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Message
Yo Rusty,
My experience has been that there are 2 basic
failure modes when oil pressure is lost.
1. At heavy loads and high RPM, (as in
race engines at WOT) the main problem is that the side housings require oil
spill from the rotors to cool them. Should the oil flow stop, and
the engine continue to be held at full throttle (which is not your
scenario), the side housings close to the crank hole tend to get hot
and buckle like a belville washer, and in the process grip the rotors like
a vice and cause the engine to seize.
I've even had a couple of blokes come to me saying
that they have experienced total lockup on the open road. This usually
occurs due to oil surge on long sweeping corners at high speed (esp long
expressway sweepers in the middle of the night!) when the oil level
is low (coz the owner hadn't checked it for the last 3 months!!), and it
uncovers the pick-up.
Lockup can occur within 10 -15 seconds of
losing oil pressure at WOT. If the driver isn't smart enough to de-clutch
immediately, the back wheels will remain locked, and flatspot the
tyres all the way to the steel belts as the car spins out of control into
whatever happens to be on the side of the road! Scary Stuff!!
Even if the engine doesn't seize, it
will have badly scuffed oil control rings and the side
housings. Additionally, there is obviously always bearing
damage, but normally, the engine will lock up on the side houings
before it will seize on the bearings.
The next time you start the engine, it will
blow copious amount of oil smoke for ever. The only solution is to split
the engine, re-machine the faces and fit new oil control rings and
bearings. However, as you took the power off the instant you noticed the
oil leak, I don't think this would have happened to your engine. (Whew he
says!!).
2. If the engine loses oil pressure say
at idle, or low RPM, the most likely damage is that it will pick up
the front stationary gear bearing. If the engine is run at moderate speeds
and light load, it can also pick up on the rotor bearings on
occasion, sometimes causing them to spin in the rotors, but the
front gear bearing is usually the first to grab.
So there are the two worst
case failure modes you can
expect. From what you have described, I would think that there would
be very little damage, if any. After all, even though the
cooler was leaking, there appears to have been some oil flow, and
you took the load off the engine the isntant you noticed the leak. I would
suspect that if there is any damage, it will only be light scuffing or wiping of
the bearings.
The only REAL way to know is to split the
engine and inspect it. However, first do some simple
preliminary diagnosis. Open up the oil filter as Lynn
suggested, and if it doesn't have any metal in it, the the engine is
probably OK. As a second check, make a small loop in a piece of
wire, and scrape the bottom of the sump through the drain plug.
If you have internal damage, you will get
metal deposits (babbitt metal any maybe some copper) on the wire
loop. Thirdly, if there happens to be fine metal in the
oil, you will be able to see it in a bottle backlit with strong
sunlight. If the oil is black, put some on a sheet of plastic or
Gladwrap and view it via transmitted light. Generally has the appearance of
metalflake paint. An oil analysis will pick up any occult metal that is too
fine to be seen with the naked eye.
If all is clear, then the engine is probably
not damaged, so fit a new filter, re-fill with oil, start
her up and do a couple of precautionary filghts as you suggested
below.
Cheers,
Leon.
----- Original Message -----
Sent: Sunday, December 19, 2004 4:36
AM
Subject: [FlyRotary] Engine damage
thoughts
Greetings
again,
I've been thinking more
about the engine, and wondering what the chances are that there's any damage
inside.
I'm pretty sure I noticed
the oil about the instant it started to lose any significant amount. As
soon as the oil started to leak, I pulled the engine back to idle, and
descended ASAP. I'm sure I was doing at least 2000 fpm from 6000 to
2000 ft, which only accounts for 2 minutes of time. At 2000 ft, is when
I tried to throttle up, and the engine quit, so no time after that
counts. I'm absolutely sure the engine quit because I had the
mixture knob set way lean for cruise, and not because it seized up.
This means that at worst,
the engine idled for 2 minutes with no oil pressure. My guess would be
that it was more like 30 seconds or less. With this in mind, I'm
thinking that it's worth doing some ground runs of the engine to see how
healthy it seems. If I can thoroughly run it on the ground without
problems, then I can follow that with about 10 hours of circling the
field. By that point, I can't imagine having any further concerns.
If there was a problem, it would damage the engine further, but still continue
to until I made it to an airport. If I'm wrong about how
much damage there might be, it will get expensive, but shouldn't be life
threatening.
Many of you have a lot
more experience with these engines than I do. Does this sound like a
reasonable plan?
Thanks,
Rusty (late for the
airport as always)
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