Slick Magneto Failure

iamtheari

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I had to cancel a trip today because of a failed magneto. Shame on me for not doing post-flight magneto checks so I might have caught it before we played musical airplanes in 25-knot winds today. During my runup, turning off the left magneto on that engine caused no RPM drop, while turning off the right magneto caused the engine to quit. So it's not firing any of the plugs. It could be a shorted P-lead, which I plan to rule out with my digital multimeter tomorrow. (Resistance between the P-lead and ground connections on the magneto.)

While I am waiting for my A&P to get eyes on it, I want to minimize my downtime if possible. If the problem is not a shorted P-lead, is there any reason not to just order the Slick 500-hour inspection parts kit? Could it be something not included in that kit? Could it be something easily obtained outside of the kit for a fraction of the kit price?
 
Could be just points, but could be something else, like the little plastic gear, won't really know till you open it up.
 
I just went through this on my non-impulses right Mag. Decided to just replace it with a SureFly electronic mag. Will take the bad right Mag and see if it is possible to convert to an impulse mag. If possible, I’ll overhaul it and convert it, and have a spare on the shelf.
 
I just went through this on my non-impulses right Mag. Decided to just replace it with a SureFly electronic mag. Will take the bad right Mag and see if it is possible to convert to an impulse mag. If possible, I’ll overhaul it and convert it, and have a spare on the shelf.
That’s tempting but I think it will have to wait. There are too many upgrades ahead of it in line.

Unfortunately, I seem to have failed at my task of measuring the P lead resistance to ground. I used the working magneto as a control group. With the magneto switches on, I read 0.6 ohms between the P lead stud and ground on both magnetos. If that were only the case for the bad magneto, I would say “aha, it’s a shorted P lead.” But since they’re both reading the same, I have a harder time trusting the measurements.

Am I doing it wrong?
 
If I understand correctly - If you had a shorted P-lead external to the mag (along the wire somewhere), then disconnecting that lead should make the mag hot and operational.

I think you want to check the wire to make sure it’s open when the ignition switch is on “both”. Disconnect the wire and check for continuity of the wire when the switch is on both - if you have continuity then you have a short.

Your faulty mag could be grounded on the inside (?), along the p-lead wire, or at the ignition switch (doubtful because it would have to be grounded in single and both).

Someone else should correct me please.
 
Have you checked your mag for Service Bulletin applicability?

IMHO the easiest way is to get your mag serial number and go to Aircraft Magneto Service website.

There are mags that were installed with 1 to 3 SBs outstanding at the time of install..

The big box guys do not check this at time of sale.

You cannot convert a mag to take an Impulse Coupling.

You can convert an engine to accept 2 Impulse Coupled mags.

There is a lot of info on their site and they are great to talk to.

IIRC their warranty is better than OEM..

One of the most common reasons for failure of the mag itself is

a defective Coil. Not cheap!

You could try running with the RIGHT p- lead disconnected..

I use a very long test lead from capacitor to the cockpit to ground RIGHT mag for starting.

Others will say it’s not needed but I’m scared of kick-back.
 
As far as I can tell from the logbooks, the mags were new with the remanufactured Continental engine in 2014, 1100 hours ago. Unfortunately, the dead one is on the left with the P lead facing down. It looks like a heck of a chore to disconnect the lead to test. (And that appears to be what I did wrong: testing resistance from P lead to ground with the magneto itself in the circuit.)
 
I read 0.6 ohms between the P lead stud and ground on both magnetos
That's getting down towards the bottom of what you can reliably read with the typical meter.
Also, with the points closed, and the P lead connected, it is directly connected to ground through the points.
With the points open, you are reading the resistance of the primary coil which is very low and the resistance you read will be influenced as much by how well you connect between your test leads and the stud as the actual resistance.
You really need to disconnect the P lead from the magneto to check for a short to ground.

Not professional advice.
 
As far as I can tell from the logbooks, the mags were new with the remanufactured Continental engine in 2014, 1100 hours ago.
Sounds like you are way past due for an OH or IRAN. Given that, P lead is probably not your problem. A broken or intermittent connection is more likely than a short, and that would result in a hot mag, not a cold one.
 
