Nasa Icing courses

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.

"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"

"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...

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

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...

Yep, that's a very old technique. Westerners call it "Damascus steel."

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

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 Sun, 08 Jan 2006 05:02:33 GMT, George Patterson
wrote:

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.

The automotive world tried out roller lifters a long time ago. They
would work fine in aircraft engines too. I've heard that some of the
engines built for the homebuilt market can and do incorporate roller
lifters. I even thought I read that at least one company was
intending to certify such an engine.

Corky Scott

wrote in message
news
On Sun, 08 Jan 2006 05:02:33 GMT, George Patterson
wrote:

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.

The automotive world tried out roller lifters a long time ago. They
would work fine in aircraft engines too. I've heard that some of the
engines built for the homebuilt market can and do incorporate roller
lifters. I even thought I read that at least one company was
intending to certify such an engine.

Corky Scott

It is not uncommon to see roller rockers on round engines.

wrote:
On Sun, 08 Jan 2006 05:02:33 GMT, George Patterson
wrote:


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.


The automotive world tried out roller lifters a long time ago. They
would work fine in aircraft engines too. I've heard that some of the
engines built for the homebuilt market can and do incorporate roller
lifters. I even thought I read that at least one company was
intending to certify such an engine.

Corky Scott


Lycoming is starting to offer roller tappets. The crankcase has
different bores for the tappets, so an upgrade to the roller tappets
requires a new crankcase, as well as a different cam, different tappets,
pushrods, pushrod tubes and seals. They are not offering a retrofit to
the older narrow deck engines like mine.