All About Spark Plugs

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All About Spark Plugs

Post  CoolzMK on Tue Apr 03, 2012 2:05 pm

All About Spark Plugs
How do "read" a spark plug?

Being able to "read" a spark plug can be a valuable tuning aid.
By examining the insulator firing nose color, an experienced
engine tuner can determine a great deal about the engine's
overall operating condition.

In general, a light tan/gray color tells you that the spark plug
is operating at optimum temperature and that the engine is
in good condition. Dark coloring, such as heavy black wet or
dry deposits can indicate an overly-rich condition, too cold a
heat range spark plug, a possible vacuum leak, low compression,
overly retarded timing or too large a plug gap.

If the deposits are wet, it can be an indication of a breached
head gasket, poor oil control from ring or valvetrain problems
or an extremely rich condition - depending on the nature of the
liquid present at the firing tip.

Signs of fouling or excessive heat must be traced quickly to
prevent further deterioration of performance and possible
engine damage.
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How do "read" a spark plug?

Normal Condition




An engine's condition can be judged by the appearance of the
spark plug's firing end. If the firing end of a spark plug is brown
or light gray, the condition can be judged to be good and the
spark plug is functioning optimally.
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Dry and Wet Fouling



Although there are many different cases, if the insulation
resistance between the center electrode and the shell is over
10 ohms, the engine can be started normally. If the insulation
resistance drops to 0 ohms, the firing end is fouled by either
wet or dry carbon.
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Overheating



When a spark plug overheats, deposits that have accumulated
on the insulator tip melt and give the insulator tip a glazed or
glossy appearance.
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Deposits




The accumulation of deposits on the firing end is influenced
by oil leakage, fuel quality and the engine's operating duration.
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Lead Fouling




Lead fouling usually appears as yellowish brown deposits on the
insulator nose. This can not be detected by a resitsance tester
at room temperature. Lead compounds combine at different
temperatures. Those formed at 370-470°C (700-790°F) having
the greatest influence on lead resistance.
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Breakage



Breakage is usually caused by thermal expansion and thermal
shock due to sudden heating or cooling.
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Normal Life




A worn spark plug not only wastes fuel but also strains the
whole ignition system because the expanded gap (due to
erosion) requires higher voltages. Normal rates of gap
growth are as follows:
Four Stroke Engines: 0.01~0.02 mm/1,000 km
(0.00063~0.000126 inches/1,000 miles)
Two Stroke Engines: 0.02~0.04 mm/1,000 km
(0.000126~0.00252 inches/1,000 miles)

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Abnormal Erosion



Abnormal electrode erosion is caused by the effects of
corrosion, oxidation and reaction with lead - all resulting
in abnormal gap growth.
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Melting



Melting is caused by overheating. Mostly, the electrode
surface is rather lustrous and uneven. The melting point
of nickel alloy is 1,200~1,300°C (2,200~2,400°F).
___________________________________________________________________________________________

Erosion, Corrosion and Oxidation




The material of the electrodes has oxidized, and when the
oxidation is heavy it will be green on the surface. The surface
of the electrodes are also fretted and rough.
___________________________________________________________________________________________

Lead Erosion




Lead erosion is caused by lead compounds in the gasoline
which react chemically with the material of the electrodes
(nickel alloy) as high temperatures; crystal of nickel alloy fall
off because of the lead compounds permeating and seperating
the grain boundary of the nickel alloy. Typical lead erosion
causes the surface of the ground electrode to become thinner,
and the tip of the electrode looks as if it has been chipped.
___________________________________________________________________________________________

Can old spark plugs be cleaned?

Yes, you can clean spark plugs. However, it is good to remember
that spark plugs are a wearable item, so it's important to make
sure you check to see if it's worth cleaning before you go through
the following steps.

If the firing end is wet, make sure you clean the spark plug with
a quick drying cleaner. (Examples: contact cleaner or brake
cleaner).

Sand blast the spark plug using low air pressure and use a dry
compound. Completely blow all the sand from the spark plug.
Using a wire brush clean the threads and re-gap.

NOTE: Insufficient cleaning of the spark plug may lead to
spark plug failure in a very short period of time. Clean the
spark plug thoroughly to avoid problems later. Remember,
if a spark plug is fouling it's usually a result of engine side
factors or incorrect heat range selection.
___________________________________________________________________________________________

How much of a performance improvement can I expect from changing plugs?

A: A common misconception is that changing spark plugs will
result in a large power increase. In most cases, removing even
seriously worn out spark plugs will only result in very modest
power gains, typically about 1-2% of total engine output. This
could be even less for computer-controlled vehicles, primarily
because most newer vehicles have more powerful ignition
systems and the vehicle's computer can make adjustments so
that vehicle operation seems smoother and more seamless.

Many people think that simply supplying more spark to the
firing tip can and will combust more fuel. What they don't
understand is that most newer cars' engines are so efficient
that they are already burning all of the available fuel. Simply
adding more spark voltage can't burn more fuel because there
is no more fuel to burn.

When a stock or near-stock engine is given a fresh set of
spark plugs, peak efficiency is restored. The power gains that
come from this restored state of tune are usually minimal.
Any company that tells you that their spark plug will provide
significant gains in power in a stock or near-stock engine is
making blanket statements that may not be supportable.
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How do choose the right spark plug?

There are several factors - such as thread reach, thread diameter,
the insulator nose projection and whether the spark plug
incorporates a gasket or is of the conical type - to consider
when choosing the correct spark plug for your needs.

In most cases, it is not until the engine is modified, or the
compression is raised significantly, that stock ignition systems
and spark plugs begin to show signs of being inadequate. At
this point, a variety of factors determine which spark plug will
be best suited for a particular configuration. In these modified
engines, specific electrode/tip combinations, electrode materials
and colder heat ranges can provide measurable gains in power.
If your vehicle has had extensive modifications, it would be best
to seek the advice of the manufacturer of your vehicle, the
aftermarket supplier who manufactured your modifications,
or your mechanic.
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What is the maximum can open or close the gap?

Since the gap size has a direct affect on the spark plug's tip
temperature and on the voltage necessary to ionize (light) the
air/fuel mixture, careful attention is required. While it is a
popular misconception that plugs are pre-gapped from the
factory, the fact remains that the gap must be adjusted for
the vehicle that the spark plug is intended for. Those with
modified engines must remember that a modified engine
with higher compression or forced induction will typically
require a smaller gap settings (to ensure ignitability in these
denser air/fuel mixtures). As a rule, the more power you are
making, the smaller the gap you will need.

A spark plug's voltage requirement is directly proportionate to
the gap size. The larger the gap, the more voltage is needed to
bridge the gap. Most experienced tuners know that opening gaps
up to present a larger spark to the air/fuel mixture maximizes
burn efficiency. It is for this reason that most racers add high
power ignition systems. The added power allows them to open
the gap yet still provide a strong spark.

With this mind, many think the larger the gap the better. In
fact, some aftermarket ignition systems boast that their
systems can tolerate gaps that are extreme. Be wary of such
claims. In most cases, the largest gap you can run may still
be smaller than you think.
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Why are there different heat ranges?

It is a common misconception that spark plugs create heat.
They don't. A heat range refers to how much heat a spark plug
is capable of removing from the combustion chamber.

Selecting a spark plug with the proper heat range will insure
that the tip will maintain a temperature high enough to prevent
fouling yet be cool enough to prevent pre-ignition. While there
are many things that can cause pre-ignition, selecting a spark
plug in the proper heat range will ensure that the spark plug
itself is not a hot spot source.
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CoolzMK
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Join date : 2012-03-12
Age : 39
Location : Singapore

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