reading plugs

grumpyvette

Administrator
Staff member
YOU REALLY NEED TO READ THRU ALL THESE THREADS AND SUB LINKS TO GET A GOOD BASIC UNDERSTANDING
viewtopic.php?f=70&t=202

http://www.4secondsflat.com/Spark_plug_reading.html

viewtopic.php?f=70&t=4683

http://www.strappe.com/plugs.html

viewtopic.php?f=55&t=109

http://garage.grumpysperformance.co...-with-ignition-knock-issues.14293/#post-72961

viewtopic.php?f=44&t=773

viewtopic.php?f=50&t=177&p=211#p211

viewtopic.php?f=50&t=2891&p=9279#p9279

viewtopic.php?f=70&t=4683

http://www.empirenet.com/pkelley2/sparkplugreading.html
gappingpl.jpg

The "Ground Strap" = Heat Range
The "Plug's Base Ring" = Jetting
The "Porcelain" = signs of preignition/detonation

spr1.jpg

Heat Range = Ground Strap, the ground strap indicates the heat-range of the spark plug. If the "color" of the ground strap "changes" too close to the ground strap's end, (which is above the center electrode), then the heat-range is "too cold" , meaning that the strap is loosing heat too quickly to the base ring, and is not able to burn off deposits until near its end. If the "color" of the strap changes near where it is welded/attached to the base ring (last thread ring), then it means that the plug heat-range is "too hot", because heat is not being tranferred/cooled from the strap to the base ring quickly enough !!!! The strap might begin to act like a "glow-plug", eventually causing preignition and/or detonation later on. Proper heat-range is when the "color" is at the half-way point on the strap, neither too cold or too hot.

spr2.jpg


spr3.jpg

Jetting = the air/fuel mixture ratio shows up on the base ring (the last thread ring, it has the strap welded to it). You want a full turn of light soot color on the base ring!!! If you want to tune for max. power, then you want 3/4 to 7/8ths of a full turn of light soot color to show up on the base ring, but this is on ragged-edge of being too lean, but will make the most HP on most engines. To be safe, leave it at a full turn of light soot color. If the base ring has a full turn of color, but there are "spots" of heavy build-up of "dry soot" on top of color, then jetting is too rich .
NOTE> If the base ring has a full turn of color with some spots of heavy dry soot, then jetting is too rich, REGARDLESS, if the porcelain is "BONE-WHITE", jetting is still TOO RICH !!! NOTE> Do not look at the porcelain to read jetting !!!


Preignition/Detonation

Porcelain = the porcelain shows up preignition/detonation, it will not accurately reveal jetting/air/fuel ratios. To look for the first/beginning signs of detonation, search the white porcelain for tiny black specks or shiny specks of aluminum that have fused to the porcelain. When detonation occurs, part of the air/fuel mixture explodes instead of burning, the explosion is heard as a "metallic knock", this audible knock is the result of a sound shock-wave, this shock wave travels back and forth across the clearance volume "disrupting" the cooler boundary layer gases that cover the entire clearance volume area. This disruption allows "more" heat to be transferred into parts, especially, domes/piston tops,...along with the very rapid rise in pressure like a hammer blow, pistons can get torched with melted sides and holes !!! With the early signs of detonation, the shock-wave will also rattle rings causing the tiny amounts of oil that now gets by rings, to be fused to the white porcelain as tiny black specks, also fused as specks are soot that was clinging to clearance volume surfaces in the relatively "still-air" of the boundary layer. One step beyond the black specks, will be tiny specks/balls of aluminum coming off the pistons that will be fused to white porcelin,....the next step to be reached is occasional pieces of the porcelain being broken-off as detonation gets worse, ETC. Soon after that are holes, blown head gaskets, broken connecting rods, ETC.

NOTE> additional signs of beginning detonation are piston rings. By comparing ring's "free-diameter" to "out-of-box" free-diameters of new unused rings will reveals beginnings of detonation before much harm is caused !!! This is a result of the above previous explanation about heat being transferred more readily because the of the relatively insulating/cooler boundary layer being disrupted by the shock-wave. A piston ring is a simple spring, when a spring is over-heated it will loose tension.

