This is one of those write-ups that although a pain in my butt
to have to deal with, is actually a bit fun to document and
write about. Magnetos are definitely and older technology,
and there I times I kick myself for being a semi-luddite.
You see, I did, on both airplanes, make the jump to Electronic
Ignition, with both planes having the Lightspeed system.
It's been a fantastic system. But I never had the
confidence to go completely mag free, so both of my airplanes
currently have one magneto, on the Left side. It's when
these Mags give me problems that I start to wonder why I don't
just take that extra leap. The truth is, I think at this
point I would, if I just took the time and effort to add a
standby alternator. I have dual-battery systems in both
planes, and I've got enough time on the ignition systems to
trust at least my Lightspeed. There are other good
manufacturers of E.I. systems as well, but some either have less
fully functional flying airplanes that use them, or perhaps a
shorter track record, so I have a hard time making the
jump. To be even more truthful, I was sold on Lightspeed
on the first day an airplane came rolling up to me running on
them, and I heard how it sounded. But I'd be willing to
look at a second EI system these days, once I get that
alternator. Maybe this is my year to shop at OSH.
The story with my Mag issue this time around, goes something
On the last couple flights, there was an engine stumble while
climbing out at maybe 800'. That alone made me curious,
but then the engine ran fine, so you kind of file it in the
"better watch for that" file, that you keep until you figure out
if you really have a problem. Fortunately, my next run-up
made it perfectly clear where to look. Too bad it happened
on the one good day we had in this official "most snowy ever
February in history" that we had here in 2019. As I did my
run-up, my E.I. side worked perfectly, but when I switched to
the Left system, the engine didn't even want to run. It
would very occasionally "pop" but it wouldn't run at all.
So at that point you know you aren't just missing a cylinder,
you're missing the whole ignition system. I did try the
insanity of "burning off the plugs", but knew that was going to
be hopeless, because in all my years of flying I've never had
more than 1 plug completely foul, and it's never been as bad
running as this was. So time to taxi back to the hangar
and tear it apart to see what was up.
Of course, I started with the simple things. I pulled the
plugs, inspected them (all pretty good), tested their resistance
(all between 1250 and 1450 ohms as best I could tell), and
checked the wires, springs, and contacts inside the plug.
I didn't find anything bad. Time to move on to the more complex
stuff, so lets add some pictures.
|After checking the wires
themselves, it was time to look at the Mag contacts.
Luckily I bought a really darn cheap approximately 1/4"
head wireless inspection camera that works with iphone,
sometime last year on everyone's favorite small-business
killer, the ever popular Prime Shipping 2-day
website. The 3 pics above were as good as I could
get by holding my iphone up to the mag. Luckily the
RV-14 has a fair amount of room. But with that mini
cam I could actually inspect right into each
contact. You can see in the first pic below that one
of the terminals had a little bit of carbon forming.
I have since cleaned that out with some q-tips and
alcohol. I also inspected the springs on the wires
at that end, and alcohol cleaned the rubber tips.
When finished I applied dielectric grease to the rubber
parts on both the spark plug and mag end, to hopefully
keep things more sealed up.
With the mag end finding nothing glaring at me so far, it was time to grab the buzz box and check the timing. I got mine very very reasonably, years ago for my RV-10, from this place: http://www.magnetotimer.com/ They're only $25 and work fine.
I was surprised to see that the timing was off. The IO-390's timing spec was 20 BTDC, and this was running maybe 6 degrees off. That was pretty unusual to me. I knew that if I were going to have to re-time the engine, I wasn't going to do it without first finding out what was wrong inside the mag. I'm not used to my timing shifting that much over time.
So a short time later I had the mag on the bench. Now, I'm absolutely no mag expert, but I compile data well. A real mag expert is someone like Mike Busch, and here's a link to a great article on Mags that he wrote. Sometimes, however, I can interpret things in a more clear way than I read them when reading other data. That led me to dig up my old web page on MyRV10.com where I had a whole compilation of magneto timing material. Here's the link to Tim's Updated Slick Timing Document. This page has actually ended up giving me a few chuckles. First, like I said, I'm no magneto expert, so I refer back to it myself whenever I have to work on mags. But one time my Ex-wife's now 2nd ex-husband told me that he was at an A&P class, and other A&P guys were talking behind him about a good reference to help understand mags...and mentioned it was on MyRV10.com. He overheard that and told me. I was shocked. People actually read this drivel that I write? I thought I was doing it for myself, so that as Alzheimers kicks in, I can remember it all. Flash forward a few years and I got an email from a factory plane rep who was helping a person in Africa of all places, work on a plane of theirs. He actually used that same link to help the guy better understand the mags. Like I said, I'm just a data gatherer, but hey, if it helps you all out, I'm glad it could be of service.
