Spark Plug

Spark Plug - Thread Repair





Special Tool(s)

CAUTION: The cylinder head must be removed from the engine before installing a tapersert. If this procedure is done with the cylinder head on the engine, the cylinder walls can be damaged by metal chips produced by the thread cutting process. Do not use power or air-driven tools for installing taperserts.

NOTE: This repair is permanent and will have no effect on cylinder head or spark plug life.





1. Clean the spark plug seat and threads





2. Start the tap into the spark plug hole, being careful to keep it correctly aligned. As the tap begins to cut new threads, apply aluminum cutting oil.
3. Continue cutting the threads and applying oil until the stop ring bottoms against the spark plug seat.
4. Remove the tap and metal chips.





5. Coat the threads of the mandrel with cutting oil.
6. Thread the tapersert onto the mandrel until one thread of the mandrel extends beyond the tapersert.





7. NOTE: A correctly installed tapersert will be either flush with or 1.0 mm (0.039 inch) below the spark plug gasket seat.

Tighten the tapersert into the spark plug hole.





8. Turn the mandrel body approximately one-half turn counterclockwise and remove.





9. Use the Feeler Gauge and a suitable straightedge to check for cylinder head flatness.
^

Spark Plug - Inspection





1. Inspect the spark plug for a bridged gap.
^ Check for deposit build-up closing the gap between the electrodes. Deposits are caused by oil or carbon fouling.
^ Clean the spark plug.





2. Check for oil fouling.
^ Check for wet, black deposits on the insulator shell bore electrodes, caused by excessive oil entering the combustion chamber through worn rings and pistons, excessive valve-to-guide clearance or worn or loose bearings.
^ Correct the oil leak concern.
^ Install a new spark plug.





3. Inspect for carbon fouling. Look for black, dry, fluffy carbon deposits on the insulator tips, exposed shell surfaces and electrodes, caused by a spark plug with an incorrect heat range, dirty air cleaner, too rich a fuel mixture or excessive idling.
^ Clean the spark plug.





4. Inspect for normal burning.
^ Check for light tan or gray deposits on the firing tip.





5. Inspect for pre-ignition, identified by melted electrodes and a possibly damaged insulator. Metallic deposits on the insulator indicate engine damage. This may be caused by incorrect ignition timing, wrong type of fuel or the installation of a heli-coil insert in place of the spark plug threads.
^ Install a new spark plug.





6. Inspect for overheating, identified by a white or light gray spots and with bluish-burnt appearance of electrodes. This is caused by engine overheating, wrong type of fuel, loose spark plugs, spark plugs with an incorrect heat range, low fuel pump pressure or incorrect ignition timing.
^ Install a new spark plug.





7. Inspect for fused deposits, identified by melted or spotty deposits resembling bubbles or blisters. These are caused by sudden acceleration.
^ Clean the spark plug.