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.

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 - 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 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.

: 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 - 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.

It's quite unfortunate that the regulations make adding an oil
accumulator/pre-oiler cost-prohibitive for most. Pushing 60-80psi oil from the last
run into the system 30-60 seconds before hitting the starer would help a lot of this.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

"George Patterson" wrote

In the absence of some catastrophe, such as a bent pushrod, this is
generally caused by not flying enough.

Whenever I see less than 200 hours on an engine in a year, it seems like
there are tales of destruction of an engine to follow.

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

Whenever I see less than 200 hours on an engine in a year, it seems like
there are tales of destruction of an engine to follow.

???

That describes almost every privately owned aircraft at our airport. Only
trainers routinely put on more than 200 hours per year.

Mary and I fly more than anyone at the airport, and we just barely put 200
hours on last year.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Whenever I see less than 200 hours on an engine in a year, it seems like
there are tales of destruction of an engine to follow.

???

That describes almost every privately owned aircraft at our airport. Only
trainers routinely put on more than 200 hours per year.

Mary and I fly more than anyone at the airport, and we just barely put 200
hours on last year.

Really? I would have thought you put far more than that on, per year.

OK, then perhaps it is the frequency of being well warmed up that is the
more important factor. I have always read that the moisture that is the
killer, and when engines sit for more than a couple weeks, frequently, that
the rust begins killing the internals.

I wonder what the minimum time per year, and maximum frequency of running is
necessary to keep rust at bay?

Still, I think that only rollers touching the cams would be beneficial. I
wonder how many kits have been designed to retrofit popular lycosaruses?
--
Jim in NC

"Morgans" wrote in message
...

Whenever I see less than 200 hours on an engine in a year, it seems like
there are tales of destruction of an engine to follow.

???

That describes almost every privately owned aircraft at our airport.
Only trainers routinely put on more than 200 hours per year.

Mary and I fly more than anyone at the airport, and we just barely put
200 hours on last year.

Really? I would have thought you put far more than that on, per year.

OK, then perhaps it is the frequency of being well warmed up that is the
more important factor. I have always read that the moisture that is the
killer, and when engines sit for more than a couple weeks, frequently,
that the rust begins killing the internals.

I wonder what the minimum time per year, and maximum frequency of running
is necessary to keep rust at bay?

Still, I think that only rollers touching the cams would be beneficial. I
wonder how many kits have been designed to retrofit popular lycosaruses?
--
Jim in NC

I wonder if there is any statistical evidence on this issue regarding
incidences per region?

Are planes out here in the desert SW less prone to this?

Just wondering out loud...

Jay Beckman
PP-ASEL
AZ Cloudbusters
Chandler, AZ

I wonder if there is any statistical evidence on this issue regarding
incidences per region?

Are planes out here in the desert SW less prone to this?

Just wondering out loud...

That would be an interesting study. It might tell how much of a factor
condensation is.
--
Jim in NC

Jay Beckman wrote:
"Morgans" wrote in message
...

Whenever I see less than 200 hours on an engine in a year, it seems like
there are tales of destruction of an engine to follow.

???

That describes almost every privately owned aircraft at our airport.
Only trainers routinely put on more than 200 hours per year.

Mary and I fly more than anyone at the airport, and we just barely put
200 hours on last year.

Really? I would have thought you put far more than that on, per year.

OK, then perhaps it is the frequency of being well warmed up that is the
more important factor. I have always read that the moisture that is the
killer, and when engines sit for more than a couple weeks, frequently,
that the rust begins killing the internals.

I wonder what the minimum time per year, and maximum frequency of running
is necessary to keep rust at bay?

Still, I think that only rollers touching the cams would be beneficial. I
wonder how many kits have been designed to retrofit popular lycosaruses?
--
Jim in NC


I wonder if there is any statistical evidence on this issue regarding
incidences per region?

Are planes out here in the desert SW less prone to this?

Just wondering out loud...

Jay Beckman
PP-ASEL
AZ Cloudbusters
Chandler, AZ


Tanis has an article on engine corrosion
http://www.tanisaircraft.com/servicebullitens.html where they list a
bunch of factors leading to cam corrosion. If you go by that list, my
score comes out to 11 or 12 which they say makes my engine a candidate
for corrosion. The surprise to me was recent overhaul puts the engine
at risk. Digging into that more, it seems that a low time engine hasn't
had a chance to build up any varnish to protect surfaces. Now, I can't
see varnish building on the cam faces, so I don't entirely buy that.

The other surprise to me was that they claim multi-weight oil is bad for
corrosion resistance if the airplane is not flown very frequently (a
couple times a week) because it drains off too quickly. I vaguely
recall seeing a similar claim a while back.

So, I still don't know what caused my cam to fail, but articles like the
tanis one seem to indicate that even a relatively new cam can get rust
pits on the cam faces that can lead to an early demise.

They also advocate a engine ventilator to be used in conjunction with
full time preheat to dry out the crankcase. that's great if you can
leave it plugged in 24/7. I can't because I am in a group hangar where
the FBO regularly shuffles the aircraft around. I guess I'll switch
back to single weight oil and make it a point to fly at least once evey
7 days instead of at least once every 20 days like I had been doing.
Hopefully I'll avoid trashing another cam. In the mean time, I will be
trying to get a forensic analysis of the old cam to hopefully learn why
it failed.

I did see the cam lobe myself, and it was spalling rather profusely.
The adjacent lobes did not appear to have any pits or rough spots on them.

It seems to me that there ought to be a way to go in through the
dipstick with a filtered compressed air wand or something to fog oil in
the crankcase to get a pre-lube, as well as to periodically lube the
inside of the engine during a period of inactivity. Once the engine is
running there is plenty of oil flying around to keep everything lubed I
think, the problem is a dry start after a relatively short period of
inactivity, and a regular pre-oiler doesn't seem like it would get the
oil to the places it is really needed, ie the cam shaft, cylinder walls,
and accessory gears.

Mary and I fly more than anyone at the airport, and we just barely put
200 hours on last year.

Really? I would have thought you put far more than that on, per year.

200 hours per year is a LOT of flying, if you're not either (a) retired, or
(b) getting paid to do it.

It's the equivalent of flying from Iowa to Michigan -- and back -- every
week.

Or, put another way, it's four 1-hour hamburger flights per week, every
week, all year long...
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"