Strange engine event

"Jim Carter" writes:


What causes the piston rings to rotate? Since the piston movement is
perpendicular to the cylinder wall, there must be some other mechanism other
than just piston movement causing them to rotate.

Very Clever Design. I can't recall the details, but ISTM there are
[automotive] patents on making 'em creep along.

Also, why would the grooves on the rings have to be lined up to allow
leakage through the groove?

It does leak lots more; the gap between the rings is not all that
far, I guess...

--
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

perpendicular to the cylinder wall, there must be some other mechanism other
than just piston movement causing them to rotate.


I just can't get it into my head how that a ring can be put in and when the
engine is torn down all of the grooves will be in the same place as when
installed.

The keepers on a two cycle boat engine (not motor) are the only anti - Rotation
device that I have seen.

Dave,
I've torn engines down before and the distance between the rings is
relatively a lot more than the gap between the ends of the ring when
compressed into the cylinder. It is such a big difference that I don't see
how the intra-ring distance could be restrictive to the flow of gasses
passing through the ring gap.

I'd really like to see some information on the "Very Clever Design" you
mentioned. Even if the cylinders were honed with a diagonal pattern,
shouldn't the ring just reverse direction at the end of the stroke and
follow the honing marks?

--
Jim Carter
"David Lesher" wrote in message
...
"Jim Carter" writes:


What causes the piston rings to rotate? Since the piston movement is
perpendicular to the cylinder wall, there must be some other mechanism
other
than just piston movement causing them to rotate.

Very Clever Design. I can't recall the details, but ISTM there are
[automotive] patents on making 'em creep along.

Also, why would the grooves on the rings have to be lined up to allow
leakage through the groove?

It does leak lots more; the gap between the rings is not all that
far, I guess...

--
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

The piston really only approximately goes straight up and down.
Engines are not perfect machines. If you looked at the general
dynamic alignment of everything on the microinch level etc, there is
probably a slight amount of rotation inherent in the structure of an
engine including the crankshaft and rod deformations. When combined
with the varying pressure fluctuations on each ring, the ring
gradually rotates
in one direction or another. Remember you are dealiung with something
that is cycling back and forth 40 times per second, so that it doesn't
take very much rotation each cycle to give a lot of eventual motion.

Put it another way - why shouldn't it rotate?

I don't think it should rotate because the action of scrubbing against the
cylinder walls will wear "micro" grooves in the rings that match up against
corresponding ridges on the cylinder wall. If the rings rotated there would
never be this ridge/groove result. Since you can see and sometimes feel the
grooves and ridges, I can only assume the rotation of the ring is not
happening.

--
Jim Carter
wrote in message
om...

....

Put it another way - why shouldn't it rotate?

Doesn't sound like a probe problem, as unlikely the 2 probes on the

If an exhaust valve stuck partially open it would raise your EGT and lower your
CHT

If an exhaust valve stuck partially open it would raise
your EGT and lower your CHT

That seems like a more likely explanation than the blocked
fuel injector. The reason I think so is that on the previous
annual the other to cylinders on that side (#3 and #5) were
removed to have their exhaust valves replaced and guides
repaired. (At only 300 hours! I guess Continental still hasn't
figured out how to make cylinders like the did in the 70's
and 80's). So if the same wear is happening on #1 it might
cause it to stick on occasion.

~Paul

"Paul Mennen" wrote in message
...
If an exhaust valve stuck partially open it would raise
your EGT and lower your CHT

That seems like a more likely explanation than the blocked
fuel injector. The reason I think so is that on the previous
annual the other to cylinders on that side (#3 and #5) were
removed to have their exhaust valves replaced and guides
repaired. (At only 300 hours! I guess Continental still hasn't
figured out how to make cylinders like the did in the 70's
and 80's). So if the same wear is happening on #1 it might
cause it to stick on occasion.

~Paul


But for that to happen here, the exhaust value must be stuck for quite a few
cycles. Assuming 2500 RPM for the duration of your 3 minute event and
dividing by 2 for the four-cycle engine means that your exhaust value chose
to stick 3750 consecutive times out of the 22,500,000 cycles it has executed
up to that point (300 hrs converted to valve cycles). I still like the
partially clogged injector that continued to bleed fuel into the cylinder
after the exhaust cycle started.


--
Jim Carter

But for that to happen here, the exhaust value must be
stuck for quite a few cycles. Assuming 2500 RPM for the
duration of your 3 minute event and dividing by 2 for the
four-cycle engine means that your exhaust value chose
to stick 3750 consecutive times out of the 22,500,000
cycles it has executed up to that point (300 hrs converted
to valve cycles).

I was at only 2300 RPM, although your 3750 is still a strong
underestimate. This is because the 3 minutes I reported was
how long it took for the cylinder to stabalize at its new
lower temperature after the event began. Despite reducing
power to 10.8 gph at about t = 3.1 minutes, the unusual
EGT order (i.e. cyl 1 being the hottest) remained until I
pulled back to near idle for the landing (at t = 16.5 minutes)

Not knowing much about engines I didn't realize that it
is inprobable that a valve could stick for that long.

I still like the partially clogged injector that
continued to bleed fuel into the cylinder after
the exhaust cycle started.
Jim Carter

Ok, not knowing any better I'll go with your suggestion.
Do you think I should have the injector checked out, or
should I just monitor it to see if it ever happens again?

~Paul

It's a fouled plug, burned valve or broken ring.
And that is straight fom the book on my engine analyzer

Tony
C-GICE


In article ,
"Paul Mennen" wrote:

For the last 200 hours I've recorded all the data from my engine
analyzer which makes it easy to look at such things. Anyway a week
ago I was flying along steady at 12 thousand feet when I noticed
an unusual shift in the engine bar graph display. Looking at the
recorded data I see that all flight data is rock steady and all
engine data (and fuel flow) is also rock steady except for EGT1
and CHT1. From the beginning of the event this is what it looked
like:

Time after event EGT1 CHT1
---------------- --------- ---------
t = 0 1355F 300F
t + 20 seconds 77F rise 7F drop
t + 80 seconds 100F rise 19F drop
t + 3 minutes 114F rise 25F drop

After that it was pretty much steady, but I reduced power after
a few more minutes. (By the way, this is a Turbonormalized IO550.)
So EGT1 which was the coolest (as usual), rose to the level of the
warmest few cylinders. And CHT1 was the coolest (as usual) and
dropped away even more below the average. Still the final temps do
not seem that alarming, but when you look at the graph it looks
really strange since I've never seen such step changes unless it
was in response to some control input.

In the few flights I have taken since that event, I haven't seen
anything unusual like this happen again.

So to those of you who understand internal combustion engines -
what can cause a sudden drop in power in one cylinder like this?
Could something have fallen into this cylinder or could a
valve stick for a while or something? Or is this a sign that
something is breaking? What would you do about it? -
- Keep a close eye on it?
- Do an oil analysis?
- Ground it?
- Have a mechanic look at it?

Can a bad mag or spark plug cause such a thing? (BTW the engine
is a factory remain with 300 hours on it).

Thanks in advance for any insights you may have.
~Paul





--

Tony Roberts
PP-ASEL
VFR OTT
Night
Almost Instrument
Cessna 172H C-GICE