Center Electrode = the very tiny sharply defined porcelain -"ditch" that encircles the center electrode, will also show up early signs of preignition/detonation and the wrong heat-range. Look for signs of the ditch beginning to be filled up with melted porcelain, you will need a 5x or 10x magnifying glass.



spr5.jpg


Lets analyze this plug, sorry the numbered points aren't clear but it's 1-4 you can figure it out.

#1 Is a timing indicator, you'll see a definite color change on the ground strap, it doesn't show well here but you can still see it right about at the arrow. Too much timing and the color change will be very close to the threaded body of the plug, too little and it'll be closer to the tip. Ideally we want it right in the apex or center of the 90 bend on the ground strap. This plug shows too much timing for the combustion chamber efficiency or octane level.

#4 Arrow shows another indicator of timing, you'll usually see a brown ring right at the tip of the porcelain area it should be a sharp and defined ring about .020 wide. Wider indicates not enough timing and any smaller , or only 1/2 way around or nonexistent as in this image is the second indication of too much timing in the motor.

#2 The tip of the ground strap is loaded with OIL deposits, fuel deposits are usually flat black in color and almost like a fine powdery deposit, this motor is leaking oil into the combustion chamber, bad valve guides, leaking valve covers allowing oil to seep through the plug threads, whatever it needs to be fixed.

#3 The threaded portion of the plug gives you the heat range, look at the threads you'll see that a few toward the tip are a dull burnt looking color the rest are black and shiny. You want about 2 threads showing the heat on the end of the plug and the rest of the threads to be shiny, this plug is impossible to read because of the oil mess. If you using a longer reach plug than this one 2.5 to 3 threads is optimum.
To increase the number of burnt threads increase the heat range of the plug, if you have 4-5-6 threads burnt you need to get a colder plug.

Looking at the color of the porcelain I'd give this carb a passing grade at the mid range and not to bad on the idle circuits although that dam oil leak makes it tough to really get a good read. I'll get some better shots for lesson 2.

I'm going to keep working on this page and try and get some real good shots of various plugs, we'll study each one and find the good and bad tell tales of each.

I'll also start pulling some plugs out of my race car at various settings and get pictures so we can see how jetting, timing and heat range affect the plugs in the same engine under the same conditions.

spr4.jpg



The plug is showing me by the deposits on the tip of the electrode and also the deposits right on the edge of the threaded body.
that it's slightly fat at idle.

The white porcelain is showing a lean condition at WOT, it's not too far advanced as the total timing mark or color change is right in the apex of the ground strap curve. The Idle timing is shown by the triangular hazing up on the flat of the ground strap and without even looking at the distributor specs I can tell you that the timing on this SB Mopar is about 18-20 initial and 34 total.

I would need a better picture of the threads to determine the heat range.

Changes:
I would try and lean it out just a touch at idle and up the jets by 2 points to fatten up the WOT circuit.

That slightly lighter color at the tip of the ground strap indicates too much gap, nothing serious but next time you change plugs I'd go to about a .036 gap from the current .040. Too much resistance caused by too wide of a plug gap can cause excessive heat on the tip which will shorten the life of the plug and really give you no benefits. I believe excessive plug gaps are not required on most Muscle and bracket cars, once you get into real big compression and major power you would open up the gap and replace plugs 2-3-4 times a year.
 
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Indycars

Administrator
Staff member
grumpyvette said:
Jetting = the air/fuel mixture ratio shows up on the base ring (the last thread ring, it has the strap welded to it). You want a full turn of light soot color on the base ring!!! If you want to tune for max. power, then you want 3/4 to 7/8ths of a full turn of light soot color to show up on the base ring, but this is on ragged-edge of being too lean, but will make the most HP on most engines. To be safe, leave it at a full turn of light soot color. If the base ring has a full turn of color, but there are "spots" of heavy build-up of "dry soot" on top of color, then jetting is too rich .
NOTE> If the base ring has a full turn of color with some spots of heavy dry soot, then jetting is too rich, REGARDLESS, if the porcelain is "BONE-WHITE", jetting is still TOO RICH !!! NOTE> Do not look at the porcelain to read jetting !!!
What is meant by Full Turn or 1/2 Turn of color on the base ring ?
 

