Mags

[tony roberts]

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

[George Patterson]

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.

[[email protected]]

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]

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)

[CriticalMass]

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.

[Dan Luke]

"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

[Matt Barrow]

"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]

> 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

[Dan Luke]

"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

[Matt Barrow]

"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!! )

[Dan Luke]

"Matt Barrow" wrote:
> > 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!! )

Hee-hee! Now *I* did it!

I meant "50 ROP in cruise."
--
Dan
C-172RG at BFM

[[email protected]]

: > 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.

For breakin (4 hours is a good minimum for when most of the breakin should
have occurred), you absolutely need to run at a very high power setting. High cruise
(~70%) is a minimum, but I've seen recommendations of 85% or so as well. At those
power settings, you'll need to have a very rich mixture to:
A) Prevent major damage from detonation
B) Keep the engine cool (CHT cooler than "normal" preferrably)

I've got an EGT in mine (now well broken in), and in a long climb I'll lean to
maintain EGT I get at takeoff (1400 on my plane). If you don't have that, you're
better off leaving it full rich while you fly around for a few hours at 85%. A few
hours at wicked rich isn't going to hurt/dirty anything... just reduce power (<70%)
before landing and lean it until it wheezes cook out the carbon buildup.

-Cory

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[TripFarmer]

Just broke in 6 new Millenium Cylinders last July and their break-in
instructions said to run them at 100% for 2 hours at 3-4,000 feet. I did
this and the temps dropped after about 30 minutes showing the rings were
beginning to seat. They have run well since.


Trip

In article >, says...
>
>: > 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.
>
> For breakin (4 hours is a good minimum for when most of the breakin should
>have occurred), you absolutely need to run at a very high power setting. High c
>ruise
>(~70%) is a minimum, but I've seen recommendations of 85% or so as well. At tho
>se
>power settings, you'll need to have a very rich mixture to:
>A) Prevent major damage from detonation
>B) Keep the engine cool (CHT cooler than "normal" preferrably)
>
> I've got an EGT in mine (now well broken in), and in a long climb I'll lean to
>maintain EGT I get at takeoff (1400 on my plane). If you don't have that, you'r
>e
>better off leaving it full rich while you fly around for a few hours at 85%. A
>few
>hours at wicked rich isn't going to hurt/dirty anything... just reduce power (<7
>0%)
>before landing and lean it until it wheezes cook out the carbon buildup.
>
>-Cory
>
>************************************************** ***********************
>* Cory Papenfuss *
>* Electrical Engineering candidate Ph.D. graduate student *
>* Virginia Polytechnic Institute and State University *
>************************************************** ***********************
>

[[email protected]]

TripFarmer > wrote:
: Just broke in 6 new Millenium Cylinders last July and their break-in
: instructions said to run them at 100% for 2 hours at 3-4,000 feet. I did
: this and the temps dropped after about 30 minutes showing the rings were
: beginning to seat. They have run well since.


Exactly. "100%" at 3-4000' is probably 85-90% unless you're turbocharged.
Gotta run them hard and cool initially to seat them.

-Cory


************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[Mike Spera]

>
> IMO, an indication of something not right in the mag. It bears watching.
>
Well, I would recommend PULLING, not watching. You may have a shorting
coil ot other problem. Often, there are visual indications. I would
rather find out on the bench than during takeoff. Also check the wire
going to the ignition switch. This wire grounds the mag when the switch
is in the "off" position. If it is shorting somewhere else, this can
also cause your condition.

The probability of a mag problem is pretty high. The probability of all
4 bottom plugs fouling completely at the same time is pretty low, unless
you are burning 2 quarts an hour.

Good Luck,
Mike