Spark Plug Intensifier

| August/September 2003

  • Spark Plus Intensifier

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

  • Spark Plus Intensifier
  • Original Meissner Intensifier

'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 operator.

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 spectators.

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


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