Burning out a Magneto Drop

I just received a booklet from TCM called "Tips on Engine Care" (a very
good book...available from TCM's website...http://www.tcmlink.com/). On
page 12 it says "Never but never attempt to "burn out" a magneto drop
with ground run-up. This 'time-honored' procedure succeeds only at the
expense of the engine's mechanical health."

Well, I was taught this time-honored way. What the book does not say is
what you are supposed to do when you get roughness in one magento. Ideas?

-Sami
N2057M, Piper Turbo Arrow III

"O. Sami Saydjari" wrote in message
...
I just received a booklet from TCM called "Tips on Engine Care" (a very
good book...available from TCM's website...http://www.tcmlink.com/). On
page 12 it says "Never but never attempt to "burn out" a magneto drop
with ground run-up. This 'time-honored' procedure succeeds only at the
expense of the engine's mechanical health."

Well, I was taught this time-honored way. What the book does not say is
what you are supposed to do when you get roughness in one magento. Ideas?

Really? Does the book say how this will hurt the engine's mechanical health?
To be honest, this "time-honored procedure" seems to have no effect
whatsoever on whether engines make it to TBO or beyond.

The implication in the book is that it will overheat the engine because
it will cause one to run the engine at high RPM on the ground where
airflow is not as good as in the air. They want you to minimize
high-RPM ground operations.
_sami

C J Campbell wrote:

"O. Sami Saydjari" wrote in message
...

I just received a booklet from TCM called "Tips on Engine Care" (a very
good book...available from TCM's website...http://www.tcmlink.com/). On
page 12 it says "Never but never attempt to "burn out" a magneto drop
with ground run-up. This 'time-honored' procedure succeeds only at the
expense of the engine's mechanical health."

Well, I was taught this time-honored way. What the book does not say is
what you are supposed to do when you get roughness in one magento. Ideas?


Really? Does the book say how this will hurt the engine's mechanical health?
To be honest, this "time-honored procedure" seems to have no effect
whatsoever on whether engines make it to TBO or beyond.

You can burn off a mag with as little as 1700 rpm for just a couple
minutes.. surely this isn't hurting anything, at least not during the
cooler months.

O. Sami Saydjari wrote:
The implication in the book is that it will overheat the engine because
it will cause one to run the engine at high RPM on the ground where
airflow is not as good as in the air. They want you to minimize
high-RPM ground operations.
_sami

C J Campbell wrote:

"O. Sami Saydjari" wrote in message
...

I just received a booklet from TCM called "Tips on Engine Care" (a very
good book...available from TCM's website...http://www.tcmlink.com/). On
page 12 it says "Never but never attempt to "burn out" a magneto drop
with ground run-up. This 'time-honored' procedure succeeds only at the
expense of the engine's mechanical health."

Well, I was taught this time-honored way. What the book does not say is
what you are supposed to do when you get roughness in one magento.
Ideas?



Really? Does the book say how this will hurt the engine's mechanical
health?
To be honest, this "time-honored procedure" seems to have no effect
whatsoever on whether engines make it to TBO or beyond.

"O. Sami Saydjari" wrote in message
...
I just received a booklet from TCM called "Tips on Engine Care" (a very
good book...available from TCM's website...http://www.tcmlink.com/). On
page 12 it says "Never but never attempt to "burn out" a magneto drop
with ground run-up. This 'time-honored' procedure succeeds only at the
expense of the engine's mechanical health."

Well, I was taught this time-honored way. What the book does not say is
what you are supposed to do when you get roughness in one magento. Ideas?

-Sami
N2057M, Piper Turbo Arrow III


When you lean your engine and rev it up on the ground you are super-heating
the heads, the sparkplugs, the pistons, the valves, seats, and guides ---
just to clean a fouled plug or two by burning the lead or carbon fouling off
the electrode. It's best to clean the fouled plug. Of course, the problem
is NOT with the mag.

My instructor (who was not at all a gearhead) once did that burn-it-off
thing in a 152's O-235 Lycoming, and it wasn't long before that engine was
in the shop for new cylinders. I remember well the heat. We could feel
it and smell it coming through the firewall, and being a gearhead I knew
that THAT was not good for that engine. Besides, an aircraft revved up on
the ground can hardly cool itself, irrespective of the fact you have leaned
the **** out of it.

I haven't seen it but have heard of burning holes in pistons by overleaning.

By the mag drop you already know which set of plugs, upper or lower, and
then all you have to do is find the misfiring cold cylinder. That's easy
enough and what if the problem is a sparkplug wire or injector? You've just
managed to fry your cylinders in the hopes of getting one out of four or six
to fire.

