Yet another mag failure

[nationwide]

So I have a ‘86 252 that has had more than its fair share of magneto issues, the latest being a failure of a 40-hr (Slick......) mag. The AMT asked if I’d thought about having a vent tube put in to keep the mag temps down. He said the failure mode (secondary coil) suggested damage from chronically high temps. I’ve never noted anyone disussing this issue on any model Mooney. Have I just been living in a bubble? Has anyone else had a chronic mag problem?

[MB65E]

I haven’t had a Single slick mag last more than 300hrs in the past 15 years. It’s shocking if they make it past 500hrs for the 500hr inspection. 
I have had much better luck with rebuilt mags than new mags out of the box. 
-Matt

[carusoam]

first question...  what failed or fails inside the mag?

hard to put a finger on why something failed within the first 40hours...

Pressurized mags for flying in the FLs... seem to be common... apparently this helps minimize loose electrical discharges that can damage the mags internally... Electrical resistance of air...

Another thing that happens is the failure of a plastic gear... the plastic gear is not very Ozone resistant... and can lose a tooth or two...

As far as mag cooling goes... some engines get blast tubes that are aimed at the mags... the details are in the Mooney parts and service Manuals... it would be great to look that up to see if cooling tubes are part of the original set-up

Realistically, there are so many threads about Mag failures around here... and they all begin with... ‘my Slick mags...’

There are many electronic mags being used lately... unfortunately not for TC’d birds yet...

But, it might be possible to obtain and OH a proper mag for your engine... at a modest price... 

PP thoughts only, not a mechanic... stuff I have read around MS...

Best regards,

-a-

[nationwide]

23 minutes ago, MB65E said:

I haven’t had a Single slick mag last more than 300hrs in the past 15 years. It’s shocking if they make it past 500hrs for the 500hr inspection. 
I have had much better luck with rebuilt mags than new mags out of the box. 
-Matt

Wow....great

[nationwide]

17 minutes ago, carusoam said:

first question...  what failed or fails inside the mag?

hard to put a finger on why something failed within the first 40hours...

This particular one was a failure in the secondary coil...it was “open” (no continuity).  Unfortunately, many of the prior failures weren’t investigated deeply enough or weren’t documented thoroughly, and I wasn’t smart enough to ask the right questions (probably still aren’t......).

[carusoam]

Jason,

Got a pic of the baked coil..?

It may have been a new part installed with the mag... or possibly not replaced...

There usually is a kit available that can be bought to aid in the OH of the mag...

You could probably find the details in your log books what was used, and what got re-used...

 

When it comes to OH of mags... many people prefer to send them out to known shops that specialize in the mag OH process...

There are probably a few dozen posts that state... ‘I use the guy that Maxwell sends his off to...’ find that guy...

 

 

PP thoughts only, not a magneto expert...

Best regards,

-a-

[nationwide]

30 minutes ago, carusoam said:

Jason,

Got a pic of the baked coil..?

It may have been a new part installed with the mag... or possibly not replaced...

There usually is a kit available that can be bought to aid in the OH of the mag...

You could probably find the details in your log books what was used, and what got re-used...

 

When it comes to OH of mags... many people prefer to send them out to known shops that specialize in the mag OH process...

There are probably a few dozen posts that state... ‘I use the guy that Maxwell sends his off to...’ find that guy...

 

 

PP thoughts only, not a magneto expert...

Best regards,

-a-

I don’t have any pics, unfortunately.

The local mech sent the mags for overhaul.  I don’t think I have any part of those mags anymore because both were here, complete, at the same time.  I’m still awaiting a core charge refund when the old ones go back.

It was $1K for this btw—not including the core charge.  That seems like a lot to me.  I thought my other mag overhauls were more like 500.

[carusoam]

See if @M20Doc is around for insight on M20K mags and their longevity...

 

Summary...

M20K

• Slick Mags
• suffering from early failures
• Last one made it 40hrs after OH

Best regards,

 -a-

[Guest]

Slick mags are known for their more frequent failures than Bendix magnetos.  Coil failure could be heat related, the pressurized air for the mag is part of the problem as its heated, a cooling blast tube would help with cooling the mag.

According to this application guide Bendix mags might be an option.

 

[aviatoreb]

8 hours ago, nationwide said:

So I have a ‘86 252 that has had more than its fair share of magneto issues, the latest being a failure of a 40-hr (Slick......) mag. The AMT asked if I’d thought about having a vent tube put in to keep the mag temps down. He said the failure mode (secondary coil) suggested damage from chronically high temps. I’ve never noted anyone disussing this issue on any model Mooney. Have I just been living in a bubble? Has anyone else had a chronic mag problem?

What kind of temps is your engine running at?

Was it an inflight failure?

[nationwide]

3 hours ago, aviatoreb said:

What kind of temps is your engine running at?

Was it an inflight failure?

CHTs?  I keep them 380 or below.  I don’t have a digital oil temp reading but it’s always in the bottom 1/3rd of the stock analog gauge.

Don't know when it failed.  Flew fine one day.  Went to fly the next and failed the run up check (died on bad mag).

i think I’m going to start doing a mag check on the termination of every flight now too.

[GeeBee]

If you fly high, you either need a mag with a big coil or a pressurized mag. Slick mags have small coils, period. However if you go to pressurized mags, you introduce a source of contamination. Many shops will tell you Slicks are "throwaway mags" and really don't want to work on them. If I were you, given your problems, I would put in a SureFly and a Bendix and send your Slicks packing. I have found after 50 years that when I try to solve a mag problem "least cost" I always end up spending more than if I just bit the bullet and bought new.