Shouldn't be hard with the cowl off. It's just a Phillips head screw and a ring terminal.

It appears you are describing the shielding ground.

The p- lead needs 3/8 inch socket / wrench to remove.

Note that over torque on install WILL ruin Capacitor..

Just one of the components in the mag that wears is the “ Carbon Brush”.

They were cheap but now are about $25.

Still a lot cheaper than a rental car, motel and fixing away from home base.

The Brush transfer spark from the Coil to the rotating Distributor Rotor.

That is one wear point. The other is the Brush fits in the Rotor and may wiggle a bit.

This in turn causes the Brush to wear at an increasing rate.

And just where do those nice conductive pieces of carbon go?

In the interior of the mag! btw. Just about all mags use this system.


So if you take a pencil against the wall and walk around the perimeter just how far can you

walk before the pencil wears out? Your mag is similar and this is a cheap item accomplished

at the 500 Hour.

Another item @ 500 Hour is checking the Impulse Coupling and replacing the Spring.

IMHO Springs fail from rust pits and low time is worse than high usage.

Again not very pricey. Failure = dead mag

The Impulse Coupling for a Slick now sells for about $700 .

However; if the IC itself fails starting is the least of your concerns .

Failing components will turn your engine to trash!
 
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If the problem is not a shorted P-lead, is there any reason not to just order the Slick 500-hour inspection parts kit?
When was the last 500hr inspection complied with?
 
Shouldn't be hard with the cowl off. It's just a Phillips head screw and a ring terminal.
On this IO-520 the right magneto is oriented with the wiring terminals away from the engine and the left (failed one) is turned 180 degrees with the terminals down toward the engine. It was a pain but we got it disconnected.

There are two ring terminals connected to this point. One reads 0 ohms to ground with the mag switch off and infinity (open circuit) with the mag switch on. The other reads 1150 ohms to ground whether the switch is on or off.

I don’t know where the 1150-ohm wire goes off to.

Bad mag or bad wiring?
 
When was the last 500hr inspection complied with?
The logs didn’t have any that leapt off the page for me. So my safe bet is “not yet.”
 
On this IO-520 the right magneto is oriented with the wiring terminals away from the engine and the left (failed one) is turned 180 degrees with the terminals down toward the engine. It was a pain but we got it disconnected.

There are two ring terminals connected to this point. One reads 0 ohms to ground with the mag switch off and infinity (open circuit) with the mag switch on. The other reads 1150 ohms to ground whether the switch is on or off.

I don’t know where the 1150-ohm wire goes off to.

Bad mag or bad wiring?
One ring terminal is for the P lead. The other is for the cable shield. The P lead is switched.

Some people ground the shield at both ends; others claim that is bad. I don't know which is correct. But it has no effect on your engine. Only impact is RF static on radios, instruments, etc.

Sounds to me like your P lead wiring is fine, and your mag maintenance is possibly way overdue.
 
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The logs didn’t have any that leapt off the page for me. So my safe bet is “not yet.”
If the mags have over 500 hours I wouldn't buy the mag kit just yet. Do you know the total time of the mags?

So if I understand you, the bad mag has two wires attached to the P-lead?

Does the other mag have 2 wires as well?
 
If the mags have over 500 hours I wouldn't buy the mag kit just yet. Do you know the total time of the mags?

So if I understand you, the bad mag has two wires attached to the P-lead?

Does the other mag have 2 wires as well?
Both mags have two connections to the P lead terminal. Both mags were new with the engine ~1100 hours ago.
 
Do you have an electronic tach?
Should have mentioned that. Yes, it’s a Garmin TXi EIS. I suppose it takes the tach signal from the P lead (evidently from both of them) and has a high impedance input that shows up as 1150 ohms DC resistance with the power off.
 
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Today I learned...