grumpyvette

Administrator
Staff member
spr3a.jpg


my computer skills suck but maybe you can clean this picture up and post it again with legible print

what hes referring to is color and width of residual ash deposited on the plugs base ring and first plug thread if it protrudes into the combustion chamber
the ash forms on the upper surface and depending on conditions may migrate to the outer edges inside and outside the edge surface

keep in mind, to get useful information from your new spark plugs,at the track you need new plugs, and set the gap at .045, subjected to a wide open throttle run and a quick shutdown. That's when the fuel/air mixture, heat range and timing indicators are most obvious.
if plugs are older theres still a great deal they can indicate but having cycled many times the heat bands are not nearly as pronounced or dependable as indications of the EXTREME range of temps
it may be a bit confusing but theres two separate but related things your looking for here, the first is only useful on a brand new plug for the first couple of hard acceleration runs and thats the extent of the color change on the base ring surface and the extent of the heat discoloration band,
spr4.jpg

on the base circle, obviously the more heat the further the discoloration, the extended ground electrode will also display that heat level as the heat discoloration band moving along its length towards the base as heat increases , the ground electrode is usually a more consistent indication.

next is the ash build up, color and composition, and any indicators of detonation, like dark flecks on the porcelain insulator or fine bits of melted aluminum, from pistons in extreme cases .
ash build-up takes time so reading new plugs and looking at heat bands and looking for micro indications of detonation is a far different deal than looking at well used plugs that have significant ash build up that have cycled thousands of times and collected far more ash, ash which gives a very good indication of the average conditions but not always the extremes of operation

14.jpg

94367.gif

http://www.harborfreight.com/3x-magnify ... 94367.html
dirt cheap plug inspection tool
heres a very useful chart to look over
http://www.4secondsflat.com/plug_chart.html

youll find a bright light and a magnifying glass very useful during inspections


Plugs002.jpg

heres a good indication of plugs running a bit rich at idle and real lean in the upper rpm range
 

Indycars

Administrator
Staff member
I understand what the Base Ring is, but what is meant by 1/2 Turn of Color??? Maybe it's one color going 1/2 way around the base ring and another shade for the other 1/2.

I couldn't do much with that photo, but if you have a good clear one I can easily add the text. Maybe something with a 1 full turn and another with 1/2 turn so I could show the difference.
 

grumpyvette

Administrator
Staff member
the "around:" referred too, is from the top center of the entire circle of the base toward the edges of the threads as heat and ash builds and works toward the combustion chamber surface

plugheatrs1.jpg

redheaders.jpg

BTW, getting the ignition timing too retarded or f/a mix too lean and exhaust temps climb, usually resulting in burnt ignition wires or plug boots
GLOWING RED HEADERS




GLOWING RED HEADERS

think it through ...thats USUALLY the result of a good deal more HEAT exiting the engine in the form of HOT exhaust gasses,exiting the cylinder and entering the headers..
hot exhaust gasses result from either overly lean fuel/air ratios
OR
a retarded ignition timing, that delays the burn of the compressed gases, and allows still burning fuel /air mix to exit the exhaust port.
OR
cam timing that is causing very effective cylinder scavenging that allows some of the fuel/air mix to enter the headers after passing through the cylinder , as inertia drags it out following the previous exhaust gases ,before the exhaust valve closes.
OR
very rarely miss firing injectors throwing excessive fuel
honestly a bit of basic engineering and thinking about a cause and effect relationship and a bit of testing can go a long way toward isolating a logical search for any problem.

pistonposition2.jpg

cycl51.png

 
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Indycars

Administrator
Staff member
Sorry, I'm still having trouble being sure. Does this picture help?

I'm thinking you are referring to Direction 1.
 

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  • SparkPlug01.jpg
    SparkPlug01.jpg
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grumpyvette

Administrator
Staff member
yes that helps make the point, but the ring doesn,t start at and progress from the ground electrode it more or less evenly spreads, the ground electrode heat band is a far better indication of heat and the color of ash helps far more in diagnosing conditions
 

mathd

solid fixture here in the forum
The porcelain can be used to read jetting in some case:
plug_section_16.gif

source: http://www.strappe.com/plugs.html (the link also show how to read timing advance on the plug)
When we are tuning the main jet into motocross dirt bike, we run the engine wide open, clutch and instantly stop/kill the engine (no idle)and read the mixture ring at the bottom of the porcelain that tell us about our main jet when data acquisition (o2 sensor)are not availlable.
Now is it the same for a car engine?

