mark.bitterlich(at)navy.m
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 Posted: Mon Mar 06, 2017 9:50 am Post subject: [Non-DoD Source] Re: M14PEngines-List Digest: 0 Msgs - 03/0 |
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Yes, I know EXACTLY how these work, have taken them apart, repaired and adjusted them on several occasions. They consist of an autotransformer where when power is supplied a relay coil is energized which opens a set of contacts. When the contacts open, power is removed from the relay coil and a spring closes it, which again completes the circuit and re-energizes the coil winding yet again. This leads to a rapid opening and closing of the relay contacts which is commonly called a "buzzer" and the sound it makes explains why it is called that. The contacts on the relay coil that when energized also power the primary portion of the autotransformer which then creates a magnetic field that passes through the rest of the windings. This produces a high voltage pulse, which also occurs when the relay contacts open and the field collapses again.
The relay contacts are not encapsulated and are easily visible if the unit is taken apart which is very easy to do. These contacts can be cleaned or "burnished" to gain some additional life and they can also be ADJUSTED for proper contact gap, which I can't remember the exact value of, I am sorry to say. However, any 24 volt DC source can power this thing, and the high voltage wire can be tied to a spark plug which is then also grounded to the negative side of the battery, allowing you to actually power it up and adjust the contacts for the biggest spark at the spark plug, or any other air gap for example.
These devices are usually blamed for hard starting, or failure to start and that is oftentimes an incorrect assumption. Bleed the air out of your system (if yours is pneumatic and hit the starter button. You should be able to easily hear this unit "buzzing" away. If it does not make a sound, it is either missing voltage, or needs to be repaired. Suspect missing voltage first and make sure you check it under load. If it makes the buzzing sound, take the cap off the mag, and rotate the prop until the rotor lines up with a plug contact on the cap. Pull the plug and check for spark when the button is depressed. While the cap is off, inspect the cap and rear most rotor point (rear most from direction of rotation) for excessive wear. Next, suspect the high tension wire that leads from the coil to the mag. It often fails.
In most designs this units 28 volt wire is attached to a terminal post inside the unit, so in order to get it out of the aircraft you'll have to take it apart anyway. A good thing to know is that the CJ-6 uses the exact same part on their engines and it is available from Doug Sapp of CJ-6 parts fame.
George Coy makes a Shower of Sparks unit selling for about $385 http://www.motorstarna.com/kits
Mark Bitterlich
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