Slick's 500-hour and almost as many dollars inspection kits do not include the distributor or coil. The coil is $752 and the distributor assembly is $759. But they supposedly come together in a maintenance kit for $998. And of course, if you only order the 500-hour kit, it will be the distributor and/or coil that is causing your problems.

In other news, my plane remains inop for another weekend. But as long as we had the plane outside for a test run, we disconnected the P lead and confirmed that there is a problem with the magneto and not the wiring. (Well, not only the wiring. Because it can be both. Because airplanes.)
 
As far as I can tell from the logbooks, the mags were new with the remanufactured Continental engine in 2014, 1100 hours ago. Unfortunately, the dead one is on the left with the P lead facing down. It looks like a heck of a chore to disconnect the lead to test. (And that appears to be what I did wrong: testing resistance from P lead to ground with the magneto itself in the circuit.)
Were they serviced every 500?
 
A cell phone camera will capture Data Plate to check info.

Check the screwheads holding the mag together for “ Yellow torque seal”.

If intact, it‘s likely not been serviced.
 
Slick's 500-hour and almost as many dollars inspection kits do not include the distributor or coil. The coil is $752 and the distributor assembly is $759. But they supposedly come together in a maintenance kit for $998. And of course, if you only order the 500-hour kit, it will be the distributor and/or coil that is causing your problems.
By the time you pay for that kit plus the labor, you might be better off buying a new magneto.

A good mechanic can determine if the coil or distributor are shot. That same good mechanic will have the Slick (Champion) magneto maintenance manual, too, which tells him all he needs to know so he doesn't just replace everything, hoping the problem goes away.

Only once, in many Slick 500-hour checks, did I replace the distributor. Not once did I need to replace a coil. Only a few times was the condenser failing. It's usually the points that are gone.
 
I've had a slick coil fail on me before, but the mag ran fine cold then quit once it was hot.
 
I've had a slick coil fail on me before, but the mag ran fine cold then quit once it was hot.
Same here, it was fine cold but then started missing once it warmed up... which will get your attention when it's a single ignition engine! Had to tape a temperature probe to the side of the mag case and go flying (circling directly over the airport) to positively identify the problem, it consistently missed above some temperature which I forget. Slick said with that behavior it was almost certainly a bad coil; I would have replaced it (the coil) but just then I got a great deal on a new mag somebody bought for his project but never used.
 
In retrospect, I wish I had known that an electronic ignition were available at a competitive price when I had the panel and EIS done on this plane just over a year ago. It would not have necessarily prevented this exact magneto from failing, but it would have helped my chances both now and in the future. In more recent retrospect, I wish I had just ordered a new magneto when I started this thread. I'd be flying today for within $200 of where I am presently sitting.

My mechanic inspected the moving parts and they are all quite worn, including the distributor. On the upside, I'm learning something new by helping.
 
At 1100 hours I’d just buy a new mag. Sounds like you may have already done so.
 
When my Slicks came due for their 500 hour, I bought 2 new ones. Installed those and sent the old ones to AMS for service. Each needed a few parts (not coils). They sit on the shelf ready to change out quickly if needed. I am a bit of a hoarder - I also have a spare voltage regulator, rebuilt starter, starter relay...
 
Well, there’s yer problem, right there…

IMG_0459.jpeg
 
Tempest used to make a PMA one I think but no idea if they still do. I'd just throw a used one at it out of my drawer of used mags if it were mine.
I already had a new coil as part of the overhaul kit so the plane is up and running again. But ... never again. I'll do what @NavAir said in post #29 next time.
 
NEW is not always BETTER.

I encountered several Slicks with outstanding Service Bulletins. ( Not ADs)

They were in effect at the time of sale and installation.

Obviously no one checked this anywhere along the line.

Warranty begins at time of installation and is generally around 1 year

although they have covered longer times.

I‘m sure there are folks on this forum that choose to ignore this and hope

the Tech checked it.

The easiest way is to get mag p/n and s/n and check SB’s on

Aircraft Magneto Service website.


It‘s not just an Ignition issue. One relating to Impulse Couplings could trash

your engine.

It‘s your choice though!
 
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