Now about the base ring, that is new to me since a few month.
Looking at Indycars's picture, that is Direction 2 when you talk about a full turn?.. Just to make sure am not confused :)
 

Indycars

Administrator
Staff member

Grumpy,
I'm just not understanding. It's trying to put into words a succinct description of the plug. The only way for me to know for sure of what your describing would be with a good picture showing what the words cannot. Don't worry if you can't find something to work in this situation, somewhere down the road it will become clear.

mathd,
That's interesting, but how do you see down there??? You can't cross section every plug.

So question for you, is there any difference when reading plugs in a two-cycle versus a four-cycle??? When I raced Karts, the leaner you could run without sticking the piston the faster you went. At least we thought we did, but that seems counter intuitive to your observation you made above where you are looking for the perfect A/F ratio.
 

grumpyvette

Administrator
Staff member
spr4.jpg


this picture has a ton of good info

the base ring color is of VERY MINOR importance,and only really useful on new plugs on your first few runs BEFORE they get multiple over layed indicators, of subsequent heat cycles, you get FAR more info from the indications in the picture above, like the heat ring location on the ground electrode and the color on the porcelain ,
 

Indycars

Administrator
Staff member
grumpyvette said:
spr4.jpg


this picture has a ton of good info

the base ring color is of VERY MINOR importance,and only really useful on new plugs on your first few runs BEFORE they get multiple over layered indicators, of subsequent heat cycles, you get FAR more info from the indications in the picture above, like the heat ring location on the ground electrode and the color on the porcelain ,

This subject is A LOT MORE INVOLVED then I ever imaged, but loads of good info. If you have pictures you would like to email me with multiple views of each type of reading, I would love to put together something with your help that describes each facet of reading plugs. For example that ground electrode needs two views to fully show the changes along it's path. Maybe break it into sections like; ground electrode, porcelin, base circle, center electrode....etc.

If you want, you can ship me some plugs and I will take the pictures and put text/arrows on them.

This is some concrete information that everyone could put to use, and not just a few times a year, but all the time ! Most can't afford a A\F ratio meter, but they already have the tools to remove spark plugs.


 

mathd

solid fixture here in the forum
Indycars said:

Grumpy,
I'm just not understanding. It's trying to put into words a succinct description of the plug. The only way for me to know for sure of what your describing would be with a good picture showing what the words cannot. Don't worry if you can't find something to work in this situation, somewhere down the road it will become clear.

mathd,
That's interesting, but how do you see down there??? You can't cross section every plug.

So question for you, is there any difference when reading plugs in a two-cycle versus a four-cycle??? When I raced Karts, the leaner you could run without sticking the piston the faster you went. At least we thought we did, but that seems counter intuitive to your observation you made above where you are looking for the perfect A/F ratio.

You can use a magnifying glass to see down there, or you chop the plug end(sorry for lack of better words).
Honestly, am not a spark plug reading guru, the base ring stuff still got me confused as you know :/,
Usually for a 2-stroke engine, i choose my oil/fuel ration(32:1) and i jet my carb for it. I read my plug on this 2 stroke engine the same way that i do on my 4 stroke sbc engine EXCEPT for the 2-stroke engine i use the plug reading only for the main jet/WOT(otherwise the plug dont "clear/clean" from the oil enough).

That is just to give a ballpark for the main jet, Most of my plug reading is about heat range and detonation.
I tune the rest of the circuit (needle and pilot)"by feel" of the engine sound and power on the 2 stroke.
I have never used the base ring method ever but am looking to use it soon.
 

Indycars

Administrator
Staff member
mathd said:
Indycars said:

Grumpy,
I'm just not understanding. It's trying to put into words a succinct description of the plug. The only way for me to know for sure of what your describing would be with a good picture showing what the words cannot. Don't worry if you can't find something to work in this situation, somewhere down the road it will become clear.

mathd,
That's interesting, but how do you see down there??? You can't cross section every plug.

So question for you, is there any difference when reading plugs in a two-cycle versus a four-cycle??? When I raced Karts, the leaner you could run without sticking the piston the faster you went. At least we thought we did, but that seems counter intuitive to your observation you made above where you are looking for the perfect A/F ratio.

