Slick Magneto 6314 failure at 700hrs

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422Phil

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422Phil
Returning from Maine to FL in my 1977 Cessna R172K XP, the left mag went bad. No prior warnings. All of the run ups checked out fine with the typical 50 to 60 RPM drops during the 15 hrs of flights the prior 6 days before the failure. Initially thought it was a bad plug, but all were pulled cleaned and tested, and were fine. I had to leave the plane in NC awaiting a new Mag. So I decided to do some digging when I got back to FL and checked the log books. Discovered both the LH & RH were last replaced in 2012 and had accumulated approx 700 hrs before the failure. No indication in the logs that a 500hr inspection had been done. Since they were the same age, I bit the bullet and had replaced both. I was very surprised that everything checked out normal with the LH Mag until it failed. I thought there would be a slow progression of increasing RPM drops. One flight it’s fine, next flight it drops over 200 RPMs and engine sounds terrible. Is this normally how these Mags fail?
 
422Phil said:
Returning from Maine to FL in my 1977 Cessna R172K XP, the left mag went bad. No prior warnings. All of the run ups checked out fine with the typical 50 to 60 RPM drops during the 15 hrs of flights the prior 6 days before the failure. Initially thought it was a bad plug, but all were pulled cleaned and tested, and were fine. I had to leave the plane in NC awaiting a new Mag. So I decided to do some digging when I got back to FL and checked the log books. Discovered both the LH & RH were last replaced in 2012 and had accumulated approx 700 hrs before the failure. No indication in the logs that a 500hr inspection had been done. Since they were the same age, I bit the bullet and had replaced both. I was very surprised that everything checked out normal with the LH Mag until it failed. I thought there would be a slow progression of increasing RPM drops. One flight it’s fine, next flight it drops over 200 RPMs and engine sounds terrible. Is this normally how these Mags fail?
Click to expand...

I can’t answer your specific question, but to try to eliminate similar things I put all the “wear items” and inspections in an excel sheet. I figure that’s a better reference than having to dig back through the logs continually... just an idea moving forward.
 
422Phil said:
Is this normally how these Mags fail?
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Sometimes. Depends what part fails. But this is not exclusive to mags. As been mentioned before, alternators and batteries can failure in similar fashion if there is a lack of preventative maintenance, inspection, and upkeep which can reduce your chances of a sudden failure when out of town.
 
Huckster79 said:
I can’t answer your specific question, but to try to eliminate similar things I put all the “wear items” and inspections in an excel sheet. I figure that’s a better reference than having to dig back through the logs continually... just an idea moving forward.
Click to expand...
How many items are on your spread sheet? Not a bad idea that's what the part 135 guys' did when I worked for them. Except it was a big chalk board that was updated every 100 hrs.
 
AKBill said:
How many items are on your spread sheet? Not a bad idea that's what the part 135 guys' did when I worked for them. Except it was a big chalk board that was updated every 100 hrs.
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I’ll look it up tomorrow- honestly not a boatload but I fly a c140 so not a lot of stuff on it.

mags, plugs, transponder now that I’m all fancy, I have a 100hr wing wire AD (yes I often have to have it done between annuals :) ), etc...

I’m thinking of converting it to a whiteboard laid out like excel sheet- now that I have a nice hangar so it’s not buried on the laptop in the same way things can get “buried” in the logbooks. That way I could add oil changes to it and such and it would be a quick reference.

I like being the guy that tells my mechanic what it’s going to need basic maintenance wise before it’s even pulled into his shop.
 
AKBill said:
How many items are on your spread sheet? Not a bad idea that's what the part 135 guys' did when I worked for them. Except it was a big chalk board that was updated every 100 hrs.
Click to expand...

I used to keep a whiteboard in the hangar with all of the biggies on it.

Next oil change due.
Next prop retorque due.
Next condition inspection due.
Next medical due.
Next Txp check due.
Etc.

It sure was convenient. I need to go back to that...
 
I keep the expiry dates of various aircraft maintenance items and pilot certifications in Google Keep. Have to remember to check it periodically, though.
 
422Phil said:
So I decided to do some digging when I got back to FL and checked the log books. Discovered both the LH & RH were last replaced in 2012 and had accumulated approx 700 hrs before the failure. No indication in the logs that a 500hr inspection had been done.
Click to expand...

Perhaps you should consider properly maintaining your aircraft. You'll have fewer surprises that way.
 
Sounds like a normal occurrence. Quality isn’t what it once was.
 
