I had a very interesting telephone conversation Friday with
a fellow from "Aircraft Magneto Service" of Bainbridge Island,
Washington (www.aircraftmagnetoservice.calls.net). It was prompted by
the 350 hour inspection of the dual pressurized Slick magnetos on my
TSIO-550E.
.......
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. The fellow told me plugs having too high of a resistance
can/will cause misfiring and potential problems with the magneto coil
and or plug harness. A spark plug bomb tester might show this plug as
good, so the ohm meter test should always be performed every time the
plugs are serviced.
Unlike an Autolite plug, a Champion spark
plug resistor can be changed. Look inside the barrel of a Champion plug
and notice the slotted screw. Remove the screw and the resistor will
fall out: it looks like a slug of carbon about 1/2 inch long and maybe
1/8 inch diameter. You can put the ohm meter on either end of this slug
and measure the resistance -- this is the element that needs to measure
from about 800 to 5000 ohms. The resistor is apparently common among
all Champion plugs so he recommended visiting your pile of old plugs;
removing the resistors; and saving the resistors that measure "good".
When you run across an otherwise servicable plug whose resistance is too
high you can change its resistor for one from the "good" pile. He says
this can cure a host of otherwise mysterious "rough running" problems
and forestall future problems.
He said some Reno racers remove
the resistor and replace it with a piece of copper wire to get a much
hotter spark for racing. Says it wears out the spark plugs very quickly
-- but does make a performance difference. Is this true?
-isaac
ES-P N7842K
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