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.