Strange engine event

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

On Sat, 26 Jun 2004 16:02:16 +0000, Paul Mennen wrote:

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


Well, I'm actually not sure you have the evidence to support that it stuck
consecutively. Would it still cause the problem if it stuck and released,
worked, and got stuck again over that same period of time? Whereby, it
stopped being stuck following some amount of wear-n-tear of the various
parts? Meaning, just for sake of explanation, if we alternated events of
open, closed, open, stuck, open, mostly closed, open, stuck, etc, or some
other random combination, wouldn't you still see the same type of
measurements? My point being, do you really have the evidence to say that
it simply stuck open over all those cycles?

Cheers,

Greg

On Fri, 25 Jun 2004 14:03:16 +0000, Jim Carter wrote:

"WARREN1157" wrote in message
...
The piston rings rotate whilethe engine is running. The grooves on all of
the
rings could have aligned up with each other for a little while and then
rotated
back into un - aligned positions. If thei happens reguarly the cylinder
could
be out of round.

This condition would make CHT go up and EGT go down

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.

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

On car motors, isn't this the reason the that you hone and crosshatch the
cylinder wall? That way, during breakin, the rings are encouraged to
rotate and mate in such a manner? Once the rings mate, they'll naturally
want to follow the same rotational, mated path. I ***assume*** the same
thing is done with plane engines. I believe the closest analogy would be
to picture a bullet in a barrel, where the spin in placed on the bullet by
the rifling. Now, just imagine the bullet traveling back and forth in the
barrel, whereby, it natually wants to rotate along the length of the
barrel, in spite of the direction of travel.

Any AP guys, feel free to correct as needed.

Cheers,

Greg

Well, I'm actually not sure you have the evidence to support that it stuck

Piston rings rotate to keep from scoring the cylinders and valves rotate or
they would score and burn. If a piece of carbon was under the valve and holding
it partially open it would lower CHT and raise EGT.

If an injector was plugged it would probably go over peak and lower CHT and
lower EGT.

If the injecter was stuck open it would flood and lower CHT and raise EGT,

The reason for raised EGT on this one is the fuel burning in the exhaust
system. This should make the EGT noticably more on this cylinder than the
others.

Life was easy before computers and analyzers. This is an interesting problem
and I swear that I am no expert on this.

****If the injecter was stuck open it would flood and lower CHT and raise
EGT, *****

Aircraft fuel injectors don't open and close, they are always open and
providing fuel. That is why they are called "constant flow."


Karl



"PInc972390" wrote in message
...


Well, I'm actually not sure you have the evidence to support that it
stuck

Piston rings rotate to keep from scoring the cylinders and valves rotate
or
they would score and burn. If a piece of carbon was under the valve and
holding
it partially open it would lower CHT and raise EGT.

If an injector was plugged it would probably go over peak and lower CHT
and
lower EGT.

If the injecter was stuck open it would flood and lower CHT and raise EGT,

The reason for raised EGT on this one is the fuel burning in the exhaust
system. This should make the EGT noticably more on this cylinder than the
others.

Life was easy before computers and analyzers. This is an interesting
problem
and I swear that I am no expert on this.

PInc972390 wrote:

Well, I'm actually not sure you have the evidence to support that it stuck


Piston rings rotate to keep from scoring the cylinders and valves rotate or
they would score and burn. If a piece of carbon was under the valve and holding
it partially open it would lower CHT and raise EGT.

I've never heard of piston rings rotating. Kind of makes staggering the
gaps a waste of time. What makes them rotate?

Yes, many valves are designed to rotate.


Matt

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

*If the injecter was stuck open it would flood and lower CHT and

This is kind of a visualising termanalogy, Sorry for the spelling.