Why did Ford use two-piece spark plugs? Was it a good idea? Ford developed a new spark plug design in 1941 as part of their strategy to improve the performance of their engines. The new design was called two-piece spark plugs, which were a direct result of a war-time shortage of lead. In addition, many other automotive manufacturers such as General Motors and Chrysler had been making a similar design, known as the “split ring,” since
What is a Spark Plug?
Spark plugs are an important component in any engine. They transfer energy between the air and fuel in the cylinder. A spark plug works on the principle of igniting the fuel/air mixture with a spark.
There are many types of spark plugs, each designed for different tasks. One example is a conventional spark plug. These are typically threaded into the cylinder head where they connect to the coil. The coil then sends a spark across the gap. The spark causes the air/fuel mixture to ignite and begin to burn.
Why Two-piece Spark Plugs?
In the mid 1930’s Ford introduced an innovation in spark plugs, using a two-piece design. Ford’s motivation to innovate can be traced back to the early 1920’s, when engineers working for Ford noticed that the two-stroke engine cycle (four strokes total) produced twice as much power than a four stroke engine. The challenge was how to harness that power.
Engineers looked to the two-stroke engine cycle and realized the piston motion, rather than rotation, was the true source of energy in a combustion engine. This insight led to the creation of a new type of spark plug.
At first the two-piece design seemed to work as intended.
Ford’s motivation to innovate can be traced back to the early 1920’s, when engineers working for Ford noticed that the two-stroke engine cycle (four strokes total) produced twice as much power than a four stroke engine. The challenge was how to harness that power.
Engineers looked to the two-stroke engine cycle and realized the piston motion, rather than rotation, was the true source of energy in a combustion engine. This insight led to the creation of a new type of spark plug.
However, the new design suffered a setback when it failed to ignite the charge properly. The two-piece design used a single coil to fire the top cap of the plug. A traditional plug had a single center contact to fire the spark and two sides, allowing for more room for the spark to disperse.
The two-piece design used a single coil to fire the top cap of the plug. A traditional plug had a single center contact to fire the spark and two sides, allowing for more room for the spark to disperse.
However, this design resulted in the two pieces of the plug being separated by the coil. This distance allowed oxygen to be able to flow around the coil and through the gap between the pieces. Without a continuous path of oxygen, the spark could not reach the ground.
The spark did not reach the ground and the engine stalled.
Is Two-piece Spark Plugs Better Than One Piece?
When you look at cars from the past, two-piece spark plugs were a standard feature. And there’s no question that these were better than the one-piece plugs that were previously used. of course, is that two-piece plugs are a bit more expensive than the one-piece plugs. And, while there was a case to be made for one-piece plugs, there really wasn’t one that could convince car makers to change over.
A study conducted by the National Fire Protection Association back in the late 1990s (PDF) had this to say about the two-piece plug: “Two-piece spark plugs have been shown to have higher resistance to plug fouling and more consistent performance compared to one-piece plugs.
The study goes on to say that the two-piece plugs have a longer service life, and is less prone to plug fouling.
Two Piece or Single Piece Spark Plugs- Pros and Cons
Two-piece spark plugs are made up of two halves, the center electrode and ground electrode.
There are multiple pros and cons to this design:
Pros
More surface area to the combustion gases, which allows better scavenging.
Better heat transfer.
Better compression.
Better combustion.
Cons
More complex manufacturing process.
They are heavier.
They are less efficient.
It took a while for two-piece spark plugs to be adopted. It wasn’t until the 1940s and 1950s that automobile makers started to include them in their vehicles.
When it comes to performance, two-piece plugs can deliver better combustion and higher compression. They can be made more efficiently and can run cleaner. They are also cheaper to produce and manufacture.
What do I Need to Know About Spark Plugs?
Two piece spark plug wires. I am talking about the kind of wire you see in an auto parts store. There are four major brands of two-piece wire. These wires have a smaller outer diameter and a larger inner diameter. The reason for this is the two-piece wire gives better spark.
So you might think, if the wire is good enough, why would Ford change. Well, if you look at Ford’s internal documents from the 1930s, you will see that they switched to two-piece wire because of the better spark. The reason Ford switched back to the old way is because of the improved wire’s ability to hold the spark better in cold weather.
The other thing to know about spark plugs is they have a tendency to heat up and expand over time. The old wire doesn’t expand as much. So Ford switched back because it would heat up more and that could lead to damage to the cylinder walls.
Conclusion
Ford used two-piece spark plugs because they were easier to produce than three-piece plugs. They were the industry standard at the time, and that was all they needed to keep making engines for decades. Ford kept two-piece plugs in production until the 1970s, but they eventually went back to three-piece plugs when technology improved.