Mag Failure

Stingray Don

Stingray Don

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Stingray Don
Well, it is a perfect day for flying. So I took a vacation day and headed for the airport. Taxied out to the run up area. Left mag - check. Right mag - engine dies. Restart the engine and check the right mag again - engine immediately dies. Put her back in the hangar and scheduled maintenance. I am now a ground dweller. Wonder how much this will cost me.
 
Recently went through the same, except I wasn’t at the home base. Had to pay tie down fee, travel time for A&P and new mag.

The repair bill break down as follows: $1,940.00
  • Troubleshoot and remove right mag
  • Install new Slick Mag MN4370.
  • Install Mag Gaskets
  • Time both magnetos
  • Run engine and perform ops check. Good
  • Labor 4.5 hours
  • Travel 2.4 hours
 
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Stingray Don said:
Well, it is a perfect day for flying. So I took a vacation day and headed for the airport. Taxied out to the run up area. Left mag - check. Right mag - engine dies. Restart the engine and check the right mag again - engine immediately dies. Put her back in the hangar and scheduled maintenance. I am now a ground dweller. Wonder how much this will cost me.
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Same thing happened to me and mine was a 15 minute fix. The p lead broke inside the mag. Took cover off, resoldered the p lead to the backing plate, (a washer) reconnected, and all was well.
 
EdFred said:
Same thing happened to me and mine was a 15 minute fix. The p lead broke inside the mag. Took cover off, resoldered the p lead to the backing plate, (a washer) reconnected, and all was well.
Click to expand...

I hope that’s all it is, but I doubt I could get that lucky.
 
EdFred said:
Same thing happened to me and mine was a 15 minute fix. The p lead broke inside the mag. Took cover off, resoldered the p lead to the backing plate, (a washer) reconnected, and all was well.
Click to expand...
A broken P lead would keep the mags hot so the engine would keep running, not quit... unless the broken end was contacting and shorting to the case.
 
No broken P-leads but I've had a coil fail in a Slick mag before. The part alone was over $300.


Most of my ignition troubles are fouled spark plugs, doesn't happen often thankfully.
 
Could be something as simple as a shorted condenser. Don't panic until you, or someone you TRUST, takes a look. Panicking in aicraft MX can cost you dearly for little return.
 
I have a backup set of Slick's in my garage just freshly overhauled. I learned it is cheaper to buy overhauled from QAA than buy parts and overhaul yourself.
 
Stingray Don said:
Well, it is a perfect day for flying. So I took a vacation day and headed for the airport. Taxied out to the run up area. Left mag - check. Right mag - engine dies. Restart the engine and check the right mag again - engine immediately dies. Put her back in the hangar and scheduled maintenance. I am now a ground dweller. Wonder how much this will cost me.
Click to expand...
Time to buy a new plane. Yours has been abused too long and is tired.
 
Eldorado said:
Check plugs first.
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All four (or six) plugs fired by that mag would have to be shot. That is VERY unlikely.

Bendix recommends mag removal and internal inspection every 400 hours. Slick advises it every 500. In the flight school fleet I did it every 500 and found the points still good, and replaced them at the next 500, or 1000 hours since new or the last points replacement. Most private airplanes don't get that level of care and so they are run until they quit, often at some really inconvenient airport far from home. The same philosophy is applied to alternators and vacuum pumps, often presenting some unpleasant surprises for the pilot. Failure is 99% inevitable when airplanes are maintained that way.
 
Dan Thomas said:
All four (or six) plugs fired by that mag would have to be shot. That is VERY unlikely.

Bendix recommends mag removal and internal inspection every 400 hours. Slick advises it every 500. In the flight school fleet I did it every 500 and found the points still good, and replaced them at the next 500, or 1000 hours since new or the last points replacement. Most private airplanes don't get that level of care and so they are run until they quit, often at some really inconvenient airport far from home. The same philosophy is applied to alternators and vacuum pumps, often presenting some unpleasant surprises for the pilot. Failure is 99% inevitable when airplanes are maintained that way.
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^^^This.
I am amazed at the lack of magneto maintenance and spark plug maintenance. I ask owners I know how many hours on the mags since the last servicing. Most of them can't even find a log entry.

I think one of the reasons is we now have a "throw the part away and replace" mentality in our societies (that's how we maintain cars now) and there are fewer and fewer really experienced mechanics that know how to service and overhaul these accessories properly. Like Dan, they are all retiring... :(
 
Maintenance on my plane is done by the book. No shortcuts or deferred maintenance. The right magneto only has about 150 hours on it.
 
Stingray Don said:
Maintenance on my plane is done by the book. No shortcuts or deferred maintenance. The right magneto only has about 150 hours on it.
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Sounds, then, like something failed in it. Will be interesting to see what is found.
 
Anyone have SureFly electronic ignition installed?
Just curious about your experience, vs magneto.
 
