Left Magneto Failed...

[xrs135]

Are you sure it is not a fuel problem?

Definitely not fuel problem. Carb full of fuel, and mag confirmed not working via JPI.

Sent from my iPhone using Tapatalk

[DXB]

On 2/6/2016 at 0:10 AM, xrs135 said:

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... 

Ah yes - the terror and exasperation of aircraft maintenance.   I've no clue if you can wreck a mag when removing it, but I'll be curious to know what they find and suspect it will be pretty hard to know if it's the mechanic's fault.  My own related anecdote is that I got stranded when my plane wouldn't start about 2-3 hours after annual, during which the mags had their 500hr IRAN. The only plus was that I got to learn the no start trouble shooting protocol, which is pretty simple (but painful when paying overtime to the on call mechanic on a Sunday).  In my case the starting vibrator was working, but the retard points on the left mag weren't getting current. It turns out the vibrator sends current back through the ignition switch on its way out to the left mag, and those connections on the switch were loose.  It had nothing to do with the mags getting pulled but but may have been related to work on my panel by an avionics shop a few months prior. But little to gain by pointing the finger at them either.   

Anyway I hope you get back to flying soon, as I always enjoy your videos!

[LANCECASPER]

Frustrating when stuff like this happens, but as you mentioned less frustrating (1) when the airplane is on the ground not in the air and (2) not stranding you hundreds of miles from home.

[StinkBug]

Sounds like a stuff happens deal to me. My plane has started perfectly every time since I got it, and fired up perfectly to come home a few weeks ago. Started running rough on descent. Got down and Left mag was dead. Who knows, yours may have just been right at the edge like mine was. Thankfully it wasn't the most expensive fix in the world. I think the overhaul was about $500. Not cheap by any means, but I've heard of a lot simpler things that cost a lot more on our birds. 

[Hank]

It hit me this summer, too. Mag check was 200-300 drop on the left. So I missed a weekend out of town . . . Coulda been worse, could have happened there, a 6-hour drive home. Ran the mag through the Kelly Aerospace factory at Montgomery for ~$450. Put it back on, retimed, no problems. FWIW, I have Slick mags, not Bendix.

Funny thing was, it cranked up just fine with the bad mag . . . Just ran like dog sh!t.

A couple of years ago it wouldn't crank. A&P said he couldn't smell gas, couldn't flood the engine and make it drip, so we OHed the carb. Cranked fine for a while, then got bad again. IRANed left mag, cranked fine for a while then got bad again. Swapped plugs, same deal. Went through the Shower of Sparks, checked points and gaps, cranked and flew great with no problems until this summer, call it 3-1/2 years from the final fix before (we fought it for 6-8 months).

Good luck with yours!

[Shadrach]

2 hours ago, Hank said:

It hit me this summer, too. Mag check was 200-300 drop on the left. So I missed a weekend out of town . . . Coulda been worse, could have happened there, a 6-hour drive home. Ran the mag through the Kelly Aerospace factory at Montgomery for ~$450. Put it back on, retimed, no problems. FWIW, I have Slick mags, not Bendix.

Funny thing was, it cranked up just fine with the bad mag . . . Just ran like dog sh!t.

A couple of years ago it wouldn't crank. A&P said he couldn't smell gas, couldn't flood the engine and make it drip, so we OHed the carb. Cranked fine for a while, then got bad again. IRANed left mag, cranked fine for a while then got bad again. Swapped plugs, same deal. Went through the Shower of Sparks, checked points and gaps, cranked and flew great with no problems until this summer, call it 3-1/2 years from the final fix before (we fought it for 6-8 months).

Good luck with yours!

So you had Bendix and you switched to slicks? Do you prefer them or was it an availability thing?

[Hank]

2 minutes ago, Shadrach said:

So you had Bendix and you switched to slicks? Do you prefer them or was it an availability thing?

Plane had Slicks when I bought it. Don't know what it left the factory with, when/if they were swapped out. But Slicks are what I've got.

Edited February 8, 2016 by Hank

[Shadrach]

22 minutes ago, Hank said:

Plane had Slicks when I bought it. Don't know what it left the factory with, when/if they were swapped out. But Slicks are what I've got.

Ok got it, when I read "shower of sparks" I immediatly thought Bendix, but nowadays folks use that term for any "retard breaker" ignition system. Like Kleenex vs Tissue.

[Hank]

I thought the SoS was the vibrator part of the ignition, not the retarded cranking points that fire around TDC. 

