PDA

View Full Version : reading used plugs



trinydex
10-08-2007, 11:52 AM
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
--------------------------------------------------------------------------------


http://www.socalevo.net/gallery/albums/userpics/10991/dia_normal.jpg



Light grey or tan deposits and slight electrode erosion


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


http://www.socalevo.net/gallery/albums/userpics/10991/dia_carbonfouling.jpg


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
--------------------------------------------------------------------------------


http://www.socalevo.net/gallery/albums/userpics/10991/dia_preignition.jpg


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
--------------------------------------------------------------------------------


http://www.socalevo.net/gallery/albums/userpics/10991/dia_overheating.jpg



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
--------------------------------------------------------------------------------


http://www.socalevo.net/gallery/albums/userpics/10991/dia_mechanicaldamage.jpg


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
--------------------------------------------------------------------------------


http://www.socalevo.net/gallery/albums/userpics/10991/dia_oilfouling.jpg


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
--------------------------------------------------------------------------------


http://www.socalevo.net/gallery/albums/userpics/10991/dia_brokeninsulator.jpg


Insulator is cracked or split

Symptoms:
Misfiring

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



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


http://www.socalevo.net/gallery/albums/userpics/10991/dia_torchedseat.jpg


Melted in the thread and seat area of the plug housing

Symptoms:
Loss of power causing engine damage

Causes:
Plug insufficiently tightened

Matz
01-19-2008, 10:41 AM
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.

RREVOVIII
01-19-2008, 10:43 AM
Great info. thanks for sharing :thumbsup:

Matz
01-20-2008, 01:29 AM
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:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgnorm1.jpg

Worn out:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgworn1.jpg

Mechanical damage: :shock:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgdamg1.jpg

Detonation:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgdetn1.jpg

Overheated:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgheat1.jpg

Ash deposits:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgashd1.jpg

Oil fouled:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgoilf1.jpg

Initial Pre-ignition:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgprei1.jpg

Sustained Pre-ignition:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgspre1.jpg

Splashed deposits:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgspld1.jpg

Carbon fouled:
http://imgred.com/http://www.centuryperformance.com/images/tech/Plgcrbn1.jpg