Mags

Hi
I'm running in my overhauled engine - 4 hrs - all a full rich.

Today I landed at a nearby airport and when I did the run-up to return
home the left mag gave a 400 rpm drop. I tried it again and got another
400 pm drop.
Third time I tried it I had no left mag at all - drop to cut-off - same
4th time.

Shut down - check all connections - everything looked good - no loose
wires etc.

Today for the first time I used my new carb-temp guage and as it was
reading 30F I added a small amout of carb heat to bring it to 37F. On
reflection I should have leaned slightly to allow for the extra richness
from the cab heat but I didn't.
I went back to the aircraft and it stated OK. I ran it leaned for a
couple of minutes, went full rich to 1700 rpm and did mag checks - both
were good. I did it 5 times, and departed for home. Aircraft ran great,
after landing I did 3 more mag checks and they were all good.

Question - Could fouling really have totally shut down my left mag?

Thanks for reading,

Tony
--

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

tony roberts wrote:

Question - Could fouling really have totally shut down my left mag?

Highly unlikely. You're talking about fouling 4 plugs, two on the top and two on
the bottom. Top plugs rarely foul.

George Patterson
There's plenty of room for all of God's creatures. Right next to the
mashed potatoes.

My O-200 Continental has the left mag firing all the lower plugs and
the right mag firing the upper plugs. What George says is true of
Lycoming engines where the mags fire 2 and 2. If indeed, the left mag
is firing the lower plugs, it could easily exhibit your problem. Pull
the lower plugs and take a look.
Tim (C-150M)

Yes - it's a 6 cylinder 0300 - the left mag fires all bottom plugs and
the right mag fires all the top plugs.

Tony


In article .com,
wrote:

My O-200 Continental has the left mag firing all the lower plugs and
the right mag firing the upper plugs. What George says is true of
Lycoming engines where the mags fire 2 and 2. If indeed, the left mag
is firing the lower plugs, it could easily exhibit your problem. Pull
the lower plugs and take a look.
Tim (C-150M)

tony roberts wrote:

I'm running in my overhauled engine - 4 hrs - all a full rich.

I don't understand why you would want to operate the engine without
leaning. No recommendation I've ever read about post-overhaul break-in
ever included anything like that.

Third time I tried it I had no left mag at all - drop to cut-off - same
4th time.

IMO, an indication of something not right in the mag. It bears watching.

Shut down - check all connections - everything looked good - no loose
wires etc.

So, an intermittent problem.

I added a small amout of carb heat to bring it to 37F. On
reflection I should have leaned slightly to allow for the extra richness
from the cab heat but I didn't.

OAT wouldn't have any bearing on the issue with the mag. Here in south
central USA, we get outside temps over 100 degrees F in summertime, and
mag drops aren't noticeably different than in winter with temps in the
30s-40s.

Question - Could fouling really have totally shut down my left mag?

Answer is no - the mag has no way to know what's going on with the
plugs. **Fouled plugs** from over-rich mixture can, and often do,
result in bad run-ups and mag-checks, but I'm more inclined to suspect
there's something going on in the mag. A look at the plugs for that mag
would be helpful in making that determination.

"CriticalMass" wrote:
I don't understand why you would want to operate the engine without
leaning. No recommendation I've ever read about post-overhaul break-in
ever included anything like that.

Well, you do want to run the engine at high power settings to seat the rings
and you don't want to get the cylinders too hot lest they glaze, so running
rich for break-in is a pretty common precaution against the latter.
--
Dan
C-172RG at BFM

"Dan Luke" wrote in message
...

"CriticalMass" wrote:
I don't understand why you would want to operate the engine without
leaning. No recommendation I've ever read about post-overhaul break-in
ever included anything like that.

Well, you do want to run the engine at high power settings to seat the
rings
and you don't want to get the cylinders too hot lest they glaze, so
running
rich for break-in is a pretty common precaution against the latter.

Um...leaner is cooler, Dan! 50 LOP is about a hot as you can get an engine
without milting it down into slag.

Um...leaner is cooler, Dan! 50 LOP is about a hot as you can get an engine
without milting it down into slag.

But Matt, you are taking about rich or lean of PEAK.
But we are talking about FULL rich - as in mixture control full in.
That is waaay cooler than getting near peak - I monitor all 6 CHT's and
EGT's on my analyzer. At full rich, lean & temp goes up, richen & it
comes down. Add carb heat and it comes down more.
I also have a digital oil temp monitor - and the oil temp also goes up
as I lean and down as I reichen.

You can go over to lean of peak and it can be a very efficient thing to
do - but you had better be fuel injected with GAMI injectors, or therte
is a good chance you will melt it into slag as you suggest.

Thanks to everyone for their responses on this - I appreciate them

Tony

--

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



In article ,
"Matt Barrow" wrote:

"Dan Luke" wrote in message
...

"CriticalMass" wrote:
I don't understand why you would want to operate the engine without
leaning. No recommendation I've ever read about post-overhaul break-in
ever included anything like that.

Well, you do want to run the engine at high power settings to seat the
rings
and you don't want to get the cylinders too hot lest they glaze, so
running
rich for break-in is a pretty common precaution against the latter.

Um...leaner is cooler, Dan! 50 LOP is about a hot as you can get an engine
without milting it down into slag.




--

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

"Matt Barrow" wrote:
Um...leaner is cooler, Dan! 50 LOP is about a hot as you can get an
engine
without milting it down into slag.

No. Highest power, and thus greatest heat, occurs ROP. Maybe that is
what you meant to say.

I routinely run my engine 50 LOP in cruise; the CHT's stay below 380
deg. How could I get it hot enough to "melt it down into slag?"

Anyhow, "leaner is cooler" is so general as to be useless as a
guideline. It is true that cylinders will run cooler at some point LOP
than they will at some point ROP, but most carbureted engines cannot run
LOP because of poor fuel distribution. The only option in that case, if
one wishes to be sure the cylinders stay cool during break-in, is to run
well rich-of-peak.
--
Dan
C172RG at BFM

"Dan Luke" wrote in message
...

"Matt Barrow" wrote:
Um...leaner is cooler, Dan! 50 LOP is about a hot as you can get an
engine
without milting it down into slag.

(contradictions in back-to-back sentences)


No. Highest power, and thus greatest heat, occurs ROP. Maybe that is
what you meant to say.

Yup...(If leaner is cooler then LOP is cooler) that's what happens when I
post five minutes before bedtime :~( (contradictions in back-to-back
sentences)

I meant ROP (especially 50 ROP) is the worst setting you can use, not only
in terms of heat but cylinder pressure as well.


I routinely run my engine 50 LOP in cruise; the CHT's stay below 380
deg. How could I get it hot enough to "melt it down into slag?"

( Never mind!! )