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Grounded Mag

flyingriki

flyingriki

Well Known Member
After fussing all day, making a new P-lead, soldering all new switching, I finally realized my mag is grounded all by itself.... checked with a meter and the post has continuity to the body of the mag.

What the heck did I do to cause this?

Anyone with a P-mag for sale........?
 
Some mags, not sure which ones, ground themselves when you remove the P-Lead. (Bendix, maybe??) It is a safety measure, so that mags aren't "hot" when removed from the engine.

Try hooking up the p-lead to the mag, and check it again. Turn the switch to "both", or turn both mags "on" before you check.

Also, turn the engine a bit and keep checking. The mag will be "grounded" when the points are closed, as well. Keep turning the engine/mag while you are testing it. It may show not grounded during a portion of the rotation. If it does, then all is normal.

Hope this makes sense.
 
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Using an ohm meter mags will always show grounded as you are reading through the primary coil, that why you need a buzz box to time one.
 
I timed it with the buzz box. But it's not doing anything. When I shut off the P-mag the engine stops. Hence my troubleshooting. Showed grounded before removing the wires. Made a new P-lead thinking that was the problem but when I pulled it out while fishing in the new one it wasn't damaged.
Worked fine prior to removal for the overhaul.....
 
I'll pull it out and start over but....how can it be alive if the lead post and the ground screw show continuity? I thought that was supposed to be done by closing the switch to that mag?
 
Guessing this is an impulse mag? Have you snapped it past TDC and then backed up 25+ degrees to time it?
 
The flat spring in some bendix mags will flex toward the p-lead boss and self-ground the mag. Pull the 4 screws and the timing cover and try it again
 
krw5927 said:
Guessing this is an impulse mag? Have you snapped it past TDC and then backed up 25+ degrees to time it?
Click to expand...

Yes. But what seems odd is it snaps before the 25? mark. It seems last time I did this it snapped at it...?

Still don't understand why there should be continuity between the post and the ground screw with nothing attached if that's ow it is shut off. It's a Slick but may have something inside that's now touching.
 
flyingriki said:
Yes. But what seems odd is it snaps before the 25° mark. It seems last time I did this it snapped at it...?
Still don't understand why there should be continuity between the post and the ground screw with nothing attached if that's ow it is shut off. It's a Slick but may have something inside that's now touching.
Click to expand...

The impulse mag should snap at TDC, not at the 25 mark. It's purpose is to retard the timing for starting.

I think Walt has already answered the other question. Your ohmmeter is reading the coil.
 
Walt and Mel, if there is continuity between the P-lead post and the ground screw on the mag all the time - what does the switch do that simply closes a circuit between the two? What am I missing here? :eek:
 
The mag switch shorts out the coil.

The coil is not a direct short, it just appears that way when using a simple ohmmeter.
 
What is being said is, that if you had a really good ohmmeter like a fluke meter set to read an ohm value you would see a ohm reading through the coil and not just shorted to ground. With the switch on, that ohm reading would be zero instead of a number of ohms.
If you were seeing zero ohms with switch in either position then there would be a problem
Bird
 
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