Strange engine event

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

Loose or wearing-out probe wire?

"Paul Mennen" wrote in message
om...
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

I'm no expert, but the symptoms seem compatible with a partially obstructed
fuel injector. This would cause the mixture in the affected cylinder to be
leaned (ergo higher EGT if you are running ROP) and power to decrease (ergo
reduction in CHT).

From your post I can't tell if the temps stayed at their altered values on
subsequent flights or reverted to the "before t = 0" norm. If my guess is
right, the latter would indicate that whatever was clogging the injector
passed through. If the temps are still shifted, I'd have my mechanic check
the #1 injector.

BTW, this doesn't sound like an instrumentation problem since it's unlikely
that both the EGT and CHT probes and/or receiving units would go bad at the
same time.

--
-Elliott Drucker

Doesn't sound like a probe problem, as unlikely the 2 probes on the
same cylinder would both defect at the same time, so has to be
something in the engine. Were you running lean, rich, peak? Fuel
injected?

I had this happen once with my IO360 but never again.

Loose or wearing-out probe wire?

No that can't be the explanation. If it were just a CHT or
an EGT reading, sure the probe could be at fault. However since
both CHT and EGT change at exactly the same time I believe one
can only rationally conclude that something happened with the
engine itself. In fact I think the EGT rise is a direct consequence
of the CHT reduction although I can't quite remember how that
connection is made.

~Paul

: engine itself. In fact I think the EGT rise is a direct consequence
: of the CHT reduction although I can't quite remember how that
: connection is made.

One plug not firing will slow the combustion event, resulting in the burning
mixture exiting via the open exhaust valve. Results in higher EGT with a
lower CHT because the heat escapes instead of being converted to work
in the cylinder.
--
Aaron Coolidge

"PaulH" wrote
Were you running lean, rich, peak? Fuel injected?

Yes it is Fuel injected (I did mention that it was an IO550).
I was running 14.8gph at WOT (which is LOP).
OAT was 52F, OilT was 188F, TAS was 160Kts, Alt was 12000ft.

I'm no expert, but the symptoms seem compatible with a partially
obstructed fuel injector. This would cause the mixture in the affected
cylinder to be leaned (ergo higher EGT if you are running ROP) and power
to decrease (ergo reduction in CHT).
-Elliott Drucker

Yes I agree that would be consistent. Although aren't there many
other explanations for the same phenomina?

From your post I can't tell if the temps stayed at their altered values
on subsequent flights or reverted to the "before t = 0" norm.

Yes I forgot to mention - on subsequent flights everything reverted
to normal.

Thanks for your inputs

~Paul

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

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

"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?

--
Jim Carter