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.
Parts are needed for both mags, but one mag shows signs of
having more trapped moisture than the other one. In particular,
the mag with the tach sensor has more rusty discoloration than
the one without the tach sensor. Apparently this is because the
mag needs to be able to vent the pressurization air to get a
steady air exchange and when a mag's aluminum plug normally
containing the .020 vent hole is replaced with the tach sensor
-- the .020 hole is gone. The person at Aircraft Magneto
Service recommended drilling an .020 vent hole in the magneto
body to restore the venting. Actually, he recommended drilling
the hole in the tach sensor body....but i'm afraid i'll drill
through something and ruin the sensor. Has anybody heard of or
done this?
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