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Discussion Starter · #1 ·
While chatting on an Aprilia RS125 forum about fixing my son's bike the question of spark plugs soon came up. A helpful member posted the following guide to plugs. Probably the most comprehensive and most helpful guide to plugs I have ever read......


Spark Plugs Overview
Spark plugs are one of the most misunderstood components
of an engine. Numerous questions have surfaced over the years, leaving many people confused.

This guide is designed to assist the technician, hobbyist, or race mechanics in understanding, using, and troubleshooting spark plugs. The information contained in this guide applies to
all types of internal combustion engines.

Spark plugs are the "window" into the engine , and can be used as a valuable diagnostic tool. Like a patient's thermometer, the spark plug displays symptoms and conditions of the engine. The experienced tuner can analyze these symptoms to track down the root cause of many problems, or determine air/fuel ratios.

SPARK PLUG BASICS:
The spark plug has two primary functions:

* Ignite air/fuel mixture
* Transfer heat from the combustion chamber

Spark plugs carry electrical energy and turn fuel into working energy. A sufficient amount of voltage must be supplied by the ignition system to spark across the spark plug's gap. This is
called "Electrical Performance."

The temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called "Thermal Performance", and is
determined by the heat range selected.

It's important to remember spark plugs do not create heat, they only remove heat. The spark plug works as a heat exchanger
by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engine's cooling
system. The heat range is defined as a plug's ability to
dissipate heat.

The rate of heat transfer is determined by:

* The insulator nose length
* Gas volume around the insulator nose
* The materials/construction of the center electrode and porcelain insulator

A spark plug's heat range has no relationship to the actual voltage transferred through the spark plug. Rather, the heat range is a measure of the spark plug's ability to remove heat from the combustion chamber. The heat range measurement is determined by several factors; the length of the ceramic center insulator nose and its' ability to absorb and transfer combustion heat, the material composition of the insulator and center electrode material.

Heat rating and heat flow path of NGK Spark Plugs



The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C.

Tip Temperature and Firing End Appearance



The firing end appearance also depends on the spark plugs tip temperature. There are three basic diagnostic criteria for spark plugs: good, fouled and overheated. The borderline between the fouling and optimum operating regions (500&def;C) is called the spark plug self-cleaning temperature. The temperature at this point is where the accumulated carbon and combustion deposits are burned off.

Keep in mind the insulator nose length is a determining factor in the heat range of a spark plug, the longer the insulator nose, the less heat is absorbed, and the further the heat must travel into the cylinder head water jackets. This means the plug has a higher internal temperature, and is said to be a hot plug. A hot spark plug maintains a higher internal operating temperature to burn off oil and carbon deposits, and has no relationship to spark quality or intensity.

Conversely, a cold spark plug has a shorter insulator nose and absorbs more combustion chamber heat. This heat travels a shorter distance, and allows the plug to operate at a lower internal temperature. A colder heat range is necessary when the engine is modified for performance, subjected to heavy loads, or is run at a high rpm for a significant period of time. Colder spark plugs remove heat quicker, reducing the chance of pre-ignition/detonation. Failure to use a cooler heat range in a modified application can lead to spark plug failure and severe engine damage.

Below is a list of external influences on a spark plug's operating temperature. The following symptoms or conditions may have an effect on the actual temperature of the spark plug. The spark plug cannot create these conditions, but it must be able to cope with the levels of heat...if not, the performance will suffer and engine damage can occur.

Air/Fuel Mixtures seriously affect engine performance and spark plug operating temperatures.

* Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor driveability
* Lean air/fuel mixtures cause plug tip and cylinder temperature to increase, resulting in pre-ignition, detonation, and possibly serious spark plug and engine damage
* It is important to read spark plugs many times during the tuning process to achieve the optimum air/ fuel mixture

Higher Compression Ratios/Forced Induction will elevate spark plug tip and in-cylinder temperatures

* Compression can be increased by performing any one of the following modifications:

a) reducing combustion chamber volume (i.e.: domed pistons, smaller chamber heads, mill ing heads, etc.)

b) adding forced induction (Nitrous, Turbocharging or Supercharging)

c) camshaft change
* As compression increases, a colder heat range plug, higher fuel octane, and careful attention to ignition timing and air/fuel ratios are necessary. Failure to select a colder spark plug can lead to spark plug/engine damage

