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Thread: reading used plugs

  1. #1

    Default reading used plugs

    http://densoiridium.com/howtoreadusedplugs.php

    Reading a Spark Plug

    NASCAR engine tuners love spark plugs they can "read". The discoloration on the insulator after a few laps helps them understand how the electrical elements of the engine are performing.


    Not all plugs allow you to "read" them. The corona, a brown deposit on the insulator, is the glow that appears above the spark plug housing around the base of the insulator. The appearance of a corona is not detrimental to the operation of the spark plug. Contrary to common belief, this condition is caused by electrical stress in the air adjacent to the insulator. Often, the corona stain is mistaken for spark plug gas leakage, but again, this does not affect spark plug performance.

    The insulator is ceramic and can be broken, although this is a rare occurrence. Typically, the most common ways the insulator becomes cracked is when the installation is done at the wrong angle, the incorrect torque is used or the removal is forced. (See Installation Guide)

    Our primary concern is that you use the appropriate tools and torque during installation. When the insulator is cracked during installation, this can cause a short circuit which will result in irregular idling and misfires during acceleration. (See Common Engine Problems)


    Diagnosis of a Used Spark Plug

    If you're seeing any of the following, you probably don't have the manufacturer's recommended spark plug installed. But the symptoms are separate from the causes and all the components in an ignition system, no matter how small, will leave some signs on the spark plugs over time if they're not in harmony. This guide can provide insight to the engine's performance.

    Normal
    --------------------------------------------------------------------------------






    Light grey or tan deposits and slight electrode erosion


    Carbon Fouling
    --------------------------------------------------------------------------------





    Dry, soft black carbon on the insulator and electrodes.

    Symptoms:
    Poor starting
    Misfiring
    Faulty acceleration

    Causes:
    Faulty choke - over rich air/fuel mixture
    Delayed ignition timing
    Bad ignition leads
    Plug heat range too cold



    Pre-Ignition
    --------------------------------------------------------------------------------





    A melted or burned center and/or ground electrode, blistered insulator and aluminum or other metallic deposits on the insulator

    Symptoms:
    Loss of power causing engine damage
    Pre-ignition occurs when combustion begins before the timed spark occurs.

    Causes:
    Plug insufficiently tightened
    Engine insufficiently cooled
    Ignition timing too advanced
    Plug heat range too hot



    Over Heating
    --------------------------------------------------------------------------------






    An extremely white insulator with small black deposits and premature electrode erosion.

    Symptoms:
    Loss of power at high-speed or during heavy load

    Causes:
    Plug insufficiently tightened
    Engine insufficiently cooled
    Ignition timing too advanced
    Plug heat range too hot



    Mechanical Damage
    --------------------------------------------------------------------------------





    Bent electrode and a broken insulator, dents often present on electrode

    Symptoms:
    Misfiring

    Causes:
    Plug nose is too long for engine head
    Foreign object (bolt/nut) in combustion chamber



    Oil Fouling
    --------------------------------------------------------------------------------





    Wet, oily black deposits on the insulator and electrodes

    Symptoms:
    Poor starting
    Misfiring

    Causes:
    Wrong piston rings, cylinders, and valve guides
    Fuel mixture oil content too high (two-stroke engines)



    Broken Insulator
    --------------------------------------------------------------------------------





    Insulator is cracked or split

    Symptoms:
    Misfiring

    Causes:
    Severe detonation
    Incorrect tool/torque applied during installation or removal
    Careless gap setting



    Torched Seat
    --------------------------------------------------------------------------------





    Melted in the thread and seat area of the plug housing

    Symptoms:
    Loss of power causing engine damage

    Causes:
    Plug insufficiently tightened
    I <3 Nisei Engineering

  2. #2
    Join Date
    Mar 2005
    Posts
    7,824

    Default Re: reading used plugs

    Great post, triny, I'm glad I found it here, because some of the stuff google gave me didn't have good pictures.

    Anyhow, what about plugs with ground electrodes completely covered with white buildup?

    What is the best way to take pics of them? Macro mode didn't work for me (wouldn't focus on the electrode), but maybe I can try another one of my cameras. Maybe you guys have tips for tricking the camera into focusing correctly?

    If I reuse my Iridiums, do you guys recommend replacing the crush washer, and if so, I guess Kragen will carry them? I could also temporarily steal them from my set of copper or Iridium plugs.

  3. #3
    Join Date
    Mar 2007
    Location
    Daly City
    Posts
    4,098

    Default Re: reading used plugs

    Great info. thanks for sharing
    2003 Evolution VIII

  4. #4
    Join Date
    Mar 2005
    Posts
    7,824

    Default Re: reading used plugs

    Here's a site with slightly larger pics. You'll get the larger images when you click on the thumbnails.

    http://www.centuryperformance.com/spark2.asp

    Summary:

    Normal:


    Worn out:


    Mechanical damage: :shock:


    Detonation:


    Overheated:


    Ash deposits:


    Oil fouled:


    Initial Pre-ignition:


    Sustained Pre-ignition:


    Splashed deposits:


    Carbon fouled:

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