2. Remove spark plug from engine. In course of engine operation, carbon and other combustion products
will be deposited on end of spark plug and will penetrate lower threads to some degree. As a result,
greater effort is frequently required for removing a plug than for its installation. Accordingly, torque
limitations given do not apply to plug removal and sufficient torque must be used to unscrew plug.
High 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.
—NOTE—
Torque indicating handle should not be used for spark plug
removal because or greater torque requirement.
3. Place spark plugs in a tray that will identify their position in engine as they are removed.
—CAUTION—
Spark plugs should not be used if they have been dropped
4. Remove seized spark plugs as follows:
a. Place a conical metal funnel over spark plug. Hole in top should be just large enough to
accommodate funnel of CO
2
bottle.
b. Release CO
2
inside funnel to chill and contract spark plug.
c. Break spark plug with a wrench.
—NOTE—
A warm cylinder at time of CO
2
application will aid in removal of
excessively seized plugs.
5. Do not allow foreign objects to enter spark plug hole.
INSPECTION AND CLEANING OF SPARK PLUGS
1. Visually inspect each spark plug for non-repairable defects as follows:
a. Severely damaged shell or shield threads nicked, stripped, or cross-threaded.
b. Badly battered or rounded shell hexagons.
c. Out-of-round or damaged shielding barrel.
d. Chipped, cracked, or broken ceramic insulator portions.
e. Badly eroded electrodes (approximately 50% of original size).
2. Clean spark plug as required, removing carbon and foreign deposits.
3. Test spark plug both electrically and for resistance.
4. Set electrode gap at 0.017 to 0.021 inches.
74 - 22 - 00
Page - 74-26
Reissued: August 1, 1986
2J22
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
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