Spark Plug Inspection - Lycoming TEO-540-C1A Maintenance Manual

5. Spark Plug Inspection

NOTICE: Corrosion and deposits are evidence of leaking spark plugs or incorrect cleaning of
the spark plugs or connector ends.
A. Remove the spark plug connector nuts.
B. Examine each spark plug and ceramics for chafing, corrosion, wear, and cracking during
every inspection. Replace any worn, cracked or corroded spark plug with a new spark plug.
NOTICE: The general guidelines in Table 2 identify acceptable and unacceptable spark plugs.
The figures in Table 2 show the condition of the fine wire ground and center
electrodes as well as the level of wear indication and condition of the spark plug.
Refer to your spark plug manufacturer's manual for specific instructions.
Spark Plug Findings
Acceptable Insulator tip gray, tan
Spark Plugs or light brown
No ash deposits
Electrodes intact, not
burnt or eroded
Partially Ash deposits
Worn Spark Electrode burnt
Plugs and/or eroded to less
than half of the
original thickness
More voltage has
been necessary to fire
the spark plugs
Worn Spark Erosion of center and
Plugs ground electrode
Extensive necking of
the fine wire ground
electrode
C. To be acceptable, the spark plug must not have any of the following:
(1) Fine wire plugs with loose center or ground electrodes.
(2) Electrodes that show signs of metal or impact damage.
(3) Massive electrode plugs with copper run-out of the center electrode.
(4) Ceramic core nose with a cracked or crazed rough surface.
74-20
Page 334
General Spark Plug Wear/Replacement Guidelines
Condition of Fine
Wire Ground
Electrode on Spark
Plug
TEO-540-C1A Engine Maintenance Manual
TEO-540-C1A Engine Maintenance Manual
Table 2
Condition of Center
Electrode on Spark
plug
© 2018 Avco Corporation. All Rights Reserved
What to do
Clean, set the
spark plug gap and
install the spark
plug per applicable
sections in this
chapter and in
Chapter 05-30.
Discard the spark
plug and replace
with a serviceable
spark plug.
Look for excessive
heat sources.
Discard the spark
plug and replace
with a serviceable
spark plug.
November 2018