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TP-6905 6/1458 Section 4 Scheduled Maintenance
Problem/Condition Means of Identification Possible Cause/Solution
Gap-bridged spark
plug
Built-up deposits and gap between electrodes
closing.
Oil or carbon fouling. Clean and regap the spark
plug.
Oil-fouled spark plug Wet, black deposits on the insulator shell, bore,
and electrodes.
Excessive oil entering combustion chamber
through worn rings and pistons, excessive
clearance between valve guides and stems, or
worn or loose bearings. Replace the spark plug.
Carbon-fouled spark
plug
Black, dry, fluffy carbon deposits on insulator
tips, exposed shell surfaces and electrodes.
Incorrect spark plug, weak ignition, clogged air
intake, overrich fuel mixture, or excessive
no-load operation. Clean and regap the spark
plug.
Lead-fouled spark plug Dark gray, black, yellow , or tan deposits; or a
glazed coating on the insulator tip.
Caused by highly leaded fuel. Replace the spark
plug.
Pre-ignition damaged
spark plug
Melted electrodes and possibly blistered
insulator. Metallic deposits on insulator suggest
internal engine damage.
Wrong type of fuel, incorrect timing or advance,
too hot a plug, burned valves, or engine
overheating. Replace the spark plug.
Overheated spark plug White or light gray insulator with small black or
gray/brown spots with bluish (burned)
appearance on electrodes.
Engine overheating, wrong type of fuel, loose
spark plugs, too hot a plug, low fuel pressure or
incorrect ignition timing. Replace the spark plug.
Worn spark plug Severely eroded or worn electrodes. Caused by normal wear and failure to replace
spark plug at prescribed interval. Replace the
spark plug.
Figure 4-9 Engine Evaluation Using Spark Plug Condition
13. Use a gapping tool to gently bend the side
electrode closer to or farther from the center
electrode to set the correct gap. See Figure 4-10.
Position the side electrode directly over the center
electrode.
1-511
Figure 4-10 Spark Plug Gap Adjustment
Note: Ensure that the spark plug tubes are seated
before installing thespark p lugs. Ifthe tubes
were removed, reinstall them before
installing the spark plugs.
14. Reinstallthespark plug.Do notbumpthe electrode
against the cylinder head. Rotate the spark plug
clockwise until you feel resistance.
15. Use a torque wrench to torque each spark plug to
18 Nm (13.3 ft. lbs.). Otherwise, hand-tighten the
spark plug until you feel resistance.
16. Use a ratchet wrench to tighten an additional 1/4
turn. Do not overtighten, as doing so may strip the
threads or alter the electrode gap setting.
17. Check the sparkplug wireconnector in the boot for
accumulated dirt, grease, and other debris, and
clean as necessary.
18. Firmly push the spark plug boot onto the spark
plug.
19. Reconnect the generator set engine starting
battery, negative (--) lead last.
20. Reconnect the power for the battery charger.