REFLECTOR: Franklin Mag

[Ron Brown]

Hi John,

On a Lycoming, the impulse coupling snaps at Top Dead Center.

The timing should be set on the advance mark, after the mag snaps.  IE, turn
the engine over until it snaps on Cylinder number 1, then turn the engine
backwards about 45 degrees.  Then go forward again and set the timing at the
advanced mark - on my 200 hp angle valve Lycoming IO 360 this is 25 degrees
Before Top Dead Center (or 22 according to a service bulletin or 20 degrees
for higher compression pistons).  Sorry, I don't know what the timing for a
Franklin is supposed to be.

You'll need a buzz box or a sensitive digital ohmmeter to sense the opening
of the points.  The resistance will change from about 0.5 ohms to about 0.7
ohms when the points open. (and don't let the mag snap while the ohmmeter is
connected - it may zap the ohmmeter).

Oh and a bit of explanation - the spark during starting needs to be retarded
or else the engine will kick back (some times so severe that it can break
the starter or starter gear).  So the impulse coupling delays the spark
until TDC while the engine is being turned slowly by the starter. Then when
the impulse coupling snaps (releases), it causes the magneto to spin faster 
thereby
generating a hotter spark for cranking.

That is one thing to look for when the engine doesn't seem to want to
crank - if you don't have the impulse coupling snapping, the spark is weak
and the engine will be difficult to start.

Ronnie

----- Original Message ----- 
From: "John Dibble" <aminetech at bluefrog.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Thursday, November 16, 2006 6:37 PM
Subject: Re: REFLECTOR: Franklin Mag


> I'm trying to set the timing on the mag.  When turning the prop by hand, 
> does the mag
> snap at the advance timing mark, or at another spot?
>
> John
>
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