Advancing Ignition Timing

* Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-100° C

Engine Speed and Load

* Increases in firing-end temperature are proportional to engine speed and load. When traveling at a consistent high rate of speed, or carrying/pushing very heavy loads, a colder heat range spark plug should be installed

Ambient Air Temperature

* As air temperature falls, air density/air volume becomes greater, resulting in leaner air/fuel mixtures.
* This creates higher cylinder pressures/temperatures and causes an increase in the spark plug's tip temperature. So, fuel delivery should be increased.
* As temperature increases, air density decreases, as does intake volume, fuel delivery should be decreased

Humidity

* As humidity increases, air intake volume decreases
* Result is lower combustion pressures and temperatures, causing a decrease in the spark plug's temperature and a reduction in available power.
* Air/fuel mixture should be leaner, depending upon ambient temperature.

Barometric Pressure/Altitude

* Also affects the spark plug's tip temperature
* The higher the altitude, the lower cylinder pressure becomes. As the cylinder temperature decreases, so does the plugs tip temperature
* Many mechanics attempt to "chase" tuning by changing spark plug heat ranges
* The real answer is to adjust air/fuel mixtures by rejetting in an effort to put more air back into the engine

Types of Abnormal Combustion

Pre-ignition

* Defined as: ignition of the air/fuel mixture before the pre-set ignition timing mark
* Caused by hot spots in the combustion chamber...can be caused
(or amplified) by over advanced timing, too hot a spark plug, low octane fuel, lean air/fuel mixture, too high compression, or insufficient engine cooling
* A change to a higher octane fuel, a colder plug, richer fuel mixture,
or lower compression may be in order
* You may also need to retard ignition timing, and check vehicle's cooling system
* Pre-ignition usually leads to detonation; pre-ignition an detonation are two separate events

Detonation

* The spark plug's worst enemy! (Besides fouling)
* Can break insulators or break off ground electrodes
* Pre-ignition most often leads to detonation
* Plug tip temperatures can spike to over 3000°F during the combustion process (in a racing engine)
* Most frequently caused by hot spots in the combustion chamber.
Hot spots will allow the air/fuel mixture to pre-ignite. As the piston is being forced upward by mechanical action of the connecting rod, the pre-ignited explosion will try to force the piston downward. If the piston can't go up (because of the force of the premature explosion) and it can't go down (because of the upward mo-tion of the connecting rod), the piston will rattle from side to side. The resulting shock wave causes an audible pinging sound. This is detonation.
* Most of the damage than an engine sustains when "detonating" is from excessive heat
* The spark plug is damaged by both the elevated temperatures and the accompanying shock wave, or concussion

Misfires

* A spark plug is said to have misfired when enough voltage has not been delivered to light off all fuel present in the combustion chamber at the proper moment of the power stroke (a few degrees before top dead center)
* A spark plug can deliver a weak spark (or no spark at all) for a variety of reasons...defective coil, too much compression with incorrect
plug gap, dry fouled or wet fouled spark plugs, insufficient ignition timing, etc.
* Slight misfires can cause a loss of performance for obvious reasons (if fuel is not lit, no energy is be-ing created)
* Severe misfires will cause poor fuel economy, poor driveability, and can lead to engine damage

Fouling

* Will occur when spark plug tip temperature is insufficient to burn off carbon, fuel, oil or other deposits
* Will cause spark to leach to metal shell...no spark across plug gap will cause a misfire
* Wet-fouled spark plugs must be changed...spark plugs will not fire
* Dry-fouled spark plugs can sometimes be cleaned by bringing engine up to operating temperature
* Before changing fouled spark plugs, be sure to eliminate root
cause of fouling

Fouling Range

Lower than the self-cleaning temperature of 400c-450c (750f-850f). Air-fuel mixture richer than 8:1 to 10:1.

Wet Fuel Fouled Wet Black Deposit

The firing-end of the spark plug becomes saturated with fuel and its insulation ability deteriorates and misfiring occurs.

Recommendation
Check for rich air/fuel mixture. Check the entire ignition system. If condition recurs, engine overhaul may be necessary.

Carbon Fouled

Black Carbon Fouling
Carbon accumulates in large quantity and, while the firing-end of the plug is dry, its insulation is abnormally decreased. This, too, is regarded as a prime cause of misfiring.

Recommendation
Check for rich air/fuel mixture. Check the entire ignition system and cooling system (excessive cooling).

