Simple Mag Question

I know this is a basic magneto question but here goes. I am running one mag and a Lightspeed ignition, each with its own on/off toggle switch. I know that when the mag circuit is closed (grounded) the mag is off. When the circuit is open, it is hot. I am running a shielded cable from the mag with the center conductor at the p-lead terminal and the shield at the ground terminal. At the switch I don't connect the shield but will ground the p-lead using the switch to the common ground. Is this correct? Also, I didn't think there should be continuity between the p-lead post and the ground post on the mag, but there is, regardless of switch position. Is this right or am I missing something. I want to be sure of these things before my first engine run.

Thanks,

That's not how I did it. My setup...Slick mag... (YMMV)

Center conductor connected to the P-lead terminal at the mag.
Shield connected to the GROUND terminal at the mag.

At the switch, center conductor on one terminal, shield on the other. Circuit is OPEN when the switch is up. Circuit is closed when the switch is down.

This is pretty much what I'm talkin' about:
http://www.aeroelectric.com/PPS/Engine/Ignition/TogMagSw.pdf

I didn't do any integration of the starter switch with the mag switch, since I only have one impulse coupled mag and I want both ignitions on for start...but that diagram should give you an idea.

I think the wiring method you mentioned would work fine, but it is dependent on the engine being grounded to the airframe. Yes, in normal cases that is not an issue. But if the engine ground breaks, then you can't shut down your mag if you locally ground the P-lead at the switch, i.e. if you use an airframe ground as opposed to the mag's own GROUND terminal.

Duh

I am using the Aeroelectric diagram for one electronic ignition and a mag with the push to start. A local guy mentioned the shield to airframe ground that's why I went that way, but I also see why you would want to ground at the switch and that is what the diagram shows anyway. I will go back and do it that way. I just answered my question about continuity between the grnd and p-lead by referencing one of my old A&P books. I feel stupid now for not thinking it through better. Duh.

mag experts

I have a couple questions for the slick magneto experts, these are not installed yet.. but Its all
I could afford till I get the extra money for the
lightspeed..

I have a new impulse mag 4371 for the left
side that shows
s/n 04121415
Lag 20, rot L , Rev C

I also have a new one on the right side a 4370 non impulse mag that shows
s/n 04104228
Lag 0 , rot L , Rev C

the engine is a built to the 0320 A1A specs
what determines the the Lag on a mag ? and
where can I find out the info on what my engine
needs as far as lag if any ? and also can a 0 lag mag
be converted to 20 or the 20 to 0 , or do they
need to match ? I have no idea about this..
any info will be much apreciated..


Danny...

bsacks05 said:

I am using the Aeroelectric diagram for one electronic ignition and a mag with the push to start. A local guy mentioned the shield to airframe ground that's why I went that way, but I also see why you would want to ground at the switch and that is what the diagram shows anyway. I will go back and do it that way. I just answered my question about continuity between the grnd and p-lead by referencing one of my old A&P books. I feel stupid now for not thinking it through better. Duh.

Click to expand...

The standard practice is to ground the shield at the source of any noise. In this case it would be the magneto. If you ground the P-lead to airframe ground at the switch, I would connect the shield to the mag ground terminal.

I just investigated this on my Grumman when I put new P-leads on it.... there seems to be no standard as to where the actual ground should occur, and what the shield should be connected to.

The P-leads do not seem to be shown on the certified plane schematics I checked, since they are not connected to any power buses, and most schematics seem to be "bus-centric".

gil in Tucson

Confused....

godspeed said:

I have a couple questions for the slick magneto experts, these are not installed yet.. but Its all
I could afford till I get the extra money for the
lightspeed..

I have a new impulse mag 4371 for the left
side that shows
s/n 04121415
Lag 20, rot L , Rev C

I also have a new one on the right side a 4370 non impulse mag that shows
s/n 04104228
Lag 0 , rot L , Rev C

the engine is a built to the 0320 A1A specs
what determines the the Lag on a mag ? and
where can I find out the info on what my engine
needs as far as lag if any ? and also can a 0 lag mag
be converted to 20 or the 20 to 0 , or do they
need to match ? I have no idea about this..
any info will be much apreciated..


Danny...

Click to expand...

Danny... I'm confused... Lycoming does not list a O-320-A1A, and if it's a O-360-A1A, then the mags are not to spec.

It should be a 4373 on the left side.

The list of mags for each Lycoming variant is here....

http://www.lycoming.textron.com/sup...ePublications/serviceInstructions/SI1443E.pdf

The Lag is the "delay" in the impulse coupling.... I don't know about converting....

gil in Tucson

godspeed said:

I have a couple questions for the slick magneto experts, these are not installed yet.. but Its all
I could afford till I get the extra money for the
lightspeed..

I have a new impulse mag 4371 for the left
side that shows
s/n 04121415
Lag 20, rot L , Rev C

I also have a new one on the right side a 4370 non impulse mag that shows
s/n 04104228
Lag 0 , rot L , Rev C

the engine is a built to the 0320 A1A specs
what determines the the Lag on a mag ? and
where can I find out the info on what my engine
needs as far as lag if any ? and also can a 0 lag mag
be converted to 20 or the 20 to 0 , or do they
need to match ? I have no idea about this..
any info will be much apreciated..


Danny...

Click to expand...

The common four cylinder impulse mag is the 4373 or the 4371. They will work pretty much interchangeably on any four cylinder engine, for experimental purposes. Whether a 320 or a 360, won't matter much. The only difference between the mags is 5 degrees of lag angle. One having a lag of 20 degrees and one with a lag of 25.
Either will work fine and in many cases either/or is approved on the same engine in the certified world.
Only an impulse mag has a lag angle and in the 4300 series of mags, the lag is not adjustable but controlled by the actual impulse coupling that is used.
Some will say one lag angle over another will produce better starting characteristics but I have never been able to discern a difference in the way an engine starts with either, and I have tried.
You should be all set with what you have.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Thanks Mahlon

If your going to be in oshkosh, let me know where
as I would like to stop by and shake your hand ,
I have never been before.. looking forward to it..

Danny..