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AKBill said:
How many items are on your spread sheet? Not a bad idea that's what the part 135 guys' did when I worked for them. Except it was a big chalk board that was updated every 100 hrs.
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Our club follows the “chalkboard” concept with a white board mounted on wall of hangar where all members see it as they arrive and make the airplane ready for their flight.
 
If it makes you feel any better, let 2019 I did the slick IRAN, 500 hrs bla bla bla

Last month at about 130 hrs on the mags, the right mag gave away. It wasn’t sudden, it was over about 3 flights.

You can be on top of mx game, do everything by the book, things will still happen.

Preventative mx doesn’t always prevent jack
 
Huckster79 said:
I like being the guy that tells my mechanic what it’s going to need basic maintenance wise before it’s even pulled into his shop.
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We had a couple of guys like that. Appreciated their care and concern for safety. Most wanted us to track it. A few didn't want to spend that money.
 
WannFly said:
Preventative mx doesn’t always prevent jack
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It all depends on the quality of that maintenance. Mags failing for no predictable reason? Maybe one chance, or less, in ten thousand. If the job isn't done right it might easily fail. For instance, in a magneto there are some small screws that hold the points in position. There is a torque spec on those, i.e. 18 inch-pounds in a Slick. Too little torque can result in the screws loosening and the points gap changing, which changes the E-Gap, so that the spark weakens and fails. Or too much torque can start the screw stripping its threads or cracking, and failure is going to happen. There are other small screws that hold the distributor in place. There are wedges that hold the coil in place. There's a specification for the condenser's capacitance. Lots of stuff in there that needs to be right. This is all in a thick manual issued by Slick, but it costs money and takes a little time to read and learn the stuff. Oh, dear. Some figure it isn't worth it, and failures like yours are the result.
 
422Phil said:
One flight it’s fine, next flight it drops over 200 RPMs and engine sounds terrible. Is this normally how these Mags fail?
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Not normally, but if the points are burning anything can happen fairly suddenly. Slick had several problems addressed by Service Bulletins around the time your mags were built.
https://7ad7ffc8-b66c-4d33-9a3f-fad...d/0b3466_a3b53cb6ad9f4296b12bd8540473f666.pdf

https://www.aeronca.org/Slick-SB3-08.pdf

https://unisonpubs.com/docs/F-1100-SB2-08A.pdf


SBs aren't mandatory by law, so they often get ignored.

Corrosion is also a factor in older mags, especially in aircraft infrequently flown, flown only for short flights, or ground-run repeatedly. Bearings and impulse springs can corrode and fail rather suddenly.
 
Dan Thomas said:
We had a couple of guys like that. Appreciated their care and concern for safety. Most wanted us to track it. A few didn't want to spend that money.
Click to expand...

right, and I’m not cocky- I want their professional input but I don’t want to have to rely on them saying “mag overhaul is due” if that makes sense...
 
Dan Thomas said:
It all depends on the quality of that maintenance. Mags failing for no predictable reason? Maybe one chance, or less, in ten thousand. If the job isn't done right it might easily fail. For instance, in a magneto there are some small screws that hold the points in position. There is a torque spec on those, i.e. 18 inch-pounds in a Slick. Too little torque can result in the screws loosening and the points gap changing, which changes the E-Gap, so that the spark weakens and fails. Or too much torque can start the screw stripping its threads or cracking, and failure is going to happen. There are other small screws that hold the distributor in place. There are wedges that hold the coil in place. There's a specification for the condenser's capacitance. Lots of stuff in there that needs to be right. This is all in a thick manual issued by Slick, but it costs money and takes a little time to read and learn the stuff. Oh, dear. Some figure it isn't worth it, and failures like yours are the result.
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I heard back from aircraft magneto service and the mag is fine. There is a capacitor leak, but that’s not the smoking gun. Once I get the mag back I am going to start chasing the P Lead / harness/switch rabbit hole
 
WannFly said:
I heard back from aircraft magneto service and the mag is fine. There is a capacitor leak, but that’s not the smoking gun. Once I get the mag back I am going to start chasing the P Lead / harness/switch rabbit hole
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WannFly said:
I heard back from aircraft magneto service and the mag is fine. There is a capacitor leak, but that’s not the smoking gun. Once I get the mag back I am going to start chasing the P Lead / harness/switch rabbit hole
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Get under the panel and see if you have an ACS or Gerdes ignition switch. There's an AD on those that is little-known, with many mechanics assuming that they're all Bendix switches, which have a different AD altogether, and they do the test for the Bendix and miss the real problem with the ACS. The ACS has three contacts in it, and one of them gets burned by the voltage spike off the starter contactor when it releases. It can cause mag troubles with the debris generated. The AD requires a diode across the starter contactor coil, to shunt that spike, and a 2000-hour internal inspection, cleaning and relube, or switch replacement. https://rgl.faa.gov/Regulatory_and_...B8ABD56539B4684886256A3E00759DBF?OpenDocument

Looks for loose terminal screws on the back of the switch, too. That can let terminals vibrate against each other.