Oil Fouled

When the firing end of a spark plug is fouled by oil, as shown above, an electrical leakage path is formed and the insulation deteriorates, consequently the available voltage from the ignition system is lowered and a spark can not jump at the spark gap.

Causes of carbon fouling
n Fuel mixture too rich
n Excessive use of choke
n Blocked air filter
n Incorrect spark plug gap setting
n Over-retarded ignition timing
n Compression loss due to imperfect cylinder-piston
n seal or valve seating
n Prolonged low speed driving or idling
n Too cold a spark plug fitted.

Causes of oil fouling
n Lubricating oil entering into combustion chamber

Firing End Appearances


OPTIMUM PERFORMANCE TEMPERATURE RANGE
The five firing-end appearances below are considered to be good.

perhaps a sticky?
 

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Ninja Thread Hijacker
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2,978 Posts
Excellent find Austin

Lots of stuff I was not aware of in there.
 

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Senior Member
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2,701 Posts
Excellent info Austin :thumb:

All stuff i have picked up over the years, but this is all in one place and very easy to understand. :cool:
 
G

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Yes it did take me a while to write that about spark plug.

My next project is dilithium crystals and warp technology! :D
General Information

Chemical Formula: Li2Te

Composition: Molecular Weight = 141.48 gm)

Lithium 9.81 % Li

Tellurium 90.19 % Te

Empirical Formula: Li2Te

Environment: Silica-poor planetesimals which did not undergo significant parent-body metamorphism during formation.

IMA Status: Not IMA Approved

Locality: Interplanetary asteroids.

Name Origin: Named after it's composition.

Synonym: Go Juice

Warp Factor 9

Classification

Dana Class: 2.0.0.0 (2)Sufide Minerals

(2.0)Without Dana Classification Numbers
(Telluride)

Strunz Class: II/X.00-00 II - Sulfides and sulphosalts
II/X - Unclassified Strunz Sulfides and sulphosalts
II/X.00 - Telluride

Crystallography
Axial Ratios: a:b = 1:1.897

Cell Dimensions: a = 7.67, b = 14.55, Z = 12; V = 855.96 Den(Calc)= 3.29

Crystal System: Orthorhombic - Disphenoidal H-M Symbol (2 2 2) Space Group: P222

Physical Properties
Cleavage: [0001] Distinct
Color: bottle brown or amber brown.
Density: 3.1 - 3.5, Average = 3.3
Diaphaniety: Transparent to translucent
Habits: Crystalline - Coarse - Occurs as well-formed coarse sized crystals., Tabular - Form dimensions are thin in
one direction.,
Hardness: 5 - Apatite
Luminescence: Triboluminescent.
Luster: Adamantine - Resinous
Streak: white

Optical Properties

Optical Data: Uniaxial (+), w=1.952-1.984, e=1.971-2.01, bire=0.0190-0.0260.

Dilithium is one substance that can safely combine matter and anti-matter into a stable stream.

The Crystal becomes the focal point where the matter/anti-matter injectors fire. The crystals then combine and refract the beam in to the Warp Core. Kinda like the reverse of a light prism. Instead of only one beam of light hitting the prism and refracting into mutiple beams of light.. it does the exact opposite. Takes 2 beams of in-compatable energy, combines them to make a single stable beam of energy and fires into the warp core chamber... and voila, you have warp power!!

I know that it would be possible for the deuterium ions to "channel" through the crystral, provided it is very pure and exactly aligned. The antideuterium is the problem, since it is supposed to have the opposite charge (negative). This would mean the ions would not behave like deuterium and would (under the same conditions) possibly collide with the dilithium nuclei: boom! This is where the TNGTM makes a nice suggestion to create a condition (high frequency excitation) to make the material porous also for antimatter. Another possibility is to accelerate them to a high speed, so that the deflection in the crystal is minimized.





Here is some of my research if it is any help.............
I'm currently working on a paper for warp technology so once it is finished I will share that with you to
Greg
 

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yet another Dave
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2,854 Posts
theres also a very simple (ie, few words, lots of pictures) troubleshooting guide in all the haynes manuals.
 

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Discussion Starter · #12 ·
More importantly... Did you fix his bike?