 

 

 

[Steve2]

My experiences with Sick mags are largely positive, I maintain a fleet of 13 172s of which all but 1 have slick mags & 7 Aztecs of which 3 or 4 engines have bendix mags.  These aircraft are flown 700 - 1000hrs/yr with no scheduled magneto inspections / maintenance other than 100hr verification/adjustment of engine to magneto timing.  From memory over the last 5 years there have been 2 or 3 bendix failures total & I'd estimate an average of 2 or 3 slick mag failures /year.  Every annual inspection all magnetos are removed, IRAN'd and reinstalled - most common part to replace is the sub $1 cam M3611, occasionally an $80 set of points and on the extreemly rare occasion a $350 coil.

[carusoam]

Great detailed input, Steve...

Makes me think flying 1000 hours per year is better for mags in a similar way as it is for the whole plane...

Do the C172s have air blast tubes aimed at their Slick mags?

How often do the coils get swapped out?

PP questions only...

Happy to see a person responsible for maintaining so many flight hours in a year... chooses an Ovation for the hours he flys himself... 

Best regards,

-a-

[carusoam]

4 hours ago, GeeBee said:

If you fly high, you either need a mag with a big coil or a pressurized mag. Slick mags have small coils, period. However if you go to pressurized mags, you introduce a source of contamination. Many shops will tell you Slicks are "throwaway mags" and really don't want to work on them. If I were you, given your problems, I would put in a SureFly and a Bendix and send your Slicks packing. I have found after 50 years that when I try to solve a mag problem "least cost" I always end up spending more than if I just bit the bullet and bought new.

 

 

 

Is the SureFly ready for prime time on a TC’d engine?

Or they are not advancing the timing yet, on the TC’d engine?

PP thoughts only, trying to improve my understanding...

Best regards,

-a-

 

[GeeBee]

According to their website,  Surely is certified. AOPA and Aviation Consumer describes them positively. No advance yet, but when it is it is easy to add just plumb into the MP line. Or you could go with the Electro Air system which has advance. When the SureFly comes out with advance, I plan on putting one on my Ovation.

 

 

[nationwide]

13 hours ago, Steve2 said:

My experiences with Sick mags are largely positive, I maintain a fleet of 13 172s of which all but 1 have slick mags & 7 Aztecs of which 3 or 4 engines have bendix mags.  These aircraft are flown 700 - 1000hrs/yr with no scheduled magneto inspections / maintenance other than 100hr verification/adjustment of engine to magneto timing.  From memory over the last 5 years there have been 2 or 3 bendix failures total & I'd estimate an average of 2 or 3 slick mag failures /year.  Every annual inspection all magnetos are removed, IRAN'd and reinstalled - most common part to replace is the sub $1 cam M3611, occasionally an $80 set of points and on the extreemly rare occasion a $350 coil.

That’s great insight, thanks for this, Steve.

I had 3x failures of Bendix mags too; I’m aware of Slick’s reputation but my experience has been neither is markedly better.

[carusoam]

Many MSers....

• prefer the Bendix over the Slick
• prefer to OH the mags on a 500 hour schedule 
• prefer to OH the mags on a separate schedule, not both at one time

 

A hand full of MSers have an electronic mag on their IO360s...

Best regards,

-a-

[Niko182]

Maybe take a look at EI or surefly. I dont think the Surefly is certified for turbo yet, but the EI is.

[nationwide]

20 hours ago, Niko182 said:

Maybe take a look at EI or surefly. I dont think the Surefly is certified for turbo yet, but the EI is.

I am definitely thinking about the ElectroAir.

[Tim Jodice]

Can you use 1200 series bendix mags? I have heard they are the best for high altitude aircraft. I have them on my baron and have had only one issue, one needed a condenser. My A&P has them on his 414 he says the 1200 series bendix mag was designed from the ground up to be a high altitude mag hence its size, Where a pressurizing a slick was a after thought. 

[nationwide]

On 11/11/2019 at 3:09 AM, airtim said:

Can you use 1200 series bendix mags? I have heard they are the best for high altitude aircraft. I have them on my baron and have had only one issue, one needed a condenser. My A&P has them on his 414 he says the 1200 series bendix mag was designed from the ground up to be a high altitude mag hence its size, Where a pressurizing a slick was a after thought. 

No.  I don't think the 1200s physically fit in there.  There may be other reasons.  M20Doc posted the application data service manual above, which shows the Bendix options.

[nationwide]

So if anyone is interested, the one overhauled in Nov that prompted this post is ill again (excessive drop, which was the warning sign every time the others died shortly thereafter).  About 18 hours on it.

[Guest]

1 hour ago, nationwide said:

So if anyone is interested, the one overhauled in Nov that prompted this post is ill again (excessive drop, which was the warning sign every time the others died shortly thereafter).  About 18 hours on it.

Did you ever get your mags pressurized?  It’s all factory installed.

Clarence

[RLCarter]

3 hours ago, nationwide said:

So if anyone is interested, the one overhauled in Nov that prompted this post is ill again (excessive drop, which was the warning sign every time the others died shortly thereafter).  About 18 hours on it.

Who's rebuilding them? same shop? Just went through a mag issue on a 172, both had 700+ hrs since points and condensers were replaced by a local A&P, the right mag  had over 2000hrs total time and according to the logs. Went with New Slick Mag Kit, which had Mags, Harness, Gskts, Plugs and Hardware, was $300 more than getting rebuilt mags and a harness