Lycoming IO-360 issues

Was going to say woes, but really, just an issue.

Airplane is an RV-8A with an IO-360 (200 hp). Had some issues with
speed in the past and posted to rah, got some useful answers. We're
getting there on the speed. Ok, new issue.

Was flying to C-22 today. Long story short. As the flight progressed,
noticed some roughness which sort of resolved. No significant loss of
power...just a bit of a stumble, which I thought got better. In
retrospect, perhaps not.

Was high, and close to the field. A few minutes later, perusing the
engine gauges (four point EGT, four point CHT (and others)) I noted
that cylinder #4's EGT was significantly hi. I mean, 1500 degrees. All
the rest were within normal range. CHT's all in normal range. Really,
everything else normal. I richened the mixture considerably and the
temp dropped somewhat. Was on the descent anyway and so I reduced the
power considerably, and it looked better...down into the 1300 degrees
where I normally lean to.

Ok, landed the airplane. Taxiing to the ramp, is running fine. I
checked the right mag, which is a normal mag, lower plugs, and it was
normal...a little extra rough, like one sees, but fine. I then checked
the left mag...which is actually a lightspeed plazma ignition.
Generally when you check that, it is absolutely smooth. No "mag check
roughness" at all. Ok, I checked it this time and it WAS rough. Sort
of like one cylinder wasn't firing (wink, wink). At least it reminded
me of my old TR-3 when one of the cylinders wasn't firing. Just to
make sure that we weren't seeing a lightspeed failure, and a live
right mag, I pulled the circuit breaker on the lightspeed...engine
died...circuit breaker in and it runs, but rough.

I didn't have time to fiddle with it today, but I'm thinking that I
failed a lightspeed plug (which is a normal automotive plug) on
cylinder #4. Anyone disagree? I read somewhere that when one of the
plugs fail on a cylinder the EGT goes up due to unburned fuel burning
in the exhaust pipe.

I'll change the plug next time I get back to the airplane, but anyone
else have an alternative explanation?

Thanks!

Jim

Hi, Jim,

High EGT could also point to a lean injector nozzle - which would also
indicate a stumble and a little roughness - running too lean in that
cylinder.

If the plugs test out ok, it would be my next place to look.

I would have thought a plug not firing would produce less heat because
of the extra cooling from the unburnt fuel.

Bill French

Jim Harper wrote:
> Was going to say woes, but really, just an issue.
>
> Airplane is an RV-8A with an IO-360 (200 hp). Had some issues with
> speed in the past and posted to rah, got some useful answers. We're
> getting there on the speed. Ok, new issue.
>
> Was flying to C-22 today. Long story short. As the flight progressed,
> noticed some roughness which sort of resolved. No significant loss of
> power...just a bit of a stumble, which I thought got better. In
> retrospect, perhaps not.
>
> Was high, and close to the field. A few minutes later, perusing the
> engine gauges (four point EGT, four point CHT (and others)) I noted
> that cylinder #4's EGT was significantly hi. I mean, 1500 degrees. All
> the rest were within normal range. CHT's all in normal range. Really,
> everything else normal. I richened the mixture considerably and the
> temp dropped somewhat. Was on the descent anyway and so I reduced the
> power considerably, and it looked better...down into the 1300 degrees
> where I normally lean to.
>
> Ok, landed the airplane. Taxiing to the ramp, is running fine. I
> checked the right mag, which is a normal mag, lower plugs, and it was
> normal...a little extra rough, like one sees, but fine. I then checked
> the left mag...which is actually a lightspeed plazma ignition.
> Generally when you check that, it is absolutely smooth. No "mag check
> roughness" at all. Ok, I checked it this time and it WAS rough. Sort
> of like one cylinder wasn't firing (wink, wink). At least it reminded
> me of my old TR-3 when one of the cylinders wasn't firing. Just to
> make sure that we weren't seeing a lightspeed failure, and a live
> right mag, I pulled the circuit breaker on the lightspeed...engine
> died...circuit breaker in and it runs, but rough.
>
> I didn't have time to fiddle with it today, but I'm thinking that I
> failed a lightspeed plug (which is a normal automotive plug) on
> cylinder #4. Anyone disagree? I read somewhere that when one of the
> plugs fail on a cylinder the EGT goes up due to unburned fuel burning
> in the exhaust pipe.
>
> I'll change the plug next time I get back to the airplane, but anyone
> else have an alternative explanation?
>
> Thanks!
>
> Jim