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Magneto Maintenance
By Steve Zeller
Due to Service Bulletin, Airworthiness
Directive, or good shop practice,
magnetos need to be removed
and inspected from time to time.
They tend be forgotten there on the back of the
engine. I have never had a magneto fail in-flight,
but also have never removed one that did not
require some sort of maintenance.
The impulse coupling in the
photo checked fine at the last 100-
hour in spection. When I removed
the magneto due to time in service,
I found a rivet missing from one
of the cam arms. The rivet head
was found down in the engine oil
sump. The mag was working fine.
Thank fully, there was no damage to
the engine.
The riveted impulse coupling has
been superseded by an improved
snap ring design. This is covered
by a rather confusing collection of
Airworthiness Directives and OEM
Service Bulletins. All the original
magneto manufacturers have been
bought and sold and changed
business names a couple of times.
You have to do
considerable research
to make sure you have all of the
required service data when working
on and inspecting an aircraft. ADs
can be listed by airframe, engine, or
component. STC modifications can
further complicate the maintenance
process. Replacement of riveted impulse
couplings is not mandatory, but
it is highly recommended. As we see,
they can fail without warning.
12 AMERICAN BONANZA SOCIETY JANUARY 2013