A capacitor leak can be a problem. Did they replace it? I sure hope so.
 
Dan Thomas said:
Get under the panel and see if you have an ACS or Gerdes ignition switch. There's an AD on those that is little-known, with many mechanics assuming that they're all Bendix switches, which have a different AD altogether, and they do the test for the Bendix and miss the real problem with the ACS. The ACS has three contacts in it, and one of them gets burned by the voltage spike off the starter contactor when it releases. It can cause mag troubles with the debris generated. The AD requires a diode across the starter contactor coil, to shunt that spike, and a 2000-hour internal inspection, cleaning and relube, or switch replacement. https://rgl.faa.gov/Regulatory_and_...B8ABD56539B4684886256A3E00759DBF?OpenDocument

Looks for loose terminal screws on the back of the switch, too. That can let terminals vibrate against each other.

A capacitor leak can be a problem. Did they replace it? I sure hope so.
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Yes they are putting in a new capacitor. I will check on the switch. Thanks for chiming in
 
For me it ended up being the faulty capacitor. All well and good now with about 70 RPM drop
 
WannFly said:
For me it ended up being the faulty capacitor. All well and good now with about 70 RPM drop
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Amazing how much difference a hotter spark makes. Some folks figure that if it sparks at all it must be ok. Not in my experience.
 
WannFly said:
For me it ended up being the faulty capacitor. All well and good now with about 70 RPM drop
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The capacitor does an important job. When the points are closed the capacitor is discharged to ground. Think of it like an empty bucket. When the points begin to open and there is a tiny gap the voltage takes the path of least resistance and charges the capacitor (fills the bucket) rather than arc across the gap between the points. When a cap goes bad the points get burned up pretty quick. When the points get burnt everything goes downhill.
 
Curious if this is something that could be prevented with a 500 hour IRAN
 
Silvaire said:
The capacitor does an important job. When the points are closed the capacitor is discharged to ground. Think of it like an empty bucket. When the points begin to open and there is a tiny gap the voltage takes the path of least resistance and charges the capacitor (fills the bucket) rather than arc across the gap between the points. When a cap goes bad the points get burned up pretty quick. When the points get burnt everything goes downhill.
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That capacitor, in absorbing the flow as the points open, enables the sudden interruption of the primary coil current necessary to get a good hot spark. Current flow across opening points not only burns them, it represents continued and gradually reducing current flow that gives little or no spark. The magneto (or any points-based ignition system) won't even work without it.

Slick's manual points out a third function of that capacitor (condenser) in a magneto: once it's full, it starts to shove the current back the other way through the coil primary in anticipation of the rotor magnet starting the flow in that direction, opposite to the previous, when the points close. It thereby improves coil performance. That only applies to magnetos, not battery ignition systems where the coil polarity does not change.
 
samiamPA said:
Curious if this is something that could be prevented with a 500 hour IRAN
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It's on the airframe manufacturer's inspection checklists. You know, the service manual stuff many mechanics ignore in favor of FAR 43 Appendix D.

upload_2021-5-28_18-58-57.png

Slick's time is 500 hours. Bendix (Continental) specifies 400 hours.

There are a lot of mags out there with over 1000 hours on them. They often strand the pilot far from home, and if they've been ignored long enough one sometimes finds stuff totally shot in there that needs replacing, stuff that could have lasted much longer if regular inspections had been done.

This one is also there:
upload_2021-5-28_19-4-58.png
upload_2021-5-28_19-4-1.png

And this one:

upload_2021-5-28_19-7-27.png
upload_2021-5-28_19-8-29.png

When I was the maintenance manager at a flight school, I learned early on that keeping up with this stuff not only made the airplane a lot safer, it meant that getting stuck at some inconvenient place very seldom happened.
 
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Dan Thomas said:
It's on the airframe manufacturer's inspection checklists. You know, the service manual stuff many mechanics ignore in favor of FAR 43 Appendix D...
Click to expand...

Okay Dan but you're going down a slippery slope. In Canada do you comply with Cessna SID's? Because on the first page, before you even get started, it says to ensure that all manufacturer service bulletins have been complied with.
 
