Nasa Icing courses

On Mon, 09 Jan 2006 16:10:22 GMT, George Patterson
wrote:

As several others have pointed out, circulation of the oil isn't the problem
with the cam lobes. Those are lubricated by splash from the crank. I've never
seen any claims that this differs much from splash while in flight, though.

I actually thought this was a joke when I read it in a previous post.
You mean to tell me that the cam REALLY gets it's lubrication from
splash?

The crankshaft has to whip it's throws into the oil in the oil pan so
that the oil gets whipped around inside the engine and THAT's how the
cam gets oiled?

Lordy, thought that technology went out with Model T's

I can't think of a single engine in the automotive world that depends
on splash oil to lubricate anything.

No wonder auto oil is not supposed to be used in airplane engines.

Corky Scott

On Sun, 8 Jan 2006 19:41:33 +0000 (UTC), David Lesher
wrote:

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...

Right, but the entire blade is heat treated so that it is tempered,
rather than hard. If it were made from the kind of steel that
camshafts were cast from, it would be very brittle.

Not many camshafts, in low rpm engines, require forged camshafts,
there just isn't much pressure on them because they spin so slowly and
the valve springs aren't very stiff. But all camshafts require heat
treating the outer layer, or they'd wear out very quickly.

Corky Scott

On 1/18/2006 11:44 AM, wrote the following:
On Mon, 09 Jan 2006 16:10:22 GMT, George Patterson
snip

I can't think of a single engine in the automotive world that depends
on splash oil to lubricate anything.


Hmm ... In every engine I've ever assembled the cam lobes running against the
tappets are splash oiled. In pushrod motors the rocker arm noses running
against the valve stems are splash oiled. Also the timing chain(s), the
distributor drive gear, ... Pretty much it is only the bearings that are
pressure oiled. i.e., mains, rods, cam(s).

YMMV, of course.

wrote:

Right, but the entire blade is heat treated so that it is tempered,
rather than hard. If it were made from the kind of steel that
camshafts were cast from, it would be very brittle.

No, David had it right. Japanese cutting tools are made by laminating hard,
brittle steel with soft, mild steel. The best place to see this these days is
chisels or plane blades. There are only two layers in these; the outside layer
is very hard and the inside very soft (for tool steel, that is).

This has the disadvantage that the cutting edge is much more easily damaged than
that of a western blade. It is, as you point out, brittle. They were never
designed to be used in buildings with concrete floors or environments that
include nails.

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

On Wed, 18 Jan 2006 13:40:21 -0600, Mitty wrote:

In pushrod motors the rocker arm noses running
against the valve stems are splash oiled. Also the timing chain(s), the
distributor drive gear, ... Pretty much it is only the bearings that are
pressure oiled. i.e., mains, rods, cam(s).

The engines pushrod engines I've assembled had hollow pushrods and fed
pressurized oil to the rocker arms. The rocker arms were hollow and
injected oil onto the valve stem to assist in cooling. Yes, the top
of the valve stem did not have any direct injection so it did require
splash oil for it's lubrication. That's where roller rockers help.

Guess I hadn't thought that much about it for a long while. I stopped
working as an auto mechanic a long time ago.

Corky Scott

How, in a horizontally opposed engine with an external oil sump (like on
the C85 or 0200 or lots of others) do the crankshaft lobes "splash" oil
anywhere meaningful? The cam has to be lubed by some other mechanism.


-----Original Message-----
From:
]
Posted At: Wednesday, January 18, 2006 3:05 PM
Posted To: rec.aviation.ifr
Conversation: Nasa Icing courses
Subject: Engine Making Metal (Was: Nasa Icing courses)

On Wed, 18 Jan 2006 13:40:21 -0600, Mitty wrote:

In pushrod motors the rocker arm noses running
against the valve stems are splash oiled. Also the timing chain(s),
the
distributor drive gear, ... Pretty much it is only the bearings that
are
pressure oiled. i.e., mains, rods, cam(s).

The engines pushrod engines I've assembled had hollow pushrods and fed
pressurized oil to the rocker arms. The rocker arms were hollow and
injected oil onto the valve stem to assist in cooling. Yes, the top
of the valve stem did not have any direct injection so it did require
splash oil for it's lubrication. That's where roller rockers help.

Guess I hadn't thought that much about it for a long while. I stopped
working as an auto mechanic a long time ago.

Corky Scott

Jim Carter wrote:
How, in a horizontally opposed engine with an external oil sump (like on
the C85 or 0200 or lots of others) do the crankshaft lobes "splash" oil
anywhere meaningful?

Disclaimer: I have no specific knowledge of the engine models mentioned.

The oil that's pushed under pressure through the crankshaft rod and main
bearings has to go somewhere. I picture it as a sort of whirling fog of oil
droplets inside the crankcase.

Specifically, *don't* picture the various crankshaft protrusions actually
contacting the surface of a pool of oil, that's not what happens.

The cam has to be lubed by some other mechanism.

The cam bearings have their own oil passages and are lubricated under pressure
from the oil pump. The cam lobes have no such lubrication.

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.

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.

It would probably require the oil to be warm to atomize it. There is a
major baffle system in the crankcases that prevent the oil from being
sucked into the whirling machinery. That baffle system would tend to
defeat most attempts at atomization in the sump. It wouldn't take much
oil though to fog things enough to eventually get the insides of the
crankcase wet. I'd like to try it sometime to find out. Anyone want
to saw a hole in their crankcase?

I generally agree with Tanis on the importance of cold start preheat,
but my '75 C172M is now at 1700 TTSN & has never been apart.
Compression and oil consumption hasn't changed, & obviously it gets
flown infrequently. The last oil analysis was 5.8 PPM of iron. It
has a Tanis score of about 17. I only preheat the oil & use a blanket
on the engine.

The key, especially with Lycomings, is to NEVER do a cold start without
preheat below like 40 degrees - warmer if it has been sitting for some
weeks & warmer if you don't have winter oil, but otherwise keep it cold
if it is not being flown.

I now have started to shut off the fuel & run the carb empty if it
isn't going to be run for a week or more. I try to purge the engine of
combustion gasses & use autofuel almost exclusively. It really helps
restarting next time with autofuel.

Ray Andraka wrote

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.

Ray, do a search on the Lyc o-320H engine. The "H" engine had a real
bad habit of cam failure until the FAA put out an AD mandating that a
particular additive be used in the oil. This seemed to fix the
problem, I taught in one particular 172N for six years with never a
problem. The additive was so good, that it is now a standard
ingredient of the AeroShell multigrade oil. I see this "snake oil"
being sold over the counter at Sun n Fun, but the name escapes me
right now. I would't switch if I were you.

Bob Moore