Spark Plug Intensifier

Author Photo
By Rob Skinner | Aug 1, 2003

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At top is an original Meissner intensifier, while below it is a modern copy made using an oiler sight glass.

‘The object of my invention is to provide a spark plus
intensifier of simple and durable construction so arranged as to
not only make visible at all times the spark but to magnify the
Spark.’ George Richard Meissner, Specification of Letter
Patent, filed Dec. 14, 1914.

Drawing from George Meissner’s patent application shows
the spark plug intensifier attached to the spark plug in its
intended position (‘Fig. 1’ in the drawing). The drawings
marked ‘Fig. 2’ and ‘Fig. 3’ are the contacts,
‘Fig. 4’ is the glass shell and ‘Fig. 5’ is an end
cap for the shell, much like that on a brass oiler.

Three things are required to make an engine run; fuel, air and
spark. Considering the simplicity of the formula, you’d think
we wouldn’t spend so much time building up our biceps by
pulling on fly-wheels. Alas, many nuances intervene to adversely
affect the trinity required to make an engine run, spark chief
among them.


Early in the development of spark ignition, it became obvious
there are factors that can prevent the spark from igniting the
fuel/air mixture. One such factor is carbon fouling of the spark
plug caused by incomplete combustion. In the worst case, the carbon
creates a direct short across the spark plug’s insulator,
preventing the engine from running. But long before a spark plug
becomes completely shorted carbon contamination has been slowly
building and degrading the intensity of the spark, effectively
reducing the engine’s efficiency.

In the standard high-tension ignition circuit, the spark is not
really instantaneous. It’s very fast, but many things happen as
the voltage builds. If we were to monitor the voltage in slow
motion as the magneto fires, we would see the voltage rise from
zero until it was sufficiently high to jump the gap on the spark
plug. Depending upon many variables, this might happen at about
8,000 volts. The voltage then remains steady for a short period
until the supply from the magneto is insufficient to maintain the
spark. Clearly, a long duration spark has a better chance of
igniting the fuel-air mixture.

In the ignition circuit with a contaminated plug, the
contamination acts as a resistor, bleeding off the voltage as it
builds. When the plug fires, it will be of shorter duration than if
the spark plug was in good condition. If the contamination is bad
enough, it will bleed off so much voltage that it never reaches the
required intensity to jump the spark plug gap.

In the early 1900s Iowan George Meissner pondered this problem.
He noticed, as many modern engine men have, that by pulling off the
spark plug wire and creating a small gap between the wire and the
plug an engine with a contaminated plug would sometimes fire.
Working from this observation Meissner invented a spark-gap
attachment, and in 1918 he patented the idea, calling it a
‘spark plug intensifies’

Spark Plug Intensifier

The idea behind the spark plug intensifier was to add a gap to
the circuit so ignition voltage would not bleed through the
contaminated spark plug. Once the voltage built up sufficiently to
jump both the intensifier and the spark plug gaps, a good spark of
long duration would result. Meissner’s spark plug intensifier
was basically a glass ball containing two electrodes.

Meissner probably wasn’t the first to seize on this idea of
intensifying spark. In fact, his patent application suggests as
much, noting the construction of his device, not its function, as
its critical attribute. Meissner’s application states that
‘… by means of my specially grooved bull’s-eye-shaped
insulator, breakage and inoperativeness, incident to the more
delicate and unsatisfactory devices in the art, are not only
overcome but the engineer is enabled to ascertain, with greater
certainty and ease, the strength of the spark which he is
obtaining.’ Meissner’s device was unique in that it acted
as a magnifying glass, making the spark easier to view by the

There are, however, drawbacks to such a system. Because there
are two gaps to bridge, voltage must be much higher before spark
will occur. If the magneto is weak, it might not be able to
generate sufficient voltage to fire the system. And even if the
magneto is in good condition, the higher voltage might cause it to
degrade faster.

Are there benefits from a spark plug intensifier? Realistically,
it’s probably best to make sure you have a good magneto and a
good spark plug. For the modern engine man, the primary benefit is
that it’s a neat little gadget to entertain observant

Contact engine enthusiast Rob Skinner at: 1721 Brookdale
Ave., La Habra, CA 90631-3229, or e-mail:

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