ignition

2000

STITT SPARK PLUG COMPANY

STITT Spark Plug Company, Conroe, TX, USA All rights reserved.

A Picture Is Worth ....

Light casting of whitish ash uniformly deposited on firing-end.

Shear fracture of steel sparkplug shell at the thread relief.

Torched-out hole in sparkplug's steel shell. Probably butnot always a melted firing-endas well.

NORMAL FIRING-END.Normal, light ash deposits arecommon indicators of healthyspark plugs from a healthyengine.

OVER-TORQUE. Spark plugsteel can only withstand somuch torque. Over-torqueingcan exceed the strength of thespark plug's thread relief.Federal Spark Plug Standardsrequire that 14mm spark plugsonly withstand 45 ft. Ibs. with-out damage; 18mm only 65 ft.Ibs.; and 7/8"-18 only 85 ft. Ibs.Only by using an indicatingtorque wrench can this over-torque damage be eliminated.

TORCH-EFFECT DETONA-TION. This is an extremelydestructive engine eventknown to blow holes in pistons,cylinder liners, and cylinderheads. Check engine timing,mixture controls, and all enginefunctions.

Many times an engine problem can be solved by carefully examining its spark plugsfor visual clues to abnormal conditions that may exist in the engines 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.

The VISUAL: The PHOTOGRAPH: The ANALYSIS:

1

Spark plug's threads flattened,torn or missing.

Orange-colored residueon threads or spark plugfiring-end .

CROSS-THREADING.Threadsthat have lost their sharpnessusually indicate that the sparkplug has been cross-threadedor installed in a port which hasbeen tapped undersize.Crossthreading can occurwhen the plug installation isnot started by hand. A goodsolution is to install all plugshand tight before final mechan-ical torque is applied.

COOLANT-ADDITIVERESIDUE. This orange coloredmaterial is the residue from anengine coolant-additive. Whenfound on the spark plugthreads, it indicates that cylin-der head is probably crackedin the area of the spark plugport threads.


2

Molten center electrode ormelted ground electrodes andcenter electrode. Possiblyfractured and melted ceramic.Occasionally, melted steelshell.

Red, grainy deposits on insula-tor nose and firing-end.

PRE-IGNITIONDETONATION.A melted nickel center elec-trode and/or melted groundelectrodes always indicate thatthe spark plug has encoun-tered higher than normaloperating temperatures. Sincethe melting temperature ofnickel is 2600F, melting nickelindicates that the spark plughas probably been a victim ofsustained pre-ignition or deto-nation. Check engine timing,mixture controls, and all enginefunctions.

IRON OXIDE DEPOSITS.Firingend deposits of iron-oxidemay prevent the discharge ofenergy across the spark gap.These iron oxide deposits usu-ally indicate that there may becorrosion in the fuel gas line orthe main transmission pipeline.If the engine has cylinder injec-tion air starters, corrosion mayalso be found there. Lastly, ironoxide deposits may indicate acracked cylinder head.


3

Crusty, white deposits accumu-lating on firing-end.

Black, fluffy deposits on firing-end.

BARIUM/CALCIUM FOULING.The use of high-ash lubricatingoils affect the performance ofan engines spark plugs. If yoususpect this operating problem,check the engine manufactur-er's lube oil specifications. Ifash content of lube oil useddoes not conform to manufac-turer's specifications, change toa recommended lube oil. Ifengine provides power cylinderlubrication, check power cylin-der lubrication rate to assurethat lubrication rate is withinspecifications. If the lube oil isone recommended by enginemanufacturer's specifications,check that cylinder liners arenot scuffed or scored. Next,check engine lube oil con-sumption history and thencheck the piston rings. If lubeoil ash deposits indicate anexcessive accumulation in onequadrant of firing end, lube oilleakage down intake valveguides may be indicated.

CARBON DEPOSITS. Fluffyblack carbon deposits usuallyindicate too rich a fuel/oxygenmixture. If a change in the mix-ture to a leaner setting fails toremedy this carbon fouling, tryusing Stitt's next hotter heatrange spark plug.


4

Coked lubricating oil on sparkplug insulator. Could also bepaint or other conductive mate-rial.

Heavy residue of gray-coloredor copper-colored compound inthreads.

CONDUCTIVE CONTAMI-NANTS ON FLASHOVERPORTION OF INSULATOR.Paint, coked lube oil, greaseand other conductive materialscan cause misfiring by promot-ing flashover. Make every effortto keep the flashover portion ofthe spark plug insulator cleanand free of conductive contami-nants.

EXCESSIVE APPLICATIONTHREAD LUBRICANT. Toomuch thread lubricant caneventually cause problems.Though thread lubricants canhave antigalling properties ifused sparingly, too much canallow an excessive increase inthe clamping force and thiscan make the spark plugimpossible to remove. If heavyquantities of thread lubricanthave been the practice ofspark plug installation, we rec-ommend that the carbonizedresidue be removed from thecylinder head's spark plugports at each plug change byusing a thread chaser/seatcleaning tool or a full bottomtap. If solid-state ignition sys-tems are being operated, spe-cial care should be taken toremove carbonized threadlubricant in the port threads.This material can add resist-ance to the ground return cir-cuit of the ignition system andcan affect ignition performance.


5

Copper deposits on centerelectrode, possibly bridgingspark gap to ground elec-trode(s).

COPPER RUN-OUT. If sparkplugs with copper in thecenter electrode operate atexcessively high temperatures,copper run-out generallyoccurs when the center elec-trode temperature has exceed-ed 1900F, a temperaturemuch higher than the design-intended operating temperatureof the electrode. This run-out ofcopper almost always shortsout the spark plug by bridgingthe spark gap. Check allengine functions that can pre-vent spark plugs from operat-ing within their design-intendedtemperature range. Check todetermine if too hot a heatrange spark plug has beenused in a high output engine.Or perhaps too much or toolittle installation torque hascaused this problem. If so,make sure that spark plugs arebeing installed with an indicat-ing torque wrench to the sparkplug manufacturer's recom-mendations . Pre-ignition mayalso be indicated when copperrunout is observed with ignitiontoo far advanced or mixturetoo lean.To extend the sparkplug's temperature range, con-sider the substitution of sparkplugs with electrodes of solidnickel, which will extend tem-perature limit of center elec-trode to 2800F before meltingoccurs.


6

STITT SPARK PLUG COMPANYShipping Address: 204 N. Loop Hwy. 336 E., Conroe, Texas 77301

Mailing Address: P.O. Box 327, Conroe, Texas 77305Phone: 936-756-7796 or 281-443-2279

Outside Texas: 800-231-8006Fax: 936-539-9762

e-mail: [email protected]

NORMALFIRING-END.OVER-TORQUE. TORCH-EFFECT DETONA-TION.CROSS-THREADING.COOLANT-ADDITIVERESIDUE.PRE-IGNITIONDETONATION.IRON OXIDE DEPOSITS.BARIUM/CALCIUM FOULING.CARBON DEPOSITS.CONDUCTIVE CONTAMI-NANTS ON FLASHOVERPORTION OF INSULATOR.EXCESSIVE APPLICATIONTHREAD LUBRICANT.COPPER RUN-OUT.Shipping Address: 204 N. Loop Hwy. 336 E., Conroe, Texas 77301Mailing Address: P.O. Box 327, Conroe, Texas 77305Phone: 936-756-7796 or 281-443-2279Outside Texas: 800-231-8006Fax: 936-539-9762e-mail:

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