Anyhow, with the timing that far off, I opened the mag. I always move slowly with mags, because they intimidate me still, due to the long gaps of time between working on them. I do like spare parts, and keep spare contacts, and cam with me wherever I go. Also, I have always carried with me a T-118 Timing pin, and the T-150 E-Gap gauge, and after this experience I bought a 2nd set so I could carry one in each plane. Additionally I've ordered a couple spare condensors, as I realized I don't have a spare for them.
I take pictures of these things because I want to fully remember the exact orientation of every wire, gear, pin, and label as I tear things apart. I'm not sure if I'm smart enough to simply throw all the parts on the bench and then figure it all back out from scratch.
As I got further into the mag, I kept snapping pics. You can see the small drive gear, with it's "L" marking pointing to the notch in the distributor cap, and the pin in the "L" hole of the mag. This is because it's a left hand rotation mag, and I pulled it out with the cylinders at TDC, pinning the mag gear in place so it won't rotate. Just make sure you don't rotate the prop with the pin in, and that the timing marks are still at TDC before you insert the mag when you're done. Still, I was finding nothing that looked bad. The points were wearing evenly and were in good shape. I used a capacitor tester and although maybe not a perfect test, was able to test the capacitor (condenser), and it tested within spec and charged and discharged appropriately. The Cam appeared to be in OK shape, as did all the teeth on the gears, and the carbon brush was fine. So far I wasn't finding anything.
I decided I was going to have to dig even deeper. Time to pull off the distributor cap, and also check the e-gap for internal timing. It was then that I struck troubleshooting gold! As I removed the main gear from under the distributor cap, i looked at the "wiper" for lack of better terminology...the electrode that sends the spark from the coil thru the carbon brush, up the gear shaft, out the wiper to the 4 individual terminals for the spark plug wires. That wiper was loose, and not just a little loose. Knowing that the job of this thing relies on the ability to transfer electricity from the shaft down that arm, you would NEVER want that arm to be loose. If it isn't a pretty tight fit on that shaft, there will be a gap. Where there's a gap, there is spark. Where there is spark, there is erosion. As you can see in the video below, I could easily pick out that arm and there was a TON of gap around the shaft, and plenty of erosion had happened.
I did remove the copper arm, polish it up to inspect it, and the put it back in place. But something was clearly wrong, because that arm either had to be pressed in to the shaft, and wasn't, or molded into the plastic and wasn't any longer.
My heart sunk because I knew I was going to have to order parts, or, rob them out of the brand new 4370 that came with the engine that I have stored in a sealed box.
Time to pull out my Champion Slick Service Manual L-1363F (G is now current at the time of this writing but F was all I had on hand), and figure out what parts I needed. As I got into the manual I located K3822 as the Distributor block and Gear assembly. As I got online to buy a K3822, figuring I'd have to spend more than I would imagine, I had NO IDEA it was going to be as outrageous as what I found. The only places that sold the K3822 sold them for $399 and up for the most part. That's absolutely insane for a few plastic pieces and a couple metal ones. Had this been for a car, it would be $30. For a boat maybe $50. But $400??!!!
The more I dug in the more I found that really, what you would end up buying is either a 500 hour mag kit, or a rebuild kit. The latter costs more like $680 and contains those parts and a few more. I remember back in 2001 or 2002 buying a magneto for $500 complete, but now they're almost $1300!! I started to get pretty down on the whole mag idea once again. This seems to happen every few years as you have mag issues. Ultimately if I can buy an E.I. system that uses aviation plugs on the bottom, I'll probably end up doing that some day. But, being aerobatic, I want plug wires that bolt on securely, and I would like a timing curve that is more conservative as the Lightspeed, simply because I trust that box and want that to be the most advanced sparking system I have.
Here are a couple of links for rebuild kits, for reference:
But keep reading, because it gets better.
Various Mag Parts for Reference(This is as much for me for as it is for you, and applies to my RV14's 4372 (and un-used 4370) Magneto, as well as some parts applying to my RV10's 6351 Magneto)
Note: Pricing below may not be current when you read this
||Optional Part #'s
||Optional Part Price
|T-150 E-Gap Timing Gauge
|T-118 Timing Pin
|K3008 Gear Kit
||Kelly ES510406 (08-16232)
|K3984 Condenser/Capacitor Kit
||Kelly AK-3984 (07-02451)
|K3215 Slick Carbon Brush Kit
|M3081 Contact Point Kit with Cam
Someone get me the Kelly # if you know it please
|M2556 Slick Cotter Pin
|M3426 Mag Gasket (Slick)
||Alternates listed below slick part
|SA534750 Mag Gasket (Superior)
||(now that's cheaper, eh?)
|LW12681 Mag Gasket (Lycoming)
|SL12681 Mag gasket (Superior)
|M1827 Slick Rotor Cam Grease