Left Magneto Failed...

[xrs135]

My plane is down for annual, and I was supposed to be picking it up tomorrow... I get a call from my mechanic saying that they are having trouble getting the plane started. I immediately think this is weird, because my plane has ALWAYS been a super reliable starter - always firing up in 1-2 blades. He informs me that they are going to keep troubleshooting to figure out what the problem is. They eventually get it started, and I guess when when they test the left mag, it shudders/dies. 

My mags are new with the engine, and only have ~200hrs on them. They have ALWAYS checked out perfectly for me, and I've never seen any sort sketchiness on either one... not to mention both were running perfectly when I dropped the plane off.

Is it possible that my mechanic messed up the left mag? He said that they had previously removed the battery box and left mag to adjust the timing... so my question is, would it be easy for him to bugger up the mag in the process of adjusting the timing?

At any rate, it is being sent out next week and checked out. Will the mag shop be able to determine why exactly it failed? If it's my mechanics fault, he'd be more than happy to cover the cost of this... but will they really be able to figure out WHY it has failed, and if it was his fault?

I knew this annual was going too smoothly... 

[Hector]

Are you sure it's not the P-leads? I would almost bet it's the P-lead and not the mag. This has happened to me before and it was the P-lead. Have him check that carefully before removing the mag.

[xrs135]

2 minutes ago, Hector said:

Are you sure it's not the P-leads? I would almost bet it's the P-lead and not the mag. This has happened to me before and it was the P-lead. Have him check that carefully before removing the mag.

What exactly should be checked on the P-lead? What was wrong with your P-lead and why did it happen?

[Hector]

It was slightly frayed, enough to ground the p-lead taking out the left mag. Was flying down to south Florida A few weeks back when I noted some roughness. Did a mag check and sure enough my left mag was dead. While I was looking fora place to put down, the problem resolved itself and since I was only 50 mile from my destination I continued without any further problems. The next day the engine would not start. Decowled the plane and looked at the P-leads on the left mag. It was slight frayed with a couple of strands of insulation grounding the P-lead. Trim that back a little bit and no more problems. When I got home I asked my mechanic to change the P-lead out completely. Problem solved.

[LANCECASPER]

Also did your mechanic look at and clean every spark plug? Sometimes a lead fouled plug will behave like a bad mag on a mag check.

[xrs135]

Also did your mechanic look at and clean every spark plug? Sometimes a lead fouled plug will behave like a bad mag on a mag check.

The plugs are all clean... Hopefully it just ends up being the P-lead problem...

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[xrs135]

It just sucks to drop something off in perfect working order and then have it fail under someone else's watch.

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[Shadrach]

6 hours ago, xrs135 said:

 

It just sucks to drop something off in perfect working order and then have it fail under someone else's watch.

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Slick or Bendix? I've only personally timed bendix mags. There are 2 marks on the on the mag gear, red and black. If he set the black mark to 25 BTDC, your timing is going to be way off. It's entirely possible for this to happen. I received my plane back from an annual once with the right mag timed into the next time zone (there was much wrong with that annual). The plane started fine, but had a 600rpm mag drop.

Edited February 6, 2016 by Shadrach

[tony]

I'm sure I'll get criticized for this one, but remove the P-lead from the left mag and see if it starts. 

[Guest]

I'm sure that they will get to the bottom of it, but it may fall into stuff happens.  Much of the wiring in these old airplanes is of poor quality and has insulation failure due to age.

We just worked on a customers plane, two days later he stops to refuel and has a flat oleo.  While fixing the the oleo they notice a fuel leak which they trace to the fuel line in the picture.  Borescope inspection of the inside of the failed line revealed interior corrosion, so stuff just happens.

Clarence

[Shadrach]

1 hour ago, M20Doc said:

I'm sure that they will get to the bottom of it, but it may fall into stuff happens.  Much of the wiring in these old airplanes is of poor quality and has insulation failure due to age.

We just worked on a customers plane, two days later he stops to refuel and has a flat oleo.  While fixing the the oleo they notice a fuel leak which they trace to the fuel line in the picture.  Borescope inspection of the inside of the failed line revealed interior corrosion, so stuff just happens.

Clarence

Stuff does just happen! However, I'm pretty sure there's data to support that it happens more frequently after maintenance...

Bad luck to have just released a plane from MX and have a strut go flat and fuel leak appear. That leak looks to be really fresh as in just a few hours.