:D

-Simon
yep, its running, quite well now actually (70mph+ ish), but I am sure it needs a top end rebuild (very low compression) and the clutch slips when the power band kicks in. Its an absolute hoot to ride, sound great - all taut, highly strung, crackly and snappy like a Terrier on speed, and handles like nothing I have ever been on. A full power one of these will be awesome:thumbright:


oh, but I am still not sure I have got the right plug in.:scratch:
 

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Huh?
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2,328 Posts
yep, its running, quite well now actually (70mph+ ish), but I am sure it needs a top end rebuild (very low compression) and the clutch slips when the power band kicks in. Its an absolute hoot to ride, sound great - all taut, highly strung, crackly and snappy like a Terrier on speed, and handles like nothing I have ever been on. A full power one of these will be awesome:thumbright:


oh, but I am still not sure I have got the right plug in.:scratch:
:thumbright: :thumbright: :thumbright:

-Simon
 

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12,768 Posts
yep, its running, quite well now actually (70mph+ ish), but I am sure it needs a top end rebuild (very low compression) and the clutch slips when the power band kicks in. Its an absolute hoot to ride, sound great - all taut, highly strung, crackly and snappy like a Terrier on speed, and handles like nothing I have ever been on. A full power one of these will be awesome:thumbright:


oh, but I am still not sure I have got the right plug in.:scratch:
The clutch slip is possibly caused by car engine oil being used.
 

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Premium Member
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Discussion Starter · #15 ·
The clutch slip is possibly caused by car engine oil being used.
yep, on my shopping list is the right spec oil - 75w/90 Gear Oil API GL-4 spec.

I can get GL-5 anywhere but GL-4 seems to be only available at specialists and I haven't managed to track a local one down yet, not that I have tried that hard mind.
 

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yet another Dave
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2,854 Posts
yep, its running, quite well now actually (70mph+ ish), but I am sure it needs a top end rebuild (very low compression) and the clutch slips when the power band kicks in. Its an absolute hoot to ride, sound great - all taut, highly strung, crackly and snappy like a Terrier on speed, and handles like nothing I have ever been on. A full power one of these will be awesome:thumbright:
talking about power bands i assume its a 2T 125 and not a newer 4T? if you think thats good try an RS250 if you can get hold of one thats not been "improved" by a previous owner. 250 GP bike with a headlight.
 
G

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yep, on my shopping list is the right spec oil - 75w/90 Gear Oil API GL-4 spec.

I can get GL-5 anywhere but GL-4 seems to be only available at specialists and I haven't managed to track a local one down yet, not that I have tried that hard mind.
Austin, any dealer that stocks mobil oil will be able to help you, either that or order from these guys
Opie Oils

The Fuel Depot
Cardrew Way
Cardrew Industrial Estate
Redruth
Cornwall
TR15 1SS

Tel: 01209 215164
Fax: 01209 314019

Email: [email protected]
 

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Premium Member
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4,354 Posts
Discussion Starter · #18 ·
Austin, any dealer that stocks mobil oil will be able to help you, either that or order from these guys
Opie Oils

The Fuel Depot
Cardrew Way
Cardrew Industrial Estate
Redruth
Cornwall
TR15 1SS

Tel: 01209 215164
Fax: 01209 314019

Email: [email protected]
Thanks,

it was through the Opie oils site that I knew the stuff exists. I was hoping to just pop into one of the local bike dealers and get 1litre from off the shelf. I have tried 3 and halfords but they none of them stock it. Their is an MX bike specialist in warrington and will give them a go tomorrow lunch time. If not I will get it mail order.
 

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Austin's Son
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190 Posts
I want to see it now, more so, I want to ride it.

I seem to have a lusting after 2T bike. A wee bit jealous of my brothers bike.
 

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Premium Member
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4,354 Posts
Discussion Starter · #20 ·
I want to see it now, more so, I want to ride it.

I seem to have a lusting after 2T bike. A wee bit jealous of my brothers bike.
Get back to studying. You will never pass if you spend all your time surfing the net, boozing and enjoying yourself. Be a good student;)

I rode it to John Carr's for an MOT this morning Charlie (he didn't turn up), but did discover the clutch now slips really badly, like every time it hits 7k rpm and all the way up the hill on the A6 from the traffic lights. Hopeless really. So today I have ordered a complete new clutch, a top end rebuild kit and a headlamp unit. All on next day delivery, I hope to get the clutch and headlight fitted friday evening,MOT saturday, and top end done in a couple of weeks time. You can come home and help!!!:D
 
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