Silvaire said:
Okay Dan but you're going down a slippery slope. In Canada do you comply with Cessna SID's? Because on the first page, before you even get started, it says to ensure that all manufacturer service bulletins have been complied with.
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No. That statement is just Cessna covering their butts. They're not legally enforceable here. I did look at all SIDs (what we used to know as CAPs: Continuing Airworthiness Program items) and I would evaluate and track those that I determined were necessary. The same applied to all Service Bulletins. There were some SBs that you knew were going to turn into ADs real quick, so we'd do those right away before the parts supplies dried up when the AD came out. And some were so bad that they should have become ADs and never did. It was all in knowing the aircraft, its type of usage, and in balancing costs and the likelihood of having problems. A flight school is a marginal operation, and lost flights don't improve that at all. The money lost in lost flights can easily cover doing the job right so it doesn't happen, and students and renters are happy.

Early on in my experience I saw a lot of flights lost, or people stuck in lousy places, because of magneto, vacuum pump or alternator failures. I determined that this was not going to happen anywhere I was managing maintenance. There is no financial benefit to running this stuff until it quits, and there are risk factors in doing so. We read about that sort of stuff here on POA almost daily.

This same sort of caution applied to stuff not listed in those component time limits: Engine and prop control cables. They can fail due to age and fatigue, and any failure can be really serious. We replaced them at engine overhauls. Incandescent landing lights got replaced with LEDs so night flights weren't getting cancelled.
 
Dan Thomas said:
No. That statement is just Cessna covering their butts. They're not legally enforceable here...
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I know but, as you may be aware, they were made mandatory in Australia where they have manage to nearly completely extinguish general aviation as we know it here in North America.
 
Silvaire said:
I know but, as you may be aware, they were made mandatory in Australia where they have manage to nearly completely extinguish general aviation as we know it here in North America.
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Yup.
 
422Phil said:
Brilliant contribution. Your IQ must be off the charts.
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While my intelligence is far above average, it doesn't take the proverbial rocket scientist to understand that failing to maintain an aircraft properly can lead to consequences much more severe than the relatively minor inconvenience of having to abandon your non-functioning aircraft at the first airport to appear underneath it.

Dan Thomas has helpfully provided the relevant service information for magnetos with this post:

https://www.pilotsofamerica.com/com...o-6314-failure-at-700hrs.132294/#post-3093296

Since your magnetos had been operated to 140% of their recommended overhaul period before one failed, it's obvious you belong to that group of aircraft owners that has maintenance performed once the object in question stops working.

You might consider reading a bit further along in Dan's post. While your airplane has two magnetos, it's probable it only has one each of a vacuum pump and alternator. When either of those quit, the result could be a life threatening issue rather than an unscheduled landing.

Allow me to utilize my superior intellect to advise you to get out your logbooks once again and "do some digging." It might prevent you from becoming "very surprised" at a most inopportune time in the future.
 
Another superior contribution from the know-it-all that can’t wait to say it all.
 
I have an issue with my Bendix magnetos that I was wondering if anybody could solve?

When you stab a Bendix magneto onto the engine it is usually positioned with the engine studs roughly in the venter of the lock rings…and it times within a few degrees of that position.

My problem…my magnetos will stab to the engine at this point but will not time until the right hand mag is clocked all the way to the advanced position and the left hand mag all the way to the retard position. Basically, I cannot advance the right or retard the left any further from that point…in which I should be able to?

Has anyone else even encountered or solved this?
 
BTW…I verified the drive gears (which are 2 separate P/Ns) to be correctly installed on the correct mag.
 
Is it possible for the gears on the engine side to be clocked incorrectly when the engine was assembled?
 
If your magneto has a gear on it rather than the two-tanged drive, the mag was installed in the wrong position. There's a window through which you can see the distributor gear, and you set the mag so that you see the red gear tooth in that window. That's the #1 firing position. Or they set the crankshaft at top dead center instead of the required ignition advance mark. Or they didn't click the impulse over lining up the red mark. Or they were misreading the mag timer; some have lights that go out when the points open, some have lights that come on instead.

It will be one of those.
 
These are Bendix mags…so no pin used.

They make a gear lock to hold the E-gap but several SBs and the FAA have outlawed them. Anyway, the red mark is in the middle of the window when the mag is stabbed and timed.
 
Cherokee Lover said:
These are Bendix mags…so no pin used.

They make a gear lock to hold the E-gap but several SBs and the FAA have outlawed them. Anyway, the red mark is in the middle of the window when the mag is stabbed and timed.
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And the crank is set at the correct ignition advance point?

I edited my original post. I was going by the thread title, which talked about Slick 6314 mags. Then I reviewed your post and saw that it was a Bendix, so I fixed that while you were typing your response.
 
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