You can use a magnifying glass to see down there, or you chop the plug end(sorry for lack of better words).
Honestly, am not a spark plug reading guru, the base ring stuff still got me confused as you know :/,
Usually for a 2-stroke engine, i choose my oil/fuel ration(32:1) and i jet my carb for it. I read my plug on this 2 stroke engine the same way that i do on my 4 stroke sbc engine EXCEPT for the 2-stroke engine i use the plug reading only for the main jet(otherwise the plug dont "clear/clean" from the oil enough to take a reading).

That is just to give a ballpark for the main jet, Most of my plug reading is about heat range and detonation.
I tune the rest of the circuit (needle and pilot)"by feel" of the engine sound and power on the 2 stroke.
I have never used the base ring method ever but am looking to use it soon.

Some of the difference in our two situations is.....I'm adjusting while driving. We had two needles, one for low speed and another for high speed. If you were behind and trying to catch your rival, then you were tempted to go leaner while watching the "Head Temp" or "Exhaust Temp", knowing that at X temp the motor was going to telling you "That's it you idiot" suddenly stopping (sticking the piston in the cylinder). But that's OK, with some Muriatic Acid between rounds to remove aluminum from the cylinder, your back again for another attempt to beat your competitor.
 

mathd

solid fixture here in the forum
Ok, you had completly different setup.
On my 2 stroke mx bike, there is only one needle. The only way to change the jetting is by, draining, removing, disassemble to modify the internal parts(jets, needle clip position). only the pilot/air screw and idle speed screw can be externally adjusted.

We have no Head or exhaust temp, no tach, to speedometer, no water temp and no gauges at all, not even an ignition switch or lights bulb just a killswitch (that often do not work over 10k rpm):). If i go too lean with my 2-stroke(in extreme case) the piston will melt or seize into the cylinder(as the connecting rod/crank bearing but that rarely happen), that mean, cylinder replating if it is still salvageable and new piston/ring/gaskets.. If the bottom is still in great shape(no debrits in the bearings from exploded piston or molten parts...)
That also mean, no compression/no racing or in my case, no riding and a long way home :/

I learned it the hard way my first season (piston and ring melted while at wot, the spark plug ground strap also melted, but the piston didnt seize in the cylinder so disassembly was easy) :/
 

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
for several years I used the spark plug magnifier posted below to inspect spark plugs and it worked fine,but I recently mis-placed it at a friends shop.
having a lighted plug magnifying inspection tool allows you to get an accurate idea of the combustion chamber conditions if you have some experience and know what your looking at, so for the under $15 cost either tool is well worth owning.

https://www.amazon.com/Performance-...cphy=9012039&hvtargid=pla-1415239622852&psc=1
61jeYCr+QnL._AC_SL1500_.jpg

http://www.harborfreight.com/3x-magnify ... 94367.html
image_14883.jpg

I was in office depot and purchased this rather compact magnifier below, its not really better or worse for the application as far as I can see but it is easier to carry , and the lens is protected to some extent when its snapped closed

Handy compact size lets you keep this magnifier in a pocket or bag
$12.29
odp_max_logo.png
it comes in a red/white blister pack marked
PO-5
5
po-55.png

  • Acrylic 5x magnification provides crystal-clear images. Aspheric lens helps reduce distortion.
  • Built-in LED lights help you see in low-lit areas.
  • Ideal for carrying with you to read small print anywhere. Measuring just 4 1/4"H x 2"W x 3/4"D, this pocket-size magnifier is easy to store and carry.
  • Sliding plastic sleeve for protection and durability.
having a spark plug holder with numbered holes and a good inspection tool helps
sparkplugholdera.jpg


IF you have a drill press you can build your own spark plug holder from some aluminum scrap
stamping each of the 8 locations with the cylinder location sure won,t hurt!

http://www.harborfreight.com/36-piece-38-in-steel-letternumber-stamping-set-60669.html
22675.jpg




pit-229.jpg


http://www.autorepairinstructions.com/?p=623

http://members.uia.net/pkelley2/sparkplugreading.html

http://www.4secondsflat.com/Spark_plug_reading.html

http://www.dragstuff.com/techarticles/plug-pictures.html

http://www.dragstuff.com/techarticles/spark-plug-cross-reference.html

http://www.strappe.com/plugs.html
 
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87vette81big

Guest
Reading Spark plugs and tuning carburators still best Grumpy .
Widebands only usefull WOT THROUGG GEARS TO REDLINE AND 140 + MPH.
 
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