Nasa Icing courses

Jay Honeck wrote:

Other than that, we haven't flown diddly squat in weeks. Our last fly-in
guest was sometime around Thanksgiving. Worst flying weather I've ever
seen.

So between the weather and my work backing up, at least my engine picked
a good time to make metal. It is off the airplane waiting for the crate
to arrive from Penn Yan. I last flew on a return trip over Thanksgiving
weekend. Pulled the filter right after that trip (11 hours after
finding metal in the filter during the october annual) and found as much
metal as the previous 30+ hour filter had in it, so I grounded it.

The engine is 26 months and 178 hours out of a new limits Penn Yan
overhaul with new ECI titan stud assemblies, new cam, new accessory
gears, new oil pump, all new accessories, etc. About all that wasn't new
was the crank and case, and those were reworked during the overhaul.

The intake cam lobe for the #3 and #4 cylinders failed and is worn down
considerably, hence the engine coming off and waiting for the crate.

The intake cam lobe for the #3 and #4 cylinders failed and is worn down
considerably, hence the engine coming off and waiting for the crate.

I've been following your engine woes with great interest, Ray, and not a
small bit of horror. To say you are living one of my worst nightmares is
not far from the truth, and I feel your pain.

Does anyone *really* know what causes a camshaft to fail like this? I read
about it happening with alarming regularity, and it's never attributed to
anything in particular. It's always treated like an act of God, or like a
weather phenomenon, rather than like the mechanical failure it is.

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?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:

Does anyone *really* know what causes a camshaft to fail like this? I read
about it happening with alarming regularity, and it's never attributed to
anything in particular.

In the absence of some catastrophe, such as a bent pushrod, this is generally
caused by not flying enough. The layer of hardened steel on a camshaft is fairly
thin. Let the plane sit long enough, and rust will form. When the engine starts
again, the rust is worn away, making the thin layer of hardened steel thinner.
The worst wear points, of course, are the tips of the lobes. Once the hardened
steel wears through, the softer steel underneath goes pretty rapidly.

"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.

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

There is also the fact that the oil pump is at one end of
the engine and the cam shaft lobe that fails is probably at
the other [a guess] and the oil takes some time to reach the
journal and establish a full oil bearing.

Add a little sludge, maybe some cold oil and an over-revved
engine, and you get cam lobe /journal failure or the lifter.

Pilot error due to poor operation.


--
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.


"George Patterson" wrote in message
news:J11wf.517$sa4.41@trnddc07...
| Jay Honeck wrote:
|
| Does anyone *really* know what causes a camshaft to fail
like this? I read
| about it happening with alarming regularity, and it's
never attributed to
| anything in particular.
|
| In the absence of some catastrophe, such as a bent
pushrod, this is generally
| caused by not flying enough. The layer of hardened steel
on a camshaft is fairly
| thin. Let the plane sit long enough, and rust will form.
When the engine starts
| again, the rust is worn away, making the thin layer of
hardened steel thinner.
| The worst wear points, of course, are the tips of the
lobes. Once the hardened
| steel wears through, the softer steel underneath goes
pretty rapidly.
|
| "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.
|
| George Patterson
| Coffee is only a way of stealing time that should by
rights belong to
| your slightly older self.

Add a little sludge, maybe some cold oil and an over-revved
engine, and you get cam lobe /journal failure or the lifter.

Can you expand on that a bit, Jim? What, exactly, is an "over-revved
engine"?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Start with the throttle 1/2 open, zero rpm to 1800 with no
oil pressure. Etc.


--
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
newsb1wf.471788$084.269539@attbi_s22...
| Add a little sludge, maybe some cold oil and an
over-revved
| engine, and you get cam lobe /journal failure or the
lifter.
|
| Can you expand on that a bit, Jim? What, exactly, is an
"over-revved
| engine"?
| --
| Jay Honeck
| Iowa City, IA
| Pathfinder N56993
| www.AlexisParkInn.com
| "Your Aviation Destination"
|
|

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.

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"

Jim Macklin wrote:
There is also the fact that the oil pump is at one end of
the engine and the cam shaft lobe that fails is probably at
the other [a guess] and the oil takes some time to reach the
journal and establish a full oil bearing.

Add a little sludge, maybe some cold oil and an over-revved
engine, and you get cam lobe /journal failure or the lifter.

Pilot error due to poor operation.



This is on an O-540. The cam lobe that wore is in the center of the shaft.

So how long is too long to sit? The longest my airplane sat between
flights since the O/H was one stretch of 7 weeks while it was in the
shop for corrosion repair on the belly. Second longest was also in the
shop for 4 weeks for a new interior. Other than that it has been flown
a minimum of every 20 days.

So if it is pilot error, I am all ears as to what I can do to improve my
technique. So far, no one has been able to tell me anything I did
wrong, including Penn Yan.

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.