Magneto failure - like a frog in a slowly heated pot.

Hang 4

Hang 4

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Hang 4
I'll pass on a recent painful experience in the hopes of helping someone else. I experienced a total magento failure (fortunately on the ground). In hindsight, I could see it coming, but didn't recognize the symptoms.
Piper PA28-180, 1973. I had my annual in September, and one symptom I mentioned was hard starting. Cleaned plugs and primers and started right up after annual. Thought problem was solved. Flew a bit since annual and hard starting seemed to come back, thinking it was plugs. Thought about ordering fine wires. Fast forward to last week and had an unplanned trip to New England from Florida. Two fuel stops and both hard starts. Barely got running after 2nd stop. Mag checks were fine at runup, so pressed on. Engine ran fine in the air.
Time to return, good weather forecast and got a reasonably early start. Cranked and cranked, had to get FBO GPU for a boost and still no start. Found on field AP and spent the afternoon on diagnosis/repair. He suspected mag and pulled to to bench test it. His initial thought was impulse coupling, but that was fine. Then bench tested for spark and again, fine. Cleaned and checked plugs, re-installed mag, timed it and tried a start - nothing. Double checked that the P-lead had an open circuit to rule out starter switch. Ended up going to a different airport in my car to pick up a rebuilt mag and installed that the next day. Once that was in and timed, it started right up.
I believe that the coil was failing due to some cracks in the windings and that the vibration of a running engine was slowly increasing the gaps, but when on the bench it Ohmed out OK.

Lesson from all that was, don't ignore a change in engine behavior. Not sure I could have diagnosed the problem without the failure, but looking back it's obvious something was amiss.
 
Coils can also break down when they got hot. When through this quite a bit on the gopher engine with its old heavyweight Bendixes.
 
Hang 4 said:
I'll pass on a recent painful experience in the hopes of helping someone else. I experienced a total magento failure (fortunately on the ground). In hindsight, I could see it coming, but didn't recognize the symptoms.
Piper PA28-180, 1973. I had my annual in September, and one symptom I mentioned was hard starting. Cleaned plugs and primers and started right up after annual. Thought problem was solved. Flew a bit since annual and hard starting seemed to come back, thinking it was plugs. Thought about ordering fine wires. Fast forward to last week and had an unplanned trip to New England from Florida. Two fuel stops and both hard starts. Barely got running after 2nd stop. Mag checks were fine at runup, so pressed on. Engine ran fine in the air.
Time to return, good weather forecast and got a reasonably early start. Cranked and cranked, had to get FBO GPU for a boost and still no start. Found on field AP and spent the afternoon on diagnosis/repair. He suspected mag and pulled to to bench test it. His initial thought was impulse coupling, but that was fine. Then bench tested for spark and again, fine. Cleaned and checked plugs, re-installed mag, timed it and tried a start - nothing. Double checked that the P-lead had an open circuit to rule out starter switch. Ended up going to a different airport in my car to pick up a rebuilt mag and installed that the next day. Once that was in and timed, it started right up.
I believe that the coil was failing due to some cracks in the windings and that the vibration of a running engine was slowly increasing the gaps, but when on the bench it Ohmed out OK.

Lesson from all that was, don't ignore a change in engine behavior. Not sure I could have diagnosed the problem without the failure, but looking back it's obvious something was amiss.
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How many hours on the offending mag?
 
That's funny you post this. My 73' PA28 180 started having hot start problems two months ago. The annual was due Oct I mentioned To my mechanic the starting problem and he said mag. Sent it off to get rebuilt don't have it back yet but am hoping it fixes the problem like yours did. It looks like mine hadn't been touched in 19 years.
 
gotta heat the coil while it's on the bench to simulate operational issues.....with a heat gun.
 
I've had a bad coil that showed up about two minutes after takeoff. Landed stopped to investigate and of course everything was fine after returning from lunch, ran it a while on the ground to get it hot and the symptom returned.

$300 later and a bunch of cussing that Slick mag had a new slick coil, my labor was free.


Hard starting could be coil related but I don't think it would be high on my list of suspects.
 
At what point do you consider throwing in electric ignition?
 
What did the points look like? A capacitor going bad can act much the same way.
BTDT.
 
