A PICTURE'S WORTH...

Many times an engine problem can be solved by carefully examining its spark plugs for visual
clues to abnormal conditions that may exist in the engine's power cylinders.

The following photographs were taken of plugs returned to our laboratory for analysis.
Each is a window to an engine and can assist in determining the source of a problem.


 VISUAL    ANALYSIS
 
Light casting of whitish ash uniformly deposited on firing-end.
NORMAL FIRING-END. Normal, light ash deposits are common indicators of healthy spark plugs from a healthy engine.
 
Shear fracture of steel spark plug shell at the thread relief.
OVER-TORQUE.
Spark plug steel can only withstand so much torque. Over-torqueing can exceed the strength of the spark plug's thread relief. Federal Spark Plug Standards require that 14mm spark plugs only withstand 45 ft. Ibs. without damage; 18mm only 65 ft. Ibs.; and 7/8"-18 only 85 ft. Ibs. Only by using an indicating torque wrench can this over-torque damage be eliminated.
 
Torched-out hole in spark plug's
steel shell.
Probably but not always a melted firing-end as well.
TORCH-EFFECT DETONATION.
This is an extremely destructive engine event known to blow holes in pistons, cylinder liners, and cylinder heads. Check engine timing, mixture controls, and all engine functions.


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