Viewed under the hood: the spark plugs

When a classic car is purchased, spark plugs are never actually looked at. If the engine starts well, then it's okay.

The spark plugs are important

The manufacturer has determined after examination which type of spark plug with which degree of heat fits best with its engine, under normal load. In the past, the designation was more specific. Now, spark plugs have a wider operating spectrum than at the time. So there is more room for wrong choices without ruinous consequences. Fortunately.

The difference remains in the distribution between hot and cold.

The warm spark plug has a long insulation nose. This keeps the heat 'in' the spark plug for longer. Through the porcelain, the temperature is kept within certain limits. Most of the heat is dissipated to the cylinder head via the gasket ring. The cold spark plug has a short insulation nose and is used in engines with a higher load, higher power, higher compression. The generated heat has a shorter escape route there.

For optimum performance, spark plugs should not exceed 850 degrees and below 400 degrees. There is a risk that the composite material of which the piston is made melts at higher temperatures, resulting in a hole in the piston. Spark plugs that are too cold will cause the engine to beat, especially with two-stroke engines.

The spark plug in Den Beginne

Around 1880 the British physicist Oliver Lodge devised the spark plug as it still looks today. He started the Lodge Spark plug factory. In 1998 there was a tsunami of spark plug patents. Names from that time? Nicola Tesla, Robert Bosch and Carl Benz. The Frenchman Albert Champion emigrated to the States and set up the Champion Ingnition Company. That later changed to AC and later to AC Delco and Champion. Rolls-Royce started the First Electric Autolite Spark Plug Company in the 1930s. These days it is Honeywell's Autolite department.

The early spark plugs were very similar to those of today

They had an insulator that separated two electrical conductors and a distance between the electrodes between which the spark had to jump. Their maximum output power was around 50 Watt and they didn't last very long. Their standing time was a kilometer or 1000. Then they had to be replaced. And even then it was already the case that a spark plug with a sealing ring was still a quarter and that a spark plug with a conical fit still had to be turned an eighth turn after it was tightened "finger-tight."

Spark plugs got better

Over the years, spark plugs became much better in terms of reliability, temperature range, and service life. The copper-coated electrodes were introduced in 1976. 1983 brought us the platinum coated electrodes and nowadays there are already Iridium coated electrodes for spark plugs with an estimated service life of 150.000 kilometers. The change is the lifespan, not even the thing that really matters: the sparks. That lifespan had to go more in line with the much longer ignition intervals.

But not much more effective

But spark plugs have not become much more effective in all this time. The peak discharge of spark plugs has remained on or close to the 50 Watt. Just like 100 years ago. The spark plugs have now become 'the weakest link' in the ignition system. All the while it has simply been assumed that so little power was sufficient to ignite a gas mixture in a cylinder. And that while the technology behind the combustion engine, together with the power development and the environmental requirements, has undergone an incredible development.

Patches and finds

Of course there have been people who have tried to do something about this. In the XNUMXs, for example, it was not uncommon to interrupt the spark plug cable and to attach the ends separately to a bone knot. "Knot" as in a trouser knot. The air gap thus created indeed acted as a booster for the final ignition spark. The technical explanation was simple. The flashover over the created air gap induced a voltage peak in the trajectory afterwards by induction. And the spark plug was also in that route. So the spark got stronger. Later that story was polished up a bit by the introduction of boosters. These were smart devices, in the best case capacitors, that had to be inserted between the spark plug wires. They were generally 'technically' designed. They were usually empty. Because they worked on the same air-gap principle as the trouser button trick.

Smoothly

In the meantime, spark plugs have become high-quality bulk goods. They usually last a lifetime without any problems.

But things can go wrong. Especially when it comes to spark plugs for classics. That starts with the fact that over the years a number of manufacturers have changed their spark plug sets and adapted the type designations of the spark plugs. For example, it may be that spark plugs for our motorcycle or car are simply no longer available.

There are alternatives

Fortunately, in most cases there are 'conversion lists' for that. With such a spark plug by a different name, but with basically the same specifications. These lists can often be found on the Internet when, for example, 'spark plug comparison table' is Googled. Our local purveyor is not difficult about this. He just has most of the books from the early XNUMX's. Plus many of the affected spark plugs. Such as the purple-pink Beru spark plugs that used to be supplied for DKW and Maico's.

Another problem is that the shaft thickness was not standardized in earlier times. Or less standardized. Especially fans of really old cars and motorbikes have to deal with that. In other words: the owners of vehicles from before WWII. Fortunately, there is a very simple solution to that problem: at fairs there are all kinds of handy wire bushings that can be used to close a suitable course between the big hole and the new spark plug. For engines such as the Ford V4s and Harley-Davidson WLA / WLC types, that problem does not apply.

And the miracle spark plugs?

And then there are the wonder spark plugs from day zero: spark plugs with a gas tap. Spark plugs with a fan on the central pole, spark plugs with various side electrodes or with electrodes forked like snake tongues ... With annular electrodes, with built-in capacitors ...

Well: they are all there. Just like hats with 'I Love Amsterdam' and face tattoos….
But we have not discovered any noticeable improvements.

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