• If you log in, the ads disappear in the forum and gallery. If you need help logging in or getting registered, send request to: webmaster@southernairboat.com

New to this, HELP with Lycoming Mags!!


Well-known member
Buddy bought a lycoming powered panther. I'm looking for same power, but thats another story...

This morning, it poured rain, thunderstorms dumped 2+ inches and he pulled the airboat about 40 miles in that rain.

Got to the ramp early, engine fired instantly and ran perfect, got in and ran up to within 100 feet of our drop off point, and engine died. Like cutting the mags off. Never would fire again. We hunted anyway till the legal noon hour and spent hours working on it alone and stranded.

I know this much, no fire from either mag. 2 wires, 1 from each mag come out and go to a switch, that should be the safety, IE it grounds the mags to the frame. There is only one other wire, comes out of each mag and goes to what looks like a capacitor. Could not get a reading off the capacitor either. Everything dead.

Finally trying to think it through, and a bunch of thoughts, called 2 folks, they kept saying the mags have to have an initial source of 12 Volt to start, there are NO other wires we see.

Curious for input. I think the mags haven't been sealed in a long time, somewhere the RTV got a tiny fracture and the water didn't get in on the trailer ride over, but once the engine was running, eventually vibrated moisture in the mag killing it.

Funny that both must have done it, OR he has one mag not working. He was hot, but I said the engine is so simple, it just takes learning what to look for.

( on the side my take looks like carry a spare starter, spare 12V jumper box,a fuel pump and spare mag and that should take care of most anything not serious)

We are trying it again in the AM, would like input before that below freezing run.

Thanks, Jeff
take off the covers and blast the points contacts with brake klean, then take a dollar bill and fold it up in such a way as to enable you to run some portion between the contacts. this removes residue build up with out leaving lint ect. Should fire up.
You're right the P-wire grounds the mag. try startin it with that wire disconnected in case the problem is from water in the switches. If it starts plug the wires back together to kill it unless you have a lean/rich cable.
Are you runing Bendix or slick mags...? Aircraft mags are self contained...
Do not hook 12v power to them. If so Zap your mags are done!!!

Thanks for the heads up, I'll call him and tell him about brake cleaner and then the dollar bill. Any reason about the dollar bill vs 600 grit sandpaper etc...? I know we didn't have allen wrenches OR brake cleaner with us.

Speed, not sure at all what he has. Looks stock to me, but I wouldn't know. Am I right on there beinga capacitor?

Whats everyone here(car guys from cars, not airboats, mostly tractors.... ) saying the mags have to have 12volt to "excite" them at first?

Thanks to all for the quick replies.

Had same issue with mine the day before Hunting season. Literally had to take the points out and file them down. It's never ran better.
And when I say file,,,,, I don't mean some woman's nail file. :D
Just got a call in, they are bendix mags supposedly if that answers anything.

Fun part about this? I should know all I need to basically, before I buy one!

Thanks, Jeff
You should only have one wire coming out of the mag. That is the P lead. If the P lead is grounded the mag will quit working or kill the motor. The capacitor is probably a noise suppressor for the radios. No radios, then you don't need it. Don't put 12 volt to anything near the magneto unless you want to ruin it. It makes it's own juice for the spark plugs. Dry it out and it should be fine. The guys who excite it with a 12 volt battery are idiots and have no business around an aircraft engine.
There are 2 wires, coming out of the same hole, one goes to the switch to ground them, the other jumps up to what looks like a capacitor. Has a male/female bullet so can be disconected, NO radios on board.

Will have to note the part about filing also.

Anyone have a specific gap? I'm assuming its like points?

Thanks again, Jeff
You could use sand paper if you got, it the less you file and wear away the contacts the better. A dollar bill will remove moisture and oil residue without transfering any of itself to the contacts and without removing any of the contact material that could affect the gap. You'll know when you examine the points if filing is necessary.
Be sure to clean the contacts with something (brake klean or starting fluid) after you sand or file to remove any debris that could foul them,
Back in the day before electric starters the only reason to carry a battery was for lights if you had 'em.
You're sure there is no fire at the plugs?
The reason I'm questioning is you said it started an ran for a while,that makes me think a water bubble in the fuel tank maybe.

We pulled the boots and slid em up the wires on wires from both mags on a cylinder and spun it over MANY times trying this and that.... It never had fire, well till the last time it all of a sudden started once we'd put it all together again. By that, we'd had a wiring fiasco fall apart on the run in, and lost our top lights and had to run the hand spotlight... We were trying to figure that out and at the same tiem the motor died adn would not start again till abotu 9 hours later.

Are you sayin' you didn't have fire to the plugs or that the engine failed to fire and try to run.
I'm still thinkin'(just a hunch) that you might have gotten some water in the fuel from the rain some how and it isn't a mag problem at all. Seems odd that both mags would drown out at the same time. Without being there and seeing how it ran before it quit it's hard to go on any thing but hunches. If it was running up to full RPM before it died i would say it was running on both mags up until the time of death.
If you have an inline fuel filter check it for water. I'm thinkin after sitting for a while the water bubble moved away from the pickup tube and allowed it to get a bit of fuel and that's why it started again.
Try pullin' the plug in the float bowl and see what comes out.

I'm about off to bed, 3am will come early again. Thanks for all the quick input!! What a super response!

IMHO, the motor fired super, ran fine and died while at idle as we were coming in to stop.

Being that as we cranked and cranked, it never jumped a spark, thats my thought... and the fact as the electric priming fuel pump ran, I could smell fuel, like as in flooded IMHO.

But I finally googled Bendix Mags and learned a bit a few minutes ago.

It's all workable, the first thing is to get all the electric wiring redone, and then check out the mags one day. I'd bet it won't hurt to work both of them over again, see where aircraft run 200-500 hours per the FAA regs until reworking/checking them.

Rost..Welcome to SA...aircraft engines will run on one mag. There really is not much way for you to know if that was the case or not...until you get it running again. When you do, alternate flipping both mag switches off...one at a time. If each makes a difference in the engine, when they are cut off, both are firing. If one switch doesn't make a difference when it is switched off, that mag is likely not firing. You say he just bought the boat...Good Luck with it...There's no real way to get a handle on the previous owner's PM...cover all the bases and that engine should run trouble free. Post a couple of close ups on your engine when you get the chance. Lots of us run a clear bottom marine type water separating fuel filter...one glance tells you if water is present in your fuel system.
Another thing to check is the wiring from the P-lead to the switch and then to the ground. Make sure the ground wire is back to the magneto or close to it on the engine. Don't connect the ground wire to anything else or to any other ground. That could be your problem when the electrical went out for the other light. As said above, check each mag off or grounded and back on then both off or grounded. If neither P-lead wire is hooked to anything then the mags should be hot.
Thanks for all the input, will forward this to my friend, the owner, ran fine this morning.

BTW how much fuel do these things suck up? Less if frog spit or the like on an aluminum hull I'd suspect?

Thanks, Jeff
rost495":3n5vy0z9 said:
Whats everyone here(car guys from cars, not airboats, mostly tractors.... ) saying the mags have to have 12volt to "excite" them at first?

The 12V to "excite" then applies to generators that loose their magnetic field and that's nothing more than a quick spark. (6V for 6 volt generators)..

Mags must be clean & dry, else they'll leave you 'high & dry'. :shock:

Follow the senior advise from Speed Wheelie and the others....they've ALL been there and done that. 8)
i accidental put 12 v power to my mag on the marsh,and fried the points and condenser,thank god my buddy had spare in his boat.the switch is to ground the out to shut them down. the create their own power ,they need no 12v or 6 v to jump start them off.