Inspection And Cleaning Of Spark Plug; Installation Of Spark Plugs - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
b. Remove the spark plug from the engine. In the course of engine operation, carbon and other
combustion products will be deposited on the end of the spark plug and will penetrate the lower threads to
some degree. As a result, greater torque is frequently required for removing a plug than for its installation.
Accordingly, the torque limitations given do not apply to plug removal and sufficient torque must be used
to unscrew the plug. The higher torque in removal is not as detrimental as in installation, since it cannot
stretch the threaded section. It does, however, impose a shearing load on this section and may, if
sufficiently severe, produce a failure in this location.
NOTE
Torque indicating handle should not be used for spark plug
removal because of the greater torque requirement.
c. Place spark plugs in a tray that will identify their position in the engine as soon as they are
removed.
NOTE
Spark plugs should not be installed if they have been dropped.
d. Removal of seized spark plugs in the cylinder may be accomplished by application of liquid carbon
dioxide by a Conical metal funnel adapter with a hole at the apex just large enough to accommodate the funnel
of a C02 bottle. (Refer to Figure 8-36.) When a seized spark plug cannot be removed by normal means, the
funnel adapter is placed over and around the spark plug. Place the funnel of the C02 bottle inside the funnel
adapter and release the carbon dioxide to chill and contract the spark plug. Break the spark plug loose with a
wrench. A warm cylinder head at the time the carbon dioxide is applied will aid in the removal of an excessively
seized plug.
e. Do not allow foreign objects to enter the spark plug hole.
8-81. INSPECTION AND CLEANING OF SPARK PLUG.
a. Visually inspect each spark plug for the following non-repairable defects:
1. Severely damaged shell or shield threads nicked up, stripped or cross-threaded.
2. Badly battered or rounded shell hexagons.
3. Out-of-round or damaged shielding barrel.
4. Chipped, cracked or broken ceramic insulator portions.
5. Badly eroded electrodes worn to approximately 50% of original size.
b. Clean the spark plug as required, removing carbon and foreign deposits.
c. Set the electrode gap at .015 to .018 inches.
d. Test the spark plug both electrically and for resistance.
8-82. INSTALLATION OF SPARK PLUGS. Before installing spark plugs, ascertain that the threads within
the cylinder are clean and not damaged.
a. Apply anti-seize compound sparingly on the threads and install gasket and spark plugs. Torque
360 to 420 inch-pounds.
CAUTION
Make certain the deep socket is properly seated on the spark plug
hexagon as damage to the plug could result if the wrench is cocked
to one side when pressure is applied.
Reissued: 9/23/80 POWER PLANT
2J8