REFLECTOR: Franklin Mag

[Ron Brown]

John,

You really do need to find out what the timing should be on your Franklin.   Having the correct timing as determined by the engine manufacturer will improve power while minimizing the chance for detonation which can really put a hurting on your wallet.  

I did a Google search on "Franklin O350 spark timing" and got this page http://www.franklinengines.com/6a.cfm  which says you should be running between 28 - 32 degrees BTDC.  As Scott suggests, if your CHT's are running too hot, then go for the lower advance - 28 degrees which will also reduce your chance of detonation if you engine is indeed running too hot.

See ya,
Ronnie

  ----- Original Message ----- 
  From: Scott Derrick 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Friday, November 17, 2006 8:27 PM
  Subject: Re: REFLECTOR: Franklin Mag


  You might run hotter because of the fixed advanced timing..

  Traditionally I was told and I had the same behavior with a lightspeed/mag combo, was a dramatic 100 rpm drop when switched to the mag and no drop when switched to the EI.

  Scott

  John Dibble wrote: 
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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