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Hit & Miss Gas Engine Discussion

Ignition System Info


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  #1  
Old 09-10-2013, 12:43:35 AM
thiggy thiggy is offline
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Default Ignition System Info

I don't need this for my specific application, but for my general information and education, as I am new to this hobby/disease. What is the difference between a low tension and high tension magneto? What is a buzz box and why is this type of ignition used sometimes and sometimes a magneto for the spark? Thanks for any info.
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Old 09-10-2013, 01:07:59 AM
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Ray Cardoza Ray Cardoza is offline
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Default Re: Ignition System Info

Hi tension is a sparkplug set up. Low tension is a igniter. The igniter is like a set of automotive points that open and close to make the spark inside the cylinder. Battery/coil set up was the early method before the magnetos made entry. I'm sure the other guys will chime in with more information about the two
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Old 09-10-2013, 10:21:34 AM
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Default Re: Ignition System Info

Ray has it right, on a low tension coil and battery or mag, it might give you a tingle, espececially if wet out side, at least the hot coils I have, now don't even think about getting bit by the business end wire of a buzz coil or high tension mag, think HEI systems today will light you up, these are almost if not hotter. Someone else could explain better, but the buzz, are a set of points, that makes the electric field in the coil break down and reenergize and that is how the spark is formed when the fields break down and reenergize, I think that is how it works, trust me you don't want to hang on to the wire that goes to the plug on a buzz coil!!
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Old 09-10-2013, 10:30:36 AM
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Default Re: Ignition System Info

Great explanation, fellows. Thanks for helping further my education. Is an igniter mounted within the head just like a spark plug, and can a plug usually be substituted using a magneto?
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Old 09-10-2013, 10:41:17 AM
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Default Re: Ignition System Info

The igniter is just two points that meet and break apart real fast in a snap thus, this creates the spark ,and for a spark plug conversion,It was done by a plate that would go over the hole for the igniter and threaded so the plug would screw into it , usally after the igniter wore out in the depression and they made do with what they could scrape up, or retrofitted with a Wico ,you have to figure out a way to make the buzz coil fire by a contact , usally on the cam gear by contact points but have seen other contraptions like a Ford commuter or a Mag set up with a bicycle chain, they done what they had to do with what they had or could find out of the junk pile, if lucky that was around.... ..
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Old 09-10-2013, 12:44:25 PM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Ignition System Info Long post

Standard explanation - Low tension:electrically simple, mechanicly complicated. Low tension usually used low voltage; anything from 6 to 18 volts, and little current. For a battery and coil set up, usually 4 large dry cells (6 volts), a simple heavy copper coil wound around a soft iron core and a set of points mounted within the combustion chamber to provide ignition. The system is not too complicated with battery and coil, a simple trip mechanism that opens the points near or at TDC compression is all that is needed. The ignitor points are usually open and only close neat the point of ignition. When they close, a current is induced in the coil from the battery. When the points break contact (point of ignition), the current tries to keep flowing, creating a flash, which ignites the fuel and air under compression. that's the easy part.

With a magneto fired ignitor, things get complicated. Everything must be 'just so' in order to get the most intense spark possible. A low tension magneto consists of a magnet, a simple coil (or 2 in series), an armature,and a means to make the assembly create a magnetic field in the coil. Some mags are rotary, that is they turn full circle, others are oscillating, that is they rock back and forth. A mag can have external magnets and an internal coil in the rotor, a magnet mounted in the rotor, and external coil, or magnets and coil on the case and an iron rotor. All 3 types generate low voltage that is peak when the magnetic lines are crossed by the rotor. With a mag system, the points must break at the exact instant of peak magnetic flux, in order to make a good flash in the combustion chamber. Worn points, worn linkages, a mis-adjustment in the device that opens the points or a mis timed mag will prevent spark. Also on damp mornings magneto ignition can be shorted out by humidity on either the wiring or the points themselves!

A high tension system is electrically complicated, mechanically simple. A low tension coil is wound around a soft iron core, and a fine high tension wire coil is usually wound on the outside of the low voltage coil. there is a set of points and a battery attached to the coil. Both the fixed point and the hightension coil are grounded to the engine. The movable point has a condenser as well as one end of the low tension side of the coil. The battery has the power side of the coil attached, usually thru a switch. When the points close, power from the battery flows thru the low tension coil, creating a magnetic field in the soft iron core. When the points open,the field collapses. As the points open, current flows into the condenser, and as current and voltage drop, the condenser reverses the flow, causing the collapse to happen more quickly. This collapse generates current and voltage in the high tension coil. This is led to the spark plug, where that high tension jumps the gap and ignites the fuel-air charge in the combustion chamber.. Most coils deliver between 15 to 25 thousand volts to the plug. New HEI systems can deliver up to 100,000 volts. In the 1970s, when GM came out with their HEI system, there were several instances where mechanics were electrocuted by the high voltage. Rare, but you don't want to mess with lightning in a can!

The buzz coil system is a high tension system - with a twist! The coil is roughly the same as a regular high tension coil BUT: At one end of the soft iron core there is a 'tremblor'. This is most often a set of points with a spring steel lever attached to a mount that allows it to be attracted toward the core when it is energized. When the points close, battery voltage flows thru the low tension coil, setting up a magnetic field in the iron core. This in turn attracts the steel plate to which one of the points are attached, and the points open. The current then flows into a condenser, reverses and causes the magnetic collapse needed to generate the high tension spark. When the magnetic field collapses, the spring tension on the point again closes them, and the cycle repeats. This can happen up to thousands of times a second! This system needs a second set of points or a ground contact, attached to the engine, in order to tell the coil when to energise and create spark. In this system, the advantage is that at low speeds, multiple sparks get to the spark plug, during the time of ignition, increasing the chance of igniting the charge in the combustion chamber. A buzz coil typically puts out between 10 and 20000 volts, but some coiils (K&W for instance) can put as much as 45000 volts out!

Magneto high tension uses the same principles as a battery and coil, with the exception that a permamant magnet generates the low voltage in the primary coil instead of a battery. These mags too can have different types of assemblies - fixed mag and rotating armature, rotating magnet, fixed coil, coil mounted on a backing plate and rotating flywheel with magnets mounted, and oscillating armature. All use the same principle, as magnetic lines are broken, low tension field collapses, creating a generation of high tension voltage in a secondary coil.

I have not explained specific mag applications, that would take up lots of Stak memory, but if you go to the stak archives, there have been many posts on each mag system.
Andrew
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Old 09-10-2013, 03:11:52 PM
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Default Re: Ignition System Info

A lot better explanation than I could ever do, Thanks Andrew!! LOL
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Old 09-10-2013, 09:08:18 PM
ScooterBob ScooterBob is offline
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Default Re: Ignition System Info

Here's a link to a bunch more ignition information, many with animated diagrams...

http://www.smokstak.com/forum/showthread.php?t=46772
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