Leaning an engine takes a little finesse. It shouldn't be done on the
ground unless you're in Denver or on a high-altitude ramp. A small fraction
of that fuel charge is cooling your heads as it evaporates and flows through
the combustion chamber and out the exhaust port. Ideally it is rich enough
to give you a perfect stoichiometric charge plus just a little for cooling.
If you burn it all by leaning you have lost your mixture's ability to
dissipate heat. In addition, some of a lean charge is burning as it
departs the combustion chamber because a lean mixture burns more slowly than
a rich one. Damned if I want my exhaust valve to glow just to clean a
sparkplug.

" jls" wrote in message
...

Leaning an engine takes a little finesse. It shouldn't be done on the
ground unless you're in Denver or on a high-altitude ramp. A small
fraction
of that fuel charge is cooling your heads as it evaporates and flows
through
the combustion chamber and out the exhaust port. Ideally it is rich
enough
to give you a perfect stoichiometric charge plus just a little for
cooling.
If you burn it all by leaning you have lost your mixture's ability to
dissipate heat. In addition, some of a lean charge is burning as it
departs the combustion chamber because a lean mixture burns more slowly
than
a rich one. Damned if I want my exhaust valve to glow just to clean a
sparkplug.

I think you are exaggerating. More than a little bit. I guarantee that even
at sea level you are going to get spark plug fouling if you do not lean your
engine somewhat during taxi -- especially when taxiing in. You just
completed a descent with the mixture full rich and the engine idling -- lots
of cooling and plenty of opportunity for spark plug buildup. I suspect that
the detonation and premature ignition that result from your recommendations
are even harder on an engine than occasionally clearing a spark plug.

"C J Campbell" wrote in message
...

" jls" wrote in message
...

Leaning an engine takes a little finesse. It shouldn't be done on the
ground unless you're in Denver or on a high-altitude ramp. A small
fraction
of that fuel charge is cooling your heads as it evaporates and flows
through
the combustion chamber and out the exhaust port. Ideally it is rich
enough
to give you a perfect stoichiometric charge plus just a little for
cooling.
If you burn it all by leaning you have lost your mixture's ability to
dissipate heat. In addition, some of a lean charge is burning as it
departs the combustion chamber because a lean mixture burns more slowly
than
a rich one. Damned if I want my exhaust valve to glow just to clean a
sparkplug.

I think you are exaggerating.

Yeah, I don't know if the exhaust valve glows or not but I know when one
gets too hot and don't plan to let it happen to my engine.

More than a little bit. I guarantee that even
at sea level you are going to get spark plug fouling if you do not lean
your
engine somewhat during taxi -- especially when taxiing in. You just
completed a descent with the mixture full rich and the engine idling --
lots
of cooling and plenty of opportunity for spark plug buildup.

I don't see any big problem with leaning as you taxi. We lean sometimes on
descent and will often lean if an engine tends to miss or surge. It
depends on the engine and airplane too. Leaning at idle, or close to it,
as in when you are taxiing, won't fry your cylinders. But leaning at high
static rpm's will, sooner or later. Thus the reason for TCM's advice not
to do it.

I suspect that
the detonation and premature ignition that result from your
recommendations
are even harder on an engine than occasionally clearing a spark plug.

Explain what recommendations I have given which will cause detonation and
premature ignition. Fuel of the improper octane, engine hot spots,
improper leaning and engine conditions I am generally opposed to cause
detonation and preignition. See, e. g.,
http://www.sacskyranch.com/eng180.htm

"C J Campbell" wrote in message
...
[...] I suspect that
the detonation and premature ignition that result from your
recommendations
are even harder on an engine than occasionally clearing a spark plug.

Here's an even better link to clear up the confusion:

http://www.sacskyranch.com/deton.htm

And I always wondered why combustion chambers in angle-valve engines were so
clean. I just learned some of the reasons why. They burn cleaner.

On Sat, 28 Feb 2004 08:11:03 -0800, C J Campbell wrote:

I think you are exaggerating. More than a little bit. I guarantee that even
at sea level you are going to get spark plug fouling if you do not lean your
engine somewhat during taxi -- especially when taxiing in. You just

Very true, and it sounds like the 152 he's talking about got cooked, not
leaned to burn off plug fouling which doesn't take that long.

I have no problem burning off a fouled plug, just like last night. Left,
lower plug, seems to be a problem. Another pilot says it is a problem
that shows up just after re-fueling and you prime before a re-start.

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