REFLECTOR: Franklin Mag

[John Dibble]

I'm back in operation.  The coupling snaps around TDC and the light changes in the
advance range.  I decided to fine tune the timing so that the mag rpm drop matches the
EI drop.  This puts the mag a bit more advanced than where it was before.  Thanks
again everyone for your help.

John

Ron Brown wrote:

> 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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