REFLECTOR: magneto question

[Barry Gibbons]

Hello
The mag  is operating when the switch is in the open position no grounding. 
Which means the mag is NOT grounded by the switch. Yes when you check the 
post on the mag it will show that it is grounded which means it will work 
when  the wire that runs from the post through the switch to GROUND will 
short out the mag.
Your left mag switch grounds out your right mag so you are running on the 
left mag
Your right mag switch grounds out your left mag so you are running on the 
right mag
Barry

-----Original Message----- 
From: sbjknox
Sent: Saturday, July 13, 2013 7:40 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: magneto question


----- Original Message ----- 
From: "Jack Prock" <jackprock at wavecable.com>
Subject: REFLECTOR: magneto question
> My problem is the mag I have seems to have a problem in that even
> when the switch is set to turn the mag on, it is still grounded. I pulled 
> the P-lead wire
> off the mag and did a conductivity test and was surprised that the P-Lead 
> post had
> conductivity to ground. Which means it is grounded all the time and would 
> not fire.

> Am I missing something here?
> Should the P-lead post be grounded all the time? I thought that was the 
> way to
> turn the mag off and on.

> I am going to run the engine again tomorrow, but I suspect the mag has a 
> problem.

> Does anyone have suggestions on looking at the mag?
> thanks,
> Jack

A typical Ohmeter will not tell you much because the internal resistance of
the mag is very low and it is really not possible to distinguish between
points open or closed.  That is why a "mag timer" is used.  It operates by
recognizes the change in inductance from points open and closed rather than
by change in resistance.

A relatively easy and safe way to check a mag is to pull the plugs (top or
bottom, no difference) so that you can easily turn the engine.

1) remove one plug from each cylinder.
2) connect the plug wires from the mag you are checking to the plugs you
removed and lay the body of the plugs against the engine, ie. make sure the
outside of the plugs are grounded. It can be hazardous to the mag to let it
fire without a plug load because the high voltage will instead find a path
inside the mag to jump to ground.  This can cause the coil (inside the mag)
to fail because of breakdown of the insulation.  Again, make sure all plug
wires have a plug load.
3) turn the engine either with the starter or by hand and observe that all
plugs are firing.  Switch off that mag and confirm that the plugs no longer
fire.

With the plugs out is also a convenient time to check the mag switch (and P
leads) and the impulse coupler(s) for proper operation.

$0.02

Sid Knox
Oklahoma

Velocity  173 RG  N199RS
Starduster  N666SK
KR2         N24TC
W7QJQ


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