Ignition systems

In 1999 at the Tri State Gas Engine Association show at Portland Indiana USA I bought a small Briggs and Stratton which had been converted into a hit-n-miss model by a friend of mine Leroy Clark.

Up until that purchase, I had never had an engine which operated from a buzz coil. I had seen plenty of them but never taken an interest. Well, now I had to. This article series is a summary of all the information I've learned over the last year regarding buzz coils, and will take you step by step through the restoration and testing of a buzz coil. By the way, the buzz coil is the small wooden box nestled between the skids near the battery on the above picture.

The most common coil you will find apart from those specific brands for a particular engine are the Ford Model-T coils, these can be had for around $5 or $10 at swap meets. While they are starting to become a little more scarce there is not shortage just yet. The Ford coils come in two types, those with Platinum points and those with Tungsten points. Internally they are the same, and externally they are very similar with only differences in the adjustment mechanism being noted. For stationary engine use they are much the same, but according to one of my favorite volumes Dyke's Automobile and Gasoline Engine Encyclopedia the tungsten (otherwise known as "K.W. Coils") are the better ones.

 

The Platinum Points Coil

The Tungsten Points Coil

The difference between the two coils can be seen clearly in the illustrations above. The guts of the Tungsten or K.W. Coil are also exposed for you. The primary coil is powered from a 6VDC to 8VDC source and draws between 1Amp and 2Amps when buzzing and no current when it is not. Many people have told me that I should not operate my coils on 12VDC as it will harm them, but I've also had an equal number of people tell me that nothing goes wrong. I personally favour the 12VDC camp as you get a better spark, and unless the insulation in the coil is dangerously close to breaking down the extra voltage will not hurt it (especially when you consider that the higher the voltage the less current it will draw - the exact same amount of energy will travel through the wires in the primary coil).

The coil is used to generate the high voltage supply needed by a spark plug by energising the core of the coil turning it into an electromagnet. This in turn pulls down the vibrator spring making a spark jump between the points of the contact spring and vibrator spring. Because electricity "wants" to continue flowing in the circuit once the sparking starts, the output of the secondary coil will increase in voltage to allow this thus building up enough current on the secondary output to create the hot blue spark we need on the spark plug.

This is part of a series of Buzzcoil articles...

Cleaning / Restoring a Buzz Coil
Wiring your engine with a Buzz Coil
A simple tester you can build
Adjusting a Buzz Coil for best spark
A cheap Buzzcoil alternative