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From: Lorn H Olsen <lorn@dynacomm.us>
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Subject: Re: Fine Wire Plug Resistance
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Pilots,

I took a bunch of old standard plugs and took out the low resistance =
resisters. I then replaced my high resistance Iridium plug resisters =
with these low resistance resisters. Here is the before and after =
resistance.

10/17/10
	Top	Bottom
1	6.6 m	2.8 m
2	1.5 k	7.7 m
3	4.5 m	2.4 m
4	24.5 k	1.2 k AL

10/18/10
	Top	Bottom
1	1.68 k	1.18 k
2	1.69 k	1.58 k
3	1.11 k	1.57 k
4	1.22 k	1.05 k AL

In my prior post below, I listed the Autolight (AL) plug in the mega ohm =
range. This was a mistake. In all of the AL plugs that I measured, the =
resistance was between 1.1 and 1.3 kilo ohms. AL's do not seem to have =
resisters that increase in resistance.

After I reinstalled my iridium plugs, the plane started immediately as =
soon as the key was turned. Before the resister change, the plane took =
3, 20 to 40 second turns to start. Over the last 2 years, the plane has =
been getting harder and harder to start. I put Iridium plugs in about 8 =
years ago.

=46rom the above charts, I can see that my right side impulse coupled =
mag which fires the 1 & 3 top and the 2 & 4 bottom plugs was firing only =
1 plug, when the plugs were damp. Of course, when trying to start the =
engine, all of my plugs are damp.

I believe that the resistance takes years to increase. Standard aircraft =
plugs are changed long before the the resistance starts to increase. My =
Iridium plugs, although looking like new, have been used for about 1,000 =
hours and 8 years.

Here are 3 web sights that will help us understand the problem.

1) A 1965 Ft Ruckers, Al study on Iridium plug resistance.

	=
http://www.dtic.mil/cgi-bin/GetTRDoc?Location=3DU2&doc=3DGetTRDoc.pdf&AD=3D=
ADA030836

2) A 1999 study by Rainier Lamers.

	=
http://www.ultralightnews.com/enginetroublshooting/resistorcapsandplugs.ht=
m

3) And finally a link to the Aircraft Magneto Service shop in Bainbridge =
Island, Wa. I talked to the owners for quite a while last week and I =
will be using them in the future for any magneto service that I need. =
They also reaffirmed that the resistance changes that I have done were =
appropriate.

	http://www.aircraftmagnetoservices.com/

Comments appreciated as always.

Lorn

> I thought that I would measure the ohms on my Iridium plugs today. 7 =
of the plugs are Champion and the other is Autolight.
>=20
> 1 top		6.6 mega ohm
> 1 bottom	2.8 mega ohm
> 2 top		1.5 kilo ohm
> 2 bottom	7.7 mega ohm
> 3 top		4.5 mega ohm
> 3 bottom	2.4 mega ohm
> 4 top		24.5 kilo ohm
> 4 bottom	1.2 mega ohm Autolight plug
>=20
> No, the above readings are not typos or misreads. Just the facts. =
Something must be wrong with the 800 - 1,200 ohms listed below. Tomorrow =
I will remeasure with an analog VOM meter.
>=20
> The plugs all looked pretty good except for the number 2 bottom. It =
looked very fouled and was not firing quite right from an in flight =
test.
>=20
> I think that I may swap the number 2 bottom's resister with one from =
an old standard plug.
>=20
> Thoughts are welcomed.
>=20
>> From: Isaac Heizer <ijheizer@comcast.net>
>> Date: October 10, 2010 10:57:35 AM EDT
>>=20
>> .
>> .
>> .
>> Then we started talking about spark plugs:  I mentioned my plane has =
Champion fine wire plugs.  He said all plugs have an internal resistor, =
and for some reason the resistance of many Champion plugs seems to =
increase as the plug ages.  Once the plug has been cleaned, the =
resistance can be measured with a standard ohm meter between the center =
electrode and the connection inside the plug barrel -- all new plugs =
should have a resistance somewhere around 800 - 1200 ohms.  If the =
resistance ever measures above 5000 ohms, the plug should not be used..
>> .
>> .
>> .
>>=20
>> -isaac
>> ES-P N7842K


--
Lorn H. 'Feathers' Olsen, MAA, ASMEL, ASES, Comm, Inst
DynaComm, Corp., 248-345-0500, mailto:lorn@dynacomm.us
LNC2, FB90/92, O-320-D1F, 1,750 hrs, N31161, Y47, SE Michigan