[N601RX]

They are both work together.  The retarded point are offset 25 deg from the main points and activate the SOS for a window of about 5deg at TDC.  The SOS has its own set of internal points that are opening and closing several hundred times a second and you get several sparks during this window.  Its interesting to watch it operate with a plug out of each cylinder with the plugs body still grounded to engine.  You can rotate the prop by hand slowly and see the window. I had posted a video a few years ago.

Here is a link to the video.  Its much longer duration that a single spark from an impulse coupling.

 

 

Shower of Sparks-1.MOV

[xrs135]

On 2/6/2016 at 2:15 AM, Shadrach said:

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.

And the winner is.... Shadrach!

The mag was fine... one of the mechanics who set the timing on the left mag somehow goofed it up! Problem solved, no overhaul required. Runs smooth as can be like it used to.

Feels good to be reunited, and in the air again!

[Hank]

Ah, another C with a J cowl, from back when the mod was both available and reasonably priced! Glad it was a simple fix. 

[Shadrach]

18 hours ago, Hank said:

I thought the SoS was the vibrator part of the ignition, not the retarded cranking points that fire around TDC. 

It is. It's just that SOS was Bendix's trademarked name for the this type of ignition system. Hence the Kleenex/tissue comparison.

[Shadrach]

4 hours ago, xrs135 said:

And the winner is.... Shadrach!

The mag was fine... one of the mechanics who set the timing on the left mag somehow goofed it up! Problem solved, no overhaul required. Runs smooth as can be like it used to.

Feels good to be reunited, and in the air again!

Glad it's squared away. Disappointed that a MX professional flubbed a pretty basic procedure, but as has been discussed, stuff happens!

[Yetti]

If aint broke don't fix it.

Why was the mag even taken off for the annual if they only had 200 hours on them?  Should have been hook up the timing box and check it.  On to the next step.  Or maybe loosen it up and tighten it up.  On to the next step.

 

[Yetti]

13 hours ago, Hank said:

Ah, another C with a J cowl, from back when the mod was both available and reasonably priced! Glad it was a simple fix. 

I know there is the guppy insert.   It does not seem like it would be that hard to create a J style insert for the guppy mouth.  Or is regulatory to change the whole cowl out?

[N601RX]

It has the ARI cowl mod.

[thinwing]

On February 6, 2016 at 7:16 AM, N201MKTurbo said:

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

No ,that is incorrect,that is not how a mag works...the P lead shorts the primarily coil ,grounding it..thus when a p lead breaks it is hot.A "shorting bar "would prevent the mag from working at all

[N201MKTurbo]

31 minutes ago, thinwing said:

No ,that is incorrect,that is not how a mag works...the P lead shorts the primarily coil ,grounding it..thus when a p lead breaks it is hot.A "shorting bar "would prevent the mag from working at all

Not correct. When you remove the P leads in some mags there is a spring loaded shorting bar that prevents the mag from firing . When the P lead is connected, it pushes the shorting bar away allowing the P leads to open the circuit.

[Yetti]

Some mechanics will put a spare p lead that they use for timing to disable the shorting bar

[DonMuncy]

Does anyone know which mags have the shorting bar and which don't.

[Yetti]

One of my bendix (the left one with the retard)  did not sure of the model.  did not take a picture of them for the records...  Something to remember to do.

Edited February 9, 2016 by Yetti

[StinkBug]

4 hours ago, N201MKTurbo said:

Not correct. When you remove the P leads in some mags there is a spring loaded shorting bar that prevents the mag from firing . When the P lead is connected, it pushes the shorting bar away allowing the P leads to open the circuit.

This just seems like a bad idea to me. If the P lead were to break in flight on a normal mag, you just keep on flying and the only problem is that you can't shut the mag off with the key. With this setup if the P lead breaks your mag quits, which could kinda spoil your day. Seems like it's kinda defeating the whole point of a magneto, which is that it provides spark no matter what.

[Cyril Gibb]

off topic removed

 

Edited February 10, 2016 by Cyril Gibb
Off topic

[Yetti]

26 minutes ago, StinkBug said:

This just seems like a bad idea to me. If the P lead were to break in flight on a normal mag, you just keep on flying and the only problem is that you can't shut the mag off with the key. With this setup if the P lead breaks your mag quits, which could kinda spoil your day. Seems like it's kinda defeating the whole point of a magneto, which is that it provides spark no matter what.

It is  spring loaded mechanical affair.   The P lead would need to come unscrewed and fall out for the shorting bar to engage.  You check the tightness when the hood is up right?