Cleaning Spark Plugs is a Simple Job...

Jay Honeck wrote:
Lately I had noticed just a smidge of roughness in the engine. Not a
roughness, really, but a slight vibration, maybe a little, tiny, occasional
miss? It was not detectable by anyone except someone who flew the plane as
often as I do (and, in fact, Mary often couldn't sense it), but it was
definitely there.

***Saga of changing oil, cleaning and gapping plugs deleted***

Jay, I'll wager that your roughness will still be there when you next
fly. I just went through this on an O320. I cleaned/gapped the plugs,
and this did not cure the roughness.

It turned out that my Slick Mags have 370 hours since new, and the
roughness resulted from the point gap in the Right Mag being too small.
The plastic block that opens the points had worn down to the point
where the point gap was reduced to ~0.006", instead of the specified
0.018".

This manifested as a slight roughness in flight, made more noticable by
shutting down the Left mag. The roughness was not noticable during a
run up (nor was there an asymetrical drop) .

Per the Slick SB, the mags are normally opened up at 500 hours, and the
point gap is set. Mine just happened to need this early...

Mike M.

Per the Slick SB, the mags are normally opened up at 500 hours, and the
point gap is set. Mine just happened to need this early...

You know, I've wondered about this. Our left mag shows a smidge more of a
drop than the right mag -- it's, again, probably not noticeable to someone
who doesn't fly the plane all the time.

What's involved with setting the mag point gap?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:
Per the Slick SB, the mags are normally opened up at 500 hours, and the
point gap is set. Mine just happened to need this early...

You know, I've wondered about this. Our left mag shows a smidge more of a
drop than the right mag -- it's, again, probably not noticeable to someone
who doesn't fly the plane all the time.

What's involved with setting the mag point gap?

Talk to your A&P. Proceedure is specified in the Service Bulletin.
Mag(s) have to be removed, split, internally inspected (particularly
the impulse coupling), lubricated, both the E gap and points gap set,
new gaskets, reinstalled on the engine, and retimed.

Mike M.

Talk to your A&P. Proceedure is specified in the Service Bulletin.
Mag(s) have to be removed, split, internally inspected (particularly
the impulse coupling), lubricated, both the E gap and points gap set,
new gaskets, reinstalled on the engine, and retimed.

The E-gap is determined by points gap; they're not separate
settings. The ideal is to set the E-gap, since wear to the points and
cam can result in the wrong E-gap if the adjustment is made using
points gap.
Most of my students struggle with the theory of the magneto's
operation, and I imagine most pilots are no better off. The E-gap is
the point at which the mag's rotor (a strong permanent magnet) is past
the neutral point after having generated a current in the primary
winding. This current generates its own field, which in beginning to
collapse tends to maintain current flow in the winding after the rotor
has passed through neutral and stopped generating. To get spark, we
open the points when the maximum magnetic flux change will happen, and
when the points open the current is arrested suddenly, the field
collapses violently, generating a large voltage in the secondary
winding. Big spark for the plug.
If the E-gap is off, the spark's strength is reduced and
roughness may occur.

Mag that are slightly mistimed can cause roughness, too. If the
engine's data plate calls for them to be set at the same TDC angle, you
want them real close to being together. If one is much later than the
other. the pressure rise in the cylinder caused by the first plug's
firing can get high enough to prevent the second plug's firing, and the
cylinder loses a bit of power. Sparkplugs need more voltage than mags
can provide to spark at high pressures.
Worn points cause resistance that prevents full current flow in
the primary winding. A worn capacitor can leak and reduce spark
intensity. An open capacitor can kill spark altogether, and one will
reduced capacity will burn the points. The Slick distributor's rotor
bushings wear and the rotor's finger gap can get too big and weaken
spark. Lots of reasons to open the mags and spend a bit of money on
them.
We've recently had trouble with AC plugs; the internal resistor
seems to be failing. Champs have had that problem for years.

Dan

Lots of reasons to open the mags and spend a bit of money on
them.

Much good stuff snipped

Wow -- thanks, Dan. I didn't understand half of what you wrote, but I've
saved your post for the future day when I've got time to figure out things
like "electricity" and "engines"...

;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"
wrote in message
oups.com...
Talk to your A&P. Proceedure is specified in the Service Bulletin.
Mag(s) have to be removed, split, internally inspected (particularly
the impulse coupling), lubricated, both the E gap and points gap set,
new gaskets, reinstalled on the engine, and retimed.

The E-gap is determined by points gap; they're not separate
settings. The ideal is to set the E-gap, since wear to the points and
cam can result in the wrong E-gap if the adjustment is made using
points gap.
Most of my students struggle with the theory of the magneto's
operation, and I imagine most pilots are no better off. The E-gap is
the point at which the mag's rotor (a strong permanent magnet) is past
the neutral point after having generated a current in the primary
winding. This current generates its own field, which in beginning to
collapse tends to maintain current flow in the winding after the rotor
has passed through neutral and stopped generating. To get spark, we
open the points when the maximum magnetic flux change will happen, and
when the points open the current is arrested suddenly, the field
collapses violently, generating a large voltage in the secondary
winding. Big spark for the plug.
If the E-gap is off, the spark's strength is reduced and
roughness may occur.

Mag that are slightly mistimed can cause roughness, too. If the
engine's data plate calls for them to be set at the same TDC angle, you
want them real close to being together. If one is much later than the
other. the pressure rise in the cylinder caused by the first plug's
firing can get high enough to prevent the second plug's firing, and the
cylinder loses a bit of power. Sparkplugs need more voltage than mags
can provide to spark at high pressures.
Worn points cause resistance that prevents full current flow in
the primary winding. A worn capacitor can leak and reduce spark
intensity. An open capacitor can kill spark altogether, and one will
reduced capacity will burn the points. The Slick distributor's rotor
bushings wear and the rotor's finger gap can get too big and weaken
We've recently had trouble with AC plugs; the internal resistor
seems to be failing. Champs have had that problem for years.

Dan

wrote:

.... good info snipped...

We've recently had trouble with AC plugs; the internal resistor
seems to be failing. Champs have had that problem for years.

Dan,
I recently used my Fluke 77 DMM to check eight Champion REM40E
spark plugs, which have a built in radio suppression resistor. I
measured Ohms between center electrodes and threads (all Open). I then
measured the resistance through the center electrode from the wire end
to the electrode end, and noticed that two of eight plugs were "Open"
(10MegOhm), while the other six ranged from 1.4K to about 7K.

I expected all of these to be the same resistance, but was surprised at
the variablity plug to plug. I am puzzled at the two that read open.
They were not misfiring before removal. What's going on?

btw- I also measured 12 brand-new RHM40Es; 4 of 12 were open end to
end???

: What's involved with setting the mag point gap?

Depends on the mag. I'm not familiar with slicks, but on my Bendix there
aren't quite enough adjustments to set everything. The wear of the points vs. the
plastic wear block is fixed by the points. If either is out of spec, new points are
required.

I'd agree with the checking of the internal mag timing (i.e. e-gap). If
you've got a few hundred hours on the mags and/or if it's had the external timing
adjusted, it may have worn a bit out of spec. We just did it on both our mags last
year. Again... it's Bendix.

-Cory


--

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

Did he also show you how to install new spark plug gaskets or re-anneal
the old ones?

Did he also show you how to install new spark plug gaskets or re-anneal
the old ones?

Yep.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:
: Did he also show you how to install new spark plug gaskets or re-anneal
: the old ones?

: Yep.

Which reminds me... should one try to do that on the spark-plug thermocouples
for measureing CHT? It's always bothered me that they *replace* the original copper
gaskets.

-Cory

--

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