 rpm so the prop would be blowing some air
through the cowl. I then think it is a good idea to
throttle back to minimum rpm, to see that the idle is smooth
at 500-700 rpm range and I do a mag grounding check at that
point and then pull the mixture to shut it down. That
should show a slight 25-50 rpm increase just as it shuts
down since idle should be a little rich.

I start the engine at minimum throttle and using as little
priming as possible [wait after priming a few seconds to a
minute in cold weather to allow the fuel to vaporize, liquid
doesn't burn and it washes the oil off the cylinder walls]
then after it starts, advance the throttle smoothly to 1000
rpm to get some prop wash cooling and generator output.

Change to oil often, it is a lot cheaper to change the oil
than to tear down the engine. Use the best oil you can find
and the multi-weight oils do start working/ pumping faster.
Oil changes can be done by the pilot/owner as preventative
maintenance. A logbook entry is required and you must
follow the service manual procedures. Be sure to check for
leaks after the change and be sure to safety any drain
plugs. A quick drain system makes it a lot easier to do,
and an extension hose on the drain will keep the cowl clean.
Filters may not need to be changed every time if the oil
change is due to calendar time and condensation draining.
The oil filter does work on engine time in service since it
only functions when the oil is flowing and being filtered.
But follow the manual, if it says change the filter with
every oil change, you should do so.


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

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Jay Honeck" wrote in message
news:_J8wf.714011$xm3.343650@attbi_s21...
| Start with the throttle 1/2 open, zero rpm to 1800 with
no
| oil pressure. Etc.
|
| I aim to keep RPMs at 1000 (or less) from start-up to
run-up. (My A&P
| showed me that 1000 RPM is too low to kick up stones, so
being patient and
| taxiing slowly really saves your prop.)
|
| What do you think causes a problem like Ray's, Jim? It
just seems to, I
| don't know -- random.
| --
| Jay Honeck
| Iowa City, IA
| Pathfinder N56993
| www.AlexisParkInn.com
| "Your Aviation Destination"
|
|

George Patterson writes:


"So why not build the shaft entirely of hardened steel?", I hear you cry. That's
because the harder steel is, the more brittle it becomes. The best strength
comes from this sort of lamination of hard and soft steels.

Saw a show w/ a Japanese craftsman making a sword. Two layers of
different steels. Pounded it thin; folded it over; pounded...
Many layers later, that was the sword...

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

"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

"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
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Spell checking is left as an excercise for the reader.