Everyone seems to have overlooked the possibility of ignition switch failure. Unhook the P-lead on the suspect mag which should make it hot. Start up and select the ignition switch to off. The engine should continue to run if the hot/disconnected mag is good. That would make me look at the lead or the switch. If the engine does not continue to run, you know the mag is not hot, even when disconnected and therefore it is the failed unit.
 
cessna180patrick said:
Everyone seems to have overlooked the possibility of ignition switch failure. Unhook the P-lead on the suspect mag which should make it hot. Start up and select the ignition switch to off. The engine should continue to run if the hot/disconnected mag is good. That would make me look at the lead or the switch. If the engine does not continue to run, you know the mag is not hot, even when disconnected and therefore it is the failed unit.
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I had considered and rejected it as unlikely. The moving contacts in the switch would have to keep the mag shorted somehow. Bad switches tend to fail to short a mag.

Now, there is a possibility that the wire terminals on the back of the mag switch have come loose or somehow been disturbed so that the relevant terminal is contacting the ground terminal. That stuff is in close quarters back there. Once in a while on annuals I have found those terminal screws loose.
 
Stingray Don said:
Maintenance on my plane is done by the book. No shortcuts or deferred maintenance. The right magneto only has about 150 hours on it.
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Yeah, Tom Wood Aviation has a very good maintenance shop.
 
Yesterday, I decided to take a friend to the beach. Went out to the run-up area, test left mag fine, test right mag the plane shakes violently and drops 300 RPM. Taxi back to tie-down and left message with the chief pilot. I'll be curious what he does to fix it.
 
Justin M said:
Yesterday, I decided to take a friend to the beach. Went out to the run-up area, test left mag fine, test right mag the plane shakes violently and drops 300 RPM. Taxi back to tie-down and left message with the chief pilot. I'll be curious what he does to fix it.
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99.99% chance they will fix it by running it up to 2000 RPM and leaning it out until it stumbles then waiting for it to clear. In nearly 20 years of runups, the only time this has not worked was when the plug wire was loose.
 
smv said:
99.99% chance they will fix it by running it up to 2000 RPM and leaning it out until it stumbles then waiting for it to clear. In nearly 20 years of runups, the only time this has not worked was when the plug wire was loose.
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Wouldn't you rather have the problem fixed, so it will stay fixed
 
smv said:
99.99% chance they will fix it by running it up to 2000 RPM and leaning it out until it stumbles then waiting for it to clear. In nearly 20 years of runups, the only time this has not worked was when the plug wire was loose.
Click to expand...

Well aware of how to clear fouled plugs. That’s not the issue.
 
I got wierd looks when I mentioned I was getting my plugs gapped n cleaned and rotated (will get the tools myself for next time)

“isn’t that just done at annual?” I was asked...

nope, not when ya fly em... but I wonder how many folks do it just at annual regardless of flying time..
 
Stingray Don said:
Well, it is a perfect day for flying. So I took a vacation day and headed for the airport. Taxied out to the run up area. Left mag - check. Right mag - engine dies. Restart the engine and check the right mag again - engine immediately dies. Put her back in the hangar and scheduled maintenance. I am now a ground dweller. Wonder how much this will cost me.
Click to expand...

Was the mag the issue, and are you back flying yet?
 
Stingray Don said:
Worth considering, but I thought they replaced the left mag. The plane starts on the left mag. It is right mag that failed.
Click to expand...

I haven't followed any of these products in a while, but I had thought at least some of the electronic ignition solutions replaced the right mag. Then the engine ends up starting on 2 mags, and that's part of how they get the improved starting.

I could be completely wrong, though, since it's been close to 3 years since I've even had to think about mags and it was back in the 310 days (so 4-5 years ago) that it was something I was actively looking at wanting to do. Of course in those days there were fewer options out there.
 
Shepherd said:
Anyone have SureFly electronic ignition installed?
Just curious about your experience, vs magneto.
Click to expand...

We put SureFly on the left mag on the -7A (IO-360) a month or so ago. Fires right up. Seems to run a little more smoothly on left mag when running mag checks. Other than that, haven't really put enough time on it to tell a difference.
 
To the OP: Could it be possible that the mag slipped time and is firing, but at wrong timing? Other than that, I would say likely a grounded wire somewhere up to and including internal to the ignition switch.
 
CJones said:
To the OP: Could it be possible that the mag slipped time and is firing, but at wrong timing? Other than that, I would say likely a grounded wire somewhere up to and including internal to the ignition switch.
Click to expand...
Firing at the wrong time causes massive power losses. Even if it fired on the exhaust stroke it would show up as a lot of afterfiring when the other mag was shut off during the runup.

Many Bendix mags had a P-lead connection similar to a sparkplug lead. A nut held an insulator with a contact on its tip in a fitting on the mag. It contacted a springy reed in the mag that grounded itself when the P-lead was disconnected or if the nut came off. They're not prone to doing that but you never know...
 
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