Rgbeard said:
We have a WINNER.

Compression ignition is not electrical, and is neither electro-mechanical nor electronic.

Please report to the blue events tent to pick up your prize.
Click to expand...

Ooooh.... what do I get?

I hope it's an Atkinson cycle.
 
Jim K said:
Ooooh.... what do I get?

I hope it's an Atkinson cycle.
Click to expand...

Good thing you have that big, accessible luggage compartment. I don't think that type of cycle folds up for transport. ;)
 
Racerx said:
At what point do you consider throwing in electric ignition?
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I just went through this, basically I was going to send my slick mags off for 500 hour inspection. It would have been their 3rd time and the shop said the impulse will likely be worn and not economical to repair. Brand new slick mag is $1600 and $700 for a rebuild. So I bought a $1700 surefly, no more 500 hour for it and they are working to certify a dual set up. Not sure how trustful I would be of dual but will see.
 
So I have a question. The outboard engine manufacturers and the industrial natural gas engine manufacturers both have available a solid state magneto ignition, with no points. The big advantage to magneto ignition is it is a fully self contained system. As long as it is timed correctly and the engine is turning it, the ignition will fire. From what I have seen none of the solid state ignition replacements are magneto ignition. Why not?? It is certainly possible to replace the points with a solid state timing mechanism, or something similar like capacitive discharge ignition where there are points but there do not carry the ignition load, only the timing signal. Dual Magneto Ignition has proven its safety in aviation, so why not a solid state magneto??
 
Chip Sylverne said:
What did the points look like? A capacitor going bad can act much the same way.
BTDT.
Click to expand...
Points looked fine. No pitting or anything. Not sure of all the failure mechanisms and 800 miles away from home I wasn't too concerned about root cause if the new one worked.

I had thought about Surefly before this happened. If it had happened at my home drone, I would have seriously considered that instead of another mag.
 
William Pete Hodges said:
Dual Magneto Ignition has proven its safety in aviation, so why not a solid state magneto??
Click to expand...
Surefly. And E-Mag. And Lycoming's ie2 engine. Solid state just means electronics that don't use vacuum tubes.

And solid-state mag still use coils that break down with age and heat and vibration.
 
Any time the magneto changes while running, you are dealing a coil issue.

WHY? because of heat will contact a different group of coils, varying the efficiency in the magnetic field.
 
Tom-D said:
Any time the magneto changes while running, you are dealing a coil issue.

WHY? because of heat will contact a different group of coils, varying the efficiency in the magnetic field.
Click to expand...
No....that’s not the failure mode of a coil. Think windings and a partial break or open. Could also be a failure in the winding insulation causing an internal short. But heat affects these failure modes.....and causes expansion and the open.
 
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Coil failures can be frustrating and intermittent. Many years ago I experienced oddball, intermittent ignition issues that could never be reproduced or traced to anything obvious, until, while on a trip to Florida, I experienced a total mag check failure on the ground in Jacksonville after a quick turnaround with the engine hot. Turned out to be a heat-sensitive coil. Once that coil was replaced, all was normal again. That was one of the cheapest airplane repairs ever.
 
Checkout_my_Six said:
No....that’s not the failure mode of a coil. Think windings and a partial break or open. Could also be a failure in the winding insulation causing an internal short. But heat affects these failure modes.....and causes expansion and the open.
Click to expand...
an open field winding will result in total failure, you must have continuity of the field.
shorted windings will a result in a weak spark.
 
Tom-D said:
an open field winding will result in total failure, you must have continuity of the field.
shorted windings will a result in a weak spark.
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you missed the word...."partial"

One can literally.....clip an Ohm meter to the coil, heat it on the bench with a heat gun and watch it open as it warms up. Or if you prefer a more controlled experiment place it in the oven....and heat to 250.
 
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Checkout_my_Six said:
you missed the word...."partial"

One can literally.....clip an Ohm meter to the coil, heat it on the bench with a heat gun and watch it open as it warms up. Or if you prefer a more controlled experiment place it in the oven....and heat to 250.
Click to expand...
deserves repeating :)
"Any time the magneto changes while running, you are dealing a coil issue."
 
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