[ELT]

I had a similar problem 2 years ago.  Plane went in for annual and before annual started great (100 hours on engine and accessories).  Changed switch twice, shower of sparks module, pleads, replaced points in starting mag.  Still would not start properly.  Mechanic wanted to replace mag.  I sent mag to overhauler to check.  He found nothing wrong with it but he set the gap on starting points to near max.  We put the mag back and have had no starting problem since.  I spent 5 days working with my mechanic, He ate 30 man hours and parts except the switch all because the gap needed to be wider.  CHECK THE STARTING POINTS GAP FIRST

[Hector]

I'm sure I'll get criticized for this one, but remove the P-lead from the left mag and see if it starts. 

For troubleshooting purposes I'm perfectly fine with this and it will tell you right away if the p-lead is the problem. Simple/quick test.

[Yetti]

"I get a call from my mechanic saying that they are having trouble getting the plane started."   It would be really hard not to say something like "maybe you should call a mechanic to help you, because that is what my friends tell me to do on the interweb"

[N201MKTurbo]

Some mags have a shorting bar inside that shorts the MAG when the P leads are removed.

[MyNameIsNobody]

47 minutes ago, Yetti said:

"I get a call from my mechanic saying that they are having trouble getting the plane started."   It would be really hard not to say something like "maybe you should call a mechanic to help you, because that is what my friends tell me to do on the interweb"

I read that line to my wife.  She said "Time to find a new mechanic".  Seriously I would turn in my man-card if I made that call...Especially if the plane was running when I received the plane.  Troubleshoot.  Diagnose.  Git 'r done.  I know "it" happens, but this is well a "non-starter" with me...

[Hank]

This type of communication is important for those who fly their plane somewhere for annual, and need to plan their return trip in advance. What bothers me most is the jump to pulling the mag off without much (apparent from secondhand information) other troubleshooting first.

[Yetti]

I would bet a dollar that the mechanic is young and newer.  There are people who can troubleshoot a system and people who start replacing parts hoping something will fix it.  Troubleshooting is hard.

[carl]

xrs135, i want to see your youtube video of this, i know your plane has cameras on it everywhere.

 

Clarence , that is a fabulous picture

 

cari

[N601RX]

Did they swap the p lead with the retard breaker lead?  

[N201MKTurbo]

25 minutes ago, N601RX said:

Did they swap the p lead with the retard breaker lead?  

Aren't they different sizes?

[N601RX]

9 minutes ago, N201MKTurbo said:

Aren't they different sizes?

On Slicks they are both a 10-32 stud. 

[xrs135]

Just a little more info/update on this...

They are Bendix mags, timed to 25, to the correct marks. The P-lead was removed, and the mag still didn't work, so I guess that rules the P-lead out. This guy isn't some noob mechanic. I've actually known him personally since about 2004. He has spend his entire career running a maintenance shop that works on GA planes... so he has been around the block a few times. Since i'm not located on the field, and had to drop the plane off, I have only spoke on the phone with him - but I trust that he has done everything to troubleshoot the mag before determining that it needs to be sent out. One more side note, when he first got the plane and ran it for the oil change and compression check, it ran fine. The next time it was fired up, (after the annual) is when the problem showed up... 

I'm with you all... It is awfully disconcerting when your mechanic calls and says he "can't get the plane started", when it was dropped off running like a clock. But since I was supposed to be flying over there with a friend the following day... he was just giving me a realistic "update" on the status of the plane so that I could plan my trip over. 

I think I just want to convince myself that it might have been something that they did, instead of just catastrophic mag failure.. so that they will cover the costs. I doubt that's the case, however. We shall see when it gets sent out to the mag shop. I'll keep this thread updated as I learn more.

I guess on the positive side of things... I didn't have a mag failure in flight, and now I will likely have one freshly overhauled mag, not two that are on the same interval.

Edited February 6, 2016 by xrs135

[N201MKTurbo]

Just to save your battery and starter, pull out all the top plugs, reconnect the spark plug wires and lay them somewhere where they are grounded. Have someone run the starter while someone else looks at the plugs to see if you are getting spark. Make sure to look at the ones connected to the retard mag. Don't let that prop hit you, it wont kill you, but it will leave a bruise.

[N201MKTurbo]

Are you sure it is not a fuel problem?